Add public profile view endpoint: favorites, friends, privacy enforcement (US-3)

- Implemented GET /api/profile/{user_id} in backend/app/routers/profiles.py
- Server-side privacy enforcement for profile_visibility, favorites_visibility, and friends_list_visibility
- Block relationships enforce restricted view (no bio, empty favorites, empty friends)
- Non-friends restricted when profile_visibility or sections set to friends-only
- Asset public check for avatar in restricted view
- No private user fields leaked (email, password excluded)
- Added 7 integration tests in backend/tests/test_profile.py covering all privacy and block permutations

Independently verified: 26/26 profile tests passing.

.gitea/workflows/checkpoint.yml

@@ -0,0 +1,39 @@
+name: checkpoint
+
+# Runs the full checkpoint suite (migrations, backend pytest, Godot smoke
+# tests, multiplayer, fresh-clone boot) on every push and PR.
+#
+# Runs on a `host`-label act_runner on the AGP box: Docker, ~/godot/godot,
+# and Python 3 are already there. Deliberately uses no JavaScript actions
+# (actions/checkout etc.) so the host needs no Node install -- checkout is a
+# plain git clone from the local Gitea. See docs/ci.md.
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  checkpoint:
+    runs-on: host
+    steps:
+      - name: Checkout
+        run: |
+          set -eu
+          rm -rf repo && mkdir repo && cd repo
+          git init -q
+          git remote add origin "http://x:${{ github.token }}@localhost:3000/${{ github.repository }}.git"
+          git fetch -q --depth 1 origin "${{ github.sha }}"
+          git checkout -q FETCH_HEAD
+
+      - name: Python env
+        working-directory: repo
+        run: |
+          set -eu
+          python3 -m venv .venv
+          .venv/bin/pip install --quiet --upgrade pip
+          .venv/bin/pip install --quiet -r backend/requirements.txt
+
+      - name: Checkpoint suite
+        working-directory: repo
+        run: .venv/bin/python scripts/run_checkpoint_tests.py --postgres-port 25690 --backend-port 18690

.gitignore

@@ -11,3 +11,4 @@ Thumbs.db
 
 # Godot UID files (regenerated from path)
 *.uid
+assets/build_info.json

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assets/avatars/catalog.json

@@ -0,0 +1,115 @@
+{
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+    "base_human_male_01": {
+      "type": "base_body",
+      "slot": "base_body",
+      "path": "res://assets/avatars/base_human_male_01.glb",
+      "version": "1.0.0",
+      "display_name": "Human Male Base"
+    },
+    "head_cyber_01": {
+      "type": "attachment",
+      "slot": "head",
+      "path": "res://assets/avatars/head_cyber_01.glb",
+      "version": "1.0.0",
+      "display_name": "Cyber Head",
+      "mount_bone": "Head"
+    },
+    "hair_mohawk_01": {
+      "type": "attachment",
+      "slot": "hair",
+      "path": "res://assets/avatars/hair_mohawk_01.glb",
+      "version": "1.0.0",
+      "display_name": "Mohawk",
+      "mount_bone": "HeadTop"
+    },
+    "hair_ponytail_01": {
+      "type": "attachment",
+      "slot": "hair",
+      "path": "res://assets/avatars/hair_ponytail_01.glb",
+      "version": "1.0.0",
+      "display_name": "Ponytail",
+      "mount_bone": "HeadTop"
+    },
+    "face_glasses_01": {
+      "type": "attachment",
+      "slot": "face",
+      "path": "res://assets/avatars/face_glasses_01.glb",
+      "version": "1.0.0",
+      "display_name": "Glasses",
+      "mount_bone": "Jaw"
+    },
+    "chest_bandit_01": {
+      "type": "attachment",
+      "slot": "chest",
+      "path": "res://assets/avatars/chest_bandit_01.glb",
+      "version": "1.0.0",
+      "display_name": "Bandit Shirt",
+      "mount_bone": "Chest"
+    },
+    "back_backpack_01": {
+      "type": "attachment",
+      "slot": "back",
+      "path": "res://assets/avatars/back_backpack_01.glb",
+      "version": "1.0.0",
+      "display_name": "Backpack",
+      "mount_bone": "Chest"
+    },
+    "pants_cargo_01": {
+      "type": "attachment",
+      "slot": "pants",
+      "path": "res://assets/avatars/pants_cargo_01.glb",
+      "version": "1.0.0",
+      "display_name": "Cargo Pants",
+      "mount_bone": "Hips"
+    },
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+      "slot": "left_hand",
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+    },
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+      "slot": "right_foot",
+      "path": "res://assets/avatars/right_foot_boot_01.glb",
+      "version": "1.0.0",
+      "display_name": "Right Boot",
+      "mount_bone": "RightFoot"
+    },
+    "accessory_belt_01": {
+      "type": "attachment",
+      "slot": "accessory",
+      "path": "res://assets/avatars/accessory_belt_01.glb",
+      "version": "1.0.0",
+      "display_name": "Belt",
+      "mount_bone": "Root"
+    },
+    "accessory_necklace_01": {
+      "type": "attachment",
+      "slot": "accessory",
+      "path": "res://assets/avatars/accessory_necklace_01.glb",
+      "version": "1.0.0",
+      "display_name": "Necklace",
+      "mount_bone": "Root"
+    }
+  }
+}

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+_subresources={}
+gltf/naming_version=2
+gltf/embedded_image_handling=1

assets/avatars/pants_cargo_01.glb.import

@@ -0,0 +1,42 @@
+[remap]
+
+importer="scene"
+importer_version=1
+type="PackedScene"
+uid="uid://yo204q1m6hs3"
+path="res://.godot/imported/pants_cargo_01.glb-00f3e3b72fd692344cbb8bfd2b8449f9.scn"
+
+[deps]
+
+source_file="res://assets/avatars/pants_cargo_01.glb"
+dest_files=["res://.godot/imported/pants_cargo_01.glb-00f3e3b72fd692344cbb8bfd2b8449f9.scn"]
+
+[params]
+
+nodes/root_type=""
+nodes/root_name=""
+nodes/root_script=null
+nodes/apply_root_scale=true
+nodes/root_scale=1.0
+nodes/import_as_skeleton_bones=false
+nodes/use_name_suffixes=true
+nodes/use_node_type_suffixes=true
+meshes/ensure_tangents=true
+meshes/generate_lods=true
+meshes/create_shadow_meshes=true
+meshes/light_baking=1
+meshes/lightmap_texel_size=0.2
+meshes/force_disable_compression=false
+skins/use_named_skins=true
+animation/import=true
+animation/fps=30
+animation/trimming=false
+animation/remove_immutable_tracks=true
+animation/import_rest_as_RESET=false
+import_script/path=""
+materials/extract=0
+materials/extract_format=0
+materials/extract_path=""
+_subresources={}
+gltf/naming_version=2
+gltf/embedded_image_handling=1

assets/avatars/right_foot_boot_01.glb.import

@@ -0,0 +1,42 @@
+[remap]
+
+importer="scene"
+importer_version=1
+type="PackedScene"
+uid="uid://30ij0eapm6ti"
+path="res://.godot/imported/right_foot_boot_01.glb-ffff27e561e5632596b7ba89fee5b5ea.scn"
+
+[deps]
+
+source_file="res://assets/avatars/right_foot_boot_01.glb"
+dest_files=["res://.godot/imported/right_foot_boot_01.glb-ffff27e561e5632596b7ba89fee5b5ea.scn"]
+
+[params]
+
+nodes/root_type=""
+nodes/root_name=""
+nodes/root_script=null
+nodes/apply_root_scale=true
+nodes/root_scale=1.0
+nodes/import_as_skeleton_bones=false
+nodes/use_name_suffixes=true
+nodes/use_node_type_suffixes=true
+meshes/ensure_tangents=true
+meshes/generate_lods=true
+meshes/create_shadow_meshes=true
+meshes/light_baking=1
+meshes/lightmap_texel_size=0.2
+meshes/force_disable_compression=false
+skins/use_named_skins=true
+animation/import=true
+animation/fps=30
+animation/trimming=false
+animation/remove_immutable_tracks=true
+animation/import_rest_as_RESET=false
+import_script/path=""
+materials/extract=0
+materials/extract_format=0
+materials/extract_path=""
+_subresources={}
+gltf/naming_version=2
+gltf/embedded_image_handling=1

assets/avatars/right_hand_glove_01.glb.import

@@ -0,0 +1,42 @@
+[remap]
+
+importer="scene"
+importer_version=1
+type="PackedScene"
+uid="uid://bcrtxtp47dv8h"
+path="res://.godot/imported/right_hand_glove_01.glb-a59875b630ac413350c3bdf6acc84bdf.scn"
+
+[deps]
+
+source_file="res://assets/avatars/right_hand_glove_01.glb"
+dest_files=["res://.godot/imported/right_hand_glove_01.glb-a59875b630ac413350c3bdf6acc84bdf.scn"]
+
+[params]
+
+nodes/root_type=""
+nodes/root_name=""
+nodes/root_script=null
+nodes/apply_root_scale=true
+nodes/root_scale=1.0
+nodes/import_as_skeleton_bones=false
+nodes/use_name_suffixes=true
+nodes/use_node_type_suffixes=true
+meshes/ensure_tangents=true
+meshes/generate_lods=true
+meshes/create_shadow_meshes=true
+meshes/light_baking=1
+meshes/lightmap_texel_size=0.2
+meshes/force_disable_compression=false
+skins/use_named_skins=true
+animation/import=true
+animation/fps=30
+animation/trimming=false
+animation/remove_immutable_tracks=true
+animation/import_rest_as_RESET=false
+import_script/path=""
+materials/extract=0
+materials/extract_format=0
+materials/extract_path=""
+_subresources={}
+gltf/naming_version=2
+gltf/embedded_image_handling=1

assets/editor/object_catalog.json

@@ -0,0 +1,40 @@
+{
+  "objects": {
+    "crate_small": {
+      "asset_id": "props/crate_small.glb",
+      "type": "prop",
+      "display_name": "Small Crate",
+      "category": "props"
+    },
+    "rock_01": {
+      "asset_id": "props/rock_01.glb",
+      "type": "prop",
+      "display_name": "Rock",
+      "category": "nature"
+    },
+    "tree_pine_01": {
+      "asset_id": "props/tree_pine_01.glb",
+      "type": "prop",
+      "display_name": "Pine Tree",
+      "category": "nature"
+    },
+    "lamp_post_01": {
+      "asset_id": "props/lamp_post_01.glb",
+      "type": "prop",
+      "display_name": "Lamp Post",
+      "category": "props"
+    },
+    "chest_01": {
+      "asset_id": "props/chest.glb",
+      "type": "interactable",
+      "display_name": "Treasure Chest",
+      "category": "interactables"
+    },
+    "spawn_point": {
+      "asset_id": "",
+      "type": "spawn_point",
+      "display_name": "Spawn Point",
+      "category": "gameplay"
+    }
+  }
+}

assets/scripting/behaviors/demo_chest.json

@@ -0,0 +1,17 @@
+{
+  "content_flags": {
+    "violence": "none",
+    "mature": false
+  },
+  "rules": [
+    {
+      "trigger": {"type": "on_interact"},
+      "conditions": [],
+      "actions": [
+        {"verb": "give_item", "item_id": "gold_coin", "count": 3},
+        {"verb": "play_sound", "sound_id": "chest_open"},
+        {"verb": "rotate", "target": "self", "degrees": 90, "axis": "y", "duration": 0.4}
+      ]
+    }
+  ]
+}

assets/scripting/spawn_catalog.json

@@ -0,0 +1,8 @@
+{
+  "templates": {
+    "small_crate": {
+      "asset_id": "props/crate_small.glb",
+      "display_name": "Small Crate"
+    }
+  }
+}

backend/alembic/env.py

@@ -8,7 +8,7 @@ from sqlalchemy.ext.asyncio import create_async_engine
 
 from app.config import settings
 from app.database import Base
-from app.models import user, session, world, asset  # noqa: F401
+from app.models import user, session, world, asset, avatar_loadout, world_content  # noqa: F401
 
 # this is the Alembic Config object, which provides
 # access to the values within the .ini file in use.

backend/alembic/versions/0004_add_avatar_loadouts_table.py

@@ -0,0 +1,39 @@
+"""add avatar_loadouts table
+
+Revision ID: 0004_add_avatar_loadouts_table
+Revises: 0003_add_refresh_tokens_table
+Create Date: 2026-09-05 00:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "0004_add_avatar_loadouts_table"
+down_revision: Union[str, None] = "0003_add_refresh_tokens_table"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Create the avatar_loadouts table (one row per user)."""
+    op.create_table(
+        "avatar_loadouts",
+        sa.Column(
+            "user_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            primary_key=True,
+        ),
+        sa.Column("data", postgresql.JSONB(), nullable=False),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+
+
+def downgrade() -> None:
+    """Drop the avatar_loadouts table."""
+    op.drop_table("avatar_loadouts")

backend/alembic/versions/0005_add_world_content_tables.py

@@ -0,0 +1,120 @@
+"""add world_rooms, world_chunks, world_chunk_revisions tables
+
+Revision ID: 0005_add_world_content_tables
+Revises: 0004_add_avatar_loadouts_table
+Create Date: 2026-09-14 00:00:00.000000
+
+See docs/architecture/world_persistence_impl.md §4. Chunk content
+(rooms, chunk payloads, chunk revisions) lives in Postgres, purely
+additive to the existing ``worlds`` table.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "0005_add_world_content_tables"
+down_revision: Union[str, None] = "0004_add_avatar_loadouts_table"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "world_rooms",
+        sa.Column("id", sa.Integer(), primary_key=True, index=True),
+        sa.Column(
+            "world_id", sa.Integer(),
+            sa.ForeignKey("worlds.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("slug", sa.String(64), nullable=False),
+        sa.Column("name", sa.String(255), nullable=False),
+        sa.Column(
+            "grid", postgresql.JSONB(), nullable=False,
+            server_default='{"size": [32, 32, 1], "origin": [0, 0, 0]}',
+        ),
+        sa.Column("bounds", postgresql.JSONB(), nullable=True),
+        sa.Column("spawn", postgresql.JSONB(), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column(
+            "updated_at", sa.DateTime(timezone=True),
+            server_default=sa.func.now(), nullable=False,
+        ),
+        sa.UniqueConstraint("world_id", "slug", name="uq_world_rooms_world_slug"),
+    )
+    op.create_index("ix_world_rooms_world_id", "world_rooms", ["world_id"])
+
+    op.create_table(
+        "world_chunks",
+        sa.Column("id", sa.Integer(), primary_key=True, index=True),
+        sa.Column(
+            "world_id", sa.Integer(),
+            sa.ForeignKey("worlds.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "room_id", sa.Integer(),
+            sa.ForeignKey("world_rooms.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("chunk_key", sa.String(160), nullable=False, unique=True),
+        sa.Column("cx", sa.Integer(), nullable=False),
+        sa.Column("cy", sa.Integer(), nullable=False),
+        sa.Column("cz", sa.Integer(), nullable=False, server_default="0"),
+        sa.Column("format_version", sa.Integer(), nullable=False, server_default="1"),
+        sa.Column("payload", sa.LargeBinary(), nullable=False),
+        sa.Column("payload_len", sa.Integer(), nullable=False),
+        sa.Column("checksum", sa.String(64), nullable=False),
+        sa.Column("revision", sa.Integer(), nullable=False, server_default="1"),
+        sa.Column("content_flags", postgresql.JSONB(), nullable=False, server_default="{}"),
+        sa.Column("is_mature", sa.Boolean(), nullable=False, server_default="false"),
+        sa.Column(
+            "updated_by_id", sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column(
+            "updated_at", sa.DateTime(timezone=True),
+            server_default=sa.func.now(), nullable=False,
+        ),
+        sa.UniqueConstraint("room_id", "cx", "cy", "cz", name="uq_world_chunks_coord"),
+    )
+    op.create_index("ix_world_chunks_world_id", "world_chunks", ["world_id"])
+    op.create_index("ix_world_chunks_room_id", "world_chunks", ["room_id"])
+    op.create_index(
+        "ix_world_chunks_room_coord", "world_chunks", ["room_id", "cx", "cy", "cz"],
+    )
+    op.create_index(
+        "ix_world_chunks_mature", "world_chunks", ["world_id"],
+        postgresql_where=sa.text("is_mature"),
+    )
+
+    op.create_table(
+        "world_chunk_revisions",
+        sa.Column("id", sa.Integer(), primary_key=True, index=True),
+        sa.Column("chunk_key", sa.String(160), nullable=False),
+        sa.Column("world_id", sa.Integer(), nullable=False),
+        sa.Column("revision", sa.Integer(), nullable=False),
+        sa.Column("action", sa.String(16), nullable=False),
+        sa.Column(
+            "actor_id", sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("checksum", sa.String(64), nullable=False),
+        sa.Column("payload", sa.LargeBinary(), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+    op.create_index("ix_world_chunk_revisions_chunk_key", "world_chunk_revisions", ["chunk_key"])
+    op.create_index("ix_world_chunk_revisions_world_id", "world_chunk_revisions", ["world_id"])
+    op.create_index("ix_world_chunk_revisions_created_at", "world_chunk_revisions", ["created_at"])
+
+
+def downgrade() -> None:
+    op.drop_table("world_chunk_revisions")
+    op.drop_table("world_chunks")
+    op.drop_table("world_rooms")

backend/alembic/versions/0006_add_presence_columns.py

@@ -0,0 +1,33 @@
+"""add presence columns to users
+
+Revision ID: 0006_add_presence_columns
+Revises: 0005_add_world_content_tables
+Create Date: 2026-09-14 00:00:00.000000
+
+Ported forward from the orphaned agent/dd2a126b57a1 branch (originally
+2a9b9873244a_add_presence_columns.py, down_revision 0001_initial) and
+rebased onto the current migration head. See app/services/presence.py /
+app/routers/presence.py.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision: str = "0006_add_presence_columns"
+down_revision: Union[str, None] = "0005_add_world_content_tables"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Add last_seen_at and status_message columns to users table."""
+    op.add_column("users", sa.Column("last_seen_at", sa.DateTime(timezone=True), nullable=True))
+    op.add_column("users", sa.Column("status_message", sa.Text(), nullable=True))
+
+
+def downgrade() -> None:
+    """Remove presence columns from users table."""
+    op.drop_column("users", "status_message")
+    op.drop_column("users", "last_seen_at")

backend/alembic/versions/0007_add_social_graph_tables.py

@@ -0,0 +1,118 @@
+"""add social graph tables (friendships, follows, blocks)
+
+Revision ID: 0007_add_social_graph_tables
+Revises: 0006_add_presence_columns
+Create Date: 2026-09-15 00:00:00.000000
+
+docs/planning/social.md US-1 / app/models/social.py. Models + migration
+only -- the request/accept/block business logic lives in the sibling
+"Friends & follow API router" task.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "0007_add_social_graph_tables"
+down_revision: Union[str, None] = "0006_add_presence_columns"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    friendship_status = postgresql.ENUM(
+        "pending", "accepted", name="friendship_status"
+    )
+    friendship_status.create(op.get_bind(), checkfirst=True)
+
+    op.create_table(
+        "friendships",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "requester_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "addressee_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "status",
+            postgresql.ENUM(
+                "pending", "accepted", name="friendship_status", create_type=False
+            ),
+            nullable=False,
+            server_default="pending",
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.UniqueConstraint("requester_id", "addressee_id", name="uq_friendships_pair"),
+    )
+    op.create_index("ix_friendships_requester_id", "friendships", ["requester_id"])
+    op.create_index("ix_friendships_addressee_id", "friendships", ["addressee_id"])
+
+    op.create_table(
+        "follows",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "follower_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "followed_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.UniqueConstraint("follower_id", "followed_id", name="uq_follows_pair"),
+    )
+    op.create_index("ix_follows_follower_id", "follows", ["follower_id"])
+    op.create_index("ix_follows_followed_id", "follows", ["followed_id"])
+
+    op.create_table(
+        "blocks",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "blocker_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "blocked_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.UniqueConstraint("blocker_id", "blocked_id", name="uq_blocks_pair"),
+    )
+    op.create_index("ix_blocks_blocker_id", "blocks", ["blocker_id"])
+    op.create_index("ix_blocks_blocked_id", "blocks", ["blocked_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_blocks_blocked_id", table_name="blocks")
+    op.drop_index("ix_blocks_blocker_id", table_name="blocks")
+    op.drop_table("blocks")
+
+    op.drop_index("ix_follows_followed_id", table_name="follows")
+    op.drop_index("ix_follows_follower_id", table_name="follows")
+    op.drop_table("follows")
+
+    op.drop_index("ix_friendships_addressee_id", table_name="friendships")
+    op.drop_index("ix_friendships_requester_id", table_name="friendships")
+    op.drop_table("friendships")
+
+    postgresql.ENUM(name="friendship_status").drop(op.get_bind(), checkfirst=True)

backend/alembic/versions/0008_add_chat_tables.py

@@ -0,0 +1,178 @@
+"""add chat tables (conversations, messages, message_reports)
+
+Revision ID: 0008_add_chat_tables
+Revises: 0007_add_social_graph_tables
+Create Date: 2026-09-15 00:00:00.000000
+
+docs/planning/social.md US-4 / app/models/chat.py. Models + migration only
+-- text filtering, rate limiting, and send/report/moderation endpoints live
+in sibling tasks that depend on this one.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "0008_add_chat_tables"
+down_revision: Union[str, None] = "0007_add_social_graph_tables"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    message_report_status = postgresql.ENUM(
+        "open", "resolved", "dismissed", name="message_report_status"
+    )
+    message_report_status.create(op.get_bind(), checkfirst=True)
+
+    op.create_table(
+        "conversations",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "user_a_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "user_b_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.UniqueConstraint("user_a_id", "user_b_id", name="uq_conversations_pair"),
+        sa.CheckConstraint("user_a_id < user_b_id", name="ck_conversations_ordered_pair"),
+    )
+    op.create_index("ix_conversations_user_a_id", "conversations", ["user_a_id"])
+    op.create_index("ix_conversations_user_b_id", "conversations", ["user_b_id"])
+
+    op.create_table(
+        "conversation_participants",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "conversation_id",
+            sa.Integer(),
+            sa.ForeignKey("conversations.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "user_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.UniqueConstraint(
+            "conversation_id", "user_id", name="uq_conversation_participants_pair"
+        ),
+    )
+    op.create_index(
+        "ix_conversation_participants_conversation_id",
+        "conversation_participants",
+        ["conversation_id"],
+    )
+    op.create_index(
+        "ix_conversation_participants_user_id", "conversation_participants", ["user_id"]
+    )
+
+    op.create_table(
+        "messages",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "sender_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column(
+            "conversation_id",
+            sa.Integer(),
+            sa.ForeignKey("conversations.id", ondelete="CASCADE"),
+            nullable=True,
+        ),
+        sa.Column(
+            "world_id",
+            sa.Integer(),
+            sa.ForeignKey("worlds.id", ondelete="CASCADE"),
+            nullable=True,
+        ),
+        sa.Column(
+            "room_id",
+            sa.Integer(),
+            sa.ForeignKey("world_rooms.id", ondelete="CASCADE"),
+            nullable=True,
+        ),
+        sa.Column("body", sa.Text(), nullable=False),
+        sa.Column("filtered", sa.Boolean(), nullable=False, server_default="false"),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+    op.create_index("ix_messages_sender_id", "messages", ["sender_id"])
+    op.create_index(
+        "ix_messages_conversation_created", "messages", ["conversation_id", "created_at"]
+    )
+    op.create_index("ix_messages_world_created", "messages", ["world_id", "created_at"])
+
+    op.create_table(
+        "message_reports",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "message_id",
+            sa.Integer(),
+            sa.ForeignKey("messages.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column(
+            "reporter_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("reason", sa.Text(), nullable=False),
+        sa.Column(
+            "status",
+            postgresql.ENUM(
+                "open", "resolved", "dismissed", name="message_report_status", create_type=False
+            ),
+            nullable=False,
+            server_default="open",
+        ),
+        sa.Column(
+            "moderator_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("resolved_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+    op.create_index("ix_message_reports_message_id", "message_reports", ["message_id"])
+    op.create_index("ix_message_reports_reporter_id", "message_reports", ["reporter_id"])
+    op.create_index("ix_message_reports_moderator_id", "message_reports", ["moderator_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_message_reports_moderator_id", table_name="message_reports")
+    op.drop_index("ix_message_reports_reporter_id", table_name="message_reports")
+    op.drop_index("ix_message_reports_message_id", table_name="message_reports")
+    op.drop_table("message_reports")
+
+    op.drop_index("ix_messages_world_created", table_name="messages")
+    op.drop_index("ix_messages_conversation_created", table_name="messages")
+    op.drop_index("ix_messages_sender_id", table_name="messages")
+    op.drop_table("messages")
+
+    op.drop_index("ix_conversation_participants_user_id", table_name="conversation_participants")
+    op.drop_index(
+        "ix_conversation_participants_conversation_id", table_name="conversation_participants"
+    )
+    op.drop_table("conversation_participants")
+
+    op.drop_index("ix_conversations_user_b_id", table_name="conversations")
+    op.drop_index("ix_conversations_user_a_id", table_name="conversations")
+    op.drop_table("conversations")
+
+    postgresql.ENUM(name="message_report_status").drop(op.get_bind(), checkfirst=True)

backend/alembic/versions/0009_add_group_tables.py

@@ -0,0 +1,80 @@
+"""add group tables (groups, group_members)
+
+Revision ID: 0009_add_group_tables
+Revises: 0008_add_chat_tables
+Create Date: 2026-09-15 00:00:00.000000
+
+docs/planning/social.md US-5 / app/models/groups.py. Models + migration only
+-- create/join/leave, role authorization, and the group page endpoint live
+in a sibling task ("Groups API") that depends on this one.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "0009_add_group_tables"
+down_revision: Union[str, None] = "0008_add_chat_tables"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    group_role = postgresql.ENUM("owner", "admin", "member", name="group_role")
+    group_role.create(op.get_bind(), checkfirst=True)
+
+    op.create_table(
+        "groups",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column("name", sa.String(length=100), nullable=False),
+        sa.Column("description", sa.Text(), nullable=True),
+        sa.Column(
+            "owner_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+    op.create_index("ix_groups_owner_id", "groups", ["owner_id"])
+
+    op.create_table(
+        "group_members",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column(
+            "group_id",
+            sa.Integer(),
+            sa.ForeignKey("groups.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "user_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            nullable=False,
+        ),
+        sa.Column(
+            "role",
+            postgresql.ENUM("owner", "admin", "member", name="group_role", create_type=False),
+            nullable=False,
+            server_default="member",
+        ),
+        sa.Column("joined_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.UniqueConstraint("group_id", "user_id", name="uq_group_members_pair"),
+    )
+    op.create_index("ix_group_members_group_id", "group_members", ["group_id"])
+    op.create_index("ix_group_members_user_id", "group_members", ["user_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_group_members_user_id", table_name="group_members")
+    op.drop_index("ix_group_members_group_id", table_name="group_members")
+    op.drop_table("group_members")
+
+    op.drop_index("ix_groups_owner_id", table_name="groups")
+    op.drop_table("groups")
+
+    postgresql.ENUM(name="group_role").drop(op.get_bind(), checkfirst=True)

backend/alembic/versions/0010_add_profile_tables.py

@@ -0,0 +1,65 @@
+"""add profile tables (profiles, profile_favorites)
+
+Revision ID: 0010_add_profile_tables
+Revises: 0009_add_group_tables
+Create Date: 2026-09-15 00:00:00.000000
+
+app/models/profile.py. Models + migration + owner-only /api/profile/me
+endpoints only -- the public profile view endpoint (GET /api/profile/{user_id})
+belongs to a sibling task that depends on this one.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "0010_add_profile_tables"
+down_revision: Union[str, None] = "0009_add_group_tables"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "profiles",
+        sa.Column("user_id", sa.Integer(), sa.ForeignKey("users.id", ondelete="CASCADE"), primary_key=True),
+        sa.Column(
+            "avatar_asset_id",
+            sa.Integer(),
+            sa.ForeignKey("assets.id", ondelete="SET NULL"),
+            nullable=True,
+        ),
+        sa.Column("bio", sa.Text(), nullable=True),
+        sa.Column("privacy_json", postgresql.JSONB(), nullable=False, server_default="{}"),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+    op.create_index("ix_profiles_avatar_asset_id", "profiles", ["avatar_asset_id"])
+
+    op.create_table(
+        "profile_favorites",
+        sa.Column(
+            "user_id",
+            sa.Integer(),
+            sa.ForeignKey("users.id", ondelete="CASCADE"),
+            primary_key=True,
+        ),
+        sa.Column(
+            "world_id",
+            sa.Integer(),
+            sa.ForeignKey("worlds.id", ondelete="CASCADE"),
+            primary_key=True,
+        ),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+    op.create_index("ix_profile_favorites_world_id", "profile_favorites", ["world_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_profile_favorites_world_id", table_name="profile_favorites")
+    op.drop_table("profile_favorites")
+
+    op.drop_index("ix_profiles_avatar_asset_id", table_name="profiles")
+    op.drop_table("profiles")

backend/alembic/versions/0011_add_dm_last_read.py

@@ -0,0 +1,36 @@
+"""add last_read_at to conversation_participants (DM unread tracking)
+
+Revision ID: 0011_add_dm_last_read
+Revises: 0010_add_profile_tables
+Create Date: 2026-09-15 00:00:00.000000
+
+app/routers/chat_dm.py (DM send/list/conversations endpoints). Unread-count
+tracking is implemented as a last-read timestamp per participant: whenever a
+user fetches a conversation's message history, their
+``conversation_participants`` row's ``last_read_at`` is bumped to "now", and
+the conversation-list endpoint counts messages with
+``created_at > last_read_at`` (or all messages if never read) as unread for
+that participant. Nullable/no default so existing rows (none yet in
+practice, but consistent with "never read") read as "everything unread".
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision: str = "0011_add_dm_last_read"
+down_revision: Union[str, None] = "0010_add_profile_tables"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "conversation_participants",
+        sa.Column("last_read_at", sa.DateTime(timezone=True), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("conversation_participants", "last_read_at")

backend/app/config.py

@@ -75,11 +75,52 @@ class Settings(BaseSettings):
     # CORS
     CORS_ORIGINS: str = "http://localhost:8080,http://localhost:3000"
 
+    # Per-IP auth rate limiting (app/rate_limit.py). Disabled by the
+    # checkpoint smoke suite, which runs every test from one client IP.
+    RATE_LIMIT_ENABLED: bool = True
+
     # File uploads
     UPLOAD_DIR: str = "uploads"
     MAX_UPLOAD_SIZE_MB: int = 100
     GLTF_MAX_FILE_SIZE_MB: int = 200
 
+    # ── Game-server orchestration ──────────────────────────────────────────
+    # The join flow (POST /api/worlds/{id}/join) ensures a headless Godot
+    # dedicated-server process exists for a world and returns its address.
+    # Disabled by default so nothing tries to spawn Godot in environments
+    # that don't have it (plain pytest, CI without the engine); the
+    # checkpoint/playtest launcher turns it on.
+    GAME_SERVERS_ENABLED: bool = False
+    # Path to the Godot 4 binary. "godot" resolves via PATH.
+    GODOT_BIN: str = str(Path.home() / "godot" / "godot")
+    # Godot project directory (the game repo root -- backend/ is a subdir).
+    GAME_PROJECT_DIR: str = str(Path(__file__).resolve().parents[2])
+    # The host clients should connect to for ENet. Defaults to the LAN IP the
+    # launcher bakes into the exe; overridable for local testing.
+    GAME_SERVER_HOST: str = "127.0.0.1"
+    # Port range for per-world dedicated servers.
+    GAME_SERVER_PORT_MIN: int = 27000
+    GAME_SERVER_PORT_MAX: int = 27099
+    # Kill a world's server this long after its last join with no active
+    # players reported.
+    GAME_SERVER_IDLE_TIMEOUT_SECONDS: int = 300
+    # How long ensure_server() waits for a spawned server to report
+    # "ready": true in its status file before giving up (503 to the
+    # joining client). See world_persistence_impl.md §7.4 -- content
+    # loading makes a slow start more likely than the old bare-port-bind
+    # wait, so this is a separate, longer-by-default budget.
+    GAME_SERVER_READY_TIMEOUT_SECONDS: float = 20.0
+    # The base URL the dedicated Godot server should call back into this
+    # backend on, for the read-only /api/internal content routes
+    # (world_persistence_impl.md §4.4 / §7).
+    GAME_SERVER_INTERNAL_API_URL: str = "http://127.0.0.1:8000"
+
+    # ── World content persistence (world_persistence_impl.md §4.4) ─────────
+    WORLD_CHUNK_MAX_PAYLOAD_BYTES: int = 1_048_576  # 1 MiB
+    WORLD_CHUNK_MAX_OBJECTS: int = 512
+    WORLD_CHUNK_MAX_BATCH: int = 64
+    WORLD_CHUNK_REVISION_KEEP: int = 20
+
     model_config = SettingsConfigDict(
         env_file=".env",
         env_file_encoding="utf-8",

backend/app/main.py

@@ -6,15 +6,18 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.config import settings
-from app.routers import auth, users, worlds, assets
+from app.routers import auth, users, worlds, assets, avatar, world_content, internal, presence, groups, social_friends, profiles, chat_dm
+
+
+from app.services.game_servers import supervisor
 
 
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     """Application lifespan: startup and shutdown events."""
-    # Startup: initialize database, connect to Redis, etc.
+    supervisor.start()
     yield
-    # Shutdown: close connections, cleanup
+    await supervisor.shutdown()
 
 
 app = FastAPI(
@@ -37,7 +40,15 @@ app.add_middleware(
 app.include_router(auth.router, prefix="/api/auth", tags=["auth"])
 app.include_router(users.router, prefix="/api/users", tags=["users"])
 app.include_router(worlds.router, prefix="/api/worlds", tags=["worlds"])
+app.include_router(world_content.router, prefix="/api/worlds", tags=["world-content"])
 app.include_router(assets.router, prefix="/api/assets", tags=["assets"])
+app.include_router(avatar.router, prefix="/api/avatar", tags=["avatar"])
+app.include_router(internal.router, prefix="/api/internal", tags=["internal"])
+app.include_router(presence.router, prefix="/api/presence", tags=["presence"])
+app.include_router(groups.router, prefix="/api/groups", tags=["groups"])
+app.include_router(social_friends.router, prefix="/api/friends", tags=["friends"])
+app.include_router(profiles.router, prefix="/api/profile", tags=["profile"])
+app.include_router(chat_dm.router, prefix="/api/chat/dm", tags=["chat-dm"])
 
 
 @app.get("/api/health")

backend/app/models/__init__.py

@@ -2,5 +2,20 @@ from app.models.user import User
 from app.models.session import Session
 from app.models.world import World
 from app.models.asset import Asset
+from app.models.avatar_loadout import AvatarLoadout
+from app.models.world_content import WorldRoom, WorldChunk, WorldChunkRevision
+from app.models.social import Friendship, Follow, Block, FriendshipStatus
+from app.models.chat import (
+    Conversation, ConversationParticipant, Message, MessageReport, ReportStatus,
+)
+from app.models.groups import Group, GroupMember, GroupRole
+from app.models.profile import Profile, ProfileFavorite, ProfileVisibility
 
-__all__ = ["User", "Session", "World", "Asset"]
+__all__ = [
+    "User", "Session", "World", "Asset", "AvatarLoadout",
+    "WorldRoom", "WorldChunk", "WorldChunkRevision",
+    "Friendship", "Follow", "Block", "FriendshipStatus",
+    "Conversation", "ConversationParticipant", "Message", "MessageReport", "ReportStatus",
+    "Group", "GroupMember", "GroupRole",
+    "Profile", "ProfileFavorite", "ProfileVisibility",
+]

backend/app/models/asset.py

@@ -23,7 +23,12 @@ class Asset(Base):
     name = Column(String(255), nullable=False)
     description = Column(Text, nullable=True)
     asset_type = Column(
-        ENUM(AssetType, name="asset_type", create_type=False),
+        ENUM(
+            AssetType,
+            name="asset_type",
+            create_type=False,
+            values_callable=lambda enum_cls: [e.value for e in enum_cls],
+        ),
         nullable=False,
     )
     file_path = Column(String(512), nullable=False)

backend/app/models/avatar_loadout.py

@@ -0,0 +1,41 @@
+from sqlalchemy import Column, Integer, ForeignKey, DateTime
+from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+# The default a brand-new account gets before they touch the customization
+# screen. Kept in sync with assets/avatars/catalog.json (the base_body id) and
+# with the client's AvatarLoadout.to_json() shape.
+DEFAULT_LOADOUT: dict = {
+    "base_body": "base_human_male_01",
+    "slots": {},
+}
+
+
+class AvatarLoadout(Base):
+    """A user's equipped avatar composition.
+
+    One row per user. The whole loadout is stored as a single JSON document
+    matching the client's ``AvatarLoadout.to_json()`` shape
+    (``{"base_body": str, "slots": {...}, "skin_tone"?: {...}}``) rather than
+    exploded into columns -- the server has no copy of the asset catalog, so
+    deep validation (does this asset exist, is it valid for this slot) stays
+    on the client. The server only enforces the envelope: valid JSON object
+    with a non-empty ``base_body``.
+    """
+
+    __tablename__ = "avatar_loadouts"
+
+    user_id = Column(
+        Integer,
+        ForeignKey("users.id", ondelete="CASCADE"),
+        primary_key=True,
+    )
+    data = Column(JSONB, nullable=False)
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False)
+
+    user = relationship("User", back_populates="avatar_loadout")

backend/app/models/chat.py

@@ -0,0 +1,221 @@
+"""Chat: DM conversations and world/room chat, plus message reports.
+
+docs/planning/social.md §4/§5 (US-4). This module is models + schema only --
+text filtering, rate limiting, and the send/list/report/moderation endpoints
+belong to sibling tasks that depend on this one.
+
+Delete-behavior choices (mirrors ``app/models/world_content.py``'s
+established convention of preserving audit/history data over cascading it
+away):
+
+- ``conversations.user_a_id`` / ``user_b_id`` -> CASCADE. A DM conversation
+  is meaningless with one of its two (and only) participants gone, so
+  deleting either user removes the conversation outright, which in turn
+  cascades to its ``conversation_participants`` rows and its ``messages``.
+- ``conversation_participants.user_id`` -> CASCADE, ``.conversation_id`` ->
+  CASCADE. Pure join-table rows; they only make sense alongside both sides.
+- ``messages.conversation_id`` -> CASCADE. Deleting a conversation deletes
+  its message history with it.
+- ``messages.sender_id`` -> SET NULL (nullable). Unlike a DM conversation
+  (which dies with its participants above), world/room chat history and any
+  message under moderation review should survive the sender's account being
+  deleted -- the row just becomes attributed to no one, matching how
+  ``WorldChunk.updated_by_id`` / ``WorldChunkRevision.actor_id`` treat
+  actor references as SET NULL rather than cascading away history.
+- ``messages.world_id`` / ``room_id`` -> CASCADE. World/room chat has no
+  meaning once the world or room it was said in is gone; consistent with
+  ``WorldChunk``'s own CASCADE from both.
+- ``message_reports.message_id`` -> SET NULL (nullable). Same audit-trail
+  reasoning as ``WorldChunkRevision`` (world_content.py): a moderation
+  report is a record that something *was* said and reported, which must
+  outlive the underlying message being removed (e.g. as the moderation
+  action taken in response to the report itself).
+- ``message_reports.reporter_id`` / ``moderator_id`` -> SET NULL (nullable).
+  Actor references for an audit record; the report itself must survive
+  either account being deleted later, matching the actor-reference
+  convention above.
+"""
+import enum
+
+from sqlalchemy import (
+    Boolean,
+    CheckConstraint,
+    Column,
+    DateTime,
+    ForeignKey,
+    Index,
+    Integer,
+    Text,
+    UniqueConstraint,
+)
+from sqlalchemy.dialects.postgresql import ENUM
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class ReportStatus(str, enum.Enum):
+    OPEN = "open"
+    RESOLVED = "resolved"
+    DISMISSED = "dismissed"
+
+
+class Conversation(Base):
+    """A DM conversation between exactly two users.
+
+    ``conversation_participants`` is the real roster (modeled as a join
+    table so a future group-DM schema change can widen it beyond two rows
+    without touching this table's shape), but a 2-party DM also needs a
+    cheap, DB-enforced "only one conversation per pair" guarantee, which a
+    plain join table can't express as a simple unique constraint. So the
+    pair is additionally denormalized here as ``user_a_id``/``user_b_id``,
+    always stored with the lower user id first (enforced by the check
+    constraint below); the API layer is responsible for normalizing the
+    pair before insert/lookup.
+    """
+
+    __tablename__ = "conversations"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_a_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    user_b_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False
+    )
+
+    participants = relationship(
+        "ConversationParticipant", back_populates="conversation", cascade="all, delete-orphan"
+    )
+    messages = relationship(
+        "Message", back_populates="conversation", cascade="all, delete-orphan"
+    )
+
+    __table_args__ = (
+        UniqueConstraint("user_a_id", "user_b_id", name="uq_conversations_pair"),
+        CheckConstraint("user_a_id < user_b_id", name="ck_conversations_ordered_pair"),
+    )
+
+
+class ConversationParticipant(Base):
+    """Join table of a conversation's members.
+
+    DMs are strictly 2-party today (enforced by ``Conversation``'s pair
+    columns above), but this is modeled as a real join table -- not folded
+    into ``Conversation`` -- so a later group-conversation feature can add
+    rows here without a schema change to this table.
+    """
+
+    __tablename__ = "conversation_participants"
+
+    id = Column(Integer, primary_key=True, index=True)
+    conversation_id = Column(
+        Integer, ForeignKey("conversations.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    user_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    # DM unread tracking (app/routers/chat_dm.py, migration 0010): bumped to
+    # "now" whenever this participant fetches the conversation's history.
+    # Null means "never read" -- everything in the conversation is unread.
+    last_read_at = Column(DateTime(timezone=True), nullable=True)
+
+    conversation = relationship("Conversation", back_populates="participants")
+    user = relationship("User")
+
+    __table_args__ = (
+        UniqueConstraint(
+            "conversation_id", "user_id", name="uq_conversation_participants_pair"
+        ),
+    )
+
+
+class Message(Base):
+    """A chat message: either a DM (``conversation_id`` set) or a
+    world/room chat message (``conversation_id`` null, ``world_id`` set and
+    optionally ``room_id``).
+
+    ``world_id`` is denormalized onto every world/room message (mirroring
+    ``WorldChunk.world_id``) so world-scoped history queries don't need a
+    join through rooms; ``room_id`` narrows further to a specific room when
+    the world subdivides chat by room, and is null for world-wide chat.
+    """
+
+    __tablename__ = "messages"
+
+    id = Column(Integer, primary_key=True, index=True)
+    sender_id = Column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    conversation_id = Column(
+        Integer, ForeignKey("conversations.id", ondelete="CASCADE"), nullable=True
+    )
+    world_id = Column(
+        Integer, ForeignKey("worlds.id", ondelete="CASCADE"), nullable=True
+    )
+    room_id = Column(
+        Integer, ForeignKey("world_rooms.id", ondelete="CASCADE"), nullable=True
+    )
+    body = Column(Text, nullable=False)
+    filtered = Column(Boolean, nullable=False, default=False, server_default="false")
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+
+    sender = relationship("User")
+    conversation = relationship("Conversation", back_populates="messages")
+    world = relationship("World")
+    room = relationship("WorldRoom")
+    reports = relationship(
+        "MessageReport", back_populates="message", cascade="all, delete-orphan"
+    )
+
+    __table_args__ = (
+        Index("ix_messages_conversation_created", "conversation_id", "created_at"),
+        Index("ix_messages_world_created", "world_id", "created_at"),
+    )
+
+
+class MessageReport(Base):
+    """A moderation report filed against a message.
+
+    ``message_id`` is nullable with ``ON DELETE SET NULL`` (rather than
+    CASCADE) so the report -- the audit record that something was said and
+    flagged -- outlives the message row, including when the message's own
+    removal is the moderation action taken in response to this report.
+    """
+
+    __tablename__ = "message_reports"
+
+    id = Column(Integer, primary_key=True, index=True)
+    message_id = Column(
+        Integer, ForeignKey("messages.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    reporter_id = Column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    reason = Column(Text, nullable=False)
+    status = Column(
+        ENUM(
+            ReportStatus,
+            name="message_report_status",
+            create_type=False,
+            values_callable=lambda enum_cls: [e.value for e in enum_cls],
+        ),
+        nullable=False,
+        default=ReportStatus.OPEN,
+        server_default=ReportStatus.OPEN.value,
+    )
+    moderator_id = Column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    resolved_at = Column(DateTime(timezone=True), nullable=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+
+    message = relationship("Message", back_populates="reports")
+    reporter = relationship("User", foreign_keys=[reporter_id])
+    moderator = relationship("User", foreign_keys=[moderator_id])

backend/app/models/groups.py

@@ -0,0 +1,97 @@
+"""Groups: named groups with owner/admin/member roles.
+
+docs/planning/social.md §4/§5 (US-5). This module is models + schema only --
+create/join/leave, role authorization (only the owner may transfer ownership
+or promote/demote admins), and the group page aggregate endpoint belong to
+the API router task ("Groups API") that depends on this one.
+
+Delete-behavior choices:
+
+- ``groups.owner_id`` -> ``SET NULL`` (nullable). A group is a durable,
+  multi-member community, not content solely attributable to one person like
+  a ``World``/``Asset``. Cascading the group away (or hard-blocking the
+  owner's account deletion) would punish every other member for the owner's
+  choice to leave the platform. Instead the group and its full membership
+  list survive with ``owner_id`` nulled out; the sibling API task is
+  responsible for surfacing an ownerless group (e.g. prompting an admin to
+  claim ownership) the same way ``Message.sender_id`` / ``WorldChunk``'s
+  actor columns already treat "the actor is gone" as a survivable state
+  elsewhere in this schema.
+- ``group_members.group_id`` -> ``CASCADE``. A membership row is meaningless
+  without the group it belongs to; deleting a group deletes its roster,
+  mirroring ``ConversationParticipant.conversation_id`` in chat.py.
+- ``group_members.user_id`` -> ``CASCADE``. Deleting a user removes their own
+  membership rows wherever they appear, matching the join-table convention
+  used by ``ConversationParticipant.user_id`` and the social-graph tables
+  (``Friendship``/``Follow``/``Block``) for plain per-user references.
+"""
+import enum
+
+from sqlalchemy import Column, DateTime, ForeignKey, Integer, String, Text, UniqueConstraint
+from sqlalchemy.dialects.postgresql import ENUM
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class GroupRole(str, enum.Enum):
+    OWNER = "owner"
+    ADMIN = "admin"
+    MEMBER = "member"
+
+
+class Group(Base):
+    """A named group. ``owner_id`` is nullable -- see module docstring for
+    why the group survives its owner's account deletion."""
+
+    __tablename__ = "groups"
+
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String(100), nullable=False)
+    description = Column(Text, nullable=True)
+    owner_id = Column(
+        Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False
+    )
+
+    owner = relationship("User", back_populates="owned_groups")
+    members = relationship(
+        "GroupMember", back_populates="group", cascade="all, delete-orphan"
+    )
+
+
+class GroupMember(Base):
+    """A group's roster: one row per (group, user) with a role."""
+
+    __tablename__ = "group_members"
+
+    id = Column(Integer, primary_key=True, index=True)
+    group_id = Column(
+        Integer, ForeignKey("groups.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    user_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    role = Column(
+        ENUM(
+            GroupRole,
+            name="group_role",
+            create_type=False,
+            values_callable=lambda enum_cls: [e.value for e in enum_cls],
+        ),
+        nullable=False,
+        default=GroupRole.MEMBER,
+        server_default=GroupRole.MEMBER.value,
+    )
+    joined_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+
+    group = relationship("Group", back_populates="members")
+    user = relationship("User", back_populates="group_memberships")
+
+    __table_args__ = (
+        UniqueConstraint("group_id", "user_id", name="uq_group_members_pair"),
+    )

backend/app/models/profile.py

@@ -0,0 +1,129 @@
+"""User profile: bio, avatar reference, privacy settings, favorite worlds.
+
+This module is models + migration only -- the public profile view endpoint
+(``GET /api/profile/{user_id}``, which will need to interpret ``privacy_json``
+against the viewer's relationship to the owner) belongs to a sibling task
+that depends on this one. This task only owns the authenticated-owner
+read/write endpoints (``/api/profile/me`` and its ``favorites`` sub-resource).
+
+Design choices:
+
+- ``profiles.user_id`` is both the primary key and the FK to ``users.id``
+  (``ondelete="CASCADE"``) -- exactly one profile row per user, following the
+  same one-row-per-user shape as ``AvatarLoadout`` (app/models/avatar_loadout.py).
+  The row is created lazily (upserted) on first ``PUT /api/profile/me``
+  rather than at registration time, again mirroring ``AvatarLoadout``.
+- ``avatar_asset_id`` -> ``assets.id`` with ``ondelete="SET NULL"``. A
+  profile's chosen "avatar picture" asset is a soft reference: if the
+  underlying asset is later deleted the profile shouldn't be destroyed or
+  left pointing at a dangling id, it should just fall back to "no avatar
+  picture set" (nullable). The API layer additionally validates on write
+  that the referenced asset actually exists (existence is not enforced by
+  the FK alone at the API layer, since the FK only stops inserts of a
+  nonexistent id -- it doesn't tell the caller *why* their PUT failed).
+- ``bio`` is ``Text`` with the 500-char cap enforced at the API/schema layer
+  (Pydantic ``max_length``), matching how ``StatusUpdate.status_message`` in
+  presence.py enforces its length cap in the router rather than the schema.
+- ``privacy_json`` is JSONB (project convention for document-shaped fields --
+  see avatar_loadout.py, world_content.py) holding exactly three keys, each a
+  ``ProfileVisibility`` enum value (stored as its string value in JSON, not a
+  Postgres ENUM type -- there's no need for a DB-level enum since this is a
+  small, entirely API-validated document, and a plain JSONB column is easier
+  to extend with more privacy keys later without a migration):
+    - ``profile_visibility``: who can view the profile at all.
+    - ``friends_list_visibility``: who can see the user's friends list.
+    - ``favorites_visibility``: who can see the user's favorited worlds.
+  Each value is one of "public", "friends", "private". Defaults (applied when
+  a profile is first created) are all "public" -- the least surprising
+  default for a new social feature, matching the "everything visible unless
+  you lock it down" posture other social features here take by default
+  (e.g. presence/status has no privacy gate at all yet).
+- Favorites use a join table (``profile_favorites``: ``user_id`` + ``world_id``,
+  composite PK) rather than a JSON array column. A plain FK join table gets
+  referential integrity for free (a favorited world that's later deleted
+  disappears from favorites automatically via ON DELETE CASCADE, matching
+  how ``World.assets``/``World.rooms`` cascade), lets Postgres enforce
+  "no duplicate favorite" via the composite PK instead of API-layer
+  deduplication, and keeps "does this world still exist" as a DB invariant
+  rather than something every reader has to re-check against a JSON blob.
+  The tradeoff (an extra table/join vs. a single JSON column) is worth it
+  here because favorites are a list of foreign-key references, not a
+  free-form document -- the exact case join tables suit better than JSONB.
+"""
+import enum
+
+from sqlalchemy import Column, Integer, ForeignKey, Text, DateTime
+from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class ProfileVisibility(str, enum.Enum):
+    PUBLIC = "public"
+    FRIENDS = "friends"
+    PRIVATE = "private"
+
+
+# Applied when a profile is created for the first time (lazy upsert on the
+# first PUT /api/profile/me). Keys match the three privacy_json fields
+# documented above.
+DEFAULT_PRIVACY: dict = {
+    "profile_visibility": ProfileVisibility.PUBLIC.value,
+    "friends_list_visibility": ProfileVisibility.PUBLIC.value,
+    "favorites_visibility": ProfileVisibility.PUBLIC.value,
+}
+
+BIO_MAX_LEN = 500
+
+
+class Profile(Base):
+    """One row per user: bio, avatar picture reference, privacy settings."""
+
+    __tablename__ = "profiles"
+
+    user_id = Column(
+        Integer,
+        ForeignKey("users.id", ondelete="CASCADE"),
+        primary_key=True,
+    )
+    avatar_asset_id = Column(
+        Integer,
+        ForeignKey("assets.id", ondelete="SET NULL"),
+        nullable=True,
+    )
+    bio = Column(Text, nullable=True)
+    privacy_json = Column(JSONB, nullable=False, server_default="{}")
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False)
+
+    user = relationship("User", back_populates="profile")
+    avatar_asset = relationship("Asset")
+    # Deliberately no ORM relationship to ProfileFavorite here: profiles and
+    # profile_favorites both independently FK users.id (no direct FK between
+    # the two tables), and the router only ever needs to query/replace a
+    # user's favorites by user_id directly -- not traverse it off a loaded
+    # Profile object. Keeping it a plain queryable table avoids a
+    # hand-spelled, easy-to-get-wrong primaryjoin for no real benefit.
+
+
+class ProfileFavorite(Base):
+    """A user's favorited world. Composite PK -- see module docstring for why
+    this is a join table rather than a JSON array column."""
+
+    __tablename__ = "profile_favorites"
+
+    user_id = Column(
+        Integer,
+        ForeignKey("users.id", ondelete="CASCADE"),
+        primary_key=True,
+    )
+    world_id = Column(
+        Integer,
+        ForeignKey("worlds.id", ondelete="CASCADE"),
+        primary_key=True,
+    )
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+
+    world = relationship("World")

backend/app/models/social.py

@@ -0,0 +1,106 @@
+"""Social graph: friendships, follows, blocks.
+
+docs/planning/social.md §4/§5 (US-1). Friends = mutual (request -> accept),
+Follow = one-way (no approval), Block = hard deny. This module is models +
+schema only -- the request/accept/block business logic (idempotent
+duplicate/self handling, removing an existing friendship/follow on block,
+etc.) belongs to the API router task that depends on this one.
+"""
+import enum
+
+from sqlalchemy import Column, Integer, ForeignKey, DateTime, UniqueConstraint
+from sqlalchemy.dialects.postgresql import ENUM
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class FriendshipStatus(str, enum.Enum):
+    PENDING = "pending"
+    ACCEPTED = "accepted"
+
+
+class Friendship(Base):
+    """A friend request, directional until accepted.
+
+    ``requester_id`` sent the request to ``addressee_id``. Once accepted the
+    friendship is mutual, but the row stays directional (who asked whom) for
+    audit purposes; the API layer treats it as symmetric once accepted.
+    """
+
+    __tablename__ = "friendships"
+
+    id = Column(Integer, primary_key=True, index=True)
+    requester_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    addressee_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    status = Column(
+        ENUM(
+            FriendshipStatus,
+            name="friendship_status",
+            create_type=False,
+            values_callable=lambda enum_cls: [e.value for e in enum_cls],
+        ),
+        nullable=False,
+        default=FriendshipStatus.PENDING,
+        server_default=FriendshipStatus.PENDING.value,
+    )
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False)
+
+    requester = relationship("User", foreign_keys=[requester_id], back_populates="sent_friend_requests")
+    addressee = relationship("User", foreign_keys=[addressee_id], back_populates="received_friend_requests")
+
+    __table_args__ = (
+        UniqueConstraint("requester_id", "addressee_id", name="uq_friendships_pair"),
+    )
+
+
+class Follow(Base):
+    """A one-way follow relationship: ``follower_id`` follows ``followed_id``."""
+
+    __tablename__ = "follows"
+
+    id = Column(Integer, primary_key=True, index=True)
+    follower_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    followed_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False)
+
+    follower = relationship("User", foreign_keys=[follower_id], back_populates="following")
+    followed = relationship("User", foreign_keys=[followed_id], back_populates="followers")
+
+    __table_args__ = (
+        UniqueConstraint("follower_id", "followed_id", name="uq_follows_pair"),
+    )
+
+
+class Block(Base):
+    """A hard deny: ``blocker_id`` has blocked ``blocked_id``."""
+
+    __tablename__ = "blocks"
+
+    id = Column(Integer, primary_key=True, index=True)
+    blocker_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    blocked_id = Column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False)
+
+    blocker = relationship("User", foreign_keys=[blocker_id], back_populates="blocks_initiated")
+    blocked = relationship("User", foreign_keys=[blocked_id], back_populates="blocked_by")
+
+    __table_args__ = (
+        UniqueConstraint("blocker_id", "blocked_id", name="uq_blocks_pair"),
+    )

backend/app/models/user.py

@@ -1,7 +1,7 @@
 from datetime import date
 from typing import Optional
 
-from sqlalchemy import Column, Integer, String, Boolean, DateTime, Date
+from sqlalchemy import Column, Integer, String, Boolean, DateTime, Date, Text
 from sqlalchemy.orm import relationship
 from sqlalchemy.sql import func
 
@@ -20,10 +20,77 @@ class User(Base):
     created_at = Column(DateTime(timezone=True), server_default=func.now())
     updated_at = Column(DateTime(timezone=True), onupdate=func.now())
 
+    # Presence / status (backend/app/services/presence.py, app/routers/presence.py)
+    last_seen_at = Column(DateTime(timezone=True), nullable=True)
+    status_message = Column(Text, nullable=True)
+
     sessions = relationship("Session", back_populates="user", cascade="all, delete-orphan")
     refresh_tokens = relationship("RefreshToken", back_populates="user", cascade="all, delete-orphan")
     worlds = relationship("World", back_populates="owner")
     assets = relationship("Asset", back_populates="owner")
+    avatar_loadout = relationship(
+        "AvatarLoadout",
+        back_populates="user",
+        uselist=False,
+        cascade="all, delete-orphan",
+    )
+
+    # Profile (app/models/profile.py): bio/avatar picture/privacy + favorites.
+    profile = relationship(
+        "Profile",
+        back_populates="user",
+        uselist=False,
+        cascade="all, delete-orphan",
+    )
+
+    # Social graph (docs/planning/social.md US-1; app/models/social.py)
+    sent_friend_requests = relationship(
+        "Friendship",
+        foreign_keys="Friendship.requester_id",
+        back_populates="requester",
+        cascade="all, delete-orphan",
+    )
+    received_friend_requests = relationship(
+        "Friendship",
+        foreign_keys="Friendship.addressee_id",
+        back_populates="addressee",
+        cascade="all, delete-orphan",
+    )
+    following = relationship(
+        "Follow",
+        foreign_keys="Follow.follower_id",
+        back_populates="follower",
+        cascade="all, delete-orphan",
+    )
+    followers = relationship(
+        "Follow",
+        foreign_keys="Follow.followed_id",
+        back_populates="followed",
+        cascade="all, delete-orphan",
+    )
+    blocks_initiated = relationship(
+        "Block",
+        foreign_keys="Block.blocker_id",
+        back_populates="blocker",
+        cascade="all, delete-orphan",
+    )
+    blocked_by = relationship(
+        "Block",
+        foreign_keys="Block.blocked_id",
+        back_populates="blocked",
+        cascade="all, delete-orphan",
+    )
+
+    # Groups (docs/planning/social.md US-5; app/models/groups.py)
+    owned_groups = relationship(
+        "Group",
+        back_populates="owner",
+    )
+    group_memberships = relationship(
+        "GroupMember",
+        back_populates="user",
+        cascade="all, delete-orphan",
+    )
 
     @property
     def is_adult(self) -> bool:

backend/app/models/world.py

@@ -34,3 +34,6 @@ class World(Base):
 
     owner = relationship("User", back_populates="worlds")
     assets = relationship("Asset", back_populates="world", cascade="all, delete-orphan")
+    # world_content.py / world_persistence_impl.md §4.1. Added here (only)
+    # so PC1/PC2 code depending on this module is otherwise untouched.
+    rooms = relationship("WorldRoom", back_populates="world", cascade="all, delete-orphan")

backend/app/models/world_content.py

@@ -0,0 +1,153 @@
+"""World content persistence models.
+
+Implements the schema decided in ``docs/architecture/world_persistence_impl.md``
+§4: chunk content (rooms, chunk payloads, chunk revisions) lives in Postgres,
+alongside ``worlds``, rather than in a per-world SQLite file
+(``docs/architecture/world.md`` §4, superseded).
+
+The chunk *payload* format itself (the 48-byte header + sectioned binary
+body) is unchanged from ``world.md`` §3.6 and is decoded/encoded by
+``app.services.chunk_codec``, not by these models -- these just store the
+opaque ``BYTEA``.
+
+Conventions follow the existing models (``app/models/world.py``,
+``app/models/avatar_loadout.py``): declarative ``Column(...)`` style,
+``Integer`` surrogate PKs, ``DateTime(timezone=True)`` with
+``server_default=func.now()``, JSONB for document-shaped fields.
+"""
+
+from sqlalchemy import (
+    Boolean,
+    Column,
+    DateTime,
+    ForeignKey,
+    Index,
+    Integer,
+    LargeBinary,
+    String,
+    UniqueConstraint,
+    text,
+)
+from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+# Default chunk grid, matching Chunk.CHUNK_SIZE_* in scripts/chunk.gd (the
+# client's source of truth for the same constants) and world.md §2.2.
+DEFAULT_ROOM_GRID: dict = {"size": [32, 32, 1], "origin": [0, 0, 0]}
+
+# The room every world gets automatically (world_persistence_impl.md §4.1).
+MAIN_ROOM_SLUG = "main"
+MAIN_ROOM_NAME = "Main"
+
+
+class WorldRoom(Base):
+    """A bounded region within a world -- a level, building, or zone
+    (world.md §2.1). Holds the chunk grid config so a world can later hold
+    rooms with different grids without touching the ``worlds`` table.
+    """
+
+    __tablename__ = "world_rooms"
+
+    id = Column(Integer, primary_key=True, index=True)
+    world_id = Column(
+        Integer, ForeignKey("worlds.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    slug = Column(String(64), nullable=False)  # url-safe; "main" by default
+    name = Column(String(255), nullable=False)
+    # {"size": [x, y, z], "origin": [x, y, z]}
+    grid = Column(
+        JSONB, nullable=False,
+        server_default='{"size": [32, 32, 1], "origin": [0, 0, 0]}',
+    )
+    bounds = Column(JSONB, nullable=True)  # {"min":[x,y,z], "max":[x,y,z]}; null = unbounded
+    spawn = Column(JSONB, nullable=True)  # {"pos":[x,y,z], "yaw": 0.0}
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False
+    )
+
+    __table_args__ = (
+        UniqueConstraint("world_id", "slug", name="uq_world_rooms_world_slug"),
+    )
+
+    world = relationship("World", back_populates="rooms")
+    chunks = relationship("WorldChunk", back_populates="room", cascade="all, delete-orphan")
+
+
+class WorldChunk(Base):
+    """One chunk's persisted content -- the atomic load/save/stream unit
+    (world.md §2.1). ``payload`` is the world.md §3.6 binary blob, stored
+    verbatim as BYTEA.
+
+    Deltas from world.md §4.4 (SQLite design): a surrogate integer PK +
+    unique coordinate constraint (rather than ``chunk_key`` as the PK), no
+    ``dirty`` column (write-behind doesn't apply over Postgres -- see
+    world_persistence_impl.md §3.3/§5), and content flags folded into this
+    row as JSONB + an indexed ``is_mature`` boolean rather than a separate
+    ``content_flags`` table (world.md §4.6).
+    """
+
+    __tablename__ = "world_chunks"
+
+    id = Column(Integer, primary_key=True, index=True)
+    world_id = Column(
+        Integer, ForeignKey("worlds.id", ondelete="CASCADE"), nullable=False, index=True
+    )  # denormalized: world-scoped queries without a join through rooms
+    room_id = Column(
+        Integer, ForeignKey("world_rooms.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    chunk_key = Column(String(160), nullable=False, unique=True)  # world.md §2.3 / §4.5
+    cx = Column(Integer, nullable=False)
+    cy = Column(Integer, nullable=False)
+    cz = Column(Integer, nullable=False, server_default="0")
+
+    format_version = Column(Integer, nullable=False, server_default="1")
+    payload = Column(LargeBinary, nullable=False)  # world.md §3.6 bytes
+    payload_len = Column(Integer, nullable=False)
+    checksum = Column(String(64), nullable=False)  # SHA-256 hex of payload body
+    revision = Column(Integer, nullable=False, server_default="1")
+
+    content_flags = Column(JSONB, nullable=False, server_default="{}")  # world.md §3.4
+    is_mature = Column(Boolean, nullable=False, server_default="false")
+
+    updated_by_id = Column(Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False)
+    updated_at = Column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False
+    )
+
+    __table_args__ = (
+        UniqueConstraint("room_id", "cx", "cy", "cz", name="uq_world_chunks_coord"),
+        Index("ix_world_chunks_room_coord", "room_id", "cx", "cy", "cz"),
+        Index("ix_world_chunks_mature", "world_id", postgresql_where=text("is_mature")),
+    )
+
+    room = relationship("WorldRoom", back_populates="chunks")
+
+
+class WorldChunkRevision(Base):
+    """Audit trail of chunk writes (world.md §4.7). ``chunk_key``/``world_id``
+    are deliberately **not** foreign keys, so deleting a chunk or a world
+    preserves the audit trail.
+
+    Retention (world_persistence_impl.md §4.3, required): only the newest
+    ``settings.WORLD_CHUNK_REVISION_KEEP`` rows per ``chunk_key`` keep a
+    non-null ``payload``; older rows are pruned (payload nulled, metadata
+    row kept) by ``WorldStore`` in the same transaction as the write that
+    triggers it.
+    """
+
+    __tablename__ = "world_chunk_revisions"
+
+    id = Column(Integer, primary_key=True, index=True)
+    chunk_key = Column(String(160), nullable=False, index=True)
+    world_id = Column(Integer, nullable=False, index=True)
+    revision = Column(Integer, nullable=False)
+    action = Column(String(16), nullable=False)  # 'create' | 'update' | 'delete'
+    actor_id = Column(Integer, ForeignKey("users.id", ondelete="SET NULL"), nullable=True)
+    checksum = Column(String(64), nullable=False)
+    payload = Column(LargeBinary, nullable=True)  # full payload at this revision; nulled by retention
+    created_at = Column(DateTime(timezone=True), server_default=func.now(), nullable=False, index=True)

backend/app/rate_limit.py

@@ -0,0 +1,114 @@
+"""Lightweight in-process rate limiting.
+
+The backend runs single-worker (required by the game-server supervisor), so a
+process-local sliding-window counter is sufficient and needs no Redis. Keyed
+by client IP. Used to blunt credential brute-force on the auth endpoints.
+
+If the backend is ever scaled to multiple workers/hosts this must move to a
+shared store (Redis) -- flagged here rather than silently under-enforcing.
+"""
+from __future__ import annotations
+
+import time
+from collections import defaultdict, deque
+
+from fastapi import HTTPException, Request, status
+
+from app.config import settings
+
+
+class SlidingWindowLimiter:
+    def __init__(self, max_hits: int, window_seconds: float) -> None:
+        self.max_hits = max_hits
+        self.window = window_seconds
+        self._hits: dict[str, deque[float]] = defaultdict(deque)
+
+    def check(self, key: str) -> None:
+        now = time.monotonic()
+        q = self._hits[key]
+        cutoff = now - self.window
+        while q and q[0] < cutoff:
+            q.popleft()
+        if len(q) >= self.max_hits:
+            retry = max(1, int(q[0] + self.window - now))
+            raise HTTPException(
+                status_code=status.HTTP_429_TOO_MANY_REQUESTS,
+                detail="Too many attempts. Try again shortly.",
+                headers={"Retry-After": str(retry)},
+            )
+        q.append(now)
+
+    def reset(self) -> None:
+        self._hits.clear()
+
+
+def _client_key(request: Request) -> str:
+    # X-Forwarded-For first hop when behind the reverse proxy, else the socket.
+    fwd = request.headers.get("x-forwarded-for", "")
+    if fwd:
+        return fwd.split(",")[0].strip()
+    return request.client.host if request.client else "unknown"
+
+
+# 10 auth attempts / minute / IP -- generous for a human, painful for a
+# brute-forcer.
+_auth_limiter = SlidingWindowLimiter(max_hits=10, window_seconds=60)
+
+# Every limiter in the process -- named limits built via `rate_limit()`
+# below register themselves here too, so `reset_all()` (the test hook) and
+# any future process-wide accounting stay correct without each caller
+# having to remember to wire it up.
+_registered_limiters: list[SlidingWindowLimiter] = [_auth_limiter]
+
+
+async def auth_rate_limit(request: Request) -> None:
+    """FastAPI dependency: rate-limit auth attempts per client IP.
+
+    A no-op when ``RATE_LIMIT_ENABLED`` is false -- the checkpoint smoke
+    suite runs every test against one backend from one client IP, so the
+    per-IP cap would trip mid-suite. The dedicated ``test_rate_limit``
+    module exercises the real behaviour regardless of this flag.
+    """
+    if not settings.RATE_LIMIT_ENABLED:
+        return
+    _auth_limiter.check(f"auth:{_client_key(request)}")
+
+
+def rate_limit(name: str, *, max_hits: int, window_seconds: float):
+    """Build a named, per-client-IP FastAPI rate-limit dependency.
+
+    Generalizes the ``auth_rate_limit`` pattern above for other endpoints
+    (e.g. chat send, message report) that want their own independent cap:
+
+        report_rate_limit = rate_limit("message_report", max_hits=5, window_seconds=60)
+
+        @router.post("/report", dependencies=[Depends(report_rate_limit)])
+        ...
+
+    Each call gets its own ``SlidingWindowLimiter`` -- counters for one
+    named limit never bleed into another, even for the same client IP --
+    and reuses ``SlidingWindowLimiter.check`` for the actual sliding-window
+    accounting and the 429 + ``Retry-After`` response. Like
+    ``auth_rate_limit``, the returned dependency is a no-op when
+    ``settings.RATE_LIMIT_ENABLED`` is false, so the checkpoint smoke suite
+    (one client IP for the whole run) doesn't trip on it.
+
+    ``name`` only needs to be unique within the process; it namespaces the
+    per-IP key so it doesn't collide with ``auth_rate_limit`` or any other
+    named limit.
+    """
+    limiter = SlidingWindowLimiter(max_hits=max_hits, window_seconds=window_seconds)
+    _registered_limiters.append(limiter)
+
+    async def _dependency(request: Request) -> None:
+        if not settings.RATE_LIMIT_ENABLED:
+            return
+        limiter.check(f"{name}:{_client_key(request)}")
+
+    return _dependency
+
+
+def reset_all() -> None:
+    """Test hook."""
+    for limiter in _registered_limiters:
+        limiter.reset()

backend/app/routers/auth.py

@@ -7,7 +7,7 @@ from fastapi import APIRouter, Depends, HTTPException, status
 from fastapi.security import OAuth2PasswordRequestForm
 from jose import JWTError, jwt
 from passlib.context import CryptContext
-from pydantic import BaseModel, EmailStr, field_validator
+from pydantic import BaseModel, EmailStr
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
@@ -16,11 +16,15 @@ from app.database import get_db
 from app.dependencies import CurrentUser
 from app.models.session import RefreshToken
 from app.models.user import User
+from app.rate_limit import auth_rate_limit
 
 pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
 
 router = APIRouter()
 
+## Minimum age to register. This platform is adults-only.
+MIN_AGE = 18
+
 
 # --- Pydantic schemas ---
 
@@ -39,24 +43,19 @@ class RegisterRequest(BaseModel):
     username: str
     email: EmailStr
     password: str
-    date_of_birth: str  # ISO format date string (YYYY-MM-DD)
+    # Real date of birth -- the server computes age from it and rejects
-
+    # anyone under MIN_AGE. Still self-attested (no document check yet), but
-    @field_validator("date_of_birth")
+    # a concrete, stored, legally-meaningful data point rather than a
-    @classmethod
+    # throwaway checkbox, and the seam for a future hard ID-verification
-    def validate_date_of_birth(cls, v: str) -> str:
+    # pass. See docs/architecture/content_moderation.md 5.2.
-        """Validate that the date string is a valid date in YYYY-MM-DD format."""
+    date_of_birth: date
-        try:
-            datetime.strptime(v, "%Y-%m-%d")
-        except ValueError:
-            raise ValueError("date_of_birth must be in YYYY-MM-DD format")
-        return v
 
 
 class UserResponse(BaseModel):
     id: int
     username: str
     email: str
-    date_of_birth: str | None = None
+    date_of_birth: date | None = None
     is_active: bool
     created_at: datetime | None = None
 
@@ -118,6 +117,10 @@ def hash_password(password: str) -> str:
 def calculate_age(birth_date: date, today: date | None = None) -> int:
     """Calculate age in years from a birth date.
 
+    Used by /register (PC3 Phase 3) to compute age from the submitted
+    date_of_birth and enforce the 18+ gate. See
+    docs/architecture/content_moderation.md 5.2.
+
     Args:
         birth_date: The person's date of birth.
         today: The reference date. Defaults to today's date (UTC).
@@ -151,20 +154,25 @@ def _issue_refresh_token(user_id: int, db: AsyncSession) -> str:
 
 # --- Endpoints ---
 
-@router.post("/register", response_model=TokenResponse, status_code=status.HTTP_201_CREATED)
+@router.post("/register", response_model=TokenResponse, status_code=status.HTTP_201_CREATED,
+             dependencies=[Depends(auth_rate_limit)])
 async def register(req: RegisterRequest, db: AsyncSession = Depends(get_db)):
     """Register a new user and return access + refresh tokens.
 
-    Requires date_of_birth and rejects users under 18.
+    Requires a date of birth; the server computes age and rejects anyone
+    under MIN_AGE (18). See docs/architecture/content_moderation.md for the
+    verification design and its self-attestation limitation.
     """
-    # Parse and validate date_of_birth
+    age = calculate_age(req.date_of_birth)
-    dob = datetime.strptime(req.date_of_birth, "%Y-%m-%d").date()
+    if age < 0 or req.date_of_birth > date.today():
-    age = calculate_age(dob)
-
-    if age < 18:
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,
-            detail=f"Must be 18 or older to register (provided date of birth: {req.date_of_birth})",
+            detail="Invalid date of birth",
+        )
+    if age < MIN_AGE:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail=f"You must be at least {MIN_AGE} to use this platform",
         )
 
     # Check if username already exists
@@ -187,7 +195,7 @@ async def register(req: RegisterRequest, db: AsyncSession = Depends(get_db)):
         username=req.username,
         email=req.email,
         hashed_password=hash_password(req.password),
-        date_of_birth=dob,
+        date_of_birth=req.date_of_birth,
     )
     db.add(user)
     await db.flush()  # flush to get user.id before creating refresh token
@@ -207,7 +215,7 @@ async def register(req: RegisterRequest, db: AsyncSession = Depends(get_db)):
     )
 
 
-@router.post("/login", response_model=TokenResponse)
+@router.post("/login", response_model=TokenResponse, dependencies=[Depends(auth_rate_limit)])
 async def login(form: OAuth2PasswordRequestForm = Depends(), db: AsyncSession = Depends(get_db)):
     """Authenticate user and return access + refresh tokens.
 

backend/app/routers/avatar.py

@@ -0,0 +1,78 @@
+"""Avatar router - the current user's persisted avatar loadout.
+
+The loadout is a single JSON document matching the client's
+``AvatarLoadout.to_json()`` shape. The server has no copy of the asset
+catalog, so it only validates the envelope (JSON object, non-empty
+``base_body``); which assets are valid for which slot is the client's job.
+"""
+
+from typing import Annotated, Any
+
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel, Field
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.dependencies import CurrentUser
+from app.models.avatar_loadout import AvatarLoadout, DEFAULT_LOADOUT
+
+router = APIRouter()
+
+DbDep = Annotated[AsyncSession, Depends(get_db)]
+
+# A loadout document is small; reject anything absurd outright.
+MAX_LOADOUT_BYTES = 16 * 1024
+
+
+class LoadoutResponse(BaseModel):
+    data: dict[str, Any]
+    is_default: bool = Field(
+        description="True when the user has never saved a loadout and this is "
+        "the server default."
+    )
+
+
+class LoadoutUpdate(BaseModel):
+    data: dict[str, Any]
+
+
+def _validate_envelope(data: dict[str, Any]) -> None:
+    base_body = data.get("base_body")
+    if not isinstance(base_body, str) or not base_body.strip():
+        raise HTTPException(
+            status_code=422,
+            detail="loadout.data must have a non-empty string 'base_body'",
+        )
+    slots = data.get("slots", {})
+    if not isinstance(slots, dict):
+        raise HTTPException(status_code=422, detail="loadout.data.slots must be an object")
+    if len(str(data)) > MAX_LOADOUT_BYTES:
+        raise HTTPException(status_code=413, detail="loadout document too large")
+
+
+@router.get("/loadout", response_model=LoadoutResponse)
+async def get_loadout(current_user: CurrentUser, db: DbDep):
+    """Return the current user's saved loadout, or the server default if they
+    have never saved one."""
+    row = await db.get(AvatarLoadout, current_user.id)
+    if row is None:
+        return LoadoutResponse(data=dict(DEFAULT_LOADOUT), is_default=True)
+    return LoadoutResponse(data=row.data, is_default=False)
+
+
+@router.put("/loadout", response_model=LoadoutResponse)
+async def put_loadout(payload: LoadoutUpdate, current_user: CurrentUser, db: DbDep):
+    """Replace the current user's loadout."""
+    _validate_envelope(payload.data)
+
+    row = await db.get(AvatarLoadout, current_user.id)
+    if row is None:
+        row = AvatarLoadout(user_id=current_user.id, data=payload.data)
+        db.add(row)
+    else:
+        row.data = payload.data
+
+    await db.commit()
+    await db.refresh(row)
+    return LoadoutResponse(data=row.data, is_default=False)

backend/app/routers/chat_dm.py

@@ -0,0 +1,396 @@
+"""Direct-message (DM) chat router.
+
+docs/planning/social.md §4/§5 (US-4). Builds the send/list REST surface on
+top of ``app/models/chat.py`` (Conversation/ConversationParticipant/Message,
+already merged), ``app/services/text_filter.py`` (already merged), and
+``app/rate_limit.py`` (already merged).
+
+Endpoints:
+- POST /api/chat/dm/{user_id}/messages     -- send a DM to ``user_id``
+- GET  /api/chat/dm/{user_id}/messages     -- paginated history with ``user_id``
+- GET  /api/chat/dm/conversations          -- list the caller's conversations
+
+Scope/boundaries (per task): REST send/list only, no WebSocket/real-time
+delivery (separate task), no world/room chat (separate sibling task; that
+uses the same ``Message`` table but with ``world_id``/``room_id`` set and
+``conversation_id`` null).
+
+Design decisions this task owns:
+
+- **Blocking.** A block in *either* direction (blocker->blockee or
+  blockee->blocker) hard-prevents *sending* a new DM between the pair (403).
+  It does not hide history the pair already has -- ``GET .../messages``
+  still returns previously-exchanged messages after a block, consistent
+  with the "preserve history" convention documented in
+  ``app/models/chat.py``'s module docstring. Only sending is blocked.
+- **Text filtering.** Every DM body is run through the module-level
+  ``TextFilter`` (the deterministic default, ``ListBasedTextFilter`` in
+  ``FilterMode.REDACT``) before storing:
+    - ALLOW -> store the body as-is, ``filtered=False``.
+    - REDACT -> store ``filtered_text`` (matched spans starred out),
+      ``filtered=True``.
+    - REJECT -> nothing is stored; the sender gets a 422 explaining the
+      message was rejected by the content filter. (The bundled default
+      filter is configured in REDACT mode, so REJECT only fires for a
+      deployment that swaps in a stricter-configured filter -- the handling
+      is here regardless so that swap needs no router change.)
+- **Rate limiting.** Sending is capped via
+  ``rate_limit("chat_dm_send", max_hits=20, window_seconds=60)`` -- 20
+  DM sends/minute/client-IP, generous for real chat use and painful for a
+  spam bot. A no-op when ``settings.RATE_LIMIT_ENABLED`` is false (see
+  ``app/rate_limit.py``), matching every other rate-limited endpoint.
+- **Unread tracking.** A last-read timestamp per participant
+  (``ConversationParticipant.last_read_at``, migration 0010). Fetching a
+  conversation's *latest* page of history (``GET .../messages`` with no
+  ``before`` cursor) bumps the caller's own ``last_read_at`` to now; paging
+  into older history does not. ``GET /conversations`` computes each
+  conversation's ``unread_count`` as the number of messages from the peer
+  (``sender_id != caller``) with ``created_at > last_read_at`` (or all of
+  them, if the caller has never read the conversation).
+- **Pagination.**
+    - History (``GET {user_id}/messages``): cursor-based, newest-first.
+      ``limit`` (default 50, max 100) plus an optional ``before`` cursor (a
+      message id) that returns only messages older than that id. Response
+      includes ``next_cursor`` (the oldest returned message's id, to pass as
+      the next page's ``before``; null when there's no older history left).
+    - Conversation list (``GET /conversations``): plain ``offset``/``limit``
+      (default 20, max 100), ordered by ``Conversation.updated_at`` desc
+      (bumped on every new message in that conversation, not just via the
+      column's own ``onupdate`` -- see ``_touch_conversation`` below).
+- Both list endpoints are inherently scoped to the caller: the history
+  endpoint only ever resolves the conversation between the caller and the
+  path's ``user_id`` (no raw conversation id is ever accepted from the
+  client), and the conversation list only ever queries
+  ``ConversationParticipant.user_id == caller``. There is no way for a
+  client to address another pair's conversation.
+"""
+
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, HTTPException, Query, status
+from pydantic import BaseModel, Field
+from sqlalchemy import and_, func, or_, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.dependencies import CurrentUser
+from app.models.chat import Conversation, ConversationParticipant, Message
+from app.models.social import Block
+from app.models.user import User
+from app.rate_limit import rate_limit
+from app.services.text_filter import FilterAction, default_text_filter
+
+router = APIRouter()
+
+DbDep = Annotated[AsyncSession, Depends(get_db)]
+
+_text_filter = default_text_filter()
+chat_dm_send_rate_limit = rate_limit("chat_dm_send", max_hits=20, window_seconds=60)
+
+_BODY_MAX_LEN = 4000
+
+# ──────────────────────────── Pydantic schemas ────────────────────────────
+
+
+class SendDMRequest(BaseModel):
+    body: str = Field(..., min_length=1, max_length=_BODY_MAX_LEN)
+
+
+class DMMessageResponse(BaseModel):
+    id: int
+    conversation_id: int
+    sender_id: int
+    recipient_id: int
+    body: str
+    filtered: bool
+    created_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class DMMessageListResponse(BaseModel):
+    messages: list[DMMessageResponse]
+    next_cursor: int | None = None
+
+
+class DMConversationSummary(BaseModel):
+    conversation_id: int
+    peer_id: int
+    peer_username: str
+    last_message: DMMessageResponse | None
+    unread_count: int
+    updated_at: datetime
+
+
+class DMConversationListResponse(BaseModel):
+    conversations: list[DMConversationSummary]
+    total: int
+
+
+# ──────────────────────────────── Helpers ──────────────────────────────────
+
+
+async def _get_target_user(db: AsyncSession, user_id: int) -> User:
+    result = await db.execute(select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if user is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")
+    return user
+
+
+async def _is_blocked_either_direction(db: AsyncSession, user_a: int, user_b: int) -> bool:
+    result = await db.execute(
+        select(Block.id).where(
+            or_(
+                and_(Block.blocker_id == user_a, Block.blocked_id == user_b),
+                and_(Block.blocker_id == user_b, Block.blocked_id == user_a),
+            )
+        ).limit(1)
+    )
+    return result.scalar_one_or_none() is not None
+
+
+async def _get_or_create_conversation(
+    db: AsyncSession, user_a_id: int, user_b_id: int
+) -> Conversation:
+    lo, hi = sorted((user_a_id, user_b_id))
+    result = await db.execute(
+        select(Conversation).where(
+            Conversation.user_a_id == lo, Conversation.user_b_id == hi
+        )
+    )
+    conversation = result.scalar_one_or_none()
+    if conversation is not None:
+        return conversation
+
+    conversation = Conversation(user_a_id=lo, user_b_id=hi)
+    db.add(conversation)
+    await db.flush()  # assign conversation.id
+    db.add(ConversationParticipant(conversation_id=conversation.id, user_id=lo))
+    db.add(ConversationParticipant(conversation_id=conversation.id, user_id=hi))
+    await db.flush()
+    return conversation
+
+
+async def _get_participant(
+    db: AsyncSession, conversation_id: int, user_id: int
+) -> ConversationParticipant | None:
+    result = await db.execute(
+        select(ConversationParticipant).where(
+            ConversationParticipant.conversation_id == conversation_id,
+            ConversationParticipant.user_id == user_id,
+        )
+    )
+    return result.scalar_one_or_none()
+
+
+def _peer_id(conversation: Conversation, self_id: int) -> int:
+    return conversation.user_b_id if conversation.user_a_id == self_id else conversation.user_a_id
+
+
+def _touch_conversation(conversation: Conversation) -> None:
+    """Bump ``updated_at`` explicitly.
+
+    ``Conversation.updated_at`` has ``onupdate=func.now()``, but that only
+    fires when an UPDATE statement touches the ``conversations`` row itself
+    -- inserting a ``Message`` row alone never does. Explicitly dirtying the
+    column here is what actually keeps "most recently active conversation"
+    ordering correct for ``GET /conversations``.
+    """
+    conversation.updated_at = datetime.now(timezone.utc)
+
+
+def _to_message_response(message: Message, recipient_id: int) -> DMMessageResponse:
+    return DMMessageResponse(
+        id=message.id,
+        conversation_id=message.conversation_id,
+        sender_id=message.sender_id,
+        recipient_id=recipient_id,
+        body=message.body,
+        filtered=message.filtered,
+        created_at=message.created_at,
+    )
+
+
+# ──────────────────────────────── Endpoints ────────────────────────────────
+
+
+@router.post(
+    "/{user_id}/messages",
+    response_model=DMMessageResponse,
+    status_code=status.HTTP_201_CREATED,
+    dependencies=[Depends(chat_dm_send_rate_limit)],
+)
+async def send_dm(
+    user_id: int,
+    body: SendDMRequest,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Send a DM to ``user_id``."""
+    if user_id == current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST, detail="Cannot send a DM to yourself"
+        )
+
+    await _get_target_user(db, user_id)
+
+    if await _is_blocked_either_direction(db, current_user.id, user_id):
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Cannot message this user",
+        )
+
+    result = _text_filter.check(body.body)
+    if result.action is FilterAction.REJECT:
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
+            detail="Message rejected by the content filter.",
+        )
+
+    conversation = await _get_or_create_conversation(db, current_user.id, user_id)
+
+    message = Message(
+        sender_id=current_user.id,
+        conversation_id=conversation.id,
+        body=result.filtered_text,
+        filtered=(result.action is FilterAction.REDACT),
+    )
+    db.add(message)
+    _touch_conversation(conversation)
+    await db.commit()
+    await db.refresh(message)
+
+    return _to_message_response(message, recipient_id=user_id)
+
+
+@router.get("/{user_id}/messages", response_model=DMMessageListResponse)
+async def get_dm_history(
+    user_id: int,
+    current_user: CurrentUser,
+    db: DbDep,
+    limit: int = Query(50, ge=1, le=100),
+    before: int | None = Query(
+        None, description="Return messages older than this message id (pagination cursor)."
+    ),
+):
+    """Paginated DM history between the caller and ``user_id``, newest first.
+
+    Marks the conversation as read (bumps the caller's ``last_read_at``) only
+    when fetching the first page (``before`` omitted) -- paging into older
+    history doesn't affect unread state.
+    """
+    await _get_target_user(db, user_id)
+
+    lo, hi = sorted((current_user.id, user_id))
+    conv_result = await db.execute(
+        select(Conversation).where(Conversation.user_a_id == lo, Conversation.user_b_id == hi)
+    )
+    conversation = conv_result.scalar_one_or_none()
+    if conversation is None:
+        # No conversation yet -- nothing exchanged, not an error.
+        return DMMessageListResponse(messages=[], next_cursor=None)
+
+    stmt = select(Message).where(Message.conversation_id == conversation.id)
+    if before is not None:
+        stmt = stmt.where(Message.id < before)
+    stmt = stmt.order_by(Message.id.desc()).limit(limit + 1)
+
+    rows = (await db.execute(stmt)).scalars().all()
+    has_more = len(rows) > limit
+    page = rows[:limit]
+    next_cursor = page[-1].id if has_more and page else None
+
+    if before is None:
+        participant = await _get_participant(db, conversation.id, current_user.id)
+        if participant is not None:
+            participant.last_read_at = datetime.now(timezone.utc)
+            await db.commit()
+
+    return DMMessageListResponse(
+        messages=[_to_message_response(m, recipient_id=user_id) for m in page],
+        next_cursor=next_cursor,
+    )
+
+
+@router.get("/conversations", response_model=DMConversationListResponse)
+async def list_conversations(
+    current_user: CurrentUser,
+    db: DbDep,
+    limit: int = Query(20, ge=1, le=100),
+    offset: int = Query(0, ge=0),
+):
+    """List the caller's DM conversations, most recently active first."""
+    total_result = await db.execute(
+        select(func.count())
+        .select_from(ConversationParticipant)
+        .where(ConversationParticipant.user_id == current_user.id)
+    )
+    total = total_result.scalar_one()
+
+    stmt = (
+        select(Conversation, ConversationParticipant)
+        .join(
+            ConversationParticipant,
+            ConversationParticipant.conversation_id == Conversation.id,
+        )
+        .where(ConversationParticipant.user_id == current_user.id)
+        .order_by(Conversation.updated_at.desc())
+        .offset(offset)
+        .limit(limit)
+    )
+    rows = (await db.execute(stmt)).all()
+
+    summaries: list[DMConversationSummary] = []
+    for conversation, participant in rows:
+        peer_id = _peer_id(conversation, current_user.id)
+
+        peer = (
+            await db.execute(select(User).where(User.id == peer_id))
+        ).scalar_one_or_none()
+        peer_username = peer.username if peer is not None else "(deleted user)"
+
+        last_message_row = (
+            await db.execute(
+                select(Message)
+                .where(Message.conversation_id == conversation.id)
+                .order_by(Message.id.desc())
+                .limit(1)
+            )
+        ).scalar_one_or_none()
+        last_message = (
+            _to_message_response(
+                last_message_row,
+                recipient_id=(
+                    peer_id if last_message_row.sender_id == current_user.id else current_user.id
+                ),
+            )
+            if last_message_row is not None
+            else None
+        )
+
+        unread_filters = [
+            Message.conversation_id == conversation.id,
+            Message.sender_id != current_user.id,
+        ]
+        if participant.last_read_at is not None:
+            unread_filters.append(Message.created_at > participant.last_read_at)
+        unread_count = (
+            await db.execute(select(func.count()).select_from(Message).where(*unread_filters))
+        ).scalar_one()
+
+        summaries.append(
+            DMConversationSummary(
+                conversation_id=conversation.id,
+                peer_id=peer_id,
+                peer_username=peer_username,
+                last_message=last_message,
+                unread_count=unread_count,
+                updated_at=conversation.updated_at,
+            )
+        )
+
+    return DMConversationListResponse(conversations=summaries, total=total)

backend/app/routers/groups.py

@@ -0,0 +1,465 @@
+"""Groups API router.
+
+Endpoints:
+- POST   /api/groups                              -- create (creator becomes owner)
+- GET    /api/groups                               -- list groups (paginated), optional mine=true
+- GET    /api/groups/{id}                          -- group page (name/description/members)
+- PATCH  /api/groups/{id}                          -- update name/description (owner/admin)
+- DELETE /api/groups/{id}                          -- delete (owner only)
+- POST   /api/groups/{id}/join                     -- join (idempotent)
+- POST   /api/groups/{id}/leave                    -- leave (owner must transfer first)
+- POST   /api/groups/{id}/members/{user_id}/role   -- set role admin/member (owner only)
+- POST   /api/groups/{id}/transfer                 -- transfer ownership (owner only)
+
+See app/models/groups.py for the schema and delete-behavior rationale
+(docs/planning/social.md US-5). This module owns create/join/leave, role
+authorization, and the group page aggregate.
+"""
+
+from datetime import datetime
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, HTTPException, Query, status
+from pydantic import BaseModel, Field, field_validator
+from sqlalchemy import func, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.dependencies import CurrentUser
+from app.models.groups import Group, GroupMember, GroupRole
+from app.models.user import User
+
+router = APIRouter()
+
+DbDep = Annotated[AsyncSession, Depends(get_db)]
+
+_NAME_MAX_LEN = 100
+_DESCRIPTION_MAX_LEN = 2000
+
+
+# ──────────────────────────── Pydantic schemas ────────────────────────────────
+
+
+class GroupCreate(BaseModel):
+    name: str = Field(..., min_length=1, max_length=_NAME_MAX_LEN)
+    description: str | None = Field(default=None, max_length=_DESCRIPTION_MAX_LEN)
+
+    @field_validator("name")
+    @classmethod
+    def strip_name(cls, v: str) -> str:
+        v = v.strip()
+        if not v:
+            raise ValueError("name must not be blank")
+        return v
+
+    @field_validator("description")
+    @classmethod
+    def strip_description(cls, v: str | None) -> str | None:
+        if v is not None:
+            v = v.strip() or None
+        return v
+
+
+class GroupUpdate(BaseModel):
+    name: str | None = Field(default=None, min_length=1, max_length=_NAME_MAX_LEN)
+    description: str | None = Field(default=None, max_length=_DESCRIPTION_MAX_LEN)
+
+    @field_validator("name")
+    @classmethod
+    def strip_name(cls, v: str | None) -> str | None:
+        if v is not None:
+            v = v.strip()
+            if not v:
+                raise ValueError("name must not be blank")
+        return v
+
+    @field_validator("description")
+    @classmethod
+    def strip_description(cls, v: str | None) -> str | None:
+        if v is not None:
+            v = v.strip() or None
+        return v
+
+
+class GroupSummary(BaseModel):
+    id: int
+    name: str
+    description: str | None
+    owner_id: int | None
+    member_count: int
+    created_at: datetime
+
+
+class GroupListResponse(BaseModel):
+    groups: list[GroupSummary]
+    total: int
+
+
+class GroupMemberOut(BaseModel):
+    """Public-safe member entry -- no email or other private User fields."""
+
+    user_id: int
+    username: str
+    role: GroupRole
+    joined_at: datetime
+
+
+class GroupDetail(BaseModel):
+    id: int
+    name: str
+    description: str | None
+    owner_id: int | None
+    member_count: int
+    members: list[GroupMemberOut]
+    created_at: datetime
+
+
+class RoleUpdateRequest(BaseModel):
+    role: GroupRole
+
+    @field_validator("role")
+    @classmethod
+    def only_admin_or_member(cls, v: GroupRole) -> GroupRole:
+        if v == GroupRole.OWNER:
+            raise ValueError(
+                "cannot set role to owner directly -- use POST /transfer"
+            )
+        return v
+
+
+class TransferRequest(BaseModel):
+    new_owner_id: int
+
+
+class MembershipOut(BaseModel):
+    group_id: int
+    user_id: int
+    role: GroupRole
+    joined_at: datetime
+
+
+# ──────────────────────────────── Helpers ─────────────────────────────────────
+
+
+async def _get_group_or_404(db: AsyncSession, group_id: int) -> Group:
+    group = await db.get(Group, group_id)
+    if group is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Group not found")
+    return group
+
+
+async def _get_membership(db: AsyncSession, group_id: int, user_id: int) -> GroupMember | None:
+    result = await db.execute(
+        select(GroupMember).where(
+            GroupMember.group_id == group_id, GroupMember.user_id == user_id
+        )
+    )
+    return result.scalar_one_or_none()
+
+
+async def _member_count(db: AsyncSession, group_id: int) -> int:
+    result = await db.execute(
+        select(func.count()).select_from(GroupMember).where(GroupMember.group_id == group_id)
+    )
+    return int(result.scalar_one())
+
+
+def _require_role(membership: GroupMember | None, *allowed: GroupRole) -> None:
+    if membership is None or membership.role not in allowed:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="You do not have permission to perform this action",
+        )
+
+
+# ──────────────────────────────── Endpoints ───────────────────────────────────
+
+
+@router.post("", response_model=GroupDetail, status_code=status.HTTP_201_CREATED)
+@router.post("/", response_model=GroupDetail, status_code=status.HTTP_201_CREATED, include_in_schema=False)
+async def create_group(
+    body: GroupCreate,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Create a group. The creator becomes its owner."""
+    group = Group(name=body.name, description=body.description, owner_id=current_user.id)
+    db.add(group)
+    await db.flush()
+
+    db.add(GroupMember(group_id=group.id, user_id=current_user.id, role=GroupRole.OWNER))
+    await db.commit()
+    await db.refresh(group)
+
+    return GroupDetail(
+        id=group.id,
+        name=group.name,
+        description=group.description,
+        owner_id=group.owner_id,
+        member_count=1,
+        members=[
+            GroupMemberOut(
+                user_id=current_user.id,
+                username=current_user.username,
+                role=GroupRole.OWNER,
+                joined_at=group.created_at,
+            )
+        ],
+        created_at=group.created_at,
+    )
+
+
+@router.get("", response_model=GroupListResponse)
+@router.get("/", response_model=GroupListResponse, include_in_schema=False)
+async def list_groups(
+    current_user: CurrentUser,
+    db: DbDep,
+    skip: int = Query(0, ge=0),
+    limit: int = Query(50, ge=1, le=100),
+    mine: bool = Query(False, description="If true, only groups the caller is a member of"),
+):
+    """List groups, paginated. With ``mine=true``, restrict to the caller's own groups."""
+    base_query = select(Group)
+    count_query = select(func.count()).select_from(Group)
+
+    if mine:
+        base_query = base_query.join(
+            GroupMember, GroupMember.group_id == Group.id
+        ).where(GroupMember.user_id == current_user.id)
+        count_query = count_query.join(
+            GroupMember, GroupMember.group_id == Group.id
+        ).where(GroupMember.user_id == current_user.id)
+
+    total = (await db.execute(count_query)).scalar_one()
+
+    result = await db.execute(
+        base_query.order_by(Group.created_at.desc()).offset(skip).limit(limit)
+    )
+    groups = result.scalars().all()
+
+    summaries = []
+    for group in groups:
+        summaries.append(
+            GroupSummary(
+                id=group.id,
+                name=group.name,
+                description=group.description,
+                owner_id=group.owner_id,
+                member_count=await _member_count(db, group.id),
+                created_at=group.created_at,
+            )
+        )
+
+    return GroupListResponse(groups=summaries, total=total)
+
+
+@router.get("/{group_id}", response_model=GroupDetail)
+async def get_group(
+    group_id: int,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Group page: name, description, member count, and member list with roles."""
+    group = await _get_group_or_404(db, group_id)
+
+    result = await db.execute(
+        select(GroupMember, User.username)
+        .join(User, User.id == GroupMember.user_id)
+        .where(GroupMember.group_id == group_id)
+        .order_by(GroupMember.joined_at.asc())
+    )
+    rows = result.all()
+
+    members = [
+        GroupMemberOut(
+            user_id=gm.user_id,
+            username=username,
+            role=gm.role,
+            joined_at=gm.joined_at,
+        )
+        for gm, username in rows
+    ]
+
+    return GroupDetail(
+        id=group.id,
+        name=group.name,
+        description=group.description,
+        owner_id=group.owner_id,
+        member_count=len(members),
+        members=members,
+        created_at=group.created_at,
+    )
+
+
+@router.patch("/{group_id}", response_model=GroupDetail)
+async def update_group(
+    group_id: int,
+    body: GroupUpdate,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Update name/description. Owner/admin only."""
+    group = await _get_group_or_404(db, group_id)
+    membership = await _get_membership(db, group_id, current_user.id)
+    _require_role(membership, GroupRole.OWNER, GroupRole.ADMIN)
+
+    if body.name is not None:
+        group.name = body.name
+    if body.description is not None:
+        group.description = body.description if body.description else None
+
+    await db.commit()
+    await db.refresh(group)
+
+    return await get_group(group_id, current_user, db)
+
+
+@router.delete("/{group_id}", status_code=status.HTTP_204_NO_CONTENT)
+async def delete_group(
+    group_id: int,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Delete a group. Owner only."""
+    group = await _get_group_or_404(db, group_id)
+    if group.owner_id != current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Only the owner can delete this group",
+        )
+
+    await db.delete(group)
+    await db.commit()
+    return None
+
+
+@router.post("/{group_id}/join", response_model=MembershipOut)
+async def join_group(
+    group_id: int,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Join a group. Idempotent -- joining an already-joined group is a no-op."""
+    await _get_group_or_404(db, group_id)
+
+    existing = await _get_membership(db, group_id, current_user.id)
+    if existing is not None:
+        return MembershipOut(
+            group_id=group_id,
+            user_id=current_user.id,
+            role=existing.role,
+            joined_at=existing.joined_at,
+        )
+
+    membership = GroupMember(group_id=group_id, user_id=current_user.id, role=GroupRole.MEMBER)
+    db.add(membership)
+    await db.commit()
+    await db.refresh(membership)
+
+    return MembershipOut(
+        group_id=group_id,
+        user_id=current_user.id,
+        role=membership.role,
+        joined_at=membership.joined_at,
+    )
+
+
+@router.post("/{group_id}/leave", response_model=dict)
+async def leave_group(
+    group_id: int,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Leave a group. The owner cannot leave without transferring ownership first."""
+    await _get_group_or_404(db, group_id)
+    membership = await _get_membership(db, group_id, current_user.id)
+    if membership is None:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="You are not a member of this group",
+        )
+
+    if membership.role == GroupRole.OWNER:
+        raise HTTPException(
+            status_code=status.HTTP_409_CONFLICT,
+            detail="Transfer ownership before leaving this group",
+        )
+
+    await db.delete(membership)
+    await db.commit()
+    return {"status": "ok"}
+
+
+@router.post("/{group_id}/members/{user_id}/role", response_model=MembershipOut)
+async def set_member_role(
+    group_id: int,
+    user_id: int,
+    body: RoleUpdateRequest,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Set a member's role (admin/member). Owner only."""
+    group = await _get_group_or_404(db, group_id)
+    if group.owner_id != current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Only the owner can change member roles",
+        )
+
+    target = await _get_membership(db, group_id, user_id)
+    if target is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Member not found")
+
+    if target.role == GroupRole.OWNER:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Use POST /transfer to change ownership",
+        )
+
+    target.role = body.role
+    await db.commit()
+    await db.refresh(target)
+
+    return MembershipOut(
+        group_id=group_id, user_id=user_id, role=target.role, joined_at=target.joined_at
+    )
+
+
+@router.post("/{group_id}/transfer", response_model=GroupDetail)
+async def transfer_ownership(
+    group_id: int,
+    body: TransferRequest,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Transfer group ownership to another existing member. Owner only."""
+    group = await _get_group_or_404(db, group_id)
+    if group.owner_id != current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Only the owner can transfer ownership",
+        )
+
+    if body.new_owner_id == current_user.id:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="You already own this group",
+        )
+
+    new_owner_membership = await _get_membership(db, group_id, body.new_owner_id)
+    if new_owner_membership is None:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="New owner must already be a member of this group",
+        )
+
+    current_owner_membership = await _get_membership(db, group_id, current_user.id)
+
+    new_owner_membership.role = GroupRole.OWNER
+    if current_owner_membership is not None:
+        current_owner_membership.role = GroupRole.ADMIN
+    group.owner_id = body.new_owner_id
+
+    await db.commit()
+
+    return await get_group(group_id, current_user, db)

backend/app/routers/internal.py

@@ -0,0 +1,146 @@
+"""Internal, dedicated-server-only content API.
+
+Implements `docs/architecture/world_persistence_impl.md` §7 + §8.3. This is
+how a spawned Godot dedicated server (`scripts/server.gd`, spawned by
+`app.services.game_servers`) pulls its world's content read-only over HTTP
+before binding its ENet port. Mounted at ``/api/internal`` -- a prefix that
+can also be blocked at the reverse proxy, per the doc's rejected-alternative
+note in §7.3.
+
+Gated by ``require_game_server`` (§7.3): a bearer token minted per spawn by
+``GameServerSupervisor._spawn`` and checked against
+``supervisor.validate_token(world_id, token)``. There is no user identity
+here at all -- these routes skip the per-user visibility check public
+routes apply, and apply no mature-content gating (gating is a client/user
+concern; the dedicated server still needs the geometry for collision).
+
+Read-only by construction: there is no write route here, and adding one
+would violate world_persistence_impl.md D2 (the FastAPI backend is the
+only writer).
+"""
+
+from __future__ import annotations
+
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, Header, HTTPException, Response
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.models.world import World
+from app.models.world_content import MAIN_ROOM_SLUG
+from app.services import chunk_codec
+from app.services.game_servers import supervisor
+from app.services.world_store import Bounds, WorldStore
+
+router = APIRouter()
+
+DbDep = Annotated[AsyncSession, Depends(get_db)]
+
+
+async def require_game_server(
+    world_id: int,
+    authorization: Annotated[str | None, Header()] = None,
+) -> None:
+    """world_persistence_impl.md §7.3. A path whose ``world_id`` differs
+    from the token's world is 403 -- ``validate_token`` enforces that by
+    construction (it looks the token up *by* ``world_id``)."""
+    if not authorization or not authorization.lower().startswith("bearer "):
+        raise HTTPException(status_code=401, detail="missing bearer token")
+    token = authorization.split(" ", 1)[1].strip()
+    if not token or not supervisor.validate_token(world_id, token):
+        raise HTTPException(status_code=403, detail="invalid or expired server token")
+
+
+async def _get_world_or_404(world_id: int, db: AsyncSession) -> World:
+    result = await db.execute(select(World).where(World.id == world_id))
+    world = result.scalar_one_or_none()
+    if world is None:
+        raise HTTPException(status_code=404, detail="World not found")
+    return world
+
+
+async def _resolve_room(store: WorldStore, db: AsyncSession, world_id: int, slug: str):
+    room = await store.get_room(world_id, slug)
+    if room is None and slug == MAIN_ROOM_SLUG:
+        room = await store.get_or_create_main_room(world_id)
+        await db.commit()
+    return room
+
+
+@router.get("/worlds/{world_id}/manifest", dependencies=[Depends(require_game_server)])
+async def manifest(world_id: int, db: DbDep):
+    await _get_world_or_404(world_id, db)
+    store = WorldStore(db)
+    rooms = await store.list_rooms(world_id)
+    if not rooms:
+        rooms = [await store.get_or_create_main_room(world_id)]
+        await db.commit()
+
+    room_payloads = []
+    for r in rooms:
+        room_payloads.append({
+            "slug": r.slug, "name": r.name, "grid": r.grid, "bounds": r.bounds,
+            "spawn": r.spawn, "chunk_count": await store.count_chunks(r.id),
+        })
+
+    return {
+        "world_id": world_id,
+        "content_revision": await store.content_revision(world_id),
+        "rooms": room_payloads,
+    }
+
+
+@router.get("/worlds/{world_id}/rooms/{slug}/chunks", dependencies=[Depends(require_game_server)])
+async def internal_list_chunks(
+    world_id: int, slug: str, db: DbDep,
+    cx_min: int | None = None, cx_max: int | None = None,
+    cy_min: int | None = None, cy_max: int | None = None,
+    cz: int | None = None,
+):
+    await _get_world_or_404(world_id, db)
+    store = WorldStore(db)
+    room = await _resolve_room(store, db, world_id, slug)
+    if room is None:
+        raise HTTPException(status_code=404, detail="room not found")
+
+    bounds = Bounds(cx_min=cx_min, cx_max=cx_max, cy_min=cy_min, cy_max=cy_max, cz=cz)
+    chunks = await store.list_chunks(world_id, room.id, bounds)
+    return {
+        "room": room.slug,
+        "content_revision": await store.content_revision(world_id),
+        "chunks": [
+            {
+                "key": c.chunk_key, "cx": c.cx, "cy": c.cy, "cz": c.cz,
+                "revision": c.revision, "checksum": c.checksum, "payload_len": c.payload_len,
+                "is_mature": c.is_mature,
+                "updated_at": c.updated_at.isoformat() if c.updated_at else None,
+            }
+            for c in chunks
+        ],
+    }
+
+
+@router.get(
+    "/worlds/{world_id}/rooms/{slug}/chunks/{cx}/{cy}/{cz}",
+    dependencies=[Depends(require_game_server)],
+)
+async def internal_get_chunk(world_id: int, slug: str, cx: int, cy: int, cz: int, db: DbDep):
+    await _get_world_or_404(world_id, db)
+    store = WorldStore(db)
+    room = await _resolve_room(store, db, world_id, slug)
+    if room is None:
+        raise HTTPException(status_code=404, detail="room not found")
+
+    key = chunk_codec.build_key(world_id, slug, cx, cy, cz)
+    chunk = await store.get_chunk(key)
+    if chunk is None:
+        raise HTTPException(status_code=404, detail="chunk not found")
+
+    return Response(
+        content=chunk.payload, media_type="application/octet-stream",
+        headers={
+            "ETag": f'"{chunk.checksum}"', "X-Chunk-Revision": str(chunk.revision), "X-Chunk-Key": key,
+        },
+    )

backend/app/routers/presence.py

@@ -0,0 +1,146 @@
+"""Presence & status router.
+
+Endpoints:
+- POST  /api/presence/heartbeat  -- record a heartbeat (sets Redis TTL key)
+- GET   /api/presence/presence   -- query presence for a list of user ids
+- PATCH /api/presence/status     -- update the authenticated user's status message
+"""
+
+from datetime import datetime, timezone
+from typing import Annotated
+
+from fastapi import APIRouter, HTTPException, status, Depends
+from pydantic import BaseModel, Field, field_validator
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.dependencies import CurrentUser
+from app.models.user import User
+from app.services.presence import presence_store
+
+router = APIRouter()
+
+DbDep = Annotated[AsyncSession, Depends(get_db)]
+
+# ──────────────────────────── Pydantic schemas ────────────────────────────────
+
+_STATUS_MAX_LEN = 140
+
+
+class HeartbeatRequest(BaseModel):
+    """Empty body -- the caller's identity comes from the JWT."""
+
+
+class PresenceUser(BaseModel):
+    user_id: int
+    is_online: bool
+    last_seen_at: datetime | None
+    status_message: str | None
+
+
+class PresenceResponse(BaseModel):
+    users: list[PresenceUser]
+
+
+class StatusUpdate(BaseModel):
+    status_message: str | None = Field(default=None, max_length=_STATUS_MAX_LEN)
+
+    @field_validator("status_message")
+    @classmethod
+    def strip_message(cls, v: str | None) -> str | None:
+        if v is not None:
+            v = v.strip()
+        return v
+
+
+# ──────────────────────────────── Endpoints ───────────────────────────────────
+
+
+@router.post("/heartbeat", response_model=dict)
+async def heartbeat(
+    _req: HeartbeatRequest,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Record a heartbeat for the authenticated user.
+
+    Sets a Redis key with a TTL so the server can derive online/offline
+    status without trusting client claims. Also persists last_seen_at to
+    the database.
+    """
+    # Update Redis TTL (presence heartbeat)
+    await presence_store.heartbeat(current_user.id)
+
+    # Persist last_seen_at to the database
+    now = datetime.now(timezone.utc)
+    result = await db.execute(select(User).where(User.id == current_user.id))
+    user = result.scalar_one_or_none()
+    if user:
+        user.last_seen_at = now
+        await db.commit()
+
+    return {"status": "ok", "user_id": current_user.id}
+
+
+@router.get("/presence", response_model=PresenceResponse)
+async def get_presence(
+    user_ids: str,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Return presence info for a comma-separated list of user ids.
+
+    Online/offline is derived from the Redis heartbeat TTL.
+    last_seen_at and status_message come from the database.
+    """
+    ids = [int(uid.strip()) for uid in user_ids.split(",") if uid.strip()]
+    if not ids:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="user_ids must contain at least one integer",
+        )
+
+    # Check Redis for online status (single round trip via MGET).
+    online_ids = await presence_store.is_online_batch(ids)
+
+    # Fetch DB records for last_seen_at and status_message
+    result = await db.execute(select(User).where(User.id.in_(ids)))
+    users = {u.id: u for u in result.scalars().all()}
+
+    presence_users = []
+    for uid in ids:
+        user = users.get(uid)
+        if user is None:
+            continue
+        presence_users.append(
+            PresenceUser(
+                user_id=uid,
+                is_online=uid in online_ids,
+                last_seen_at=user.last_seen_at,
+                status_message=user.status_message,
+            )
+        )
+
+    return PresenceResponse(users=presence_users)
+
+
+@router.patch("/status", response_model=dict)
+async def update_status(
+    body: StatusUpdate,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Update the authenticated user's status message (length-limited)."""
+    result = await db.execute(select(User).where(User.id == current_user.id))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="User not found",
+        )
+
+    user.status_message = body.status_message
+    await db.commit()
+
+    return {"status": "ok", "status_message": body.status_message}

backend/app/routers/profiles.py

@@ -0,0 +1,365 @@
+"""Profile router -- the authenticated user's own profile + favorites.
+
+Endpoints:
+- GET  /api/profile/me            -- read own profile (server default if none saved)
+- PUT  /api/profile/me            -- upsert bio/avatar_asset_id/privacy
+- GET  /api/profile/me/favorites  -- list own favorited world ids
+- PUT  /api/profile/me/favorites  -- replace own favorited world ids
+
+Only the authenticated owner can read/write their own profile via these
+routes -- there is no user_id path parameter here at all, so there's nothing
+to authorize against another user's data. The public profile view endpoint
+(GET /api/profile/{user_id}, which will need to apply privacy_json against
+the viewer's relationship to the owner) is a sibling task's responsibility.
+"""
+
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel, Field, field_validator
+from sqlalchemy import select, or_, and_
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.dependencies import CurrentUser
+from app.models.asset import Asset
+from app.models.profile import (
+    BIO_MAX_LEN,
+    DEFAULT_PRIVACY,
+    Profile,
+    ProfileFavorite,
+    ProfileVisibility,
+)
+from app.models.social import Friendship, Block, FriendshipStatus
+from app.models.user import User
+from app.models.world import World
+
+router = APIRouter()
+
+DbDep = Annotated[AsyncSession, Depends(get_db)]
+
+_PRIVACY_KEYS = ("profile_visibility", "friends_list_visibility", "favorites_visibility")
+_VISIBILITY_VALUES = {v.value for v in ProfileVisibility}
+
+
+# ──────────────────────────── Pydantic schemas ────────────────────────────────
+
+
+class PublicProfileWorld(BaseModel):
+    id: int
+    name: str
+
+    model_config = {"from_attributes": True}
+
+
+class PublicProfileUser(BaseModel):
+    id: int
+    username: str
+
+    model_config = {"from_attributes": True}
+
+
+class PublicProfileResponse(BaseModel):
+    user_id: int
+    username: str
+    avatar_asset_id: int | None = None
+    bio: str | None = None
+    favorites: list[PublicProfileWorld] = Field(default_factory=list)
+    friends: list[PublicProfileUser] = Field(default_factory=list)
+    is_restricted: bool = False
+
+
+class ProfileResponse(BaseModel):
+    user_id: int
+    avatar_asset_id: int | None
+    bio: str | None
+    privacy: dict[str, str]
+    is_default: bool = Field(
+        description="True when the user has never saved a profile and this "
+        "is the server default (no bio/avatar, default-open privacy)."
+    )
+
+
+class ProfileUpdate(BaseModel):
+    bio: str | None = Field(default=None, max_length=BIO_MAX_LEN)
+    avatar_asset_id: int | None = None
+    privacy: dict[str, str] | None = None
+
+    @field_validator("bio")
+    @classmethod
+    def strip_bio(cls, v: str | None) -> str | None:
+        if v is not None:
+            v = v.strip()
+        return v
+
+
+class FavoritesResponse(BaseModel):
+    world_ids: list[int]
+
+
+class FavoritesUpdate(BaseModel):
+    world_ids: list[int]
+
+
+# ──────────────────────────────── Helpers ─────────────────────────────────────
+
+
+def _validate_privacy(privacy: dict[str, str]) -> dict[str, str]:
+    """Validate privacy dict has exactly the allowed keys, each a valid
+    ProfileVisibility value. Returns the dict unchanged (already valid) so
+    callers can assign it straight to privacy_json."""
+    extra = set(privacy.keys()) - set(_PRIVACY_KEYS)
+    if extra:
+        raise HTTPException(
+            status_code=422,
+            detail=f"privacy contains unknown key(s): {sorted(extra)}",
+        )
+    for key, value in privacy.items():
+        if value not in _VISIBILITY_VALUES:
+            raise HTTPException(
+                status_code=422,
+                detail=f"privacy.{key} must be one of {sorted(_VISIBILITY_VALUES)}, got {value!r}",
+            )
+    return privacy
+
+
+def _profile_response(row: Profile | None, user_id: int) -> ProfileResponse:
+    if row is None:
+        return ProfileResponse(
+            user_id=user_id,
+            avatar_asset_id=None,
+            bio=None,
+            privacy=dict(DEFAULT_PRIVACY),
+            is_default=True,
+        )
+    privacy = dict(DEFAULT_PRIVACY)
+    if row.privacy_json:
+        privacy.update(row.privacy_json)
+    return ProfileResponse(
+        user_id=row.user_id,
+        avatar_asset_id=row.avatar_asset_id,
+        bio=row.bio,
+        privacy=privacy,
+        is_default=False,
+    )
+
+
+# ──────────────────────────────── Endpoints ───────────────────────────────────
+
+
+@router.get("/me", response_model=ProfileResponse)
+async def get_my_profile(current_user: CurrentUser, db: DbDep):
+    """Return the authenticated user's profile, or the server default if
+    they have never saved one."""
+    row = await db.get(Profile, current_user.id)
+    return _profile_response(row, current_user.id)
+
+
+@router.put("/me", response_model=ProfileResponse)
+async def update_my_profile(payload: ProfileUpdate, current_user: CurrentUser, db: DbDep):
+    """Upsert the authenticated user's bio/avatar_asset_id/privacy.
+
+    Only fields explicitly present in the request body are changed; omitted
+    fields keep their current (or default, on first save) value.
+    """
+    fields_set = payload.model_fields_set
+
+    if "avatar_asset_id" in fields_set and payload.avatar_asset_id is not None:
+        asset = await db.get(Asset, payload.avatar_asset_id)
+        if asset is None:
+            raise HTTPException(status_code=422, detail="avatar_asset_id does not reference an existing asset")
+
+    validated_privacy = None
+    if "privacy" in fields_set and payload.privacy is not None:
+        validated_privacy = _validate_privacy(payload.privacy)
+
+    row = await db.get(Profile, current_user.id)
+    if row is None:
+        row = Profile(
+            user_id=current_user.id,
+            bio=payload.bio if "bio" in fields_set else None,
+            avatar_asset_id=payload.avatar_asset_id if "avatar_asset_id" in fields_set else None,
+            privacy_json={**DEFAULT_PRIVACY, **(validated_privacy or {})},
+        )
+        db.add(row)
+    else:
+        if "bio" in fields_set:
+            row.bio = payload.bio
+        if "avatar_asset_id" in fields_set:
+            row.avatar_asset_id = payload.avatar_asset_id
+        if validated_privacy is not None:
+            merged = dict(row.privacy_json or DEFAULT_PRIVACY)
+            merged.update(validated_privacy)
+            row.privacy_json = merged
+
+    await db.commit()
+    await db.refresh(row)
+    return _profile_response(row, current_user.id)
+
+
+@router.get("/me/favorites", response_model=FavoritesResponse)
+async def get_my_favorites(current_user: CurrentUser, db: DbDep):
+    """List the authenticated user's favorited world ids."""
+    result = await db.execute(
+        select(ProfileFavorite.world_id).where(ProfileFavorite.user_id == current_user.id)
+    )
+    return FavoritesResponse(world_ids=[wid for wid in result.scalars().all()])
+
+
+@router.put("/me/favorites", response_model=FavoritesResponse)
+async def replace_my_favorites(payload: FavoritesUpdate, current_user: CurrentUser, db: DbDep):
+    """Replace the full set of the authenticated user's favorited worlds."""
+    world_ids = list(dict.fromkeys(payload.world_ids))  # de-dupe, preserve order
+
+    if world_ids:
+        result = await db.execute(select(World.id).where(World.id.in_(world_ids)))
+        existing_ids = set(result.scalars().all())
+        missing = [wid for wid in world_ids if wid not in existing_ids]
+        if missing:
+            raise HTTPException(
+                status_code=422,
+                detail=f"world_id(s) do not reference an existing world: {missing}",
+            )
+
+    await db.execute(
+        ProfileFavorite.__table__.delete().where(ProfileFavorite.user_id == current_user.id)
+    )
+    for wid in world_ids:
+        db.add(ProfileFavorite(user_id=current_user.id, world_id=wid))
+
+    await db.commit()
+    return FavoritesResponse(world_ids=world_ids)
+
+
+@router.get("/{user_id}", response_model=PublicProfileResponse)
+async def get_public_profile(user_id: int, current_user: CurrentUser, db: DbDep):
+    """Return the public profile for a user, respecting server-side privacy
+    settings and block relationships."""
+    user_res = await db.execute(select(User).where(User.id == user_id))
+    target_user = user_res.scalar_one_or_none()
+    if target_user is None or not target_user.is_active:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    profile = await db.get(Profile, user_id)
+    avatar_asset = None
+    if profile and profile.avatar_asset_id:
+        avatar_asset = await db.get(Asset, profile.avatar_asset_id)
+
+    privacy = dict(DEFAULT_PRIVACY)
+    if profile and profile.privacy_json:
+        privacy.update(profile.privacy_json)
+
+    is_self = current_user.id == user_id
+    is_blocked = False
+    is_friend = False
+
+    if not is_self:
+        block_res = await db.execute(
+            select(Block.id).where(
+                or_(
+                    and_(Block.blocker_id == current_user.id, Block.blocked_id == user_id),
+                    and_(Block.blocker_id == user_id, Block.blocked_id == current_user.id),
+                )
+            )
+        )
+        is_blocked = block_res.scalar_one_or_none() is not None
+
+        if not is_blocked:
+            friend_res = await db.execute(
+                select(Friendship.id).where(
+                    or_(
+                        and_(Friendship.requester_id == current_user.id, Friendship.addressee_id == user_id),
+                        and_(Friendship.requester_id == user_id, Friendship.addressee_id == current_user.id),
+                    ),
+                    Friendship.status == FriendshipStatus.ACCEPTED,
+                )
+            )
+            is_friend = friend_res.scalar_one_or_none() is not None
+
+    profile_vis = privacy.get("profile_visibility", ProfileVisibility.PUBLIC.value)
+    if profile_vis is False:
+        profile_vis = ProfileVisibility.PRIVATE.value
+    elif profile_vis is True:
+        profile_vis = ProfileVisibility.PUBLIC.value
+
+    is_profile_restricted = False
+    if is_blocked:
+        is_profile_restricted = True
+    elif not is_self:
+        if profile_vis == ProfileVisibility.PRIVATE.value:
+            is_profile_restricted = True
+        elif profile_vis == ProfileVisibility.FRIENDS.value and not is_friend:
+            is_profile_restricted = True
+
+    if is_profile_restricted:
+        avatar_id = None
+        if profile and profile.avatar_asset_id:
+            if avatar_asset and avatar_asset.is_public:
+                avatar_id = profile.avatar_asset_id
+        return PublicProfileResponse(
+            user_id=target_user.id,
+            username=target_user.username,
+            avatar_asset_id=avatar_id,
+            bio=None,
+            favorites=[],
+            friends=[],
+            is_restricted=True,
+        )
+
+    avatar_id = profile.avatar_asset_id if profile else None
+    bio = profile.bio if profile else None
+
+    fav_vis = privacy.get("favorites_visibility", ProfileVisibility.PUBLIC.value)
+    if fav_vis is False:
+        fav_vis = ProfileVisibility.PRIVATE.value
+    elif fav_vis is True:
+        fav_vis = ProfileVisibility.PUBLIC.value
+
+    can_see_favorites = is_self or (fav_vis == ProfileVisibility.PUBLIC.value) or (fav_vis == ProfileVisibility.FRIENDS.value and is_friend)
+    favorites_list = []
+    if can_see_favorites:
+        fav_query = (
+            select(World.id, World.name)
+            .join(ProfileFavorite, ProfileFavorite.world_id == World.id)
+            .where(ProfileFavorite.user_id == user_id)
+            .order_by(ProfileFavorite.created_at.desc())
+        )
+        fav_res = await db.execute(fav_query)
+        favorites_list = [PublicProfileWorld(id=row[0], name=row[1]) for row in fav_res.all()]
+
+    fr_vis = privacy.get("friends_list_visibility", ProfileVisibility.PUBLIC.value)
+    if fr_vis is False:
+        fr_vis = ProfileVisibility.PRIVATE.value
+    elif fr_vis is True:
+        fr_vis = ProfileVisibility.PUBLIC.value
+
+    can_see_friends = is_self or (fr_vis == ProfileVisibility.PUBLIC.value) or (fr_vis == ProfileVisibility.FRIENDS.value and is_friend)
+    friends_list = []
+    if can_see_friends:
+        fr_res = await db.execute(
+            select(Friendship).where(
+                or_(Friendship.requester_id == user_id, Friendship.addressee_id == user_id),
+                Friendship.status == FriendshipStatus.ACCEPTED,
+            )
+        )
+        friendships = fr_res.scalars().all()
+        other_ids = [
+            fr.addressee_id if fr.requester_id == user_id else fr.requester_id
+            for fr in friendships
+        ]
+        if other_ids:
+            users_res = await db.execute(
+                select(User.id, User.username).where(User.id.in_(other_ids), User.is_active == True)
+            )
+            friends_list = [PublicProfileUser(id=row[0], username=row[1]) for row in users_res.all()]
+
+    return PublicProfileResponse(
+        user_id=target_user.id,
+        username=target_user.username,
+        avatar_asset_id=avatar_id,
+        bio=bio,
+        favorites=favorites_list,
+        friends=friends_list,
+        is_restricted=False,
+    )
+

backend/app/routers/social_friends.py

@@ -0,0 +1,362 @@
+"""Friends/follow/block router.
+
+docs/planning/social.md §4/§5 (US-1). Builds the request/accept/block
+business logic on top of the models in app/models/social.py (already
+merged): friend requests are directional (requester -> addressee) until
+accepted, at which point the relationship is treated as mutual; follow is
+one-way with no approval step; block is a hard deny that clears any
+existing friendship/follow between the two users and is queryable so a
+later layer (e.g. chat) can check it -- enforcing the block anywhere but
+here is out of scope for this router.
+
+Endpoints:
+- POST   /api/friends/requests                -- send a friend request
+- GET    /api/friends/requests                -- list incoming (pending) requests
+- POST   /api/friends/requests/{id}/accept    -- accept an incoming request
+- POST   /api/friends/requests/{id}/decline   -- decline an incoming request
+- DELETE /api/friends/{user_id}                -- unfriend
+- POST   /api/friends/{user_id}/follow         -- follow a user
+- DELETE /api/friends/{user_id}/follow         -- unfollow a user
+- POST   /api/friends/{user_id}/block          -- block a user
+- DELETE /api/friends/{user_id}/block          -- unblock a user
+- GET    /api/friends                          -- list friends
+- GET    /api/friends/following                -- list users followed
+- GET    /api/friends/blocked                  -- list blocked users
+"""
+
+from datetime import datetime
+from typing import Annotated
+
+from fastapi import APIRouter, HTTPException, status, Depends
+from pydantic import BaseModel
+from sqlalchemy import select, delete, or_, and_
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.dependencies import CurrentUser
+from app.models.social import Friendship, Follow, Block, FriendshipStatus
+from app.models.user import User
+
+router = APIRouter()
+
+DbDep = Annotated[AsyncSession, Depends(get_db)]
+
+# ──────────────────────────── Pydantic schemas ────────────────────────────────
+
+
+class FriendRequestCreate(BaseModel):
+    user_id: int
+
+
+class FriendRequestResponse(BaseModel):
+    id: int
+    requester_id: int
+    addressee_id: int
+    status: FriendshipStatus
+    created_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class UserSummary(BaseModel):
+    id: int
+    username: str
+
+    model_config = {"from_attributes": True}
+
+
+class FriendRequestListResponse(BaseModel):
+    requests: list[FriendRequestResponse]
+
+
+class FriendListResponse(BaseModel):
+    friends: list[UserSummary]
+
+
+class FollowListResponse(BaseModel):
+    following: list[UserSummary]
+
+
+class BlockedListResponse(BaseModel):
+    blocked: list[UserSummary]
+
+
+class ActionResponse(BaseModel):
+    status: str
+
+
+# ──────────────────────────────── Helpers ──────────────────────────────────────
+
+
+def _friendship_pair(a: int, b: int):
+    """SQLAlchemy predicate matching a Friendship row between a and b,
+    regardless of which one is the requester/addressee."""
+    return or_(
+        and_(Friendship.requester_id == a, Friendship.addressee_id == b),
+        and_(Friendship.requester_id == b, Friendship.addressee_id == a),
+    )
+
+
+def _follow_pair(a: int, b: int):
+    """Predicate matching a Follow row in either direction between a and b."""
+    return or_(
+        and_(Follow.follower_id == a, Follow.followed_id == b),
+        and_(Follow.follower_id == b, Follow.followed_id == a),
+    )
+
+
+async def _is_blocked_either_direction(db: AsyncSession, a: int, b: int) -> bool:
+    result = await db.execute(
+        select(Block.id).where(
+            or_(
+                and_(Block.blocker_id == a, Block.blocked_id == b),
+                and_(Block.blocker_id == b, Block.blocked_id == a),
+            )
+        )
+    )
+    return result.scalar_one_or_none() is not None
+
+
+async def _get_user_or_404(db: AsyncSession, user_id: int) -> User:
+    result = await db.execute(select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+    if user is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")
+    return user
+
+
+# ──────────────────────────────── Requests ─────────────────────────────────────
+
+
+@router.post("/requests", response_model=FriendRequestResponse, status_code=status.HTTP_201_CREATED)
+async def send_friend_request(body: FriendRequestCreate, current_user: CurrentUser, db: DbDep):
+    """Send a friend request to another user."""
+    target_id = body.user_id
+    if target_id == current_user.id:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Cannot send a friend request to yourself")
+
+    await _get_user_or_404(db, target_id)
+
+    if await _is_blocked_either_direction(db, current_user.id, target_id):
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Cannot send a friend request to this user")
+
+    existing = await db.execute(select(Friendship).where(_friendship_pair(current_user.id, target_id)))
+    if existing.scalar_one_or_none() is not None:
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Friend request or friendship already exists")
+
+    fr = Friendship(requester_id=current_user.id, addressee_id=target_id)
+    db.add(fr)
+    try:
+        await db.commit()
+    except IntegrityError:
+        await db.rollback()
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Friend request or friendship already exists")
+    await db.refresh(fr)
+    return fr
+
+
+@router.get("/requests", response_model=FriendRequestListResponse)
+async def list_incoming_requests(current_user: CurrentUser, db: DbDep):
+    """List pending friend requests sent *to* the authenticated user."""
+    result = await db.execute(
+        select(Friendship).where(
+            Friendship.addressee_id == current_user.id,
+            Friendship.status == FriendshipStatus.PENDING,
+        )
+    )
+    return FriendRequestListResponse(requests=list(result.scalars().all()))
+
+
+@router.post("/requests/{request_id}/accept", response_model=FriendRequestResponse)
+async def accept_friend_request(request_id: int, current_user: CurrentUser, db: DbDep):
+    """Accept an incoming friend request, making the friendship mutual."""
+    result = await db.execute(select(Friendship).where(Friendship.id == request_id))
+    fr = result.scalar_one_or_none()
+    # 404 (not a 403) both when the row doesn't exist and when it isn't
+    # addressed to the caller, so ids can't be enumerated to probe other
+    # accounts' pending requests.
+    if fr is None or fr.addressee_id != current_user.id or fr.status != FriendshipStatus.PENDING:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Friend request not found")
+
+    fr.status = FriendshipStatus.ACCEPTED
+    await db.commit()
+    await db.refresh(fr)
+    return fr
+
+
+@router.post("/requests/{request_id}/decline", response_model=ActionResponse)
+async def decline_friend_request(request_id: int, current_user: CurrentUser, db: DbDep):
+    """Decline (and remove) an incoming friend request."""
+    result = await db.execute(select(Friendship).where(Friendship.id == request_id))
+    fr = result.scalar_one_or_none()
+    if fr is None or fr.addressee_id != current_user.id or fr.status != FriendshipStatus.PENDING:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Friend request not found")
+
+    await db.delete(fr)
+    await db.commit()
+    return ActionResponse(status="declined")
+
+
+# ──────────────────────────────── Friends ──────────────────────────────────────
+
+
+@router.get("", response_model=FriendListResponse)
+async def list_friends(current_user: CurrentUser, db: DbDep):
+    """List the authenticated user's accepted friends."""
+    result = await db.execute(
+        select(Friendship).where(
+            or_(Friendship.requester_id == current_user.id, Friendship.addressee_id == current_user.id),
+            Friendship.status == FriendshipStatus.ACCEPTED,
+        )
+    )
+    friendships = result.scalars().all()
+    other_ids = [
+        fr.addressee_id if fr.requester_id == current_user.id else fr.requester_id
+        for fr in friendships
+    ]
+    if not other_ids:
+        return FriendListResponse(friends=[])
+
+    users_result = await db.execute(select(User).where(User.id.in_(other_ids)))
+    return FriendListResponse(friends=list(users_result.scalars().all()))
+
+
+@router.delete("/{user_id}", response_model=ActionResponse)
+async def unfriend(user_id: int, current_user: CurrentUser, db: DbDep):
+    """Remove an existing (accepted) friendship."""
+    if user_id == current_user.id:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Cannot unfriend yourself")
+
+    result = await db.execute(
+        select(Friendship).where(
+            _friendship_pair(current_user.id, user_id),
+            Friendship.status == FriendshipStatus.ACCEPTED,
+        )
+    )
+    fr = result.scalar_one_or_none()
+    if fr is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Not friends with this user")
+
+    await db.delete(fr)
+    await db.commit()
+    return ActionResponse(status="unfriended")
+
+
+# ──────────────────────────────── Follow ───────────────────────────────────────
+
+
+@router.post("/{user_id}/follow", response_model=ActionResponse, status_code=status.HTTP_201_CREATED)
+async def follow_user(user_id: int, current_user: CurrentUser, db: DbDep):
+    """Follow another user (one-way, no approval)."""
+    if user_id == current_user.id:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Cannot follow yourself")
+
+    await _get_user_or_404(db, user_id)
+
+    if await _is_blocked_either_direction(db, current_user.id, user_id):
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="Cannot follow this user")
+
+    existing = await db.execute(
+        select(Follow).where(Follow.follower_id == current_user.id, Follow.followed_id == user_id)
+    )
+    if existing.scalar_one_or_none() is not None:
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Already following this user")
+
+    db.add(Follow(follower_id=current_user.id, followed_id=user_id))
+    try:
+        await db.commit()
+    except IntegrityError:
+        await db.rollback()
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Already following this user")
+    return ActionResponse(status="followed")
+
+
+@router.delete("/{user_id}/follow", response_model=ActionResponse)
+async def unfollow_user(user_id: int, current_user: CurrentUser, db: DbDep):
+    """Unfollow a user."""
+    if user_id == current_user.id:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Cannot unfollow yourself")
+
+    result = await db.execute(
+        select(Follow).where(Follow.follower_id == current_user.id, Follow.followed_id == user_id)
+    )
+    follow = result.scalar_one_or_none()
+    if follow is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Not following this user")
+
+    await db.delete(follow)
+    await db.commit()
+    return ActionResponse(status="unfollowed")
+
+
+@router.get("/following", response_model=FollowListResponse)
+async def list_following(current_user: CurrentUser, db: DbDep):
+    """List users the authenticated user follows."""
+    result = await db.execute(select(Follow).where(Follow.follower_id == current_user.id))
+    followed_ids = [f.followed_id for f in result.scalars().all()]
+    if not followed_ids:
+        return FollowListResponse(following=[])
+
+    users_result = await db.execute(select(User).where(User.id.in_(followed_ids)))
+    return FollowListResponse(following=list(users_result.scalars().all()))
+
+
+# ──────────────────────────────── Block ────────────────────────────────────────
+
+
+@router.post("/{user_id}/block", response_model=ActionResponse, status_code=status.HTTP_201_CREATED)
+async def block_user(user_id: int, current_user: CurrentUser, db: DbDep):
+    """Block a user: hard deny that also clears any existing friendship/follow
+    between the two users in either direction."""
+    if user_id == current_user.id:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Cannot block yourself")
+
+    await _get_user_or_404(db, user_id)
+
+    existing = await db.execute(
+        select(Block).where(Block.blocker_id == current_user.id, Block.blocked_id == user_id)
+    )
+    if existing.scalar_one_or_none() is not None:
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="User already blocked")
+
+    db.add(Block(blocker_id=current_user.id, blocked_id=user_id))
+    await db.execute(delete(Friendship).where(_friendship_pair(current_user.id, user_id)))
+    await db.execute(delete(Follow).where(_follow_pair(current_user.id, user_id)))
+
+    try:
+        await db.commit()
+    except IntegrityError:
+        await db.rollback()
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="User already blocked")
+    return ActionResponse(status="blocked")
+
+
+@router.delete("/{user_id}/block", response_model=ActionResponse)
+async def unblock_user(user_id: int, current_user: CurrentUser, db: DbDep):
+    """Remove a block."""
+    if user_id == current_user.id:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Cannot unblock yourself")
+
+    result = await db.execute(
+        select(Block).where(Block.blocker_id == current_user.id, Block.blocked_id == user_id)
+    )
+    block = result.scalar_one_or_none()
+    if block is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User is not blocked")
+
+    await db.delete(block)
+    await db.commit()
+    return ActionResponse(status="unblocked")
+
+
+@router.get("/blocked", response_model=BlockedListResponse)
+async def list_blocked(current_user: CurrentUser, db: DbDep):
+    """List users the authenticated user has blocked."""
+    result = await db.execute(select(Block).where(Block.blocker_id == current_user.id))
+    blocked_ids = [b.blocked_id for b in result.scalars().all()]
+    if not blocked_ids:
+        return BlockedListResponse(blocked=[])
+
+    users_result = await db.execute(select(User).where(User.id.in_(blocked_ids)))
+    return BlockedListResponse(blocked=list(users_result.scalars().all()))

backend/app/routers/world_content.py

@@ -0,0 +1,451 @@
+"""World content router -- rooms + chunks, for the editor and player client.
+
+Implements `docs/architecture/world_persistence_impl.md` §8.1. JWT-authenticated
+(``CurrentUser``, same as ``app/routers/worlds.py``). All chunk content
+reads/writes go through ``WorldStore``; this module is HTTP plumbing +
+authorization only.
+
+Authorization (doc §5.3):
+ - **Read** (world visibility, room listing, chunk fetch/index/revisions):
+   same rule as ``GET /api/worlds/{id}`` -- 404 (not 403) if the world is
+   neither PUBLIC nor owned by the caller. See ``_get_world_readable``.
+ - **Write** (room create, chunk PUT/DELETE/rollback): caller must be
+   ``world.owner_id``, matching ``update_world`` -- 403 otherwise, with
+   *no* visibility gate (this deliberately mirrors ``update_world``, which
+   also has no visibility check; see ``_get_world_writable``).
+"""
+
+from __future__ import annotations
+
+import base64
+import binascii
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, Header, HTTPException, Request, Response
+from fastapi.responses import JSONResponse
+from pydantic import BaseModel, Field
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.config import settings
+from app.database import get_db
+from app.dependencies import CurrentUser
+from app.models.user import User
+from app.models.world import World, WorldVisibility
+from app.models.world_content import MAIN_ROOM_SLUG, WorldRoom
+from app.services import chunk_codec
+from app.services.game_servers import supervisor
+from app.services.world_store import Bounds, RevisionConflict, RevisionNotAvailable, WorldStore
+
+router = APIRouter()
+
+DbDep = Annotated[AsyncSession, Depends(get_db)]
+
+# world_persistence_impl.md §8.1: "Bounds are capped (default 32x32 chunks
+# per query) and return 422 beyond that."
+MAX_BOUNDS_SPAN = 32
+# §8.1 batch write cap, beyond WORLD_CHUNK_MAX_BATCH chunks: "Capped at ...
+# 8 MB."
+MAX_BATCH_TOTAL_BYTES = 8 * 1024 * 1024
+
+
+# ─────────────────────────── auth helpers ───────────────────────────
+
+async def _get_world_readable(world_id: int, current_user: User, db: AsyncSession) -> World:
+    result = await db.execute(select(World).where(World.id == world_id))
+    world = result.scalar_one_or_none()
+    if world is None:
+        raise HTTPException(status_code=404, detail="World not found")
+    if world.visibility != WorldVisibility.PUBLIC and world.owner_id != current_user.id:
+        raise HTTPException(status_code=404, detail="World not found")
+    return world
+
+
+async def _get_world_writable(world_id: int, current_user: User, db: AsyncSession) -> World:
+    result = await db.execute(select(World).where(World.id == world_id))
+    world = result.scalar_one_or_none()
+    if world is None:
+        raise HTTPException(status_code=404, detail="World not found")
+    if world.owner_id != current_user.id:
+        raise HTTPException(status_code=403, detail="Not owner of this world")
+    return world
+
+
+async def _resolve_room(store: WorldStore, db: AsyncSession, world_id: int, slug: str) -> WorldRoom | None:
+    """world_persistence_impl.md §4.1: lazily create the main room for
+    worlds that predate this feature, on first read/write."""
+    room = await store.get_room(world_id, slug)
+    if room is None and slug == MAIN_ROOM_SLUG:
+        room = await store.get_or_create_main_room(world_id)
+        await db.commit()
+    return room
+
+
+def _is_live(world_id: int) -> bool:
+    return any(s["world_id"] == str(world_id) for s in supervisor.debug_state())
+
+
+def _validation_error_body(exc: chunk_codec.ChunkValidationError) -> dict:
+    return {"detail": "chunk validation failed", "reason": exc.reason}
+
+
+def _conflict_body(exc: RevisionConflict) -> dict:
+    body: dict = {
+        "detail": "revision conflict",
+        "current_revision": exc.current_revision,
+        "current_checksum": exc.current_checksum,
+    }
+    if exc.coord is not None:
+        body["coord"] = list(exc.coord)
+    return body
+
+
+# ─────────────────────────── schemas ───────────────────────────
+
+class RoomResponse(BaseModel):
+    id: int
+    slug: str
+    name: str
+    grid: dict
+    bounds: dict | None
+    spawn: dict | None
+    chunk_count: int
+
+
+class RoomCreate(BaseModel):
+    slug: str = Field(..., min_length=1, max_length=64, pattern=r"^[a-z0-9_-]+$")
+    name: str = Field(..., min_length=1, max_length=255)
+    grid: dict | None = None
+    bounds: dict | None = None
+    spawn: dict | None = None
+
+
+# ─────────────────────────── rooms ───────────────────────────
+
+@router.get("/{world_id}/rooms", response_model=list[RoomResponse])
+async def list_rooms(world_id: int, current_user: CurrentUser, db: DbDep):
+    await _get_world_readable(world_id, current_user, db)
+    store = WorldStore(db)
+    rooms = await store.list_rooms(world_id)
+    if not rooms:
+        rooms = [await store.get_or_create_main_room(world_id)]
+        await db.commit()
+    return [
+        RoomResponse(
+            id=r.id, slug=r.slug, name=r.name, grid=r.grid, bounds=r.bounds, spawn=r.spawn,
+            chunk_count=await store.count_chunks(r.id),
+        )
+        for r in rooms
+    ]
+
+
+@router.post("/{world_id}/rooms", response_model=RoomResponse, status_code=201)
+async def create_room(world_id: int, body: RoomCreate, current_user: CurrentUser, db: DbDep):
+    await _get_world_writable(world_id, current_user, db)
+    store = WorldStore(db)
+    if await store.get_room(world_id, body.slug) is not None:
+        raise HTTPException(status_code=409, detail="a room with this slug already exists")
+    room = await store.create_room(
+        world_id, body.slug, body.name, grid=body.grid, bounds=body.bounds, spawn=body.spawn
+    )
+    await db.commit()
+    await db.refresh(room)
+    return RoomResponse(
+        id=room.id, slug=room.slug, name=room.name, grid=room.grid,
+        bounds=room.bounds, spawn=room.spawn, chunk_count=0,
+    )
+
+
+# ─────────────────────────── chunk index ───────────────────────────
+
+@router.get("/{world_id}/rooms/{slug}/chunks")
+async def list_chunks(
+    world_id: int, slug: str, current_user: CurrentUser, db: DbDep,
+    cx_min: int | None = None, cx_max: int | None = None,
+    cy_min: int | None = None, cy_max: int | None = None,
+    cz: int | None = None,
+):
+    await _get_world_readable(world_id, current_user, db)
+    store = WorldStore(db)
+    room = await _resolve_room(store, db, world_id, slug)
+    if room is None:
+        raise HTTPException(status_code=404, detail="room not found")
+
+    if cx_min is not None and cx_max is not None and (cx_max - cx_min + 1) > MAX_BOUNDS_SPAN:
+        raise HTTPException(status_code=422, detail=f"cx bounds span exceeds {MAX_BOUNDS_SPAN}")
+    if cy_min is not None and cy_max is not None and (cy_max - cy_min + 1) > MAX_BOUNDS_SPAN:
+        raise HTTPException(status_code=422, detail=f"cy bounds span exceeds {MAX_BOUNDS_SPAN}")
+
+    bounds = Bounds(cx_min=cx_min, cx_max=cx_max, cy_min=cy_min, cy_max=cy_max, cz=cz)
+    chunks = await store.list_chunks(world_id, room.id, bounds)
+    content_revision = await store.content_revision(world_id)
+    return {
+        "room": room.slug,
+        "content_revision": content_revision,
+        "chunks": [
+            {
+                "key": c.chunk_key, "cx": c.cx, "cy": c.cy, "cz": c.cz,
+                "revision": c.revision, "checksum": c.checksum, "payload_len": c.payload_len,
+                "is_mature": c.is_mature,
+                "updated_at": c.updated_at.isoformat() if c.updated_at else None,
+            }
+            for c in chunks
+        ],
+    }
+
+
+# ─────────────────────────── chunk fetch ───────────────────────────
+
+@router.get("/{world_id}/rooms/{slug}/chunks/{cx}/{cy}/{cz}")
+async def get_chunk(
+    world_id: int, slug: str, cx: int, cy: int, cz: int,
+    current_user: CurrentUser, db: DbDep,
+    accept: Annotated[str | None, Header()] = None,
+    if_none_match: Annotated[str | None, Header(alias="If-None-Match")] = None,
+):
+    await _get_world_readable(world_id, current_user, db)
+    store = WorldStore(db)
+    room = await _resolve_room(store, db, world_id, slug)
+    if room is None:
+        raise HTTPException(status_code=404, detail="room not found")
+
+    key = chunk_codec.build_key(world_id, slug, cx, cy, cz)
+    chunk = await store.get_chunk(key)
+    if chunk is None:
+        raise HTTPException(status_code=404, detail="chunk not found")
+
+    etag = f'"{chunk.checksum}"'
+    headers = {"ETag": etag, "X-Chunk-Revision": str(chunk.revision), "X-Chunk-Key": key}
+
+    if if_none_match is not None and if_none_match.strip('"') == chunk.checksum:
+        return Response(status_code=304, headers=headers)
+
+    wants_json = (
+        accept is not None
+        and "application/json" in accept
+        and "application/octet-stream" not in accept
+    )
+    if wants_json:
+        decoded = chunk_codec.decode_binary(chunk.payload)
+        body = chunk_codec.to_json_dict(decoded, key=key, chunk_checksum=chunk.checksum)
+        return JSONResponse(content=body, headers=headers)
+
+    return Response(content=chunk.payload, media_type="application/octet-stream", headers=headers)
+
+
+# ─────────────────────────── chunk write ───────────────────────────
+
+async def _read_write_payload(request: Request, x_base_revision: int | None) -> tuple[bytes, int]:
+    content_type = request.headers.get("content-type", "")
+    if "application/json" in content_type:
+        body = await request.json()
+        try:
+            payload_bytes = base64.b64decode(body["payload_b64"], validate=True)
+        except (KeyError, binascii.Error, ValueError) as exc:
+            raise HTTPException(status_code=422, detail=f"invalid payload_b64: {exc}")
+        base_revision = int(body.get("base_revision", 0))
+        return payload_bytes, base_revision
+    payload_bytes = await request.body()
+    return payload_bytes, (x_base_revision if x_base_revision is not None else 0)
+
+
+@router.put("/{world_id}/rooms/{slug}/chunks/{cx}/{cy}/{cz}")
+async def put_chunk(
+    world_id: int, slug: str, cx: int, cy: int, cz: int,
+    request: Request, current_user: CurrentUser, db: DbDep,
+    x_base_revision: Annotated[int | None, Header(alias="X-Base-Revision")] = None,
+):
+    await _get_world_writable(world_id, current_user, db)
+    store = WorldStore(db)
+    room = await _resolve_room(store, db, world_id, slug)
+    if room is None:
+        raise HTTPException(status_code=404, detail="room not found")
+
+    payload_bytes, base_revision = await _read_write_payload(request, x_base_revision)
+    if len(payload_bytes) > settings.WORLD_CHUNK_MAX_PAYLOAD_BYTES:
+        raise HTTPException(
+            status_code=413,
+            detail=f"payload exceeds WORLD_CHUNK_MAX_PAYLOAD_BYTES ({settings.WORLD_CHUNK_MAX_PAYLOAD_BYTES})",
+        )
+
+    try:
+        chunk = await store.put_chunk(
+            room=room, cx=cx, cy=cy, cz=cz, payload_bytes=payload_bytes,
+            base_revision=base_revision, actor_id=current_user.id,
+        )
+    except chunk_codec.ChunkCodecError as exc:
+        await db.rollback()
+        return JSONResponse(status_code=422, content={"detail": "chunk decode failed", "reason": "malformed", "message": str(exc)})
+    except chunk_codec.ChunkValidationError as exc:
+        await db.rollback()
+        return JSONResponse(status_code=422, content=_validation_error_body(exc))
+    except RevisionConflict as exc:
+        # Nothing must stick from a failed write. Returning a JSONResponse
+        # here (rather than raising) means no exception propagates through
+        # `get_db`, so this rollback has to be explicit -- see the note on
+        # the batch endpoint below, where this is load-bearing for
+        # all-or-nothing semantics.
+        await db.rollback()
+        return JSONResponse(status_code=409, content=_conflict_body(exc))
+
+    await db.commit()
+    await db.refresh(chunk)
+
+    return {
+        "key": chunk.chunk_key, "revision": chunk.revision, "checksum": chunk.checksum,
+        "payload_len": chunk.payload_len,
+        "updated_at": chunk.updated_at.isoformat() if chunk.updated_at else None,
+        "is_mature": chunk.is_mature, "live_session": _is_live(world_id),
+    }
+
+
+# ─────────────────────────── batch write ───────────────────────────
+
+class BatchChunkItem(BaseModel):
+    cx: int
+    cy: int
+    cz: int
+    base_revision: int
+    payload_b64: str
+
+
+class BatchPutRequest(BaseModel):
+    chunks: list[BatchChunkItem]
+
+
+@router.put("/{world_id}/rooms/{slug}/chunks")
+async def put_chunks_batch(
+    world_id: int, slug: str, body: BatchPutRequest, current_user: CurrentUser, db: DbDep,
+):
+    await _get_world_writable(world_id, current_user, db)
+    store = WorldStore(db)
+    room = await _resolve_room(store, db, world_id, slug)
+    if room is None:
+        raise HTTPException(status_code=404, detail="room not found")
+
+    if len(body.chunks) > settings.WORLD_CHUNK_MAX_BATCH:
+        raise HTTPException(
+            status_code=422,
+            detail=f"batch of {len(body.chunks)} exceeds WORLD_CHUNK_MAX_BATCH ({settings.WORLD_CHUNK_MAX_BATCH})",
+        )
+
+    items = []
+    total_bytes = 0
+    for item in body.chunks:
+        try:
+            payload_bytes = base64.b64decode(item.payload_b64, validate=True)
+        except (binascii.Error, ValueError) as exc:
+            raise HTTPException(status_code=422, detail=f"invalid payload_b64 for ({item.cx},{item.cy},{item.cz}): {exc}")
+        total_bytes += len(payload_bytes)
+        items.append({
+            "cx": item.cx, "cy": item.cy, "cz": item.cz,
+            "base_revision": item.base_revision, "payload_bytes": payload_bytes,
+        })
+
+    if total_bytes > MAX_BATCH_TOTAL_BYTES:
+        raise HTTPException(status_code=413, detail=f"batch exceeds {MAX_BATCH_TOTAL_BYTES} bytes")
+
+    try:
+        rows = await store.put_chunks_batch(room=room, items=items, actor_id=current_user.id)
+    except chunk_codec.ChunkCodecError as exc:
+        # All-or-nothing (world_persistence_impl.md §8.1): earlier items in
+        # this batch may already be flushed (but never committed) to this
+        # transaction. Rolling back here is what actually makes the batch
+        # atomic -- without it, returning a JSONResponse instead of raising
+        # means no exception reaches `get_db`, and its own transaction
+        # handling would otherwise commit those earlier writes anyway.
+        await db.rollback()
+        return JSONResponse(status_code=422, content={"detail": "chunk decode failed", "reason": "malformed", "message": str(exc)})
+    except chunk_codec.ChunkValidationError as exc:
+        await db.rollback()
+        return JSONResponse(status_code=422, content=_validation_error_body(exc))
+    except RevisionConflict as exc:
+        await db.rollback()
+        return JSONResponse(status_code=409, content=_conflict_body(exc))
+
+    await db.commit()
+    for row in rows:
+        await db.refresh(row)
+
+    return {
+        "live_session": _is_live(world_id),
+        "chunks": [
+            {
+                "key": r.chunk_key, "revision": r.revision, "checksum": r.checksum,
+                "payload_len": r.payload_len,
+                "updated_at": r.updated_at.isoformat() if r.updated_at else None,
+                "is_mature": r.is_mature,
+            }
+            for r in rows
+        ],
+    }
+
+
+# ─────────────────────────── delete ───────────────────────────
+
+@router.delete("/{world_id}/rooms/{slug}/chunks/{cx}/{cy}/{cz}", status_code=204)
+async def delete_chunk(
+    world_id: int, slug: str, cx: int, cy: int, cz: int, current_user: CurrentUser, db: DbDep,
+):
+    await _get_world_writable(world_id, current_user, db)
+    store = WorldStore(db)
+    room = await _resolve_room(store, db, world_id, slug)
+    if room is None:
+        raise HTTPException(status_code=404, detail="room not found")
+
+    key = chunk_codec.build_key(world_id, slug, cx, cy, cz)
+    await store.delete_chunk(key, current_user.id)
+    await db.commit()
+    return Response(status_code=204)
+
+
+# ─────────────────────────── revisions + rollback ───────────────────────────
+
+@router.get("/{world_id}/rooms/{slug}/chunks/{cx}/{cy}/{cz}/revisions")
+async def chunk_revisions(
+    world_id: int, slug: str, cx: int, cy: int, cz: int, current_user: CurrentUser, db: DbDep,
+):
+    # doc: "(owner)" -- same gate as writes.
+    await _get_world_writable(world_id, current_user, db)
+    store = WorldStore(db)
+    key = chunk_codec.build_key(world_id, slug, cx, cy, cz)
+    revisions = await store.list_revisions(key)
+    return [
+        {
+            "revision": r.revision, "action": r.action, "actor_id": r.actor_id,
+            "checksum": r.checksum, "payload_available": r.payload is not None,
+            "created_at": r.created_at.isoformat() if r.created_at else None,
+        }
+        for r in revisions
+    ]
+
+
+class RollbackRequest(BaseModel):
+    revision: int
+
+
+@router.post("/{world_id}/rooms/{slug}/chunks/{cx}/{cy}/{cz}/rollback")
+async def rollback_chunk(
+    world_id: int, slug: str, cx: int, cy: int, cz: int,
+    body: RollbackRequest, current_user: CurrentUser, db: DbDep,
+):
+    await _get_world_writable(world_id, current_user, db)
+    store = WorldStore(db)
+    key = chunk_codec.build_key(world_id, slug, cx, cy, cz)
+    try:
+        chunk = await store.rollback_chunk(key, body.revision, current_user.id)
+    except RevisionNotAvailable as exc:
+        await db.rollback()
+        return JSONResponse(status_code=404, content={"detail": str(exc)})
+    except chunk_codec.ChunkValidationError as exc:
+        await db.rollback()
+        return JSONResponse(status_code=422, content=_validation_error_body(exc))
+
+    await db.commit()
+    await db.refresh(chunk)
+    return {
+        "key": chunk.chunk_key, "revision": chunk.revision, "checksum": chunk.checksum,
+        "payload_len": chunk.payload_len,
+        "updated_at": chunk.updated_at.isoformat() if chunk.updated_at else None,
+        "is_mature": chunk.is_mature, "live_session": _is_live(world_id),
+    }

backend/app/routers/worlds.py

@@ -12,6 +12,8 @@ from sqlalchemy.orm import selectinload
 from app.database import get_db
 from app.dependencies import CurrentUser
 from app.models.world import World, WorldVisibility
+from app.services.game_servers import supervisor
+from app.services.world_store import WorldStore
 
 router = APIRouter()
 
@@ -106,13 +108,52 @@ async def get_world(
     return world
 
 
+class JoinResponse(BaseModel):
+    """Address of the dedicated server hosting this world."""
+    world_id: int
+    host: str
+    port: int
+
+
+@router.post("/{world_id}/join", response_model=JoinResponse)
+async def join_world(
+    world_id: int,
+    current_user: CurrentUser,
+    db: DbDep,
+):
+    """Ensure a dedicated game server is running for this world and return its
+    ENet address for the client to connect to.
+
+    503 if game-server orchestration isn't enabled on this backend (e.g. a
+    plain dev/test instance with no Godot binary).
+    """
+    result = await db.execute(select(World).where(World.id == world_id))
+    world = result.scalar_one_or_none()
+    if not world:
+        raise HTTPException(status_code=404, detail="World not found")
+    if world.visibility != WorldVisibility.PUBLIC and world.owner_id != current_user.id:
+        raise HTTPException(status_code=404, detail="World not found")
+
+    try:
+        info = await supervisor.ensure_server(str(world_id))
+    except RuntimeError as exc:
+        raise HTTPException(status_code=503, detail=str(exc))
+
+    return JoinResponse(world_id=world_id, host=info["host"], port=info["port"])
+
+
 @router.post("/", response_model=WorldResponse, status_code=201)
 async def create_world(
     world_data: WorldCreate,
     current_user: CurrentUser,
     db: DbDep,
 ):
-    """Create a new world."""
+    """Create a new world.
+
+    Also creates the world's "main" room (world_persistence_impl.md §4.1) --
+    every world gets one so chunk content has somewhere to live from the
+    start.
+    """
     world = World(
         name=world_data.name,
         description=world_data.description,
@@ -120,6 +161,8 @@ async def create_world(
         visibility=world_data.visibility,
     )
     db.add(world)
+    await db.flush()  # assigns world.id, needed for the room's FK
+    await WorldStore(db).get_or_create_main_room(world.id)
     await db.commit()
     await db.refresh(world)
     return world

backend/app/services/chunk_codec.py

@@ -0,0 +1,676 @@
+"""Python port of the chunk binary/JSON codec, `docs/architecture/world.md` §3.
+
+This is the server-side half of the "single shared format, two
+implementations" contract world.md §5.2 and
+`world_persistence_impl.md` §5.5/§9 call for. The Godot-side implementation
+is `scripts/chunk_data_decoder.gd`; this module must decode anything it
+produces and produce bytes it can decode.
+
+IMPORTANT DEVIATION (see the "Known cross-codec divergence" note at the
+bottom of this file): the current `scripts/chunk_data_decoder.gd` does not
+actually implement IEEE-754 float32 for the `pos`/`rot`/`scale`/`bounds`
+fields -- it performs a lossy numeric `int`/`float` cast instead of a bit
+reinterpretation, which both truncates fractional values and does not
+write IEEE-754 bits at all. This module implements the format as
+*specified* (real `<f` IEEE-754 float32, matching every other field in the
+spec and matching what any conformant decoder would assume). See the note
+for what this means for cross-codec byte parity today.
+
+Nothing here talks to a database or the FastAPI app; it is a pure,
+side-effect-free codec so it can be golden-file tested in isolation.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import struct
+from dataclasses import dataclass, field
+
+MAGIC = b"AGPC"
+HEADER_SIZE = 48
+CURRENT_VERSION = 1
+
+SECTION_META = 0x01
+SECTION_TILE = 0x02
+SECTION_OBJECT = 0x03
+SECTION_FLAGS = 0x04
+SECTION_REVISION_META = 0x05
+
+CATEGORY_FIELDS = (
+    "violence", "sexual", "language", "substance",
+    "gambling", "horror", "hate", "custom",
+)
+
+
+class ChunkCodecError(Exception):
+    """Malformed bytes -- the payload isn't shaped like a chunk at all."""
+
+
+class ChunkValidationError(Exception):
+    """A structurally-valid chunk failed a content/business-rule check.
+
+    ``reason`` is the machine-readable code the API surface (world_persistence_impl.md
+    §8.1) puts in the 422 response body's ``reason`` field, e.g.
+    ``"checksum_mismatch"``, ``"layer_dims"``, ``"object_out_of_bounds"``.
+    """
+
+    def __init__(self, reason: str, message: str | None = None) -> None:
+        self.reason = reason
+        super().__init__(message or reason)
+
+
+# ───────────────────────── Logical model ─────────────────────────
+
+@dataclass
+class TileDef:
+    id: int
+    asset_id: str = ""
+    solid: bool = False
+    flags: int = 0
+    variants: int = 1
+
+
+@dataclass
+class TileLayer:
+    name: str
+    layer_id: int = 0
+    width: int = 0
+    height: int = 0
+    depth: int = 1
+    palette: list[TileDef] = field(default_factory=list)
+    tiles: list[int] = field(default_factory=list)  # flattened, row-major
+
+
+@dataclass
+class ContentFlags:
+    violence: int = 0
+    sexual: int = 0
+    language: int = 0
+    substance: int = 0
+    gambling: int = 0
+    horror: int = 0
+    hate: int = 0
+    custom: int = 0
+    mature: bool = False
+    sources: list[str] = field(default_factory=list)
+
+    def to_dict(self) -> dict:
+        return {
+            "categories": {name: getattr(self, name) for name in CATEGORY_FIELDS},
+            "mature": self.mature,
+            "sources": list(self.sources),
+        }
+
+    @classmethod
+    def from_dict(cls, d: dict) -> "ContentFlags":
+        cats = d.get("categories", {})
+        return cls(
+            **{name: int(cats.get(name, 0)) for name in CATEGORY_FIELDS},
+            mature=bool(d.get("mature", False)),
+            sources=list(d.get("sources", [])),
+        )
+
+
+@dataclass
+class WorldObject:
+    id: str
+    type: str
+    asset_id: str
+    pos: tuple[float, float, float] = (0.0, 0.0, 0.0)
+    rot: tuple[float, float, float, float] = (0.0, 0.0, 0.0, 1.0)
+    scale: tuple[float, float, float] = (1.0, 1.0, 1.0)
+    dynamic: bool = False
+    properties: dict = field(default_factory=dict)
+    flags: ContentFlags = field(default_factory=ContentFlags)
+
+
+@dataclass
+class ChunkBounds:
+    """Stored here as min-corner + size (matching the Godot client's AABB
+    type) for convenience, but the §3.6 BINARY wire format is min + max
+    (world.md §3.1, and the client's actual ChunkDataDecoder) -- fixed
+    2026-09-14 after a real client/server interop test caught this class's
+    original binary codec writing min+size on the wire, which the client
+    decoder (unaware of the "size" convention) read as a second min/max
+    pair, corrupting every chunk's bounds. The two representations are
+    fully recoverable from each other; `max` below is computed for exactly
+    this reason."""
+
+    min: tuple[float, float, float] = (0.0, 0.0, 0.0)
+    size: tuple[float, float, float] = (0.0, 0.0, 0.0)
+
+    @property
+    def max(self) -> tuple[float, float, float]:
+        return tuple(a + b for a, b in zip(self.min, self.size))
+
+
+@dataclass
+class ChunkPayload:
+    version: int = CURRENT_VERSION
+    world_id: str = ""
+    room_id: str = ""
+    coord: tuple[int, int, int] = (0, 0, 0)
+    bounds: ChunkBounds = field(default_factory=ChunkBounds)
+    tile_layers: list[TileLayer] = field(default_factory=list)
+    objects: list[WorldObject] = field(default_factory=list)
+    flags: ContentFlags = field(default_factory=ContentFlags)
+    created_at: int = 0
+    updated_at: int = 0
+    revision: int = 0
+    author: str = ""
+
+
+def build_key(world_id: str | int, room_slug: str, cx: int, cy: int, cz: int) -> str:
+    """world_persistence_impl.md §4.5: ``"{world.id}:{room.slug}:{cx}:{cy}:{cz}"``."""
+    return f"{world_id}:{room_slug}:{cx}:{cy}:{cz}"
+
+
+# ───────────────────────── Binary primitives ─────────────────────────
+# All integers little-endian, matching world.md §3.6.3. Floats are packed
+# as real IEEE-754 float32 -- see the module docstring's deviation note.
+
+def _read_u16(data: bytes, off: int) -> int:
+    return struct.unpack_from("<H", data, off)[0]
+
+
+def _read_u32(data: bytes, off: int) -> int:
+    return struct.unpack_from("<I", data, off)[0]
+
+
+def _read_i32(data: bytes, off: int) -> int:
+    return struct.unpack_from("<i", data, off)[0]
+
+
+def _read_i64(data: bytes, off: int) -> int:
+    return struct.unpack_from("<q", data, off)[0]
+
+
+def _read_f32(data: bytes, off: int) -> float:
+    return struct.unpack_from("<f", data, off)[0]
+
+
+def _w_u16(v: int) -> bytes:
+    return struct.pack("<H", v & 0xFFFF)
+
+
+def _w_u32(v: int) -> bytes:
+    return struct.pack("<I", v & 0xFFFFFFFF)
+
+
+def _w_i32(v: int) -> bytes:
+    return struct.pack("<i", v)
+
+
+def _w_i64(v: int) -> bytes:
+    return struct.pack("<q", v)
+
+
+def _w_f32(v: float) -> bytes:
+    return struct.pack("<f", v)
+
+
+def _read_str(data: bytes, off: int) -> tuple[str, int]:
+    """Length-prefixed UTF-8 string. Returns (value, next_offset)."""
+    n = _read_u16(data, off)
+    off += 2
+    s = data[off:off + n].decode("utf-8")
+    return s, off + n
+
+
+def _w_str(s: str) -> bytes:
+    b = s.encode("utf-8")
+    if len(b) > 0xFFFF:
+        raise ChunkCodecError(f"string field too long to encode ({len(b)} bytes)")
+    return _w_u16(len(b)) + b
+
+
+def checksum(payload_body: bytes) -> str:
+    """SHA-256 hex digest of the payload body (world.md §3.6.3)."""
+    return hashlib.sha256(payload_body).hexdigest()
+
+
+# ───────────────────────── Section codecs ─────────────────────────
+
+def _encode_metadata(payload: ChunkPayload) -> bytes:
+    out = bytearray()
+    out += _w_str(payload.world_id)
+    out += _w_str(payload.room_id)
+    out += _w_i32(payload.coord[0])
+    out += _w_i32(payload.coord[1])
+    out += _w_i32(payload.coord[2])
+    out += _w_f32(payload.bounds.min[0])
+    out += _w_f32(payload.bounds.min[1])
+    out += _w_f32(payload.bounds.min[2])
+    out += _w_f32(payload.bounds.max[0])
+    out += _w_f32(payload.bounds.max[1])
+    out += _w_f32(payload.bounds.max[2])
+    return bytes(out)
+
+
+def _decode_metadata(data: bytes, result: ChunkPayload) -> None:
+    off = 0
+    result.world_id, off = _read_str(data, off)
+    result.room_id, off = _read_str(data, off)
+    coord = (_read_i32(data, off), _read_i32(data, off + 4), _read_i32(data, off + 8))
+    off += 12
+    min_pos = (_read_f32(data, off), _read_f32(data, off + 4), _read_f32(data, off + 8))
+    max_pos = (_read_f32(data, off + 12), _read_f32(data, off + 16), _read_f32(data, off + 20))
+    size = tuple(a - b for a, b in zip(max_pos, min_pos))
+    result.coord = coord
+    result.bounds = ChunkBounds(min=min_pos, size=size)
+
+
+def _encode_tile_layer(layer: TileLayer) -> bytes:
+    out = bytearray()
+    out += _w_str(layer.name)
+    out += _w_u16(layer.layer_id)
+    out += _w_u16(layer.width)
+    out += _w_u16(layer.height)
+    out += _w_u16(layer.depth)
+    out += _w_u16(len(layer.palette))
+    for td in layer.palette:
+        out += _w_u16(td.id)
+        out += _w_str(td.asset_id)
+        out += bytes([1 if td.solid else 0])
+        out += _w_u32(td.flags)
+        out += bytes([td.variants & 0xFF])
+    out += _w_u32(len(layer.tiles))
+    for tile_id in layer.tiles:
+        out += _w_u16(tile_id)
+    return bytes(out)
+
+
+def _decode_tile_layer(data: bytes) -> TileLayer:
+    off = 0
+    name, off = _read_str(data, off)
+    layer_id = _read_u16(data, off); off += 2
+    width = _read_u16(data, off); off += 2
+    height = _read_u16(data, off); off += 2
+    depth = _read_u16(data, off); off += 2
+    palette_count = _read_u16(data, off); off += 2
+    palette: list[TileDef] = []
+    for _ in range(palette_count):
+        tid = _read_u16(data, off); off += 2
+        asset_id, off = _read_str(data, off)
+        solid = data[off] != 0; off += 1
+        flags = _read_u32(data, off); off += 4
+        variants = data[off]; off += 1
+        palette.append(TileDef(id=tid, asset_id=asset_id, solid=solid, flags=flags, variants=variants))
+    tile_count = _read_u32(data, off); off += 4
+    tiles: list[int] = []
+    for _ in range(tile_count):
+        tiles.append(_read_u16(data, off))
+        off += 2
+    return TileLayer(name=name, layer_id=layer_id, width=width, height=height,
+                      depth=depth, palette=palette, tiles=tiles)
+
+
+def _encode_flags(flags: ContentFlags) -> bytes:
+    out = bytearray()
+    for name in CATEGORY_FIELDS:
+        out.append(getattr(flags, name) & 0xFF)
+    out.append(1 if flags.mature else 0)
+    out += _w_u16(len(flags.sources))
+    for src in flags.sources:
+        out += _w_str(src)
+    return bytes(out)
+
+
+def _decode_flags(data: bytes) -> ContentFlags:
+    off = 0
+    values = {}
+    for name in CATEGORY_FIELDS:
+        values[name] = data[off]
+        off += 1
+    mature = data[off] != 0
+    off += 1
+    source_count = _read_u16(data, off)
+    off += 2
+    sources = []
+    for _ in range(source_count):
+        s, off = _read_str(data, off)
+        sources.append(s)
+    return ContentFlags(**values, mature=mature, sources=sources)
+
+
+def _encode_object(obj: WorldObject) -> bytes:
+    out = bytearray()
+    out += _w_str(obj.id)
+    out += _w_str(obj.type)
+    out += _w_str(obj.asset_id)
+    for v in obj.pos:
+        out += _w_f32(v)
+    for v in obj.rot:
+        out += _w_f32(v)
+    for v in obj.scale:
+        out += _w_f32(v)
+    out.append(1 if obj.dynamic else 0)
+    # Canonical JSON: keys sorted lexicographically (world.md §3.6.3).
+    props_json = json.dumps(obj.properties, sort_keys=True, separators=(",", ":"))
+    out += _w_str(props_json)
+    out += _encode_flags(obj.flags)
+    return bytes(out)
+
+
+def _decode_object(data: bytes) -> WorldObject:
+    off = 0
+    oid, off = _read_str(data, off)
+    otype, off = _read_str(data, off)
+    asset_id, off = _read_str(data, off)
+    pos = (_read_f32(data, off), _read_f32(data, off + 4), _read_f32(data, off + 8))
+    off += 12
+    rot = (
+        _read_f32(data, off), _read_f32(data, off + 4),
+        _read_f32(data, off + 8), _read_f32(data, off + 12),
+    )
+    off += 16
+    scale = (_read_f32(data, off), _read_f32(data, off + 4), _read_f32(data, off + 8))
+    off += 12
+    dynamic = data[off] != 0
+    off += 1
+    props_str, off = _read_str(data, off)
+    try:
+        properties = json.loads(props_str) if props_str else {}
+    except json.JSONDecodeError as exc:
+        raise ChunkCodecError(f"object {oid!r}: invalid properties JSON") from exc
+    obj_flags = _decode_flags(data[off:])
+    return WorldObject(id=oid, type=otype, asset_id=asset_id, pos=pos, rot=rot,
+                        scale=scale, dynamic=dynamic, properties=properties, flags=obj_flags)
+
+
+def _encode_revision_meta(payload: ChunkPayload) -> bytes:
+    out = bytearray()
+    out += _w_i64(payload.created_at)
+    out += _w_i64(payload.updated_at)
+    out += _w_u32(payload.revision)
+    out += _w_str(payload.author)
+    return bytes(out)
+
+
+def _decode_revision_meta(data: bytes, result: ChunkPayload) -> None:
+    off = 0
+    result.created_at = _read_i64(data, off); off += 8
+    result.updated_at = _read_i64(data, off); off += 8
+    result.revision = _read_u32(data, off); off += 4
+    result.author, off = _read_str(data, off)
+
+
+def _wrap_section(section_id: int, data: bytes) -> bytes:
+    return bytes([section_id]) + _w_u32(len(data)) + data
+
+
+# ───────────────────────── Top-level encode/decode ─────────────────────────
+
+def encode_binary(payload: ChunkPayload) -> bytes:
+    """Encode a ChunkPayload to the world.md §3.6 wire format."""
+    sections = bytearray()
+    sections += _wrap_section(SECTION_META, _encode_metadata(payload))
+    for layer in payload.tile_layers:
+        sections += _wrap_section(SECTION_TILE, _encode_tile_layer(layer))
+    for obj in payload.objects:
+        sections += _wrap_section(SECTION_OBJECT, _encode_object(obj))
+    sections += _wrap_section(SECTION_FLAGS, _encode_flags(payload.flags))
+    sections += _wrap_section(SECTION_REVISION_META, _encode_revision_meta(payload))
+
+    payload_body = bytes(sections)
+    digest = hashlib.sha256(payload_body).digest()  # 32 raw bytes
+
+    header = bytearray()
+    header += MAGIC
+    header += _w_u16(CURRENT_VERSION)
+    header += _w_u16(HEADER_SIZE - 8)  # header_len: bytes of header after this field (spec-correct)
+    header += _w_u32(0)  # flags (reserved)
+    header += _w_u32(len(payload_body))
+    header += digest
+
+    return bytes(header) + payload_body
+
+
+def decode_binary(data: bytes) -> ChunkPayload:
+    """Decode a world.md §3.6 binary chunk. Raises ChunkCodecError on
+    structurally malformed input (short buffer, bad magic, unsupported
+    version, truncated payload)."""
+    if len(data) < HEADER_SIZE:
+        raise ChunkCodecError(f"data too short for header ({len(data)} bytes)")
+
+    if data[0:4] != MAGIC:
+        raise ChunkCodecError("bad magic bytes")
+
+    version = _read_u16(data, 4)
+    if version < 1 or version > CURRENT_VERSION:
+        raise ChunkCodecError(f"unsupported chunk format version {version}")
+
+    # header_len (offset 6) is intentionally not used for offset math --
+    # both this decoder and the Godot one always slice at the fixed
+    # HEADER_SIZE, matching the reference implementation's actual (if
+    # spec-inconsistent) behaviour.
+    payload_len = _read_u32(data, 12)
+    # bytes 16:48 are the header's advisory checksum -- decode_and_validate
+    # re-reads it directly and recomputes against the parsed payload body.
+
+    if len(data) - HEADER_SIZE != payload_len:
+        raise ChunkCodecError(
+            f"declared payload_len ({payload_len}) does not match actual "
+            f"remaining bytes ({len(data) - HEADER_SIZE})"
+        )
+
+    payload_body = data[HEADER_SIZE:HEADER_SIZE + payload_len]
+
+    result = ChunkPayload(version=version)
+
+    offset = 0
+    while offset < len(payload_body):
+        if offset + 5 > len(payload_body):
+            raise ChunkCodecError("truncated section header")
+        section_id = payload_body[offset]
+        section_len = _read_u32(payload_body, offset + 1)
+        data_start = offset + 5
+        data_end = data_start + section_len
+        if data_end > len(payload_body):
+            raise ChunkCodecError("truncated section body")
+        section_data = payload_body[data_start:data_end]
+
+        if section_id == SECTION_META:
+            _decode_metadata(section_data, result)
+        elif section_id == SECTION_TILE:
+            result.tile_layers.append(_decode_tile_layer(section_data))
+        elif section_id == SECTION_OBJECT:
+            result.objects.append(_decode_object(section_data))
+        elif section_id == SECTION_FLAGS:
+            result.flags = _decode_flags(section_data)
+        elif section_id == SECTION_REVISION_META:
+            _decode_revision_meta(section_data, result)
+        # Unknown section ids are skipped (forward-compat), matching the
+        # Godot decoder's match-with-no-default behaviour.
+
+        offset = data_end
+
+    return result
+
+
+# ───────────────────────── JSON encoding (world.md §3.5) ─────────────────────────
+# Derived, never stored (world_persistence_impl.md §8.1) -- produced here
+# from a decoded ChunkPayload for the ``Accept: application/json`` path.
+
+def to_json_dict(payload: ChunkPayload, *, key: str, chunk_checksum: str) -> dict:
+    return {
+        "version": payload.version,
+        "key": key,
+        "world_id": payload.world_id,
+        "room_id": payload.room_id,
+        "coord": {"cx": payload.coord[0], "cy": payload.coord[1], "cz": payload.coord[2]},
+        "bounds": {
+            "min_x": payload.bounds.min[0], "min_y": payload.bounds.min[1], "min_z": payload.bounds.min[2],
+            "max_x": payload.bounds.max[0], "max_y": payload.bounds.max[1], "max_z": payload.bounds.max[2],
+        },
+        "tiles": [
+            {
+                "name": layer.name,
+                "layer_id": layer.layer_id,
+                "width": layer.width,
+                "height": layer.height,
+                "depth": layer.depth,
+                "palette": [
+                    {"id": td.id, "asset_id": td.asset_id, "solid": td.solid,
+                     "flags": td.flags, "variants": td.variants}
+                    for td in layer.palette
+                ],
+                "tiles": list(layer.tiles),
+            }
+            for layer in payload.tile_layers
+        ],
+        "objects": [
+            {
+                "id": obj.id, "type": obj.type, "asset_id": obj.asset_id,
+                "transform": {
+                    "pos": list(obj.pos), "rot": list(obj.rot), "scale": list(obj.scale),
+                },
+                "properties": obj.properties,
+                "dynamic": obj.dynamic,
+                "flags": obj.flags.to_dict(),
+            }
+            for obj in payload.objects
+        ],
+        "flags": payload.flags.to_dict(),
+        "meta": {
+            "created_at": payload.created_at, "updated_at": payload.updated_at,
+            "revision": payload.revision, "author": payload.author,
+        },
+        "checksum": chunk_checksum,
+    }
+
+
+# ───────────────────────── Validation (world_persistence_impl.md §5.5) ─────────────────────────
+
+# Not precisely quantified by the design doc beyond "length limits" --
+# these are this implementation's conservative defaults (world.md §7).
+MAX_STRING_FIELD_LEN = 256
+MAX_PROPERTIES_JSON_LEN = 16_384
+MAX_SOURCES_PER_FLAGSET = 32
+
+
+def _check_string_lengths(obj: WorldObject) -> None:
+    for field_name, value in (("id", obj.id), ("type", obj.type), ("asset_id", obj.asset_id)):
+        if len(value) > MAX_STRING_FIELD_LEN:
+            raise ChunkValidationError(
+                "string_field_too_long", f"object.{field_name} exceeds {MAX_STRING_FIELD_LEN} chars"
+            )
+    props_json = json.dumps(obj.properties)
+    if len(props_json) > MAX_PROPERTIES_JSON_LEN:
+        raise ChunkValidationError(
+            "string_field_too_long", f"object {obj.id!r} properties exceed {MAX_PROPERTIES_JSON_LEN} bytes"
+        )
+    if len(obj.flags.sources) > MAX_SOURCES_PER_FLAGSET:
+        raise ChunkValidationError("string_field_too_long", f"object {obj.id!r} has too many flag sources")
+
+
+def decode_and_validate(
+    data: bytes,
+    *,
+    expected_key: str,
+    grid_size: tuple[int, int, int],
+    max_objects: int,
+) -> ChunkPayload:
+    """Decode + fully validate a client-submitted chunk payload.
+
+    This is the boundary world_persistence_impl.md §5.5 requires: "the
+    backend must not trust the client". Raises ``ChunkCodecError`` for
+    structurally malformed bytes (mapped to a 422 by the router with a
+    generic reason) or ``ChunkValidationError`` with a specific ``reason``
+    code for a well-formed-but-invalid payload.
+    """
+    payload = decode_binary(data)  # raises ChunkCodecError for structural problems first
+
+    # Checksum is advisory in the header (world.md §7); the value that
+    # matters is recomputed from the actual payload body we just parsed.
+    payload_body = data[HEADER_SIZE:]
+    recomputed = checksum(payload_body)
+    header_checksum_hex = data[16:48].hex()
+    if header_checksum_hex != recomputed:
+        raise ChunkValidationError(
+            "checksum_mismatch",
+            "header checksum does not match the recomputed SHA-256 of the payload body",
+        )
+
+    actual_key = build_key(payload.world_id, payload.room_id, *payload.coord)
+    if actual_key != expected_key:
+        raise ChunkValidationError(
+            "chunk_key_mismatch",
+            f"payload key {actual_key!r} does not match URL {expected_key!r}",
+        )
+
+    for layer in payload.tile_layers:
+        if (layer.width, layer.height, layer.depth) != tuple(grid_size):
+            raise ChunkValidationError(
+                "layer_dims",
+                f"tile layer {layer.name!r} dims {(layer.width, layer.height, layer.depth)} "
+                f"!= room grid {tuple(grid_size)}",
+            )
+        valid_ids = {0} | {td.id for td in layer.palette}
+        for tile_id in layer.tiles:
+            if tile_id not in valid_ids:
+                raise ChunkValidationError(
+                    "tile_out_of_palette",
+                    f"tile layer {layer.name!r} references palette id {tile_id} not in its palette",
+                )
+        if len(layer.tiles) != layer.width * layer.height * layer.depth:
+            raise ChunkValidationError(
+                "layer_dims",
+                f"tile layer {layer.name!r} has {len(layer.tiles)} cells, expected "
+                f"{layer.width * layer.height * layer.depth}",
+            )
+
+    if len(payload.objects) > max_objects:
+        raise ChunkValidationError(
+            "too_many_objects", f"{len(payload.objects)} objects exceeds max {max_objects}"
+        )
+
+    bmin, bmax = payload.bounds.min, payload.bounds.max
+    for obj in payload.objects:
+        _check_string_lengths(obj)
+        if not all(bmin[i] <= obj.pos[i] <= bmax[i] for i in range(3)):
+            raise ChunkValidationError(
+                "object_out_of_bounds",
+                f"object {obj.id!r} position {obj.pos} outside chunk bounds "
+                f"[{bmin}, {bmax}]",
+            )
+
+    if len(payload.author) > MAX_STRING_FIELD_LEN:
+        raise ChunkValidationError("string_field_too_long", "meta.author too long")
+
+    return payload
+
+
+# ───────────────────────── Known cross-codec divergence ─────────────────────────
+#
+# `scripts/chunk_data_decoder.gd`'s `_read_float32`/`_write_float32` do:
+#
+#     static func _write_float32(val: float) -> PackedByteArray:
+#         var bits := val as int
+#         return _write_uint32(bits)
+#
+#     static func _read_float32(data: PackedByteArray, offset: int) -> float:
+#         var bits := _read_uint32(data, offset)
+#         return bits as float
+#
+# `as` between int and float in GDScript is a numeric conversion, not a bit
+# reinterpretation (verified empirically against Godot 4.6.2 headless:
+# `1.5 as int` -> `1`, `1 as float` -> `1.0`; the IEEE-754 bit pattern of
+# 1.5f is 0x3FC00000 = 1069547520, not 1). So the shipped client codec
+# truncates every float32 field (bounds, object pos/rot/scale) to its
+# integer part and stores that integer as a raw int32 -- not as float32
+# bits at all. This is a real bug in already-merged, client-side code
+# (scripts/ is out of scope for this task) that breaks the "byte-stable
+# across two implementations" guarantee world.md §3.6.3 states.
+#
+# This module implements the *specified* format (real IEEE-754 float32)
+# rather than replicating that bug, because world.md §3.6 is normative and
+# says "float32" for these fields, and mirroring the bug would mean the
+# backend also corrupts every non-integer transform/bounds value it
+# stores. Practical effect until the client-side bug is fixed: payloads
+# with integer-only floats will decode identically on both sides; any
+# payload with a fractional position/rotation/scale/bounds value will not
+# be byte-identical (or numerically identical) between this module and the
+# current `scripts/chunk_data_decoder.gd`. This is flagged for the
+# client/editor follow-on task, not fixed here.

backend/app/services/game_servers.py

@@ -0,0 +1,239 @@
+"""Game-server orchestration.
+
+On ``POST /api/worlds/{id}/join`` the backend ensures a headless Godot
+dedicated-server process is running for that world and returns its address.
+One process per world, keyed by ``world_id``. A background reaper kills a
+world's server once its status file reports zero players for
+``GAME_SERVER_IDLE_TIMEOUT_SECONDS``.
+
+This lives in-process (a module-level singleton) rather than as a separate
+service, so the backend MUST run single-worker -- which it does
+(``uvicorn app.main:app`` with no ``--workers``). The Godot binary and
+project are on the host (see ``settings.GODOT_BIN`` / ``GAME_PROJECT_DIR``);
+the backend spawns them as subprocesses.
+
+Design notes / limits (PC3):
+ - Port allocation is a linear scan of the configured range.
+ - No crash-restart: if a server process dies, the next join respawns it.
+   With world content now durable in Postgres (world_persistence_impl.md
+   D2), this is genuinely safe rather than merely tolerated: the sim
+   process holds no unsaved world content, so a reap/crash/kill can never
+   lose world data.
+
+Per-spawn auth token (world_persistence_impl.md §7.3): each spawned server
+gets a random ``secrets.token_urlsafe(32)`` on its command line, which it
+uses as a Bearer token against ``/api/internal`` to pull its world's
+content read-only before binding its ENet port. The token grants access to
+exactly one world and dies with its process (the reaper's
+``del self._servers[wid]`` invalidates it; see ``validate_token``).
+"""
+from __future__ import annotations
+
+import asyncio
+import hmac
+import json
+import secrets
+import socket
+import subprocess
+import tempfile
+import time
+from dataclasses import dataclass, field
+from pathlib import Path
+
+from app.config import settings
+
+
+@dataclass
+class _WorldServer:
+    world_id: str
+    port: int
+    proc: subprocess.Popen
+    status_path: Path
+    token: str
+    started_at: float = field(default_factory=time.time)
+    last_join: float = field(default_factory=time.time)
+
+    def status(self) -> dict:
+        try:
+            return json.loads(self.status_path.read_text())
+        except (OSError, ValueError):
+            return {}
+
+    def player_count(self) -> int:
+        return int(self.status().get("players", 0))
+
+    def is_ready(self) -> bool:
+        return self.status().get("ready") is True
+
+    def alive(self) -> bool:
+        return self.proc.poll() is None
+
+    def stop(self) -> None:
+        if self.alive():
+            self.proc.terminate()
+            try:
+                self.proc.wait(timeout=10)
+            except subprocess.TimeoutExpired:
+                self.proc.kill()
+        self.status_path.unlink(missing_ok=True)
+
+
+class GameServerSupervisor:
+    def __init__(self) -> None:
+        self._servers: dict[str, _WorldServer] = {}
+        self._lock = asyncio.Lock()
+        self._reaper: asyncio.Task | None = None
+        self._runtime_dir = Path(tempfile.gettempdir()) / "agp-game-servers"
+        self._runtime_dir.mkdir(parents=True, exist_ok=True)
+
+    # ── lifecycle ────────────────────────────────────────────────────────
+    def start(self) -> None:
+        if not settings.GAME_SERVERS_ENABLED:
+            return
+        if self._reaper is None or self._reaper.done():
+            self._reaper = asyncio.create_task(self._reap_loop())
+
+    async def shutdown(self) -> None:
+        if self._reaper:
+            self._reaper.cancel()
+        async with self._lock:
+            for srv in list(self._servers.values()):
+                srv.stop()
+            self._servers.clear()
+
+    # ── join ─────────────────────────────────────────────────────────────
+    async def ensure_server(self, world_id: str) -> dict:
+        """Return ``{"host", "port", "world_id"}`` for the world's dedicated
+        server, spawning it if needed. Raises RuntimeError if orchestration
+        is disabled or no port/engine is available."""
+        if not settings.GAME_SERVERS_ENABLED:
+            raise RuntimeError("game servers are not enabled on this backend")
+
+        async with self._lock:
+            srv = self._servers.get(world_id)
+            if srv is not None and not srv.alive():
+                srv.stop()
+                srv = None
+                del self._servers[world_id]
+
+            if srv is None:
+                srv = self._spawn(world_id)
+                self._servers[world_id] = srv
+                try:
+                    await self._await_ready(srv)
+                except TimeoutError:
+                    # Real failure now, not a silent "hope it's fine" --
+                    # see _await_ready's docstring. Don't leave a possibly
+                    # half-started process registered.
+                    srv.stop()
+                    del self._servers[world_id]
+                    raise RuntimeError(
+                        f"dedicated server for world {world_id} did not become ready in time"
+                    )
+
+            srv.last_join = time.time()
+            return {"host": settings.GAME_SERVER_HOST, "port": srv.port, "world_id": world_id}
+
+    def validate_token(self, world_id: str, token: str) -> bool:
+        """`require_game_server` dependency support (world_persistence_impl.md
+        §7.3): true iff *token* is the live token for *world_id*'s server.
+        A dict lookup, as the doc specifies, plus a constant-time compare
+        since it's a bearer credential."""
+        srv = self._servers.get(str(world_id))
+        if srv is None or not srv.alive():
+            return False
+        return hmac.compare_digest(srv.token, token)
+
+    # ── internals ────────────────────────────────────────────────────────
+    def _spawn(self, world_id: str) -> _WorldServer:
+        port = self._free_port()
+        token = secrets.token_urlsafe(32)
+        status_path = self._runtime_dir / f"world_{world_id}_{port}.json"
+        status_path.unlink(missing_ok=True)
+        cmd = [
+            settings.GODOT_BIN, "--headless",
+            "--path", settings.GAME_PROJECT_DIR,
+            "res://scenes/server.tscn", "--",
+            "--port", str(port),
+            "--world", str(world_id),
+            "--status-file", str(status_path),
+            "--api-url", settings.GAME_SERVER_INTERNAL_API_URL,
+            "--server-token", token,
+        ]
+        proc = subprocess.Popen(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+        return _WorldServer(
+            world_id=world_id, port=port, proc=proc, status_path=status_path, token=token
+        )
+
+    def _free_port(self) -> int:
+        used = {s.port for s in self._servers.values()}
+        for p in range(settings.GAME_SERVER_PORT_MIN, settings.GAME_SERVER_PORT_MAX + 1):
+            if p in used:
+                continue
+            with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as s:
+                try:
+                    s.bind(("0.0.0.0", p))
+                    return p
+                except OSError:
+                    continue
+        raise RuntimeError("no free game-server port in the configured range")
+
+    async def _await_ready(self, srv: _WorldServer) -> None:
+        """Wait for a ``"ready": true`` field in the status file
+        (world_persistence_impl.md §7.4).
+
+        This replaces the old ``_await_port``, which had two real bugs:
+        it treated a bound UDP port as "ready", but with content loading
+        the port binds *before* the server has fetched its world's rooms
+        and chunks (world_persistence_impl.md §7.2 step 4) -- so a client
+        could get handed an address for a server still mid-fetch. And it
+        *failed open*: past its 8s deadline it simply returned, with no
+        error, so ``ensure_server`` reported success for a server that may
+        never have started at all. This raises ``TimeoutError`` instead,
+        which ``ensure_server`` turns into a real 503 for the joining
+        client, and also bails out early (same exception) if the process
+        has already exited.
+        """
+        deadline = time.time() + settings.GAME_SERVER_READY_TIMEOUT_SECONDS
+        while time.time() < deadline:
+            if srv.is_ready():
+                return
+            if not srv.alive():
+                raise TimeoutError(
+                    f"server process for world {srv.world_id} exited before becoming ready"
+                )
+            await asyncio.sleep(0.25)
+        raise TimeoutError(
+            f"server for world {srv.world_id} did not report ready within "
+            f"{settings.GAME_SERVER_READY_TIMEOUT_SECONDS}s"
+        )
+
+    async def _reap_loop(self) -> None:
+        try:
+            while True:
+                await asyncio.sleep(30)
+                async with self._lock:
+                    now = time.time()
+                    for wid, srv in list(self._servers.items()):
+                        if not srv.alive():
+                            srv.stop()
+                            del self._servers[wid]
+                            continue
+                        idle_for = now - srv.last_join
+                        if idle_for > settings.GAME_SERVER_IDLE_TIMEOUT_SECONDS and srv.player_count() == 0:
+                            srv.stop()
+                            del self._servers[wid]
+        except asyncio.CancelledError:
+            pass
+
+    def debug_state(self) -> list[dict]:
+        return [
+            {
+                "world_id": s.world_id, "port": s.port, "alive": s.alive(),
+                "players": s.player_count(), "uptime_s": round(time.time() - s.started_at),
+            }
+            for s in self._servers.values()
+        ]
+
+
+supervisor = GameServerSupervisor()

backend/app/services/presence.py

@@ -0,0 +1,145 @@
+"""Redis-backed presence store.
+
+Presence is determined by a heartbeat TTL key in Redis:
+- heartbeat(user_id) sets a TTL key per user (default 60 s).
+- is_online(user_id) / is_online_batch(user_ids) check whether the key(s)
+  exist.
+
+status_message and last_seen_at are persisted in the ``users`` table by the
+router (app/routers/presence.py); this store only owns the Redis side.
+
+The Redis client is created lazily, on first actual use, rather than
+requiring an explicit ``connect()`` call during app startup. This matters
+because FastAPI's lifespan handler does not run under the plain
+``TestClient(app)`` instantiation this codebase's tests use (no
+``with`` block), so anything that only connected during lifespan startup
+would never connect in tests. Lazy connection means the store works
+identically whether the app was started for real or is being driven by
+pytest.
+
+The client is also cached per-*event loop* rather than globally: the same
+plain ``TestClient(app)`` pattern can dispatch different requests onto
+different event loops (see the NullPool comment on ``_override_db`` in
+tests/conftest.py for the analogous asyncpg problem), and an
+``aioredis.Redis`` connection, like an asyncpg connection, breaks with
+"Event loop is closed" if reused across loops. In the real running server
+there is exactly one event loop for the process lifetime, so this
+degrades to a single cached, pooled connection there.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+
+import redis.asyncio as aioredis
+
+from app.config import settings
+
+logger = logging.getLogger(__name__)
+
+# Key prefix for heartbeat entries.
+_PRESENCE_KEY_PREFIX = "presence:heartbeat:"
+
+# Default heartbeat TTL in seconds (1 minute).
+# Clients should heartbeat at least once per interval.
+_DEFAULT_HEARTBEAT_TTL = 60
+
+
+class PresenceStore:
+    """Redis-backed presence store with async, lazily-connected operations."""
+
+    def __init__(self, redis_url: str | None = None, heartbeat_ttl: int = _DEFAULT_HEARTBEAT_TTL):
+        # redis_url is resolved from settings at first use (not at
+        # construction time) so tests that override settings.REDIS_URL
+        # before the first call still take effect -- this module is
+        # imported (and the module-level singleton below constructed)
+        # well before any such override runs.
+        self._redis_url = redis_url
+        self._heartbeat_ttl = heartbeat_ttl
+        # Keyed by id(running loop) -- see the module docstring.
+        self._clients: dict[int, aioredis.Redis] = {}
+        self._connect_lock = asyncio.Lock()
+
+    # ------------------------------------------------------------------
+    # Lifecycle
+    # ------------------------------------------------------------------
+
+    async def _ensure_client(self) -> aioredis.Redis:
+        """Return a connected client for the current event loop, connecting
+        on first use per loop."""
+        loop_key = id(asyncio.get_running_loop())
+        client = self._clients.get(loop_key)
+        if client is None:
+            async with self._connect_lock:
+                client = self._clients.get(loop_key)
+                if client is None:
+                    url = self._redis_url or settings.REDIS_URL
+                    client = aioredis.from_url(
+                        url,
+                        encoding="utf-8",
+                        decode_responses=True,
+                    )
+                    try:
+                        await client.ping()
+                    except Exception:
+                        logger.warning("Redis ping failed for %s", url)
+                        raise
+                    self._clients[loop_key] = client
+        return client
+
+    async def close(self) -> None:
+        """Close the Redis connection for the current event loop, if one was
+        opened."""
+        loop_key = id(asyncio.get_running_loop())
+        client = self._clients.pop(loop_key, None)
+        if client is not None:
+            await client.aclose()
+
+    # ------------------------------------------------------------------
+    # Heartbeat
+    # ------------------------------------------------------------------
+
+    async def heartbeat(self, user_id: int) -> None:
+        """Record a heartbeat for *user_id*.
+
+        Sets a TTL key so that the user is considered online as long as
+        heartbeats arrive at least once per heartbeat_ttl seconds.
+        """
+        client = await self._ensure_client()
+        await client.set(self._heartbeat_key(user_id), "1", ex=self._heartbeat_ttl)
+
+    # ------------------------------------------------------------------
+    # Online checks
+    # ------------------------------------------------------------------
+
+    async def is_online(self, user_id: int) -> bool:
+        """Return True if the user has a valid heartbeat key."""
+        client = await self._ensure_client()
+        exists = await client.exists(self._heartbeat_key(user_id))
+        return bool(exists)
+
+    async def is_online_batch(self, user_ids: list[int]) -> set[int]:
+        """Return the subset of user_ids that currently have a valid
+        heartbeat key. Uses MGET (one round trip) rather than one EXISTS
+        per user.
+        """
+        if not user_ids:
+            return set()
+        client = await self._ensure_client()
+        keys = [self._heartbeat_key(uid) for uid in user_ids]
+        values = await client.mget(keys)
+        return {uid for uid, v in zip(user_ids, values) if v is not None}
+
+    # ------------------------------------------------------------------
+    # Helpers
+    # ------------------------------------------------------------------
+
+    @staticmethod
+    def _heartbeat_key(user_id: int) -> str:
+        return f"{_PRESENCE_KEY_PREFIX}{user_id}"
+
+
+# Singleton instance shared by the router, so all requests share the same
+# connection pool.
+presence_store = PresenceStore()

backend/app/services/text_filter.py

@@ -0,0 +1,304 @@
+"""Pluggable server-side text filtering, `docs/planning/social.md` §4/§5 (US-4).
+
+social.md §4 calls for a "Pluggable `TextFilter` interface with a
+deterministic default (profanity list + normalization) so it runs without
+external services; third-party hook later". This module is that interface
+plus the default implementation:
+
+- `TextFilter` is a `Protocol` -- the extension point. A future third-party
+  moderation provider (a paid API, an ML classifier, etc.) just needs to
+  implement `check(text) -> FilterResult`; nothing else in this module
+  needs to change, and callers depend on the protocol, not a concrete
+  class.
+- `ListBasedTextFilter` is the deterministic default: a configurable
+  term list (JSON file, see `text_filter_terms.json` next to this module)
+  matched against a normalized form of the input text so that trivial
+  evasion (case changes, leetspeak substitutions, and punctuation/spacing
+  inserted between letters) doesn't slip through.
+
+Nothing here talks to a database, an HTTP client, or the FastAPI app -- it
+is a pure, side-effect-free (aside from reading the term list file once, at
+construction) service so it can be unit tested in isolation. It is NOT
+wired into any router/endpoint by this task; that's for the chat feature
+tasks that depend on it (social.md §6) to do.
+
+Normalization approach
+-----------------------
+Matching naively against raw text misses "sh1t", "@ss", or "s.h.i.t". To
+catch these without a real tokenizer, every character of the input is
+independently normalized to at most one lowercase ASCII alphanumeric
+character (case-folded, then run through a small leetspeak substitution
+table); characters that don't reduce to `[a-z0-9]` (punctuation, spacing,
+symbols, non-ASCII) are dropped entirely rather than kept as separators.
+This collapses "s.h.i.t", "s h i t", and "SHIT" to the same normalized
+string ("shit") that a plain lowercase term list entry matches, while a
+side table (`index_map`) remembers which original character produced each
+surviving normalized character -- so a match found in the normalized
+string can still be translated back into a span of the *original* text for
+redaction.
+
+This is a deliberate precision/recall tradeoff common to list-based
+filters: stripping separators and folding leetspeak increases recall
+against evasion at the cost of occasionally matching a term inside an
+unrelated longer word (e.g. a 3-letter term inside a longer benign word).
+That tradeoff is exactly why this is pluggable -- a deployment that needs
+tighter precision can swap in a smarter `TextFilter` implementation behind
+the same protocol.
+"""
+
+from __future__ import annotations
+
+import json
+import re
+from dataclasses import dataclass
+from enum import Enum
+from pathlib import Path
+from typing import Iterable, Protocol, runtime_checkable
+
+# ---------------------------------------------------------------------------
+# Public result / protocol
+# ---------------------------------------------------------------------------
+
+
+class FilterAction(str, Enum):
+    """What the caller should do with a checked message."""
+
+    ALLOW = "allow"
+    REDACT = "redact"
+    REJECT = "reject"
+
+
+@dataclass(frozen=True)
+class FilterResult:
+    """Outcome of running a piece of text through a `TextFilter`.
+
+    - `action`: ALLOW (no matches), REDACT (matches replaced in
+      `filtered_text`), or REJECT (matches found; the message should be
+      blocked -- callers should not persist/deliver it even though
+      `filtered_text` is populated for logging/audit purposes).
+    - `filtered_text`: the text to actually store/deliver. Equal to the
+      input for ALLOW and REJECT; has matched spans replaced for REDACT.
+    - `matched_terms`: the distinct matched terms (original, un-normalized
+      list entries), in first-occurrence order. Empty for ALLOW.
+    """
+
+    action: FilterAction
+    filtered_text: str
+    matched_terms: tuple[str, ...] = ()
+
+
+@runtime_checkable
+class TextFilter(Protocol):
+    """Extension point for text filtering/moderation providers.
+
+    Any implementation -- the deterministic default below, or a future
+    third-party service call -- just needs this one method.
+    """
+
+    def check(self, text: str) -> FilterResult:
+        """Check `text` and return the action to take plus filtered text."""
+        ...
+
+
+class FilterMode(str, Enum):
+    """Configures what `ListBasedTextFilter` does when it finds a match."""
+
+    REDACT = "redact"
+    REJECT = "reject"
+
+
+# ---------------------------------------------------------------------------
+# Normalization
+# ---------------------------------------------------------------------------
+
+# Common leetspeak / lookalike substitutions, applied after case-folding.
+# Keys are already-lowercased single characters.
+_LEET_MAP: dict[str, str] = {
+    "0": "o",
+    "1": "i",
+    "!": "i",
+    "3": "e",
+    "4": "a",
+    "@": "a",
+    "5": "s",
+    "$": "s",
+    "7": "t",
+    "+": "t",
+    "8": "b",
+    "|": "l",
+}
+
+_ALNUM_RE = re.compile(r"[a-z0-9]")
+
+
+def _normalize(text: str) -> tuple[str, list[int]]:
+    """Fold `text` to a lowercase-alnum-only string plus an index map.
+
+    Returns `(normalized, index_map)` where `index_map[i]` is the index
+    into the *original* `text` that produced `normalized[i]`. Characters
+    that don't reduce to a single `[a-z0-9]` character (punctuation,
+    whitespace, symbols, most non-ASCII) are dropped from both outputs.
+    """
+    normalized_chars: list[str] = []
+    index_map: list[int] = []
+    for i, ch in enumerate(text):
+        folded = ch.casefold()
+        # case-fold can expand to multiple characters for some unicode
+        # (e.g. German "ß" -> "ss"); such characters are not part of the
+        # leetspeak table and are not plain ascii alnum, so just skip them
+        # like any other non-matching character rather than guessing.
+        if len(folded) != 1:
+            continue
+        folded = _LEET_MAP.get(folded, folded)
+        if _ALNUM_RE.fullmatch(folded):
+            normalized_chars.append(folded)
+            index_map.append(i)
+    return "".join(normalized_chars), index_map
+
+
+def _normalize_term(term: str) -> str:
+    normalized, _ = _normalize(term)
+    return normalized
+
+
+# ---------------------------------------------------------------------------
+# Default term list loading
+# ---------------------------------------------------------------------------
+
+DEFAULT_TERMS_PATH = Path(__file__).with_name("text_filter_terms.json")
+
+
+def load_terms(path: Path | str | None = None) -> list[str]:
+    """Load a term list from a JSON file shaped `{"terms": [...]}`.
+
+    Any other top-level keys (e.g. `_readme`) are ignored. Defaults to the
+    bundled `text_filter_terms.json` next to this module.
+    """
+    resolved = Path(path) if path is not None else DEFAULT_TERMS_PATH
+    with resolved.open("r", encoding="utf-8") as f:
+        data = json.load(f)
+    terms = data.get("terms", [])
+    if not isinstance(terms, list):
+        raise ValueError(f"{resolved}: 'terms' must be a list")
+    return [str(t) for t in terms]
+
+
+# ---------------------------------------------------------------------------
+# Span merging / redaction helpers
+# ---------------------------------------------------------------------------
+
+
+def _merge_spans(spans: list[tuple[int, int, str]]) -> list[tuple[int, int]]:
+    """Merge overlapping/adjacent (start, end) spans, sorted by start."""
+    if not spans:
+        return []
+    ordered = sorted((s, e) for s, e, _ in spans)
+    merged: list[tuple[int, int]] = [ordered[0]]
+    for start, end in ordered[1:]:
+        last_start, last_end = merged[-1]
+        if start <= last_end:
+            merged[-1] = (last_start, max(last_end, end))
+        else:
+            merged.append((start, end))
+    return merged
+
+
+def _apply_redactions(text: str, merged_spans: list[tuple[int, int]], redaction_char: str) -> str:
+    if not merged_spans:
+        return text
+    pieces: list[str] = []
+    cursor = 0
+    for start, end in merged_spans:
+        pieces.append(text[cursor:start])
+        pieces.append(redaction_char * (end - start))
+        cursor = end
+    pieces.append(text[cursor:])
+    return "".join(pieces)
+
+
+# ---------------------------------------------------------------------------
+# Default implementation
+# ---------------------------------------------------------------------------
+
+
+class ListBasedTextFilter:
+    """Deterministic `TextFilter`: normalized substring match against a term list.
+
+    `mode` controls what happens on a match:
+    - `FilterMode.REDACT` (default): matched spans in the *original* text
+      are replaced with `redaction_char` repeated to the matched span's
+      original length; `action` is REDACT if anything matched, else ALLOW.
+    - `FilterMode.REJECT`: `filtered_text` is returned unchanged but
+      `action` is REJECT if anything matched (callers should treat this as
+      "do not store/deliver"), else ALLOW.
+
+    An empty or whitespace-only string always returns ALLOW with no
+    matches -- there is nothing to filter.
+    """
+
+    def __init__(
+        self,
+        terms: Iterable[str] | None = None,
+        *,
+        mode: FilterMode = FilterMode.REDACT,
+        terms_path: Path | str | None = None,
+        redaction_char: str = "*",
+    ) -> None:
+        if terms is None:
+            terms = load_terms(terms_path)
+        # De-dupe while preserving order; drop blanks.
+        seen: dict[str, None] = {}
+        for t in terms:
+            t = t.strip()
+            if t:
+                seen.setdefault(t, None)
+        self._terms: tuple[str, ...] = tuple(seen)
+        # Pre-normalize once at construction; skip terms that normalize to
+        # nothing (e.g. a term that's pure punctuation).
+        self._normalized_terms: list[tuple[str, str]] = [
+            (normalized, original)
+            for original in self._terms
+            if (normalized := _normalize_term(original))
+        ]
+        self.mode = mode
+        self.redaction_char = redaction_char
+
+    def check(self, text: str) -> FilterResult:
+        if not text or not text.strip():
+            return FilterResult(action=FilterAction.ALLOW, filtered_text=text, matched_terms=())
+
+        normalized, index_map = _normalize(text)
+        if not normalized:
+            return FilterResult(action=FilterAction.ALLOW, filtered_text=text, matched_terms=())
+
+        spans: list[tuple[int, int, str]] = []
+        for normalized_term, original_term in self._normalized_terms:
+            start = 0
+            term_len = len(normalized_term)
+            while True:
+                idx = normalized.find(normalized_term, start)
+                if idx == -1:
+                    break
+                end = idx + term_len
+                orig_start = index_map[idx]
+                orig_end = index_map[end - 1] + 1
+                spans.append((orig_start, orig_end, original_term))
+                start = end  # non-overlapping: resume after this match
+
+        if not spans:
+            return FilterResult(action=FilterAction.ALLOW, filtered_text=text, matched_terms=())
+
+        spans.sort(key=lambda s: s[0])
+        matched_terms = tuple(dict.fromkeys(term for _, _, term in spans))
+
+        if self.mode is FilterMode.REJECT:
+            return FilterResult(action=FilterAction.REJECT, filtered_text=text, matched_terms=matched_terms)
+
+        merged = _merge_spans(spans)
+        filtered_text = _apply_redactions(text, merged, self.redaction_char)
+        return FilterResult(action=FilterAction.REDACT, filtered_text=filtered_text, matched_terms=matched_terms)
+
+
+def default_text_filter(mode: FilterMode = FilterMode.REDACT) -> ListBasedTextFilter:
+    """Convenience factory for the bundled default term list."""
+    return ListBasedTextFilter(mode=mode)

backend/app/services/text_filter_terms.json

@@ -0,0 +1,20 @@
+{
+  "_readme": "Default deterministic term list for app.services.text_filter.ListBasedTextFilter. This is a minimal, illustrative starter list (common mild-to-strong English profanity, no slurs) meant to be replaced/extended per-deployment -- swap this file, or pass an explicit `terms`/`terms_path` to the filter, rather than editing this list in place for production moderation policy.",
+  "terms": [
+    "fuck",
+    "shit",
+    "ass",
+    "asshole",
+    "bitch",
+    "bastard",
+    "damn",
+    "crap",
+    "dick",
+    "piss",
+    "slut",
+    "whore",
+    "cunt",
+    "douche",
+    "bullshit"
+  ]
+}

backend/app/services/world_store.py

@@ -0,0 +1,431 @@
+"""World content storage service.
+
+Implements the `world.md` §5.1 service interface over Postgres, per
+`world_persistence_impl.md` §9 -- **minus** ``flush_dirty`` and
+``rebuild_index``, which don't apply once there is no write-behind dirty
+set and no derived index to rebuild (see that doc's §3.3 and §4.2).
+
+This is the *only* place chunk content is written (world_persistence_impl.md
+D2 / §5). Callers (the routers) own transaction boundaries: methods here
+``flush()`` so later statements in the same request see earlier ones and so
+integrity errors surface before a caller commits, but they never
+``commit()`` -- that mirrors the existing convention in
+``app/routers/worlds.py`` (``get_db`` docs: "Handlers are responsible for
+committing or rolling back their own transactions").
+
+Known gap this module had to resolve on its own (flagged, not silently
+decided): `world_persistence_impl.md` §6/§7.2/§8.1 all reference a world's
+monotonic ``content_revision`` ("bumped on every chunk write"), but no
+column for it is defined anywhere in §4's schema. Rather than add an
+undocumented column, ``content_revision()`` below derives it as
+``MAX(id)`` over ``world_chunk_revisions`` scoped to the world: that table
+is append-only (retention only nulls ``payload``, it never deletes rows),
+so the value is genuinely monotonic and increments on every
+create/update/delete/rollback.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from sqlalchemy import func, select, update
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import load_only
+
+from app.config import settings
+from app.models.world_content import (
+    MAIN_ROOM_NAME,
+    MAIN_ROOM_SLUG,
+    WorldChunk,
+    WorldChunkRevision,
+    WorldRoom,
+)
+from app.services import chunk_codec
+
+
+class RevisionConflict(Exception):
+    """Optimistic-concurrency conflict (world.md §5.4). ``current_revision``
+    is 0 and ``current_checksum`` is None when the caller's ``base_revision``
+    assumed a chunk exists but it doesn't."""
+
+    def __init__(
+        self,
+        current_revision: int,
+        current_checksum: str | None,
+        coord: tuple[int, int, int] | None = None,
+    ) -> None:
+        self.current_revision = current_revision
+        self.current_checksum = current_checksum
+        self.coord = coord
+        super().__init__(f"revision conflict: current_revision={current_revision}")
+
+
+class RevisionNotAvailable(Exception):
+    """Raised by ``rollback_chunk`` when the requested revision doesn't
+    exist, or exists but its payload was pruned by the retention policy
+    (world_persistence_impl.md §4.3)."""
+
+
+@dataclass
+class Bounds:
+    cx_min: int | None = None
+    cx_max: int | None = None
+    cy_min: int | None = None
+    cy_max: int | None = None
+    cz: int | None = None
+
+
+class WorldStore:
+    """Owns chunk/room read/write operations over the async session
+    handed to it. One instance per request is the expected usage
+    (``WorldStore(db)`` where ``db`` is the ``DbDep`` session)."""
+
+    def __init__(self, db: AsyncSession) -> None:
+        self.db = db
+
+    # ── rooms ────────────────────────────────────────────────────────────
+
+    async def get_room(self, world_id: int, slug: str) -> WorldRoom | None:
+        result = await self.db.execute(
+            select(WorldRoom).where(WorldRoom.world_id == world_id, WorldRoom.slug == slug)
+        )
+        return result.scalar_one_or_none()
+
+    async def list_rooms(self, world_id: int) -> list[WorldRoom]:
+        result = await self.db.execute(
+            select(WorldRoom).where(WorldRoom.world_id == world_id).order_by(WorldRoom.id)
+        )
+        return list(result.scalars().all())
+
+    async def create_room(
+        self,
+        world_id: int,
+        slug: str,
+        name: str,
+        *,
+        grid: dict | None = None,
+        bounds: dict | None = None,
+        spawn: dict | None = None,
+    ) -> WorldRoom:
+        room = WorldRoom(world_id=world_id, slug=slug, name=name)
+        if grid is not None:
+            room.grid = grid
+        if bounds is not None:
+            room.bounds = bounds
+        if spawn is not None:
+            room.spawn = spawn
+        self.db.add(room)
+        await self.db.flush()
+        await self.db.refresh(room)
+        return room
+
+    async def get_or_create_main_room(self, world_id: int) -> WorldRoom:
+        """world_persistence_impl.md §4.1: every world gets a ``main`` room.
+        Called from ``create_world`` for new worlds, and lazily here for
+        worlds that predate this migration."""
+        room = await self.get_room(world_id, MAIN_ROOM_SLUG)
+        if room is not None:
+            return room
+        try:
+            return await self.create_room(world_id, MAIN_ROOM_SLUG, MAIN_ROOM_NAME)
+        except IntegrityError:
+            # Lost a race with a concurrent creator; the row now exists.
+            await self.db.rollback()
+            room = await self.get_room(world_id, MAIN_ROOM_SLUG)
+            if room is None:
+                raise
+            return room
+
+    async def count_chunks(self, room_id: int) -> int:
+        result = await self.db.execute(
+            select(func.count()).select_from(WorldChunk).where(WorldChunk.room_id == room_id)
+        )
+        return int(result.scalar_one())
+
+    async def content_revision(self, world_id: int) -> int:
+        """See module docstring for why this is derived rather than stored."""
+        result = await self.db.execute(
+            select(func.max(WorldChunkRevision.id)).where(WorldChunkRevision.world_id == world_id)
+        )
+        return int(result.scalar() or 0)
+
+    # ── chunk reads ──────────────────────────────────────────────────────
+
+    async def get_chunk(self, key: str) -> WorldChunk | None:
+        result = await self.db.execute(select(WorldChunk).where(WorldChunk.chunk_key == key))
+        return result.scalar_one_or_none()
+
+    async def get_chunk_by_coord(self, room_id: int, cx: int, cy: int, cz: int) -> WorldChunk | None:
+        result = await self.db.execute(
+            select(WorldChunk).where(
+                WorldChunk.room_id == room_id, WorldChunk.cx == cx,
+                WorldChunk.cy == cy, WorldChunk.cz == cz,
+            )
+        )
+        return result.scalar_one_or_none()
+
+    async def get_chunk_binary(self, key: str) -> bytes | None:
+        chunk = await self.get_chunk(key)
+        return chunk.payload if chunk is not None else None
+
+    async def get_chunk_flags(self, key: str) -> dict | None:
+        chunk = await self.get_chunk(key)
+        return chunk.content_flags if chunk is not None else None
+
+    async def list_chunks(
+        self,
+        world_id: int,
+        room_id: int | None = None,
+        bounds: Bounds | None = None,
+    ) -> list[WorldChunk]:
+        """Index query -- world.md §5.1's ``list_chunks``. Payload bytes are
+        deliberately not loaded (world_persistence_impl.md §8.1: "Payloads
+        are not included")."""
+        query = select(WorldChunk).options(
+            load_only(
+                WorldChunk.id, WorldChunk.world_id, WorldChunk.room_id, WorldChunk.chunk_key,
+                WorldChunk.cx, WorldChunk.cy, WorldChunk.cz, WorldChunk.revision,
+                WorldChunk.checksum, WorldChunk.payload_len, WorldChunk.is_mature,
+                WorldChunk.updated_at,
+            )
+        ).where(WorldChunk.world_id == world_id)
+        if room_id is not None:
+            query = query.where(WorldChunk.room_id == room_id)
+        if bounds is not None:
+            if bounds.cx_min is not None:
+                query = query.where(WorldChunk.cx >= bounds.cx_min)
+            if bounds.cx_max is not None:
+                query = query.where(WorldChunk.cx <= bounds.cx_max)
+            if bounds.cy_min is not None:
+                query = query.where(WorldChunk.cy >= bounds.cy_min)
+            if bounds.cy_max is not None:
+                query = query.where(WorldChunk.cy <= bounds.cy_max)
+            if bounds.cz is not None:
+                query = query.where(WorldChunk.cz == bounds.cz)
+        query = query.order_by(WorldChunk.cx, WorldChunk.cy, WorldChunk.cz)
+        result = await self.db.execute(query)
+        return list(result.scalars().all())
+
+    # ── chunk writes ─────────────────────────────────────────────────────
+
+    async def put_chunk(
+        self,
+        *,
+        room: WorldRoom,
+        cx: int,
+        cy: int,
+        cz: int,
+        payload_bytes: bytes,
+        base_revision: int,
+        actor_id: int | None,
+    ) -> WorldChunk:
+        """Full-chunk write with optimistic concurrency (world.md §5.4,
+        world_persistence_impl.md §5.4/§8.2). Validates the payload
+        server-side (§5.5) before ever touching a row. ``base_revision=0``
+        means "create; 409 if it already exists"."""
+        key = chunk_codec.build_key(room.world_id, room.slug, cx, cy, cz)
+        grid_size = tuple(room.grid.get("size", [32, 32, 1]))
+
+        # Raises ChunkCodecError / ChunkValidationError -- the router maps
+        # those to 422. Nothing below trusts the request body's own claims
+        # about content_flags/is_mature; both come from `decoded`.
+        decoded = chunk_codec.decode_and_validate(
+            payload_bytes,
+            expected_key=key,
+            grid_size=grid_size,
+            max_objects=settings.WORLD_CHUNK_MAX_OBJECTS,
+        )
+        body_checksum = chunk_codec.checksum(payload_bytes[chunk_codec.HEADER_SIZE:])
+
+        result = await self.db.execute(
+            select(WorldChunk)
+            .where(
+                WorldChunk.room_id == room.id, WorldChunk.cx == cx,
+                WorldChunk.cy == cy, WorldChunk.cz == cz,
+            )
+            .with_for_update()
+        )
+        row = result.scalar_one_or_none()
+
+        if base_revision == 0:
+            if row is not None:
+                raise RevisionConflict(row.revision, row.checksum, (cx, cy, cz))
+            row = WorldChunk(
+                world_id=room.world_id, room_id=room.id, chunk_key=key,
+                cx=cx, cy=cy, cz=cz, revision=1,
+            )
+            self.db.add(row)
+            action = "create"
+        else:
+            if row is None or row.revision != base_revision:
+                raise RevisionConflict(
+                    row.revision if row else 0, row.checksum if row else None, (cx, cy, cz)
+                )
+            row.revision = row.revision + 1
+            action = "update"
+
+        row.format_version = decoded.version
+        row.payload = payload_bytes
+        row.payload_len = len(payload_bytes)
+        row.checksum = body_checksum
+        row.content_flags = decoded.flags.to_dict()
+        row.is_mature = decoded.flags.mature
+        row.updated_by_id = actor_id
+
+        try:
+            await self.db.flush()
+        except IntegrityError:
+            # Lost a create race to a concurrent writer between our SELECT
+            # and this flush. Roll back and report the real current state.
+            await self.db.rollback()
+            existing = await self.get_chunk_by_coord(room.id, cx, cy, cz)
+            raise RevisionConflict(
+                existing.revision if existing else 0,
+                existing.checksum if existing else None,
+                (cx, cy, cz),
+            )
+
+        await self._record_revision(key, room.world_id, row.revision, action, actor_id, body_checksum, payload_bytes)
+        await self.db.refresh(row)
+        return row
+
+    async def put_chunks_batch(
+        self,
+        *,
+        room: WorldRoom,
+        items: list[dict],
+        actor_id: int | None,
+    ) -> list[WorldChunk]:
+        """Batch write (world_persistence_impl.md §8.1). One transaction,
+        all-or-nothing: none of this ``commit()``s, so a ``RevisionConflict``
+        raised partway leaves nothing persisted once the caller's request
+        handler lets the exception (or the HTTPException it becomes)
+        propagate through ``get_db``, which rolls back on any exception."""
+        rows: list[WorldChunk] = []
+        for item in items:
+            row = await self.put_chunk(
+                room=room, cx=item["cx"], cy=item["cy"], cz=item["cz"],
+                payload_bytes=item["payload_bytes"], base_revision=item["base_revision"],
+                actor_id=actor_id,
+            )
+            rows.append(row)
+        return rows
+
+    async def delete_chunk(self, key: str, actor_id: int | None) -> None:
+        row = await self.get_chunk(key)
+        if row is None:
+            return
+        await self._record_revision(key, row.world_id, row.revision, "delete", actor_id, row.checksum, None)
+        await self.db.delete(row)
+        await self.db.flush()
+
+    async def rollback_chunk(self, key: str, revision: int, actor_id: int | None) -> WorldChunk:
+        """Restore a chunk to a previously-recorded revision's payload
+        (world.md §5.1). Raises ``RevisionNotAvailable`` if that revision
+        was never recorded, its payload was pruned by retention, or the
+        chunk has since been deleted outright (nothing to update in place)."""
+        rev_result = await self.db.execute(
+            select(WorldChunkRevision)
+            .where(WorldChunkRevision.chunk_key == key, WorldChunkRevision.revision == revision)
+            .order_by(WorldChunkRevision.id.desc())
+            .limit(1)
+        )
+        rev_row = rev_result.scalar_one_or_none()
+        if rev_row is None:
+            raise RevisionNotAvailable(f"no revision {revision} recorded for {key!r}")
+        if rev_row.payload is None:
+            raise RevisionNotAvailable(f"revision {revision} of {key!r} was pruned; payload unavailable")
+
+        chunk = await self.get_chunk(key)
+        if chunk is None:
+            raise RevisionNotAvailable(f"chunk {key!r} no longer exists; cannot roll back in place")
+
+        room_result = await self.db.execute(select(WorldRoom).where(WorldRoom.id == chunk.room_id))
+        room = room_result.scalar_one()
+        grid_size = tuple(room.grid.get("size", [32, 32, 1]))
+        decoded = chunk_codec.decode_and_validate(
+            rev_row.payload, expected_key=key, grid_size=grid_size,
+            max_objects=settings.WORLD_CHUNK_MAX_OBJECTS,
+        )
+        body_checksum = chunk_codec.checksum(rev_row.payload[chunk_codec.HEADER_SIZE:])
+
+        chunk.revision = chunk.revision + 1
+        chunk.payload = rev_row.payload
+        chunk.payload_len = len(rev_row.payload)
+        chunk.checksum = body_checksum
+        chunk.format_version = decoded.version
+        chunk.content_flags = decoded.flags.to_dict()
+        chunk.is_mature = decoded.flags.mature
+        chunk.updated_by_id = actor_id
+
+        await self.db.flush()
+        # Tagged "update" (not a fourth action value) to keep the
+        # documented 'create'|'update'|'delete' action enum intact.
+        await self._record_revision(
+            key, chunk.world_id, chunk.revision, "update", actor_id, body_checksum, rev_row.payload
+        )
+        await self.db.refresh(chunk)
+        return chunk
+
+    async def list_revisions(self, chunk_key: str, limit: int = 50) -> list[WorldChunkRevision]:
+        """Not in world.md §5.1's interface by name, but required to
+        implement the revision-history endpoint world_persistence_impl.md
+        §8.1 lists (``GET .../revisions``)."""
+        result = await self.db.execute(
+            select(WorldChunkRevision)
+            .where(WorldChunkRevision.chunk_key == chunk_key)
+            .order_by(WorldChunkRevision.revision.desc(), WorldChunkRevision.id.desc())
+            .limit(limit)
+        )
+        return list(result.scalars().all())
+
+    async def migrate(self) -> None:
+        """No-op. `world.md` §4.8's hand-rolled SQLite migration runner is
+        superseded by Alembic (`backend/alembic/`) now that content lives
+        in Postgres (world_persistence_impl.md §3.3). Kept only so this
+        class's shape still matches the §5.1 interface it's implementing
+        a subset of."""
+        return None
+
+    # ── internals ────────────────────────────────────────────────────────
+
+    async def _record_revision(
+        self,
+        chunk_key: str,
+        world_id: int,
+        revision: int,
+        action: str,
+        actor_id: int | None,
+        checksum_hex: str,
+        payload_bytes: bytes | None,
+    ) -> None:
+        """Append an audit row and enforce the retention policy
+        (world_persistence_impl.md §4.3, required): keep the newest
+        ``WORLD_CHUNK_REVISION_KEEP`` payloads per ``chunk_key``, null out
+        ``payload`` on older rows, in the same transaction as the write."""
+        rev = WorldChunkRevision(
+            chunk_key=chunk_key, world_id=world_id, revision=revision, action=action,
+            actor_id=actor_id, checksum=checksum_hex, payload=payload_bytes,
+        )
+        self.db.add(rev)
+        await self.db.flush()
+
+        keep = settings.WORLD_CHUNK_REVISION_KEEP
+        keep_ids_result = await self.db.execute(
+            select(WorldChunkRevision.id)
+            .where(WorldChunkRevision.chunk_key == chunk_key)
+            .order_by(WorldChunkRevision.id.desc())
+            .limit(keep)
+        )
+        keep_ids = [row[0] for row in keep_ids_result.all()]
+        if keep_ids:
+            await self.db.execute(
+                update(WorldChunkRevision)
+                .where(
+                    WorldChunkRevision.chunk_key == chunk_key,
+                    WorldChunkRevision.id.notin_(keep_ids),
+                    WorldChunkRevision.payload.isnot(None),
+                )
+                .values(payload=None)
+            )

backend/tests/conftest.py

@@ -1,38 +1,249 @@
-"""Shared pytest fixtures.
+"""Shared pytest fixtures + hermetic-DB/Redis bootstrap.
 
-The auth integration tests hit the *real* Postgres database (per
+The integration tests hit a real Postgres (Postgres-specific types: JSONB,
-``DATABASE_URL``), so they persist data between runs.  Without cleanup a
+native ENUMs) and, for presence tests, a real Redis (TTL semantics aren't
-second run of the suite fails with 409 conflicts because the users it
+worth faking). To make ``cd backend && pytest`` work from a clean checkout
-registered on the first run already exist.  The session-scoped fixture below
+with no manual setup, ``pytest_configure`` below brings up ephemeral
-truncates all application tables once before the first test, making the suite
+Postgres/Redis containers via docker compose and runs the migrations IF
-re-runnable.
+``DATABASE_URL``/``REDIS_URL`` aren't already pointing at something
+reachable. When they are (dev loop, or the checkpoint runner which stands
+these up itself), that path is skipped and the existing services are
+reused.
 
-Truncation order doesn't strictly matter because ``CASCADE`` follows foreign
+If Docker isn't available and nothing is reachable, the whole
-keys, but the tables are listed explicitly for clarity.
+DB/Redis-backed suite is skipped with a clear message rather than erroring
+out dozens of times.
 """
 
 import asyncio
+import hashlib
+import os
+import socket
+import subprocess
+import sys
+import time
+from pathlib import Path
+from urllib.parse import urlsplit
 
 import pytest
 from sqlalchemy import text
-from sqlalchemy.ext.asyncio import create_async_engine
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
 
 from app.config import settings
+from app.database import get_db
+from app.main import app
 
-TEST_TABLES = ("assets", "worlds", "sessions", "refresh_tokens", "users")
+TEST_TABLES = (
+    "avatar_loadouts", "assets",
+    # Profile (app/models/profile.py) -- both FK users.id, profile_favorites
+    # additionally FKs worlds.id; list explicitly for clarity/consistency.
+    "profile_favorites", "profiles",
+    # world_chunk_revisions has no FK to worlds/world_chunks (world.md §4.7 /
+    # world_persistence_impl.md §4.3, deliberate -- deleting a chunk or world
+    # must not lose the audit trail), so it won't be cascade-truncated via
+    # `worlds` the way world_rooms/world_chunks would be. List all three
+    # explicitly rather than rely on cascade for some of them.
+    "world_chunk_revisions", "world_chunks", "world_rooms",
+    "worlds",
+    # Social graph (app/models/social.py) -- all three FK users with
+    # ON DELETE CASCADE, but list explicitly for clarity/consistency.
+    "friendships", "follows", "blocks",
+    # Chat (app/models/chat.py). message_reports.message_id is ON DELETE SET
+    # NULL (not CASCADE, deliberately -- see chat.py), so it wouldn't be
+    # reached by cascading a truncate of messages/conversations; list it
+    # explicitly along with the rest for clarity/consistency.
+    "message_reports", "messages", "conversation_participants", "conversations",
+    # Groups (app/models/groups.py). groups.owner_id is ON DELETE SET NULL
+    # (not CASCADE, deliberately -- see groups.py), so it wouldn't be reached
+    # by cascading a truncate of users; list it explicitly for clarity too.
+    "group_members", "groups",
+    "sessions", "refresh_tokens", "users",
+)
+
+BACKEND_DIR = Path(__file__).resolve().parents[1]
+
+# A hardcoded project name/port here would mean every concurrent checkout
+# running `pytest` (e.g. several Claude Agent-tool subagents, each in their
+# own ~/agp/workspace/task_<id> clone) fights over the exact same Docker
+# Compose project and host ports -- one run's pytest_unconfigure teardown
+# can yank the ephemeral Postgres out from under a completely unrelated
+# concurrent run, surfacing as "connection was closed in the middle of
+# operation" with no obvious cause. Confirmed live 2026-09-15 running 3
+# parallel subagents. Same root cause and fix pattern as the agent_core
+# workspace/Docker-Compose collision documented in project_agp memory --
+# derive both the project name and the port from a hash of the checkout
+# directory, so different concurrent checkouts land on different projects/
+# ports while the same checkout is stable across repeated runs.
+_WORKSPACE_HASH = hashlib.sha256(str(BACKEND_DIR.parent).encode()).hexdigest()[:10]
+_COMPOSE_PROJECT = f"agp-pytest-{_WORKSPACE_HASH}"
+_EPHEMERAL_PG_PORT = 25400 + (int(_WORKSPACE_HASH, 16) % 100)
+_EPHEMERAL_REDIS_PORT = 26300 + (int(_WORKSPACE_HASH, 16) % 100)
+
+# Set by pytest_configure() when it starts container(s) it owns; torn down in
+# pytest_unconfigure.
+_started_container = False
+_db_unavailable_reason: str | None = None
+
+
+def _port_open(host: str, port: int, timeout: float = 1.0) -> bool:
+    try:
+        with socket.create_connection((host, port), timeout=timeout):
+            return True
+    except OSError:
+        return False
+
+
+def _db_reachable(url: str) -> bool:
+    parts = urlsplit(url)
+    return _port_open(parts.hostname or "localhost", parts.port or 5432)
+
+
+def _redis_reachable(url: str) -> bool:
+    parts = urlsplit(url)
+    return _port_open(parts.hostname or "localhost", parts.port or 6379)
+
+
+def _run(cmd: list[str], **kw) -> subprocess.CompletedProcess:
+    return subprocess.run(cmd, cwd=BACKEND_DIR, capture_output=True, text=True, **kw)
+
+
+def pytest_configure(config):
+    global _started_container, _db_unavailable_reason
+
+    need_db = not _db_reachable(settings.DATABASE_URL)
+    need_redis = not _redis_reachable(settings.REDIS_URL)
+
+    if not need_db and not need_redis:
+        return  # dev loop / checkpoint runner already provided both
+
+    if not _run(["docker", "--version"]).returncode == 0:
+        _db_unavailable_reason = (
+            "no reachable DATABASE_URL/REDIS_URL and docker is unavailable -- run "
+            "the checkpoint suite (scripts/run_checkpoint_tests.py) or start "
+            "Postgres/Redis manually"
+        )
+        return
+
+    env = os.environ.copy()
+    env["COMPOSE_PROJECT_NAME"] = _COMPOSE_PROJECT
+    env["POSTGRES_HOST_PORT"] = str(_EPHEMERAL_PG_PORT)
+    env["POSTGRES_PORT"] = str(_EPHEMERAL_PG_PORT)
+    env["REDIS_HOST_PORT"] = str(_EPHEMERAL_REDIS_PORT)
+
+    services = [s for s, need in (("postgres", need_db), ("redis", need_redis)) if need]
+    up = _run(["docker", "compose", "up", "-d", *services], env=env)
+    if up.returncode != 0:
+        _db_unavailable_reason = f"docker compose up {' '.join(services)} failed:\n{up.stderr[-800:]}"
+        return
+    _started_container = True
+
+    if need_db:
+        for _ in range(30):
+            r = _run(
+                ["docker", "compose", "exec", "-T", "postgres",
+                 "pg_isready", "-U", "agp_user", "-d", "agp_db"],
+                env=env,
+            )
+            if r.returncode == 0:
+                break
+            time.sleep(1)
+        else:
+            _db_unavailable_reason = "ephemeral Postgres never became ready"
+            return
+
+        url = f"postgresql+asyncpg://agp_user:agp_password@localhost:{_EPHEMERAL_PG_PORT}/agp_db"
+        os.environ["DATABASE_URL"] = url
+        settings.DATABASE_URL = url
+
+        mig = _run([sys.executable, "-m", "alembic", "upgrade", "head"],
+                   env={**os.environ, "DATABASE_URL": url})
+        if mig.returncode != 0:
+            _db_unavailable_reason = f"alembic upgrade head failed:\n{mig.stderr[-800:]}"
+            return
+
+    if need_redis:
+        for _ in range(30):
+            r = _run(
+                ["docker", "compose", "exec", "-T", "redis", "redis-cli", "ping"],
+                env=env,
+            )
+            if r.returncode == 0 and "PONG" in r.stdout:
+                break
+            time.sleep(1)
+        else:
+            _db_unavailable_reason = "ephemeral Redis never became ready"
+            return
+
+        redis_url = f"redis://localhost:{_EPHEMERAL_REDIS_PORT}/0"
+        os.environ["REDIS_URL"] = redis_url
+        settings.REDIS_URL = redis_url
+
+
+def pytest_unconfigure(config):
+    if not _started_container:
+        return
+    env = os.environ.copy()
+    env["COMPOSE_PROJECT_NAME"] = _COMPOSE_PROJECT
+    env["POSTGRES_HOST_PORT"] = str(_EPHEMERAL_PG_PORT)
+    env["POSTGRES_PORT"] = str(_EPHEMERAL_PG_PORT)
+    env["REDIS_HOST_PORT"] = str(_EPHEMERAL_REDIS_PORT)
+    _run(["docker", "compose", "down", "-v"], env=env)
 
 
 @pytest.fixture(scope="session", autouse=True)
 def _reset_database():
     """Truncate all application tables once per test session."""
+    if _db_unavailable_reason:
+        pytest.skip(_db_unavailable_reason, allow_module_level=True)
 
     async def _truncate() -> None:
         engine = create_async_engine(settings.DATABASE_URL)
         async with engine.begin() as conn:
-            await conn.execute(
+            await conn.execute(text(f"TRUNCATE TABLE {', '.join(TEST_TABLES)} CASCADE"))
-                text(f"TRUNCATE TABLE {', '.join(TEST_TABLES)} CASCADE")
-            )
         await engine.dispose()
 
     asyncio.run(_truncate())
     yield
+
+
+@pytest.fixture(autouse=True)
+def _reset_rate_limiter():
+    """Every TestClient request looks like the same client IP, so the
+    per-IP auth limiter would trip mid-suite. Clear it between tests; the
+    dedicated rate-limit test disables this to exercise the real behaviour.
+    """
+    from app import rate_limit
+    rate_limit.reset_all()
+    yield
+
+
+@pytest.fixture(autouse=True)
+def _override_db():
+    """Override get_db so the app uses a fresh session per test.
+
+    Deliberately does NOT reuse app.database's shared engine: FastAPI's
+    (sync) TestClient runs each request through anyio's blocking-portal
+    machinery, which can hand different requests different event loops.
+    asyncpg connections are bound to the loop they were created on, so
+    reusing one from the shared pool across requests raises "attached to a
+    different loop" the moment a test makes more than one request. NullPool
+    sidesteps it: every checkout is a brand-new connection.
+    """
+    test_engine = create_async_engine(settings.DATABASE_URL, poolclass=NullPool)
+    test_session_factory = async_sessionmaker(test_engine, expire_on_commit=False)
+
+    async def _get_db():
+        async_session = test_session_factory()
+        try:
+            yield async_session
+            await async_session.commit()
+        except Exception:
+            await async_session.rollback()
+            raise
+        finally:
+            await async_session.close()
+
+    app.dependency_overrides[get_db] = _get_db
+    yield
+    app.dependency_overrides.clear()

backend/tests/fixtures/chunks/generate_fixtures.py

@@ -0,0 +1,105 @@
+"""Generates the golden-file chunk fixtures in this directory.
+
+These pin the world.md §3.6 binary format so the Python codec
+(app/services/chunk_codec.py) and any future Godot-side test fixture can be
+checked for drift (world_persistence_impl.md §5.5's "drift control"
+requirement). No Godot-side golden fixture existed at the time this was
+written (searched scripts/ and tests/ for AGPC / binary-format test
+vectors -- none found), so these are authored here, from this
+implementation, as the first golden files for the format. The client/editor
+follow-on task should decode these same files with
+`ChunkDataDecoder.decode_binary()` and assert the same logical values
+(see the note in chunk_codec.py about a confirmed float32 handling bug in
+that decoder that will need fixing for full byte parity on non-integer
+transforms).
+
+Run with: `python tests/fixtures/chunks/generate_fixtures.py` from `backend/`.
+Fixtures are checked in; this script is for regenerating them if the format
+or these examples change, not run as part of the test suite.
+"""
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[3]))  # backend/
+
+from app.services import chunk_codec as cc
+
+FIXTURES_DIR = Path(__file__).resolve().parent
+
+
+def _empty_chunk() -> cc.ChunkPayload:
+    return cc.ChunkPayload(
+        world_id="7", room_id="main", coord=(0, 0, 0),
+        bounds=cc.ChunkBounds(min=(0.0, 0.0, 0.0), size=(32.0, 32.0, 1.0)),
+        tile_layers=[], objects=[],
+        flags=cc.ContentFlags(),
+        created_at=1_700_000_000, updated_at=1_700_000_000, revision=1, author="fixture-gen",
+    )
+
+
+def _simple_tile_chunk() -> cc.ChunkPayload:
+    layer = cc.TileLayer(
+        name="ground", layer_id=0, width=4, height=4, depth=1,
+        palette=[
+            cc.TileDef(id=0, asset_id="", solid=False, flags=0, variants=1),
+            cc.TileDef(id=1, asset_id="tiles/grass", solid=False, flags=1, variants=4),
+            cc.TileDef(id=2, asset_id="tiles/stone", solid=True, flags=2, variants=2),
+        ],
+        tiles=[0, 1, 1, 0, 1, 2, 2, 1, 1, 2, 2, 1, 0, 1, 1, 0],
+    )
+    return cc.ChunkPayload(
+        world_id="12", room_id="main", coord=(3, -1, 0),
+        bounds=cc.ChunkBounds(min=(96.0, -32.0, 0.0), size=(32.0, 32.0, 1.0)),
+        tile_layers=[layer], objects=[],
+        flags=cc.ContentFlags(violence=0, mature=False, sources=[]),
+        created_at=1_700_000_000, updated_at=1_700_000_500, revision=2, author="fixture-gen",
+    )
+
+
+def _chunk_with_objects() -> cc.ChunkPayload:
+    layer = cc.TileLayer(
+        name="ground", layer_id=0, width=2, height=2, depth=1,
+        palette=[cc.TileDef(id=0, asset_id="", solid=False, flags=0, variants=1)],
+        tiles=[0, 0, 0, 0],
+    )
+    obj1 = cc.WorldObject(
+        id="obj_0001", type="interactable", asset_id="props/chest",
+        pos=(101.5, -110.25, 0.5), rot=(0.0, 0.0, 0.0, 1.0), scale=(1.0, 1.0, 1.0),
+        dynamic=False,
+        properties={"locked": False, "loot_table": "chest_basic"},
+        flags=cc.ContentFlags(violence=0, mature=False, sources=[]),
+    )
+    obj2 = cc.WorldObject(
+        id="obj_0002", type="spawn_point", asset_id="",
+        pos=(96.0, -128.0, 1.0), rot=(0.0, 0.7071, 0.0, 0.7071), scale=(1.0, 1.0, 1.0),
+        dynamic=True,
+        properties={},
+        flags=cc.ContentFlags(violence=1, mature=False, sources=["asset:props/chest"]),
+    )
+    return cc.ChunkPayload(
+        world_id="12", room_id="main", coord=(3, -4, 0),
+        bounds=cc.ChunkBounds(min=(96.0, -128.0, 0.0), size=(32.0, 32.0, 1.0)),
+        tile_layers=[layer], objects=[obj1, obj2],
+        flags=cc.ContentFlags(violence=1, mature=False, sources=["asset:props/chest"]),
+        created_at=1_700_000_000, updated_at=1_700_001_000, revision=5, author="agent-bot",
+    )
+
+
+FIXTURES = {
+    "empty_chunk.bin": _empty_chunk,
+    "simple_tile_chunk.bin": _simple_tile_chunk,
+    "chunk_with_objects.bin": _chunk_with_objects,
+}
+
+
+def main() -> None:
+    for filename, builder in FIXTURES.items():
+        payload = builder()
+        data = cc.encode_binary(payload)
+        (FIXTURES_DIR / filename).write_bytes(data)
+        print(f"wrote {filename} ({len(data)} bytes)")
+
+
+if __name__ == "__main__":
+    main()

backend/tests/test_auth_age_gate.py

@@ -3,92 +3,102 @@
 from datetime import date, timedelta
 
 import pytest
+from fastapi.testclient import TestClient
 
-from app.routers.auth import calculate_age
+from app.main import app
+from app.routers.auth import calculate_age, MIN_AGE, RegisterRequest
 
 
 class TestCalculateAge:
     """Unit tests for the calculate_age helper."""
 
     def test_exactly_18(self):
-        """A person born exactly 18 years ago today is 18."""
+        today = date(2026, 6, 15)
-        today = date(2025, 6, 15)
         dob = today.replace(year=today.year - 18)
         assert calculate_age(dob, today=today) == 18
 
     def test_just_turned_18(self):
-        """A person who turned 18 yesterday is 18."""
+        today = date(2026, 6, 15)
-        today = date(2025, 6, 15)
         dob = today.replace(year=today.year - 18) - timedelta(days=1)
         assert calculate_age(dob, today=today) == 18
 
     def test_one_day_short_of_18(self):
-        """A person born one day after their 18th birthday is 17."""
+        today = date(2026, 6, 15)
-        today = date(2025, 6, 15)
         dob = today.replace(year=today.year - 18) + timedelta(days=1)
         assert calculate_age(dob, today=today) == 17
 
-    def test_17_years_old(self):
+    def test_leap_day_birthday_before(self):
-        """A person who is 17 years old today is 17."""
+        assert calculate_age(date(2000, 2, 29), today=date(2024, 2, 28)) == 23
-        today = date(2025, 6, 15)
-        dob = date(2008, 6, 15)
-        assert calculate_age(dob, today=today) == 17
 
-    def test_65_years_old(self):
+    def test_leap_day_birthday_after(self):
-        """A person who is 65 is correctly calculated."""
+        assert calculate_age(date(2000, 2, 29), today=date(2024, 3, 1)) == 24
-        today = date(2025, 6, 15)
-        dob = today.replace(year=today.year - 65)
-        assert calculate_age(dob, today=today) == 65
-
-    def test_newborn(self):
-        """A newborn is 0."""
-        today = date(2025, 6, 15)
-        dob = today
-        assert calculate_age(dob, today=today) == 0
-
-    def test_birthday_not_yet_this_year(self):
-        """Person born Dec 31, 2000 — on Jan 1, 2025 they are still 24."""
-        dob = date(2000, 12, 31)
-        assert calculate_age(dob, today=date(2025, 1, 1)) == 24
-
-    def test_birthday_today(self):
-        """Person born Dec 31, 2000 — on Dec 31, 2024 they turn 24."""
-        dob = date(2000, 12, 31)
-        assert calculate_age(dob, today=date(2024, 12, 31)) == 24
 
 
-class TestRegisterRequestDateValidation:
+class TestRegisterRequestDob:
-    """Tests for the RegisterRequest date_of_birth field validator."""
+    def test_dob_parsed_from_iso_string(self):
+        req = RegisterRequest(username="u", email="u@example.com", password="p",
+                              date_of_birth="1990-01-01")
+        assert req.date_of_birth == date(1990, 1, 1)
 
-    @pytest.mark.parametrize(
+    def test_dob_required(self):
-        "dob",
+        with pytest.raises(Exception):
-        [
+            RegisterRequest(username="u", email="u@example.com", password="p")
-            "2000-01-01",
-            "1990-12-31",
-            "2004-02-29",  # leap day
-        ],
-    )
-    def test_valid_dates(self, dob):
-        """Valid YYYY-MM-DD dates pass validation."""
-        from app.routers.auth import RegisterRequest
 
-        req = RegisterRequest(username="u", email="u@example.com", password="p", date_of_birth=dob)
+    def test_bad_dob_string_rejected(self):
-        assert req.date_of_birth == dob
+        with pytest.raises(Exception):
+            RegisterRequest(username="u", email="u@example.com", password="p",
+                            date_of_birth="not-a-date")
 
-    @pytest.mark.parametrize(
-        "dob",
-        [
-            "01-01-2000",
-            "2000/01/01",
-            "2000-13-01",
-            "2000-00-10",
-            "not-a-date",
-            "",
-        ],
-    )
-    def test_invalid_dates_rejected(self, dob):
-        """Invalid dates are rejected by the validator."""
-        from app.routers.auth import RegisterRequest
 
-        with pytest.raises(ValueError):
+class TestRegisterAgeGate:
-            RegisterRequest(username="u", email="u@example.com", password="p", date_of_birth=dob)
+    """End-to-end: the /register endpoint computes age from the DOB."""
+
+    def _dob_for_age(self, years: int) -> str:
+        return (date.today().replace(year=date.today().year - years)).isoformat()
+
+    def test_adult_accepted(self):
+        client = TestClient(app)
+        r = client.post("/api/auth/register", json={
+            "username": "gate_adult", "email": "gate_adult@e.com",
+            "password": "secret123", "date_of_birth": self._dob_for_age(25),
+        })
+        assert r.status_code == 201, r.text
+
+    def test_minor_rejected(self):
+        client = TestClient(app)
+        r = client.post("/api/auth/register", json={
+            "username": "gate_minor", "email": "gate_minor@e.com",
+            "password": "secret123", "date_of_birth": self._dob_for_age(15),
+        })
+        assert r.status_code == 403
+        assert str(MIN_AGE) in r.json()["detail"]
+
+    def test_exactly_18_accepted(self):
+        client = TestClient(app)
+        r = client.post("/api/auth/register", json={
+            "username": "gate_18", "email": "gate_18@e.com",
+            "password": "secret123",
+            "date_of_birth": (date.today().replace(year=date.today().year - 18) - timedelta(days=1)).isoformat(),
+        })
+        assert r.status_code == 201, r.text
+
+    def test_future_dob_rejected(self):
+        client = TestClient(app)
+        r = client.post("/api/auth/register", json={
+            "username": "gate_future", "email": "gate_future@e.com",
+            "password": "secret123", "date_of_birth": "2999-01-01",
+        })
+        assert r.status_code == 400
+
+    def test_dob_is_stored(self):
+        client = TestClient(app)
+        dob = self._dob_for_age(30)
+        reg = client.post("/api/auth/register", json={
+            "username": "gate_stored", "email": "gate_stored@e.com",
+            "password": "secret123", "date_of_birth": dob,
+        })
+        assert reg.status_code == 201
+        me = client.get("/api/auth/me", headers={
+            "Authorization": f"Bearer {reg.json()['access_token']}"
+        })
+        assert me.json()["date_of_birth"] == dob

backend/tests/test_auth_endpoints.py

@@ -73,7 +73,7 @@ class TestRegister:
                 "username": "newuser",
                 "email": "new@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "date_of_birth": "1990-01-01",
             },
         )
         assert resp.status_code == 201
@@ -81,20 +81,23 @@ class TestRegister:
         assert "access_token" in data
         assert data["token_type"] == "bearer"
 
-    def test_register_rejects_underage(self):
+    def test_register_rejects_under_18(self):
-        """Users under 18 get a 400 with a detail message."""
+        """A DOB that computes to under 18 gets a 403 (see test_auth_age_gate
+        for the age-math coverage)."""
+        from datetime import date
         client = TestClient(app)
+        minor_dob = date.today().replace(year=date.today().year - 14).isoformat()
         resp = client.post(
             "/api/auth/register",
             json={
                 "username": "kid",
                 "email": "kid@example.com",
                 "password": "secret123",
-                "date_of_birth": "2010-06-15",  # ~15 years old
+                "date_of_birth": minor_dob,
             },
         )
-        assert resp.status_code == 400
+        assert resp.status_code == 403
-        assert "18 or older" in resp.json()["detail"]
+        assert "at least 18" in resp.json()["detail"]
 
     def test_register_rejects_duplicate_username(self):
         """Registering the same username twice returns 409."""
@@ -106,7 +109,7 @@ class TestRegister:
                 "username": "duplicate",
                 "email": "dup1@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "date_of_birth": "1990-01-01",
             },
         )
         # Second registration with same username, different email
@@ -116,7 +119,7 @@ class TestRegister:
                 "username": "duplicate",
                 "email": "dup2@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "date_of_birth": "1990-01-01",
             },
         )
         assert resp.status_code == 409
@@ -131,7 +134,7 @@ class TestRegister:
                 "username": "user1",
                 "email": "same@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "date_of_birth": "1990-01-01",
             },
         )
         resp = client.post(
@@ -140,14 +143,14 @@ class TestRegister:
                 "username": "user2",
                 "email": "same@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "date_of_birth": "1990-01-01",
             },
         )
         assert resp.status_code == 409
         assert "Email already registered" in resp.json()["detail"]
 
-    def test_register_invalid_date_format(self):
+    def test_register_missing_dob(self):
-        """Invalid date format returns 422 validation error."""
+        """Missing the required date_of_birth field returns 422."""
         client = TestClient(app)
         resp = client.post(
             "/api/auth/register",
@@ -155,25 +158,10 @@ class TestRegister:
                 "username": "user",
                 "email": "user@example.com",
                 "password": "secret123",
-                "date_of_birth": "01-01-2000",  # wrong format
             },
         )
         assert resp.status_code == 422
 
-    def test_register_exactly_18(self):
-        """A user who just turned 18 can register."""
-        client = TestClient(app)
-        resp = client.post(
-            "/api/auth/register",
-            json={
-                "username": "just18",
-                "email": "just18@example.com",
-                "password": "secret123",
-                "date_of_birth": "2007-06-15",
-            },
-        )
-        assert resp.status_code == 201
-
 
 # ---------------------------------------------------------------------------
 # Login endpoint
@@ -193,7 +181,7 @@ class TestLogin:
                 "username": username,
                 "email": email,
                 "password": password,
-                "date_of_birth": "2000-01-01",
+                "date_of_birth": "1990-01-01",
             },
         )
         assert resp.status_code == 201

backend/tests/test_auth_expired_token.py

@@ -93,7 +93,7 @@ def _register_user(client: TestClient, username: str) -> str:
             "username": username,
             "email": f"{username}@example.com",
             "password": "secret123",
-            "date_of_birth": "2000-01-01",
+            "date_of_birth": "1990-01-01",
         },
     )
     assert resp.status_code == 201

backend/tests/test_avatar_loadout.py

@@ -0,0 +1,91 @@
+"""Integration tests for GET/PUT /api/avatar/loadout.
+
+Hits the real app against the configured Postgres (same contract as the
+other integration tests -- migrations applied first).
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.main import app
+from app.models.avatar_loadout import DEFAULT_LOADOUT
+
+
+def _auth_headers(client: TestClient, username: str) -> dict:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    return {"Authorization": f"Bearer {resp.json()['access_token']}"}
+
+
+class TestGetLoadout:
+    def test_new_user_gets_the_default(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "av_default")
+        resp = client.get("/api/avatar/loadout", headers=headers)
+        assert resp.status_code == 200
+        body = resp.json()
+        assert body["is_default"] is True
+        assert body["data"] == DEFAULT_LOADOUT
+
+    def test_requires_auth(self):
+        client = TestClient(app)
+        assert client.get("/api/avatar/loadout").status_code == 401
+
+
+class TestPutLoadout:
+    def test_save_then_read_back(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "av_save")
+        loadout = {
+            "base_body": "base_human_male_01",
+            "slots": {"hair": "hair_mohawk_01", "accessory": ["accessory_belt_01"]},
+            "skin_tone": {"r": 0.8, "g": 0.6, "b": 0.5, "a": 1.0},
+        }
+        put = client.put("/api/avatar/loadout", headers=headers, json={"data": loadout})
+        assert put.status_code == 200, put.text
+        assert put.json()["is_default"] is False
+
+        got = client.get("/api/avatar/loadout", headers=headers)
+        assert got.status_code == 200
+        assert got.json()["is_default"] is False
+        assert got.json()["data"] == loadout
+
+    def test_put_is_idempotent_replace(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "av_replace")
+        client.put(
+            "/api/avatar/loadout", headers=headers,
+            json={"data": {"base_body": "base_human_male_01", "slots": {"hair": "hair_mohawk_01"}}},
+        )
+        second = {"base_body": "base_human_male_01", "slots": {"chest": "chest_bandit_01"}}
+        client.put("/api/avatar/loadout", headers=headers, json={"data": second})
+        got = client.get("/api/avatar/loadout", headers=headers)
+        assert got.json()["data"] == second
+
+    def test_rejects_missing_base_body(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "av_nobase")
+        resp = client.put("/api/avatar/loadout", headers=headers, json={"data": {"slots": {}}})
+        assert resp.status_code == 422
+
+    def test_rejects_non_object_slots(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "av_badslots")
+        resp = client.put(
+            "/api/avatar/loadout", headers=headers,
+            json={"data": {"base_body": "base_human_male_01", "slots": "nope"}},
+        )
+        assert resp.status_code == 422
+
+    def test_requires_auth(self):
+        client = TestClient(app)
+        resp = client.put("/api/avatar/loadout", json={"data": {"base_body": "x", "slots": {}}})
+        assert resp.status_code == 401

backend/tests/test_chat_dm.py

@@ -0,0 +1,312 @@
+"""Integration tests for the DM chat router (app/routers/chat_dm.py):
+
+- POST /api/chat/dm/{user_id}/messages
+- GET  /api/chat/dm/{user_id}/messages
+- GET  /api/chat/dm/conversations
+
+The block-relationship router doesn't exist yet (sibling task), so blocks
+are inserted directly against the ``Block`` model, same pattern already
+used by ``tests/test_chat_models.py`` for direct model setup.
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app import rate_limit
+from app.config import settings
+from app.main import app
+from app.models.social import Block
+
+
+def _register(client: TestClient, username: str) -> dict:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    token = resp.json()["access_token"]
+    headers = {"Authorization": f"Bearer {token}"}
+    me = client.get("/api/users/me", headers=headers)
+    assert me.status_code == 200, me.text
+    return {"headers": headers, "id": me.json()["id"], "username": username}
+
+
+async def _insert_block(blocker_id: int, blocked_id: int) -> None:
+    engine = create_async_engine(settings.DATABASE_URL, poolclass=NullPool)
+    session_factory = async_sessionmaker(engine, expire_on_commit=False)
+    async with session_factory() as session:
+        session.add(Block(blocker_id=blocker_id, blocked_id=blocked_id))
+        await session.commit()
+    await engine.dispose()
+
+
+class TestSendAndRetrieve:
+    def test_send_then_fetch_history(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_alice1")
+        bob = _register(client, "dm_bob1")
+
+        resp = client.post(
+            f"/api/chat/dm/{bob['id']}/messages",
+            json={"body": "hey bob"},
+            headers=alice["headers"],
+        )
+        assert resp.status_code == 201, resp.text
+        sent = resp.json()
+        assert sent["sender_id"] == alice["id"]
+        assert sent["recipient_id"] == bob["id"]
+        assert sent["body"] == "hey bob"
+        assert sent["filtered"] is False
+        assert sent["id"] is not None
+        assert sent["created_at"] is not None
+
+        hist_alice = client.get(f"/api/chat/dm/{bob['id']}/messages", headers=alice["headers"])
+        assert hist_alice.status_code == 200, hist_alice.text
+        msgs = hist_alice.json()["messages"]
+        assert len(msgs) == 1
+        assert msgs[0]["body"] == "hey bob"
+
+        hist_bob = client.get(f"/api/chat/dm/{alice['id']}/messages", headers=bob["headers"])
+        assert hist_bob.status_code == 200, hist_bob.text
+        assert len(hist_bob.json()["messages"]) == 1
+        assert hist_bob.json()["messages"][0]["body"] == "hey bob"
+
+    def test_cannot_message_self(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_self1")
+        resp = client.post(
+            f"/api/chat/dm/{alice['id']}/messages",
+            json={"body": "hi me"},
+            headers=alice["headers"],
+        )
+        assert resp.status_code == 400
+
+    def test_target_user_must_exist(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_noexist1")
+        resp = client.post(
+            "/api/chat/dm/999999999/messages",
+            json={"body": "hello?"},
+            headers=alice["headers"],
+        )
+        assert resp.status_code == 404
+
+    def test_requires_auth(self):
+        client = TestClient(app)
+        resp = client.post("/api/chat/dm/1/messages", json={"body": "hi"})
+        assert resp.status_code == 401
+
+    def test_history_pagination_cursor(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_page_a")
+        bob = _register(client, "dm_page_b")
+
+        for i in range(5):
+            r = client.post(
+                f"/api/chat/dm/{bob['id']}/messages",
+                json={"body": f"msg {i}"},
+                headers=alice["headers"],
+            )
+            assert r.status_code == 201, r.text
+
+        page1 = client.get(
+            f"/api/chat/dm/{bob['id']}/messages",
+            params={"limit": 2},
+            headers=alice["headers"],
+        )
+        assert page1.status_code == 200
+        body1 = page1.json()
+        assert len(body1["messages"]) == 2
+        assert body1["messages"][0]["body"] == "msg 4"  # newest first
+        assert body1["next_cursor"] is not None
+
+        page2 = client.get(
+            f"/api/chat/dm/{bob['id']}/messages",
+            params={"limit": 2, "before": body1["next_cursor"]},
+            headers=alice["headers"],
+        )
+        assert page2.status_code == 200
+        body2 = page2.json()
+        assert [m["body"] for m in body2["messages"]] == ["msg 2", "msg 1"]
+
+    def test_no_conversation_yet_returns_empty_history(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_empty_a")
+        bob = _register(client, "dm_empty_b")
+        resp = client.get(f"/api/chat/dm/{bob['id']}/messages", headers=alice["headers"])
+        assert resp.status_code == 200
+        assert resp.json() == {"messages": [], "next_cursor": None}
+
+
+class TestConversationList:
+    def test_lists_peer_last_message_and_unread_count(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_conv_a")
+        bob = _register(client, "dm_conv_b")
+
+        client.post(
+            f"/api/chat/dm/{bob['id']}/messages",
+            json={"body": "first"},
+            headers=alice["headers"],
+        )
+        client.post(
+            f"/api/chat/dm/{bob['id']}/messages",
+            json={"body": "second"},
+            headers=alice["headers"],
+        )
+
+        convs_bob = client.get("/api/chat/dm/conversations", headers=bob["headers"])
+        assert convs_bob.status_code == 200, convs_bob.text
+        data = convs_bob.json()
+        assert data["total"] == 1
+        conv = data["conversations"][0]
+        assert conv["peer_id"] == alice["id"]
+        assert conv["peer_username"] == "dm_conv_a"
+        assert conv["last_message"]["body"] == "second"
+        assert conv["unread_count"] == 2  # bob hasn't read yet
+
+        # Bob reads the latest page -> unread resets to 0.
+        client.get(f"/api/chat/dm/{alice['id']}/messages", headers=bob["headers"])
+        convs_bob_after = client.get("/api/chat/dm/conversations", headers=bob["headers"])
+        assert convs_bob_after.json()["conversations"][0]["unread_count"] == 0
+
+        # Alice sent them, so her own unread count for this conversation is 0.
+        convs_alice = client.get("/api/chat/dm/conversations", headers=alice["headers"])
+        assert convs_alice.json()["conversations"][0]["unread_count"] == 0
+
+    def test_scoped_to_authenticated_user_only(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_scope_a")
+        bob = _register(client, "dm_scope_b")
+        carol = _register(client, "dm_scope_c")
+
+        client.post(
+            f"/api/chat/dm/{bob['id']}/messages",
+            json={"body": "hi bob"},
+            headers=alice["headers"],
+        )
+
+        convs_carol = client.get("/api/chat/dm/conversations", headers=carol["headers"])
+        assert convs_carol.status_code == 200
+        assert convs_carol.json() == {"conversations": [], "total": 0}
+
+    def test_cannot_read_another_pairs_conversation(self):
+        """A user's history endpoint only ever resolves *their own* pairing
+        with the given peer id -- there is no conversation id in the URL an
+        outsider could guess/pass to read someone else's DMs."""
+        client = TestClient(app)
+        alice = _register(client, "dm_iso_a")
+        bob = _register(client, "dm_iso_b")
+        carol = _register(client, "dm_iso_c")
+
+        client.post(
+            f"/api/chat/dm/{bob['id']}/messages",
+            json={"body": "secret to bob"},
+            headers=alice["headers"],
+        )
+
+        # Carol asking for her "history with bob" gets her own (empty)
+        # conversation, never alice's.
+        resp = client.get(f"/api/chat/dm/{bob['id']}/messages", headers=carol["headers"])
+        assert resp.status_code == 200
+        assert resp.json()["messages"] == []
+
+
+class TestBlocking:
+    async def test_blocker_cannot_send_to_blocked(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_block_a1")
+        bob = _register(client, "dm_block_b1")
+        await _insert_block(alice["id"], bob["id"])
+
+        resp = client.post(
+            f"/api/chat/dm/{bob['id']}/messages",
+            json={"body": "let me in"},
+            headers=alice["headers"],
+        )
+        assert resp.status_code == 403
+
+    async def test_blocked_cannot_send_to_blocker(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_block_a2")
+        bob = _register(client, "dm_block_b2")
+        await _insert_block(alice["id"], bob["id"])
+
+        resp = client.post(
+            f"/api/chat/dm/{alice['id']}/messages",
+            json={"body": "please respond"},
+            headers=bob["headers"],
+        )
+        assert resp.status_code == 403
+
+
+class TestTextFilter:
+    def test_message_tripping_filter_is_redacted_and_flagged(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_filter_a")
+        bob = _register(client, "dm_filter_b")
+
+        resp = client.post(
+            f"/api/chat/dm/{bob['id']}/messages",
+            json={"body": "you are a bastard"},
+            headers=alice["headers"],
+        )
+        assert resp.status_code == 201, resp.text
+        data = resp.json()
+        assert data["filtered"] is True
+        assert "bastard" not in data["body"]
+        assert "*" in data["body"]
+
+        # The stored/delivered copy is the redacted one, not the raw text.
+        hist = client.get(f"/api/chat/dm/{alice['id']}/messages", headers=bob["headers"])
+        assert hist.json()["messages"][0]["body"] == data["body"]
+
+    def test_clean_message_is_not_flagged(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_clean_a")
+        bob = _register(client, "dm_clean_b")
+        resp = client.post(
+            f"/api/chat/dm/{bob['id']}/messages",
+            json={"body": "have a nice day"},
+            headers=alice["headers"],
+        )
+        assert resp.status_code == 201
+        assert resp.json()["filtered"] is False
+        assert resp.json()["body"] == "have a nice day"
+
+
+class TestRateLimit:
+    @pytest.fixture(autouse=True)
+    def _enable_rate_limiting(self):
+        prev = settings.RATE_LIMIT_ENABLED
+        settings.RATE_LIMIT_ENABLED = True
+        rate_limit.reset_all()
+        yield
+        rate_limit.reset_all()
+        settings.RATE_LIMIT_ENABLED = prev
+
+    def test_send_rate_limit_exceeded_returns_429(self):
+        client = TestClient(app)
+        alice = _register(client, "dm_rl_a")
+        bob = _register(client, "dm_rl_b")
+
+        codes = []
+        for i in range(25):
+            r = client.post(
+                f"/api/chat/dm/{bob['id']}/messages",
+                json={"body": f"spam {i}"},
+                headers=alice["headers"],
+            )
+            codes.append(r.status_code)
+
+        assert codes[:20] == [201] * 20
+        assert 429 in codes[20:]
+        assert codes[-1] == 429

backend/tests/test_chat_models.py

@@ -0,0 +1,344 @@
+"""Model-level tests for chat: conversations, messages, message reports.
+
+app/models/chat.py / alembic/versions/0008_add_chat_tables.py
+(docs/planning/social.md US-4). This is the models+migration task only --
+there are no API endpoints yet (sibling tasks own filtering, rate limiting,
+and the routers), so these tests exercise the ORM models and the real
+Postgres constraints directly rather than going through HTTP.
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+from sqlalchemy import delete, select
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import settings
+from app.main import app
+from app.models.chat import (
+    Conversation,
+    ConversationParticipant,
+    Message,
+    MessageReport,
+    ReportStatus,
+)
+from app.models.user import User
+from app.models.world import World
+
+
+def _register(client: TestClient, username: str) -> int:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    headers = {"Authorization": f"Bearer {resp.json()['access_token']}"}
+    me = client.get("/api/users/me", headers=headers)
+    assert me.status_code == 200, me.text
+    return me.json()["id"]
+
+
+def _session_factory():
+    engine = create_async_engine(settings.DATABASE_URL, poolclass=NullPool)
+    return engine, async_sessionmaker(engine, expire_on_commit=False)
+
+
+class TestConversationCreation:
+    async def test_create_conversation_with_participants_and_messages(self):
+        client = TestClient(app)
+        a = _register(client, "chat_conv_a")
+        b = _register(client, "chat_conv_b")
+
+        engine, factory = _session_factory()
+        try:
+            lo, hi = sorted((a, b))
+            async with factory() as session:
+                convo = Conversation(user_a_id=lo, user_b_id=hi)
+                session.add(convo)
+                await session.flush()
+                session.add_all(
+                    [
+                        ConversationParticipant(conversation_id=convo.id, user_id=a),
+                        ConversationParticipant(conversation_id=convo.id, user_id=b),
+                    ]
+                )
+                session.add(
+                    Message(sender_id=a, conversation_id=convo.id, body="hi there")
+                )
+                await session.commit()
+                convo_id = convo.id
+
+            async with factory() as session:
+                participants = (
+                    await session.execute(
+                        select(ConversationParticipant).where(
+                            ConversationParticipant.conversation_id == convo_id
+                        )
+                    )
+                ).scalars().all()
+                messages = (
+                    await session.execute(
+                        select(Message).where(Message.conversation_id == convo_id)
+                    )
+                ).scalars().all()
+                assert len(participants) == 2
+                assert len(messages) == 1
+                assert messages[0].sender_id == a
+                assert messages[0].filtered is False
+        finally:
+            await engine.dispose()
+
+    async def test_duplicate_pair_rejected(self):
+        client = TestClient(app)
+        a = _register(client, "chat_uq_a")
+        b = _register(client, "chat_uq_b")
+        lo, hi = sorted((a, b))
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                session.add(Conversation(user_a_id=lo, user_b_id=hi))
+                await session.commit()
+
+            async with factory() as session:
+                session.add(Conversation(user_a_id=lo, user_b_id=hi))
+                with pytest.raises(IntegrityError):
+                    await session.commit()
+        finally:
+            await engine.dispose()
+
+    async def test_unordered_pair_rejected_by_check_constraint(self):
+        client = TestClient(app)
+        a = _register(client, "chat_ck_a")
+        b = _register(client, "chat_ck_b")
+        lo, hi = sorted((a, b))
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                # Reversed order violates ck_conversations_ordered_pair.
+                session.add(Conversation(user_a_id=hi, user_b_id=lo))
+                with pytest.raises(IntegrityError):
+                    await session.commit()
+        finally:
+            await engine.dispose()
+
+
+class TestWorldRoomChat:
+    async def test_world_message_has_null_conversation(self):
+        client = TestClient(app)
+        owner = _register(client, "chat_world_owner")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                world = World(name="Chat Test World", owner_id=owner)
+                session.add(world)
+                await session.flush()
+                msg = Message(sender_id=owner, world_id=world.id, body="hello world")
+                session.add(msg)
+                await session.commit()
+                world_id = world.id
+
+            async with factory() as session:
+                rows = (
+                    await session.execute(
+                        select(Message).where(Message.world_id == world_id)
+                    )
+                ).scalars().all()
+                assert len(rows) == 1
+                assert rows[0].conversation_id is None
+                assert rows[0].room_id is None
+        finally:
+            await engine.dispose()
+
+
+class TestMessageReports:
+    async def test_create_report_defaults_to_open(self):
+        client = TestClient(app)
+        sender = _register(client, "chat_rpt_sender")
+        reporter = _register(client, "chat_rpt_reporter")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                world = World(name="Report World", owner_id=sender)
+                session.add(world)
+                await session.flush()
+                msg = Message(sender_id=sender, world_id=world.id, body="bad words")
+                session.add(msg)
+                await session.flush()
+                report = MessageReport(
+                    message_id=msg.id, reporter_id=reporter, reason="spam"
+                )
+                session.add(report)
+                await session.commit()
+                report_id = report.id
+
+            async with factory() as session:
+                report = await session.get(MessageReport, report_id)
+                assert report.status == ReportStatus.OPEN
+                assert report.moderator_id is None
+                assert report.resolved_at is None
+        finally:
+            await engine.dispose()
+
+
+class TestCascadeDelete:
+    async def test_deleting_conversation_deletes_participants_and_messages(self):
+        client = TestClient(app)
+        a = _register(client, "chat_cd_conv_a")
+        b = _register(client, "chat_cd_conv_b")
+        lo, hi = sorted((a, b))
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                convo = Conversation(user_a_id=lo, user_b_id=hi)
+                session.add(convo)
+                await session.flush()
+                session.add_all(
+                    [
+                        ConversationParticipant(conversation_id=convo.id, user_id=a),
+                        ConversationParticipant(conversation_id=convo.id, user_id=b),
+                    ]
+                )
+                session.add(Message(sender_id=a, conversation_id=convo.id, body="bye"))
+                await session.commit()
+                convo_id = convo.id
+
+            async with factory() as session:
+                # Core delete against the conversations table directly, so
+                # the real ON DELETE CASCADE does the work (not the ORM).
+                await session.execute(
+                    delete(Conversation).where(Conversation.id == convo_id)
+                )
+                await session.commit()
+
+            async with factory() as session:
+                participants = (
+                    await session.execute(
+                        select(ConversationParticipant).where(
+                            ConversationParticipant.conversation_id == convo_id
+                        )
+                    )
+                ).scalars().all()
+                messages = (
+                    await session.execute(
+                        select(Message).where(Message.conversation_id == convo_id)
+                    )
+                ).scalars().all()
+                assert participants == []
+                assert messages == []
+        finally:
+            await engine.dispose()
+
+    async def test_deleting_user_removes_conversation_but_keeps_report_and_message_id_null(self):
+        """Deleting a conversation participant cascades away the whole DM
+        (conversation + participants + messages -- there's no third party
+        left to care about the history). Deleting the sender of a
+        world-chat message, by contrast, must NOT delete the message or its
+        report -- sender_id is SET NULL and message_reports.message_id
+        follows the message (also SET NULL, never CASCADE) so the audit
+        trail survives account deletion."""
+        client = TestClient(app)
+        a = _register(client, "chat_cd_user_a")
+        b = _register(client, "chat_cd_user_b")
+        reporter = _register(client, "chat_cd_user_reporter")
+        lo, hi = sorted((a, b))
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                convo = Conversation(user_a_id=lo, user_b_id=hi)
+                session.add(convo)
+                await session.flush()
+                session.add_all(
+                    [
+                        ConversationParticipant(conversation_id=convo.id, user_id=a),
+                        ConversationParticipant(conversation_id=convo.id, user_id=b),
+                    ]
+                )
+                session.add(Message(sender_id=a, conversation_id=convo.id, body="dm"))
+
+                world = World(name="Sender Delete World", owner_id=b)
+                session.add(world)
+                await session.flush()
+                world_msg = Message(sender_id=a, world_id=world.id, body="world chat")
+                session.add(world_msg)
+                await session.flush()
+                report = MessageReport(
+                    message_id=world_msg.id, reporter_id=reporter, reason="rude"
+                )
+                session.add(report)
+                await session.commit()
+                convo_id = convo.id
+                world_msg_id = world_msg.id
+                report_id = report.id
+
+            async with factory() as session:
+                # Delete `a`: participant in the DM (cascades the whole
+                # conversation) and sender of the world message (SET NULL).
+                await session.execute(delete(User).where(User.id == a))
+                await session.commit()
+
+            async with factory() as session:
+                convo_row = await session.get(Conversation, convo_id)
+                dm_messages = (
+                    await session.execute(
+                        select(Message).where(Message.conversation_id == convo_id)
+                    )
+                ).scalars().all()
+                world_msg = await session.get(Message, world_msg_id)
+                report = await session.get(MessageReport, report_id)
+
+                assert convo_row is None
+                assert dm_messages == []
+                # World message survives with sender_id nulled out.
+                assert world_msg is not None
+                assert world_msg.sender_id is None
+                assert world_msg.body == "world chat"
+                # Report still points at the surviving message.
+                assert report is not None
+                assert report.message_id == world_msg_id
+        finally:
+            await engine.dispose()
+
+    async def test_deleting_message_nulls_report_message_id(self):
+        client = TestClient(app)
+        sender = _register(client, "chat_cd_msg_sender")
+        reporter = _register(client, "chat_cd_msg_reporter")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                world = World(name="Msg Delete World", owner_id=sender)
+                session.add(world)
+                await session.flush()
+                msg = Message(sender_id=sender, world_id=world.id, body="to be removed")
+                session.add(msg)
+                await session.flush()
+                report = MessageReport(
+                    message_id=msg.id, reporter_id=reporter, reason="spam"
+                )
+                session.add(report)
+                await session.commit()
+                msg_id = msg.id
+                report_id = report.id
+
+            async with factory() as session:
+                await session.execute(delete(Message).where(Message.id == msg_id))
+                await session.commit()
+
+            async with factory() as session:
+                report = await session.get(MessageReport, report_id)
+                assert report is not None
+                assert report.message_id is None
+        finally:
+            await engine.dispose()

backend/tests/test_chunk_codec.py

@@ -0,0 +1,219 @@
+"""Tests for app.services.chunk_codec -- the Python port of world.md §3.6.
+
+Pure unit tests: no database, no app, no network. Golden fixtures live in
+tests/fixtures/chunks/ (see generate_fixtures.py there for how/why).
+"""
+
+from pathlib import Path
+
+import pytest
+
+from app.services import chunk_codec as cc
+
+FIXTURES_DIR = Path(__file__).resolve().parent / "fixtures" / "chunks"
+
+
+def _read_fixture(name: str) -> bytes:
+    return (FIXTURES_DIR / name).read_bytes()
+
+
+class TestGoldenFixtures:
+    """Byte-stability: decode a committed fixture, re-encode it, and the
+    bytes must match exactly (world.md §3.6.3)."""
+
+    @pytest.mark.parametrize("filename", [
+        "empty_chunk.bin", "simple_tile_chunk.bin", "chunk_with_objects.bin",
+    ])
+    def test_round_trip_is_byte_identical(self, filename):
+        original = _read_fixture(filename)
+        decoded = cc.decode_binary(original)
+        re_encoded = cc.encode_binary(decoded)
+        assert re_encoded == original
+
+    def test_simple_tile_chunk_logical_values(self):
+        decoded = cc.decode_binary(_read_fixture("simple_tile_chunk.bin"))
+        assert decoded.world_id == "12"
+        assert decoded.room_id == "main"
+        assert decoded.coord == (3, -1, 0)
+        assert decoded.bounds.min == (96.0, -32.0, 0.0)
+        assert decoded.bounds.size == (32.0, 32.0, 1.0)
+        assert len(decoded.tile_layers) == 1
+        layer = decoded.tile_layers[0]
+        assert layer.name == "ground"
+        assert (layer.width, layer.height, layer.depth) == (4, 4, 1)
+        assert len(layer.palette) == 3
+        assert layer.tiles == [0, 1, 1, 0, 1, 2, 2, 1, 1, 2, 2, 1, 0, 1, 1, 0]
+        assert decoded.revision == 2
+        assert decoded.author == "fixture-gen"
+
+    def test_chunk_with_objects_logical_values(self):
+        decoded = cc.decode_binary(_read_fixture("chunk_with_objects.bin"))
+        assert len(decoded.objects) == 2
+        obj1, obj2 = decoded.objects
+        assert obj1.id == "obj_0001"
+        assert obj1.type == "interactable"
+        assert obj1.pos == (101.5, -110.25, 0.5)
+        assert obj1.properties == {"locked": False, "loot_table": "chest_basic"}
+        assert obj2.id == "obj_0002"
+        assert obj2.dynamic is True
+        assert obj2.flags.violence == 1
+        assert obj2.flags.sources == ["asset:props/chest"]
+        assert decoded.flags.violence == 1
+        assert decoded.flags.sources == ["asset:props/chest"]
+
+    def test_empty_chunk_has_no_layers_or_objects(self):
+        decoded = cc.decode_binary(_read_fixture("empty_chunk.bin"))
+        assert decoded.tile_layers == []
+        assert decoded.objects == []
+
+
+class TestChecksum:
+    def test_checksum_is_sha256_hex(self):
+        import hashlib
+        assert cc.checksum(b"") == hashlib.sha256(b"").hexdigest()
+        assert len(cc.checksum(b"")) == 64
+
+    def test_header_checksum_matches_recomputed_for_valid_fixture(self):
+        data = _read_fixture("simple_tile_chunk.bin")
+        header_checksum_hex = data[16:48].hex()
+        body = data[cc.HEADER_SIZE:]
+        assert header_checksum_hex == cc.checksum(body)
+
+
+class TestBuildKey:
+    def test_matches_world_persistence_impl_4_5_format(self):
+        assert cc.build_key(12, "main", 3, -1, 0) == "12:main:3:-1:0"
+        assert cc.build_key("12", "main", 3, -1, 0) == "12:main:3:-1:0"
+
+
+class TestFloat32Fidelity:
+    """This is the concrete regression test for the cross-codec divergence
+    documented at the bottom of chunk_codec.py: this module must encode
+    real IEEE-754 float32, including fractional and negative values,
+    round-tripping exactly (up to float32 precision) -- unlike
+    scripts/chunk_data_decoder.gd's current int-truncating implementation."""
+
+    def test_fractional_and_negative_floats_survive_round_trip(self):
+        payload = cc.ChunkPayload(
+            world_id="1", room_id="main", coord=(0, 0, 0),
+            bounds=cc.ChunkBounds(min=(-17.25, 0.125, -3.0), size=(32.0, 32.0, 1.0)),
+            objects=[cc.WorldObject(
+                id="o1", type="prop", asset_id="a",
+                pos=(1.5, -2.75, 0.001), rot=(0.0, 0.7071068, 0.0, 0.7071068),
+                scale=(1.0, 1.0, 1.0),
+            )],
+        )
+        encoded = cc.encode_binary(payload)
+        decoded = cc.decode_binary(encoded)
+        assert decoded.bounds.min == pytest.approx((-17.25, 0.125, -3.0), abs=1e-6)
+        assert decoded.objects[0].pos == pytest.approx((1.5, -2.75, 0.001), abs=1e-6)
+        assert decoded.objects[0].rot == pytest.approx(
+            (0.0, 0.7071068, 0.0, 0.7071068), abs=1e-6
+        )
+
+
+class TestMalformedInput:
+    def test_bad_magic_raises_codec_error(self):
+        data = bytearray(_read_fixture("empty_chunk.bin"))
+        data[0:4] = b"XXXX"
+        with pytest.raises(cc.ChunkCodecError):
+            cc.decode_binary(bytes(data))
+
+    def test_too_short_raises_codec_error(self):
+        with pytest.raises(cc.ChunkCodecError):
+            cc.decode_binary(b"AGPC\x01\x00")
+
+    def test_unsupported_version_raises_codec_error(self):
+        data = bytearray(_read_fixture("empty_chunk.bin"))
+        data[4:6] = (99).to_bytes(2, "little")
+        with pytest.raises(cc.ChunkCodecError):
+            cc.decode_binary(bytes(data))
+
+    def test_payload_len_mismatch_raises_codec_error(self):
+        data = bytearray(_read_fixture("empty_chunk.bin"))
+        # Corrupt the declared payload_len (offset 12..16).
+        data[12:16] = (99999).to_bytes(4, "little")
+        with pytest.raises(cc.ChunkCodecError):
+            cc.decode_binary(bytes(data))
+
+
+class TestValidation:
+    """decode_and_validate: the server-side "don't trust the client"
+    boundary (world_persistence_impl.md §5.5)."""
+
+    def _valid_args(self):
+        return {
+            "expected_key": "12:main:3:-1:0",
+            "grid_size": (4, 4, 1),
+            "max_objects": 512,
+        }
+
+    def test_valid_payload_passes(self):
+        data = _read_fixture("simple_tile_chunk.bin")
+        payload = cc.decode_and_validate(data, **self._valid_args())
+        assert payload.coord == (3, -1, 0)
+
+    def test_checksum_mismatch_detected(self):
+        data = bytearray(_read_fixture("simple_tile_chunk.bin"))
+        # Corrupt one byte of the header's advisory checksum field
+        # (offset 16..48) only -- magic/version/payload_len and the whole
+        # payload body stay untouched, so this exercises exactly the
+        # "recomputed checksum disagrees with the header" path rather than
+        # also breaking structural decoding.
+        data[16] ^= 0xFF
+        with pytest.raises(cc.ChunkValidationError) as exc_info:
+            cc.decode_and_validate(bytes(data), **self._valid_args())
+        assert exc_info.value.reason == "checksum_mismatch"
+
+    def test_chunk_key_mismatch_detected(self):
+        data = _read_fixture("simple_tile_chunk.bin")
+        args = self._valid_args()
+        args["expected_key"] = "12:main:99:99:0"  # doesn't match the payload's own coord
+        with pytest.raises(cc.ChunkValidationError) as exc_info:
+            cc.decode_and_validate(data, **args)
+        assert exc_info.value.reason == "chunk_key_mismatch"
+
+    def test_layer_dims_mismatch_detected(self):
+        data = _read_fixture("simple_tile_chunk.bin")
+        args = self._valid_args()
+        args["grid_size"] = (8, 8, 1)  # fixture's layer is 4x4x1
+        with pytest.raises(cc.ChunkValidationError) as exc_info:
+            cc.decode_and_validate(data, **args)
+        assert exc_info.value.reason == "layer_dims"
+
+    def test_too_many_objects_detected(self):
+        data = _read_fixture("chunk_with_objects.bin")  # has 2 objects
+        args = self._valid_args()
+        args["expected_key"] = "12:main:3:-4:0"
+        args["grid_size"] = (2, 2, 1)
+        args["max_objects"] = 1
+        with pytest.raises(cc.ChunkValidationError) as exc_info:
+            cc.decode_and_validate(data, **args)
+        assert exc_info.value.reason == "too_many_objects"
+
+    def test_object_out_of_bounds_detected(self):
+        payload = cc.ChunkPayload(
+            world_id="1", room_id="main", coord=(0, 0, 0),
+            bounds=cc.ChunkBounds(min=(0.0, 0.0, 0.0), size=(32.0, 32.0, 1.0)),
+            objects=[cc.WorldObject(id="o1", type="prop", asset_id="a", pos=(9999.0, 0.0, 0.0))],
+        )
+        data = cc.encode_binary(payload)
+        with pytest.raises(cc.ChunkValidationError) as exc_info:
+            cc.decode_and_validate(
+                data, expected_key="1:main:0:0:0", grid_size=(32, 32, 1), max_objects=10
+            )
+        assert exc_info.value.reason == "object_out_of_bounds"
+
+    def test_tile_out_of_palette_detected(self):
+        layer = cc.TileLayer(
+            name="ground", width=2, height=2, depth=1,
+            palette=[cc.TileDef(id=1)],  # tile 5 below isn't in this palette
+            tiles=[1, 5, 0, 1],
+        )
+        payload = cc.ChunkPayload(world_id="1", room_id="main", coord=(0, 0, 0), tile_layers=[layer])
+        data = cc.encode_binary(payload)
+        with pytest.raises(cc.ChunkValidationError) as exc_info:
+            cc.decode_and_validate(
+                data, expected_key="1:main:0:0:0", grid_size=(2, 2, 1), max_objects=10
+            )
+        assert exc_info.value.reason == "tile_out_of_palette"

backend/tests/test_game_servers.py

@@ -0,0 +1,153 @@
+"""Unit tests for the game_servers.py changes made for world persistence
+(world_persistence_impl.md §7.3/§7.4): per-spawn token validation, and the
+``_await_ready`` replacement for the old, fail-open ``_await_port``.
+
+No real Godot process is spawned here (that stays a manual/checkpoint
+integration test, per test_world_join.py's docstring) -- these exercise
+``GameServerSupervisor`` against a fake process object standing in for
+``subprocess.Popen``.
+"""
+
+import json
+
+import pytest
+
+from app.config import settings
+from app.services.game_servers import GameServerSupervisor, _WorldServer
+
+
+class _FakeProc:
+    """Stands in for subprocess.Popen: only .poll() is needed by the code
+    paths under test here."""
+
+    def __init__(self, exited: bool = False):
+        self._exited = exited
+
+    def poll(self):
+        return 0 if self._exited else None
+
+    def terminate(self):
+        self._exited = True
+
+    def wait(self, timeout=None):
+        return 0
+
+    def kill(self):
+        self._exited = True
+
+
+def _make_srv(tmp_path, token="secret", alive=True) -> _WorldServer:
+    status_path = tmp_path / "status.json"
+    return _WorldServer(
+        world_id="7", port=27000, proc=_FakeProc(exited=not alive),
+        status_path=status_path, token=token,
+    )
+
+
+class TestValidateToken:
+    def test_unknown_world_is_false(self):
+        sup = GameServerSupervisor()
+        assert sup.validate_token("no-such-world", "anything") is False
+
+    def test_correct_token_is_true(self, tmp_path):
+        sup = GameServerSupervisor()
+        sup._servers["7"] = _make_srv(tmp_path, token="secret")
+        assert sup.validate_token("7", "secret") is True
+        # world_id is looked up as str(world_id), so an int works too --
+        # this matters because the FastAPI path param is an int.
+        assert sup.validate_token(7, "secret") is True
+
+    def test_wrong_token_is_false(self, tmp_path):
+        sup = GameServerSupervisor()
+        sup._servers["7"] = _make_srv(tmp_path, token="secret")
+        assert sup.validate_token("7", "wrong") is False
+
+    def test_token_scoped_to_its_own_world_only(self, tmp_path):
+        sup = GameServerSupervisor()
+        sup._servers["7"] = _make_srv(tmp_path, token="secret")
+        # Same token, different world_id -- must not authenticate (§7.3:
+        # "a path whose world_id differs from the token's world is 403").
+        assert sup.validate_token("8", "secret") is False
+
+    def test_dead_server_token_is_false(self, tmp_path):
+        sup = GameServerSupervisor()
+        sup._servers["7"] = _make_srv(tmp_path, token="secret", alive=False)
+        assert sup.validate_token("7", "secret") is False
+
+    def test_reaping_invalidates_the_token(self, tmp_path):
+        """§7.3: "dies with its process" -- once removed from _servers
+        (what the reaper does), the same token no longer validates."""
+        sup = GameServerSupervisor()
+        sup._servers["7"] = _make_srv(tmp_path, token="secret")
+        assert sup.validate_token("7", "secret") is True
+        del sup._servers["7"]
+        assert sup.validate_token("7", "secret") is False
+
+
+class TestAwaitReady:
+    """Replaces the old _await_port, which (a) treated a bound UDP port as
+    readiness even though content loading happens before create_server, and
+    (b) failed open past its deadline with no error at all."""
+
+    async def test_raises_timeout_error_when_never_ready(self, tmp_path, monkeypatch):
+        monkeypatch.setattr(settings, "GAME_SERVER_READY_TIMEOUT_SECONDS", 0.3)
+        sup = GameServerSupervisor()
+        srv = _make_srv(tmp_path)  # status file never written
+        with pytest.raises(TimeoutError):
+            await sup._await_ready(srv)
+
+    async def test_returns_once_status_file_reports_ready(self, tmp_path, monkeypatch):
+        monkeypatch.setattr(settings, "GAME_SERVER_READY_TIMEOUT_SECONDS", 5.0)
+        sup = GameServerSupervisor()
+        srv = _make_srv(tmp_path)
+        srv.status_path.write_text(json.dumps({"ready": True, "players": 0}))
+        await sup._await_ready(srv)  # must not raise / must not hang
+
+    async def test_ready_false_is_not_ready(self, tmp_path, monkeypatch):
+        monkeypatch.setattr(settings, "GAME_SERVER_READY_TIMEOUT_SECONDS", 0.3)
+        sup = GameServerSupervisor()
+        srv = _make_srv(tmp_path)
+        srv.status_path.write_text(json.dumps({"ready": False, "players": 0}))
+        with pytest.raises(TimeoutError):
+            await sup._await_ready(srv)
+
+    async def test_raises_promptly_if_process_already_exited(self, tmp_path, monkeypatch):
+        # A long deadline, but the process is already dead -- must not wait
+        # out the full deadline (this is the "no crash restart mid-wait"
+        # case: don't silently poll a corpse for 20s).
+        monkeypatch.setattr(settings, "GAME_SERVER_READY_TIMEOUT_SECONDS", 20.0)
+        sup = GameServerSupervisor()
+        srv = _make_srv(tmp_path, alive=False)
+        with pytest.raises(TimeoutError):
+            await sup._await_ready(srv)
+
+
+class TestSpawnCommandLine:
+    def test_spawn_includes_api_url_and_server_token(self, monkeypatch, tmp_path):
+        """world_persistence_impl.md §7.2 step 1 / §7.4: `_spawn` must pass
+        --api-url and --server-token on the command line."""
+        sup = GameServerSupervisor()
+        monkeypatch.setattr(sup, "_free_port", lambda: 27050)
+
+        captured = {}
+
+        class _Proc:
+            def poll(self):
+                return None
+
+        def _fake_popen(cmd, **kwargs):
+            captured["cmd"] = cmd
+            return _Proc()
+
+        monkeypatch.setattr(
+            "app.services.game_servers.subprocess.Popen", _fake_popen
+        )
+        srv = sup._spawn("42")
+
+        cmd = captured["cmd"]
+        assert "--api-url" in cmd
+        assert cmd[cmd.index("--api-url") + 1] == settings.GAME_SERVER_INTERNAL_API_URL
+        assert "--server-token" in cmd
+        token_in_cmd = cmd[cmd.index("--server-token") + 1]
+        assert token_in_cmd == srv.token
+        assert len(srv.token) > 20  # secrets.token_urlsafe(32) -- not a short/guessable value

backend/tests/test_group_models.py

@@ -0,0 +1,258 @@
+"""Model-level tests for groups: groups and group_members.
+
+app/models/groups.py / alembic/versions/0009_add_group_tables.py
+(docs/planning/social.md US-5). This is the models+migration task only --
+there are no API endpoints yet (a sibling task, "Groups API", owns
+create/join/leave/role authorization and the group page endpoint), so these
+tests exercise the ORM models and the real Postgres constraints directly
+rather than going through HTTP.
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+from sqlalchemy import delete, select
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import settings
+from app.main import app
+from app.models.groups import Group, GroupMember, GroupRole
+from app.models.user import User
+
+
+def _register(client: TestClient, username: str) -> int:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    headers = {"Authorization": f"Bearer {resp.json()['access_token']}"}
+    me = client.get("/api/users/me", headers=headers)
+    assert me.status_code == 200, me.text
+    return me.json()["id"]
+
+
+def _session_factory():
+    engine = create_async_engine(settings.DATABASE_URL, poolclass=NullPool)
+    return engine, async_sessionmaker(engine, expire_on_commit=False)
+
+
+class TestGroupCreationAndRoles:
+    async def test_create_group_with_members_of_different_roles(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_role_owner")
+        admin = _register(client, "grp_role_admin")
+        member = _register(client, "grp_role_member")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                group = Group(name="Explorers", description="We explore worlds", owner_id=owner)
+                session.add(group)
+                await session.flush()
+                session.add_all(
+                    [
+                        GroupMember(group_id=group.id, user_id=owner, role=GroupRole.OWNER),
+                        GroupMember(group_id=group.id, user_id=admin, role=GroupRole.ADMIN),
+                        GroupMember(group_id=group.id, user_id=member, role=GroupRole.MEMBER),
+                    ]
+                )
+                await session.commit()
+                group_id = group.id
+
+            async with factory() as session:
+                fetched = await session.get(Group, group_id)
+                members = (
+                    await session.execute(
+                        select(GroupMember).where(GroupMember.group_id == group_id)
+                    )
+                ).scalars().all()
+                by_user = {m.user_id: m.role for m in members}
+                assert fetched.owner_id == owner
+                assert len(members) == 3
+                assert by_user[owner] == GroupRole.OWNER
+                assert by_user[admin] == GroupRole.ADMIN
+                assert by_user[member] == GroupRole.MEMBER
+        finally:
+            await engine.dispose()
+
+    async def test_membership_role_defaults_to_member(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_default_owner")
+        joiner = _register(client, "grp_default_joiner")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                group = Group(name="Defaults", owner_id=owner)
+                session.add(group)
+                await session.flush()
+                session.add(GroupMember(group_id=group.id, user_id=joiner))
+                await session.commit()
+                group_id = group.id
+
+            async with factory() as session:
+                gm = (
+                    await session.execute(
+                        select(GroupMember).where(
+                            GroupMember.group_id == group_id, GroupMember.user_id == joiner
+                        )
+                    )
+                ).scalar_one()
+                assert gm.role == GroupRole.MEMBER
+        finally:
+            await engine.dispose()
+
+
+class TestUniqueMembershipConstraint:
+    async def test_duplicate_membership_rejected(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_uq_owner")
+        member = _register(client, "grp_uq_member")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                group = Group(name="Uniqueness", owner_id=owner)
+                session.add(group)
+                await session.flush()
+                session.add(GroupMember(group_id=group.id, user_id=member))
+                await session.commit()
+                group_id = group.id
+
+            async with factory() as session:
+                session.add(GroupMember(group_id=group_id, user_id=member))
+                with pytest.raises(IntegrityError):
+                    await session.commit()
+        finally:
+            await engine.dispose()
+
+
+class TestCascadeDelete:
+    async def test_deleting_group_deletes_members(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_cd_group_owner")
+        member = _register(client, "grp_cd_group_member")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                group = Group(name="To Delete", owner_id=owner)
+                session.add(group)
+                await session.flush()
+                session.add_all(
+                    [
+                        GroupMember(group_id=group.id, user_id=owner, role=GroupRole.OWNER),
+                        GroupMember(group_id=group.id, user_id=member),
+                    ]
+                )
+                await session.commit()
+                group_id = group.id
+
+            async with factory() as session:
+                # Core delete against groups directly, so the real ON DELETE
+                # CASCADE does the work (not the ORM).
+                await session.execute(delete(Group).where(Group.id == group_id))
+                await session.commit()
+
+            async with factory() as session:
+                members = (
+                    await session.execute(
+                        select(GroupMember).where(GroupMember.group_id == group_id)
+                    )
+                ).scalars().all()
+                assert members == []
+        finally:
+            await engine.dispose()
+
+    async def test_deleting_member_user_removes_only_their_membership(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_cd_user_owner")
+        member = _register(client, "grp_cd_user_member")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                group = Group(name="Membership Cascade", owner_id=owner)
+                session.add(group)
+                await session.flush()
+                session.add_all(
+                    [
+                        GroupMember(group_id=group.id, user_id=owner, role=GroupRole.OWNER),
+                        GroupMember(group_id=group.id, user_id=member),
+                    ]
+                )
+                await session.commit()
+                group_id = group.id
+
+            async with factory() as session:
+                await session.execute(delete(User).where(User.id == member))
+                await session.commit()
+
+            async with factory() as session:
+                remaining = (
+                    await session.execute(
+                        select(GroupMember).where(GroupMember.group_id == group_id)
+                    )
+                ).scalars().all()
+                # Only the deleted member's row is gone; the group and the
+                # owner's membership survive.
+                assert len(remaining) == 1
+                assert remaining[0].user_id == owner
+
+                group = await session.get(Group, group_id)
+                assert group is not None
+                assert group.owner_id == owner
+        finally:
+            await engine.dispose()
+
+    async def test_deleting_owner_survives_with_owner_id_null(self):
+        """Deleting the owner's account must not delete the group or its
+        other members -- only ``owner_id`` is nulled out (SET NULL), per the
+        module docstring in app/models/groups.py."""
+        client = TestClient(app)
+        owner = _register(client, "grp_cd_owner_owner")
+        member = _register(client, "grp_cd_owner_member")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                group = Group(name="Survives Owner Deletion", owner_id=owner)
+                session.add(group)
+                await session.flush()
+                session.add_all(
+                    [
+                        GroupMember(group_id=group.id, user_id=owner, role=GroupRole.OWNER),
+                        GroupMember(group_id=group.id, user_id=member),
+                    ]
+                )
+                await session.commit()
+                group_id = group.id
+
+            async with factory() as session:
+                await session.execute(delete(User).where(User.id == owner))
+                await session.commit()
+
+            async with factory() as session:
+                group = await session.get(Group, group_id)
+                assert group is not None
+                assert group.owner_id is None
+                assert group.name == "Survives Owner Deletion"
+
+                # The owner's own membership row is gone (user_id CASCADE),
+                # but the other member's row survives untouched.
+                members = (
+                    await session.execute(
+                        select(GroupMember).where(GroupMember.group_id == group_id)
+                    )
+                ).scalars().all()
+                assert len(members) == 1
+                assert members[0].user_id == member
+        finally:
+            await engine.dispose()

backend/tests/test_groups_api.py

@@ -0,0 +1,437 @@
+"""Integration tests for the Groups API router (app/routers/groups.py).
+
+app/models/groups.py owns the schema (see test_group_models.py); this
+covers create/join/leave, role authorization, ownership transfer, and the
+group page's member-list privacy.
+"""
+
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+def _register(client: TestClient, username: str) -> dict:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    token = resp.json()["access_token"]
+    headers = {"Authorization": f"Bearer {token}"}
+    me = client.get("/api/users/me", headers=headers)
+    assert me.status_code == 200, me.text
+    return {"headers": headers, "id": me.json()["id"], "username": username}
+
+
+def _create_group(client: TestClient, headers: dict, name: str, description: str | None = None) -> dict:
+    resp = client.post(
+        "/api/groups",
+        json={"name": name, "description": description},
+        headers=headers,
+    )
+    assert resp.status_code == 201, resp.text
+    return resp.json()
+
+
+class TestCreateGroup:
+    def test_create_makes_creator_owner(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_create_owner")
+
+        group = _create_group(client, owner["headers"], "Explorers", "We explore worlds")
+        assert group["name"] == "Explorers"
+        assert group["description"] == "We explore worlds"
+        assert group["owner_id"] == owner["id"]
+        assert group["member_count"] == 1
+        assert len(group["members"]) == 1
+        assert group["members"][0]["user_id"] == owner["id"]
+        assert group["members"][0]["role"] == "owner"
+
+    def test_requires_auth(self):
+        client = TestClient(app)
+        resp = client.post("/api/groups", json={"name": "No Auth"})
+        assert resp.status_code == 401
+
+    def test_blank_name_rejected(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_blank_name")
+        resp = client.post("/api/groups", json={"name": "   "}, headers=owner["headers"])
+        assert resp.status_code == 422
+
+    def test_name_over_max_length_rejected(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_long_name")
+        resp = client.post(
+            "/api/groups", json={"name": "x" * 101}, headers=owner["headers"]
+        )
+        assert resp.status_code == 422
+
+
+class TestGroupPage:
+    def test_get_group_page_shows_members_and_roles_no_private_fields(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_page_owner")
+        member = _register(client, "grp_api_page_member")
+
+        group = _create_group(client, owner["headers"], "Page Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+
+        resp = client.get(f"/api/groups/{group['id']}", headers=member["headers"])
+        assert resp.status_code == 200, resp.text
+        body = resp.json()
+        assert body["name"] == "Page Group"
+        assert body["member_count"] == 2
+        by_user = {m["user_id"]: m for m in body["members"]}
+        assert by_user[owner["id"]]["role"] == "owner"
+        assert by_user[member["id"]]["role"] == "member"
+        assert by_user[member["id"]]["username"] == member["username"]
+
+        # No private User fields (email, hashed_password, etc.) leak.
+        for m in body["members"]:
+            assert set(m.keys()) == {"user_id", "username", "role", "joined_at"}
+
+    def test_get_nonexistent_group_is_404(self):
+        client = TestClient(app)
+        user = _register(client, "grp_api_404")
+        resp = client.get("/api/groups/999999999", headers=user["headers"])
+        assert resp.status_code == 404
+
+
+class TestJoinLeave:
+    def test_join_is_idempotent(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_join_owner")
+        joiner = _register(client, "grp_api_join_joiner")
+        group = _create_group(client, owner["headers"], "Join Group")
+
+        r1 = client.post(f"/api/groups/{group['id']}/join", headers=joiner["headers"])
+        assert r1.status_code == 200, r1.text
+        r2 = client.post(f"/api/groups/{group['id']}/join", headers=joiner["headers"])
+        assert r2.status_code == 200, r2.text
+        assert r1.json()["role"] == r2.json()["role"] == "member"
+
+        page = client.get(f"/api/groups/{group['id']}", headers=owner["headers"]).json()
+        assert page["member_count"] == 2  # not 3 -- duplicate join didn't add a row
+
+    def test_leave_removes_membership(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_leave_owner")
+        member = _register(client, "grp_api_leave_member")
+        group = _create_group(client, owner["headers"], "Leave Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+
+        resp = client.post(f"/api/groups/{group['id']}/leave", headers=member["headers"])
+        assert resp.status_code == 200, resp.text
+
+        page = client.get(f"/api/groups/{group['id']}", headers=owner["headers"]).json()
+        assert page["member_count"] == 1
+        assert all(m["user_id"] != member["id"] for m in page["members"])
+
+    def test_owner_cannot_leave_without_transfer(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_owner_leave")
+        group = _create_group(client, owner["headers"], "Owner Leave Group")
+
+        resp = client.post(f"/api/groups/{group['id']}/leave", headers=owner["headers"])
+        assert resp.status_code == 409, resp.text
+
+    def test_leave_when_not_a_member_is_404(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_notmember_owner")
+        stranger = _register(client, "grp_api_notmember_stranger")
+        group = _create_group(client, owner["headers"], "Not A Member Group")
+
+        resp = client.post(f"/api/groups/{group['id']}/leave", headers=stranger["headers"])
+        assert resp.status_code == 404
+
+
+class TestRoleAuthorization:
+    def test_owner_can_promote_and_demote(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_role_owner")
+        member = _register(client, "grp_api_role_member")
+        group = _create_group(client, owner["headers"], "Role Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+
+        promote = client.post(
+            f"/api/groups/{group['id']}/members/{member['id']}/role",
+            json={"role": "admin"},
+            headers=owner["headers"],
+        )
+        assert promote.status_code == 200, promote.text
+        assert promote.json()["role"] == "admin"
+
+        demote = client.post(
+            f"/api/groups/{group['id']}/members/{member['id']}/role",
+            json={"role": "member"},
+            headers=owner["headers"],
+        )
+        assert demote.status_code == 200, demote.text
+        assert demote.json()["role"] == "member"
+
+    def test_plain_member_cannot_promote(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_noauth_owner")
+        member = _register(client, "grp_api_noauth_member")
+        other = _register(client, "grp_api_noauth_other")
+        group = _create_group(client, owner["headers"], "No Auth Promote Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+        client.post(f"/api/groups/{group['id']}/join", headers=other["headers"])
+
+        resp = client.post(
+            f"/api/groups/{group['id']}/members/{other['id']}/role",
+            json={"role": "admin"},
+            headers=member["headers"],
+        )
+        assert resp.status_code == 403
+
+    def test_admin_cannot_promote_or_demote(self):
+        """Only the owner may change roles -- admins cannot, per spec."""
+        client = TestClient(app)
+        owner = _register(client, "grp_api_adminauth_owner")
+        admin = _register(client, "grp_api_adminauth_admin")
+        other = _register(client, "grp_api_adminauth_other")
+        group = _create_group(client, owner["headers"], "Admin Cannot Promote Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=admin["headers"])
+        client.post(f"/api/groups/{group['id']}/join", headers=other["headers"])
+        client.post(
+            f"/api/groups/{group['id']}/members/{admin['id']}/role",
+            json={"role": "admin"},
+            headers=owner["headers"],
+        )
+
+        resp = client.post(
+            f"/api/groups/{group['id']}/members/{other['id']}/role",
+            json={"role": "admin"},
+            headers=admin["headers"],
+        )
+        assert resp.status_code == 403
+
+    def test_plain_member_cannot_delete_group(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_nodelete_owner")
+        member = _register(client, "grp_api_nodelete_member")
+        group = _create_group(client, owner["headers"], "No Delete Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+
+        resp = client.delete(f"/api/groups/{group['id']}", headers=member["headers"])
+        assert resp.status_code == 403
+
+    def test_admin_cannot_delete_group(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_admindelete_owner")
+        admin = _register(client, "grp_api_admindelete_admin")
+        group = _create_group(client, owner["headers"], "Admin No Delete Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=admin["headers"])
+        client.post(
+            f"/api/groups/{group['id']}/members/{admin['id']}/role",
+            json={"role": "admin"},
+            headers=owner["headers"],
+        )
+
+        resp = client.delete(f"/api/groups/{group['id']}", headers=admin["headers"])
+        assert resp.status_code == 403
+
+    def test_plain_member_cannot_transfer_ownership(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_notransfer_owner")
+        member = _register(client, "grp_api_notransfer_member")
+        group = _create_group(client, owner["headers"], "No Transfer Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+
+        resp = client.post(
+            f"/api/groups/{group['id']}/transfer",
+            json={"new_owner_id": member["id"]},
+            headers=member["headers"],
+        )
+        assert resp.status_code == 403
+
+    def test_cannot_set_role_to_owner_via_role_endpoint(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_noownerrole_owner")
+        member = _register(client, "grp_api_noownerrole_member")
+        group = _create_group(client, owner["headers"], "No Owner Role Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+
+        resp = client.post(
+            f"/api/groups/{group['id']}/members/{member['id']}/role",
+            json={"role": "owner"},
+            headers=owner["headers"],
+        )
+        assert resp.status_code == 422
+
+
+class TestOwnershipTransfer:
+    def test_transfer_moves_ownership_and_demotes_old_owner(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_xfer_owner")
+        member = _register(client, "grp_api_xfer_member")
+        group = _create_group(client, owner["headers"], "Transfer Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+
+        resp = client.post(
+            f"/api/groups/{group['id']}/transfer",
+            json={"new_owner_id": member["id"]},
+            headers=owner["headers"],
+        )
+        assert resp.status_code == 200, resp.text
+        body = resp.json()
+        assert body["owner_id"] == member["id"]
+        by_user = {m["user_id"]: m for m in body["members"]}
+        assert by_user[member["id"]]["role"] == "owner"
+        assert by_user[owner["id"]]["role"] == "admin"
+
+        # Exactly one owner remains.
+        owners = [m for m in body["members"] if m["role"] == "owner"]
+        assert len(owners) == 1
+
+        # Old owner can now leave (no longer the owner).
+        leave = client.post(f"/api/groups/{group['id']}/leave", headers=owner["headers"])
+        assert leave.status_code == 200, leave.text
+
+        # New owner cannot leave without transferring again.
+        leave2 = client.post(f"/api/groups/{group['id']}/leave", headers=member["headers"])
+        assert leave2.status_code == 409
+
+    def test_transfer_target_must_be_a_member(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_xfernonmember_owner")
+        stranger = _register(client, "grp_api_xfernonmember_stranger")
+        group = _create_group(client, owner["headers"], "Transfer Nonmember Group")
+
+        resp = client.post(
+            f"/api/groups/{group['id']}/transfer",
+            json={"new_owner_id": stranger["id"]},
+            headers=owner["headers"],
+        )
+        assert resp.status_code == 404
+
+    def test_transfer_to_self_rejected(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_xferself_owner")
+        group = _create_group(client, owner["headers"], "Transfer Self Group")
+
+        resp = client.post(
+            f"/api/groups/{group['id']}/transfer",
+            json={"new_owner_id": owner["id"]},
+            headers=owner["headers"],
+        )
+        assert resp.status_code == 400
+
+
+class TestUpdateGroup:
+    def test_owner_can_update_name_and_description(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_update_owner")
+        group = _create_group(client, owner["headers"], "Old Name", "Old desc")
+
+        resp = client.patch(
+            f"/api/groups/{group['id']}",
+            json={"name": "New Name", "description": "New desc"},
+            headers=owner["headers"],
+        )
+        assert resp.status_code == 200, resp.text
+        assert resp.json()["name"] == "New Name"
+        assert resp.json()["description"] == "New desc"
+
+    def test_admin_can_update(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_adminupdate_owner")
+        admin = _register(client, "grp_api_adminupdate_admin")
+        group = _create_group(client, owner["headers"], "Admin Update Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=admin["headers"])
+        client.post(
+            f"/api/groups/{group['id']}/members/{admin['id']}/role",
+            json={"role": "admin"},
+            headers=owner["headers"],
+        )
+
+        resp = client.patch(
+            f"/api/groups/{group['id']}",
+            json={"name": "Updated By Admin"},
+            headers=admin["headers"],
+        )
+        assert resp.status_code == 200, resp.text
+        assert resp.json()["name"] == "Updated By Admin"
+
+    def test_plain_member_cannot_update(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_noupdate_owner")
+        member = _register(client, "grp_api_noupdate_member")
+        group = _create_group(client, owner["headers"], "No Update Group")
+        client.post(f"/api/groups/{group['id']}/join", headers=member["headers"])
+
+        resp = client.patch(
+            f"/api/groups/{group['id']}",
+            json={"name": "Hacked Name"},
+            headers=member["headers"],
+        )
+        assert resp.status_code == 403
+
+    def test_non_member_cannot_update(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_strangernoupdate_owner")
+        stranger = _register(client, "grp_api_strangernoupdate_stranger")
+        group = _create_group(client, owner["headers"], "Stranger No Update Group")
+
+        resp = client.patch(
+            f"/api/groups/{group['id']}",
+            json={"name": "Hacked Name"},
+            headers=stranger["headers"],
+        )
+        assert resp.status_code == 403
+
+
+class TestDeleteGroup:
+    def test_owner_can_delete(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_delete_owner")
+        group = _create_group(client, owner["headers"], "Delete Group")
+
+        resp = client.delete(f"/api/groups/{group['id']}", headers=owner["headers"])
+        assert resp.status_code == 204, resp.text
+
+        after = client.get(f"/api/groups/{group['id']}", headers=owner["headers"])
+        assert after.status_code == 404
+
+
+class TestListGroups:
+    def test_list_all_groups_paginated(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_list_owner")
+        _create_group(client, owner["headers"], "List Group A")
+        _create_group(client, owner["headers"], "List Group B")
+
+        resp = client.get("/api/groups", params={"limit": 1}, headers=owner["headers"])
+        assert resp.status_code == 200, resp.text
+        body = resp.json()
+        assert len(body["groups"]) == 1
+        assert body["total"] >= 2
+
+    def test_list_mine_only_returns_own_groups(self):
+        client = TestClient(app)
+        owner = _register(client, "grp_api_listmine_owner")
+        other_owner = _register(client, "grp_api_listmine_other")
+        mine = _create_group(client, owner["headers"], "Mine Group")
+        _create_group(client, other_owner["headers"], "Not Mine Group")
+
+        resp = client.get("/api/groups", params={"mine": True}, headers=owner["headers"])
+        assert resp.status_code == 200, resp.text
+        ids = [g["id"] for g in resp.json()["groups"]]
+        assert mine["id"] in ids
+        assert all(
+            g["id"] != mine["id"] or g["owner_id"] == owner["id"]
+            for g in resp.json()["groups"]
+        )
+        # The other owner's group must not appear.
+        other_group_ids = [
+            g["id"] for g in client.get(
+                "/api/groups", params={"mine": True}, headers=other_owner["headers"]
+            ).json()["groups"]
+        ]
+        assert mine["id"] not in other_group_ids

backend/tests/test_presence.py

@@ -0,0 +1,221 @@
+"""Integration tests for the presence feature:
+
+- POST  /api/presence/heartbeat
+- GET   /api/presence/presence
+- PATCH /api/presence/status
+
+Hits the real app against the configured Postgres *and* a real Redis
+(conftest.py brings up an ephemeral instance of each when neither is
+already reachable) -- presence is fundamentally "does a TTL key exist in
+Redis", which isn't worth faking with a mock.
+
+Also covers the regression fixed in 47ab492 ("Fix StatusUpdate field
+annotation and is_online batch-call mismatch"): the router used to call
+``PresenceStore.is_online(ids)`` with a *list* of ids and then evaluate
+``uid in online_ids`` against the returned bool, which raised a TypeError
+on the first real multi-id batch call, and ``StatusUpdate.status_message``
+used the invalid annotation ``str | Field(...)``. Both are exercised below.
+"""
+
+import asyncio
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.main import app
+from app.services.presence import PresenceStore
+
+
+def _register(client: TestClient, username: str) -> dict:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    token = resp.json()["access_token"]
+    headers = {"Authorization": f"Bearer {token}"}
+    me = client.get("/api/users/me", headers=headers)
+    assert me.status_code == 200, me.text
+    return {"headers": headers, "id": me.json()["id"]}
+
+
+class TestHeartbeat:
+    def test_heartbeat_sets_online(self):
+        client = TestClient(app)
+        user = _register(client, "presence_hb1")
+
+        resp = client.post("/api/presence/heartbeat", json={}, headers=user["headers"])
+        assert resp.status_code == 200, resp.text
+        assert resp.json() == {"status": "ok", "user_id": user["id"]}
+
+        presence = client.get(
+            "/api/presence/presence",
+            params={"user_ids": str(user["id"])},
+            headers=user["headers"],
+        )
+        assert presence.status_code == 200, presence.text
+        body = presence.json()["users"]
+        assert len(body) == 1
+        assert body[0]["user_id"] == user["id"]
+        assert body[0]["is_online"] is True
+        assert body[0]["last_seen_at"] is not None
+
+    def test_requires_auth(self):
+        client = TestClient(app)
+        resp = client.post("/api/presence/heartbeat", json={})
+        assert resp.status_code == 401
+
+    def test_never_seen_user_is_offline_with_null_last_seen(self):
+        client = TestClient(app)
+        user = _register(client, "presence_never_hb")
+
+        presence = client.get(
+            "/api/presence/presence",
+            params={"user_ids": str(user["id"])},
+            headers=user["headers"],
+        )
+        assert presence.status_code == 200
+        body = presence.json()["users"][0]
+        assert body["is_online"] is False
+        assert body["last_seen_at"] is None
+
+
+class TestBatchPresence:
+    """Covers the batch-call path fixed in 47ab492 (is_online_batch via MGET)."""
+
+    def test_batch_query_mixes_online_offline_and_unknown_ids(self):
+        client = TestClient(app)
+        online_user = _register(client, "presence_batch_online")
+        offline_user = _register(client, "presence_batch_offline")
+
+        client.post("/api/presence/heartbeat", json={}, headers=online_user["headers"])
+
+        unknown_id = max(online_user["id"], offline_user["id"]) + 999_999
+        ids = f"{online_user['id']},{offline_user['id']},{unknown_id}"
+
+        resp = client.get(
+            "/api/presence/presence",
+            params={"user_ids": ids},
+            headers=online_user["headers"],
+        )
+        assert resp.status_code == 200, resp.text
+        by_id = {u["user_id"]: u for u in resp.json()["users"]}
+
+        # Unknown id is silently dropped (not in the DB), not a 500 or 404.
+        assert unknown_id not in by_id
+        assert by_id[online_user["id"]]["is_online"] is True
+        assert by_id[offline_user["id"]]["is_online"] is False
+
+    def test_empty_user_ids_is_a_400(self):
+        client = TestClient(app)
+        user = _register(client, "presence_empty_ids")
+        resp = client.get(
+            "/api/presence/presence",
+            params={"user_ids": ""},
+            headers=user["headers"],
+        )
+        assert resp.status_code == 400
+
+
+class TestStatusMessage:
+    def test_update_and_read_back_status_message(self):
+        client = TestClient(app)
+        user = _register(client, "presence_status1")
+
+        resp = client.patch(
+            "/api/presence/status",
+            json={"status_message": "  brb, making coffee  "},
+            headers=user["headers"],
+        )
+        assert resp.status_code == 200, resp.text
+        # The router strips whitespace (StatusUpdate.strip_message).
+        assert resp.json()["status_message"] == "brb, making coffee"
+
+        presence = client.get(
+            "/api/presence/presence",
+            params={"user_ids": str(user["id"])},
+            headers=user["headers"],
+        )
+        assert presence.json()["users"][0]["status_message"] == "brb, making coffee"
+
+    def test_status_message_over_max_length_is_rejected(self):
+        client = TestClient(app)
+        user = _register(client, "presence_status_toolong")
+        resp = client.patch(
+            "/api/presence/status",
+            json={"status_message": "x" * 141},
+            headers=user["headers"],
+        )
+        # StatusUpdate.status_message: str | None = Field(..., max_length=140)
+        # This is exactly the annotation 47ab492 fixed (it used to be the
+        # invalid `str | Field(...)`, which breaks model construction
+        # entirely rather than validating length).
+        assert resp.status_code == 422
+
+    def test_status_message_at_max_length_is_accepted(self):
+        client = TestClient(app)
+        user = _register(client, "presence_status_maxlen")
+        resp = client.patch(
+            "/api/presence/status",
+            json={"status_message": "x" * 140},
+            headers=user["headers"],
+        )
+        assert resp.status_code == 200, resp.text
+
+    def test_null_status_message_clears_it(self):
+        client = TestClient(app)
+        user = _register(client, "presence_status_clear")
+        client.patch("/api/presence/status", json={"status_message": "hi"}, headers=user["headers"])
+        resp = client.patch("/api/presence/status", json={"status_message": None}, headers=user["headers"])
+        assert resp.status_code == 200
+        assert resp.json()["status_message"] is None
+
+
+class TestPresenceStoreTTL:
+    """Exercises the real Redis TTL semantics directly against the service,
+    with a short heartbeat_ttl so the test doesn't need to sleep for the
+    real 60s default used in production. This is the cheap, real proxy for
+    "TTL expiry means offline" the task asked for -- same code path
+    (real Redis SET ... EX / EXISTS / MGET), just a much shorter window.
+    """
+
+    async def test_ttl_expiry_flips_online_to_offline(self):
+        store = PresenceStore(heartbeat_ttl=1)
+        try:
+            uid = 987654321  # doesn't need to exist in Postgres; Redis-only check
+            assert await store.is_online(uid) is False
+
+            await store.heartbeat(uid)
+            assert await store.is_online(uid) is True
+
+            await asyncio.sleep(1.5)
+            assert await store.is_online(uid) is False
+        finally:
+            await store.close()
+
+    async def test_is_online_batch_matches_is_online_semantics(self):
+        """Regression coverage for 47ab492: is_online_batch must return a
+        set of ids usable with `in`, not a bool."""
+        store = PresenceStore(heartbeat_ttl=30)
+        try:
+            online_uid, offline_uid = 111222333, 444555666
+            await store.heartbeat(online_uid)
+
+            result = await store.is_online_batch([online_uid, offline_uid])
+            assert isinstance(result, set)
+            assert online_uid in result
+            assert offline_uid not in result
+        finally:
+            await store.close()
+
+    async def test_is_online_batch_empty_list(self):
+        store = PresenceStore()
+        try:
+            assert await store.is_online_batch([]) == set()
+        finally:
+            await store.close()

backend/tests/test_profile.py

@@ -0,0 +1,406 @@
+"""Integration tests for /api/profile/me and /api/profile/me/favorites.
+
+Hits the real app against the configured Postgres (same contract as the
+other integration tests -- migrations applied first).
+"""
+
+import asyncio
+
+import pytest
+from fastapi.testclient import TestClient
+from sqlalchemy import text
+from sqlalchemy.ext.asyncio import create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import settings
+from app.main import app
+from app.models.profile import DEFAULT_PRIVACY
+
+
+def _auth_headers(client: TestClient, username: str) -> dict:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    return {"Authorization": f"Bearer {resp.json()['access_token']}"}
+
+
+def _me_id(client: TestClient, headers: dict) -> int:
+    me = client.get("/api/users/me", headers=headers)
+    assert me.status_code == 200, me.text
+    return me.json()["id"]
+
+
+def _make_world(client: TestClient, headers: dict, name: str = "W") -> int:
+    r = client.post("/api/worlds/", headers=headers, json={"name": name, "visibility": "public"})
+    assert r.status_code == 201, r.text
+    return r.json()["id"]
+
+
+def _make_asset(client: TestClient, headers: dict, name: str = "A") -> int:
+    """Insert an asset row directly via raw SQL.
+
+    Not going through POST /api/assets/, and not through the Asset ORM
+    model, deliberately: Asset.asset_type's ENUM column has no
+    values_callable, so SQLAlchemy sends the Python enum *name* (e.g.
+    "IMAGE") to Postgres instead of the lowercase value the DB enum
+    actually stores ("image"), and both the router and a plain ORM insert
+    500/fail on it. That's a pre-existing bug unrelated to this task; these
+    tests only need a real asset row to reference by id, so insert with raw
+    SQL to sidestep the buggy enum type entirely.
+    """
+    owner_id = _me_id(client, headers)
+
+    async def _create() -> int:
+        engine = create_async_engine(settings.DATABASE_URL, poolclass=NullPool)
+        async with engine.begin() as conn:
+            result = await conn.execute(
+                text(
+                    "INSERT INTO assets (name, asset_type, file_path, owner_id, is_public) "
+                    "VALUES (:name, 'image', '', :owner_id, false) RETURNING id"
+                ),
+                {"name": name, "owner_id": owner_id},
+            )
+            asset_id = result.scalar_one()
+        await engine.dispose()
+        return asset_id
+
+    return asyncio.run(_create())
+
+
+class TestGetProfile:
+    def test_new_user_gets_the_default(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "pf_default")
+        resp = client.get("/api/profile/me", headers=headers)
+        assert resp.status_code == 200
+        body = resp.json()
+        assert body["is_default"] is True
+        assert body["bio"] is None
+        assert body["avatar_asset_id"] is None
+        assert body["privacy"] == DEFAULT_PRIVACY
+
+    def test_requires_auth(self):
+        client = TestClient(app)
+        assert client.get("/api/profile/me").status_code == 401
+
+
+class TestPutProfile:
+    def test_save_then_read_back(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "pf_save")
+        asset_id = _make_asset(client, headers)
+
+        put = client.put(
+            "/api/profile/me", headers=headers,
+            json={"bio": "hello world", "avatar_asset_id": asset_id,
+                  "privacy": {"profile_visibility": "friends"}},
+        )
+        assert put.status_code == 200, put.text
+        body = put.json()
+        assert body["is_default"] is False
+        assert body["bio"] == "hello world"
+        assert body["avatar_asset_id"] == asset_id
+        assert body["privacy"]["profile_visibility"] == "friends"
+        # unspecified privacy keys keep their default
+        assert body["privacy"]["friends_list_visibility"] == "public"
+
+        got = client.get("/api/profile/me", headers=headers)
+        assert got.status_code == 200
+        assert got.json() == body
+
+    def test_partial_update_preserves_other_fields(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "pf_partial")
+        client.put("/api/profile/me", headers=headers, json={"bio": "first bio"})
+        put2 = client.put("/api/profile/me", headers=headers, json={"privacy": {"favorites_visibility": "private"}})
+        assert put2.status_code == 200, put2.text
+        body = put2.json()
+        assert body["bio"] == "first bio"
+        assert body["privacy"]["favorites_visibility"] == "private"
+
+    def test_other_user_cannot_edit_my_profile(self):
+        """There is no user_id-scoped edit route at all -- PUT /me always
+        acts on the caller's own JWT identity, so another user's token can
+        never touch this user's profile."""
+        client = TestClient(app)
+        headers_a = _auth_headers(client, "pf_owner")
+        headers_b = _auth_headers(client, "pf_other")
+
+        client.put("/api/profile/me", headers=headers_a, json={"bio": "owner's bio"})
+        client.put("/api/profile/me", headers=headers_b, json={"bio": "other's bio"})
+
+        got_a = client.get("/api/profile/me", headers=headers_a).json()
+        got_b = client.get("/api/profile/me", headers=headers_b).json()
+        assert got_a["bio"] == "owner's bio"
+        assert got_b["bio"] == "other's bio"
+        assert got_a["user_id"] != got_b["user_id"]
+
+    def test_rejects_invalid_avatar_asset_id(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "pf_badasset")
+        resp = client.put("/api/profile/me", headers=headers, json={"avatar_asset_id": 999999})
+        assert resp.status_code == 422
+
+    def test_rejects_over_length_bio(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "pf_longbio")
+        resp = client.put("/api/profile/me", headers=headers, json={"bio": "x" * 501})
+        assert resp.status_code == 422
+
+    def test_accepts_bio_at_max_length(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "pf_maxbio")
+        resp = client.put("/api/profile/me", headers=headers, json={"bio": "x" * 500})
+        assert resp.status_code == 200, resp.text
+
+    def test_rejects_unknown_privacy_key(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "pf_badprivkey")
+        resp = client.put("/api/profile/me", headers=headers, json={"privacy": {"nonsense_key": "public"}})
+        assert resp.status_code == 422
+
+    def test_rejects_invalid_privacy_value(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "pf_badprivval")
+        resp = client.put("/api/profile/me", headers=headers, json={"privacy": {"profile_visibility": "nope"}})
+        assert resp.status_code == 422
+
+    def test_requires_auth(self):
+        client = TestClient(app)
+        resp = client.put("/api/profile/me", json={"bio": "x"})
+        assert resp.status_code == 401
+
+
+class TestFavorites:
+    def test_new_user_has_no_favorites(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "fav_default")
+        resp = client.get("/api/profile/me/favorites", headers=headers)
+        assert resp.status_code == 200
+        assert resp.json() == {"world_ids": []}
+
+    def test_replace_then_read_back(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "fav_save")
+        w1 = _make_world(client, headers, "W1")
+        w2 = _make_world(client, headers, "W2")
+
+        put = client.put("/api/profile/me/favorites", headers=headers, json={"world_ids": [w1, w2]})
+        assert put.status_code == 200, put.text
+        assert set(put.json()["world_ids"]) == {w1, w2}
+
+        got = client.get("/api/profile/me/favorites", headers=headers)
+        assert set(got.json()["world_ids"]) == {w1, w2}
+
+    def test_replace_is_a_full_replace_not_append(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "fav_replace")
+        w1 = _make_world(client, headers, "W1")
+        w2 = _make_world(client, headers, "W2")
+
+        client.put("/api/profile/me/favorites", headers=headers, json={"world_ids": [w1]})
+        second = client.put("/api/profile/me/favorites", headers=headers, json={"world_ids": [w2]})
+        assert second.json()["world_ids"] == [w2]
+
+        got = client.get("/api/profile/me/favorites", headers=headers)
+        assert got.json()["world_ids"] == [w2]
+
+    def test_replace_with_empty_list_clears_favorites(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "fav_clear")
+        w1 = _make_world(client, headers, "W1")
+        client.put("/api/profile/me/favorites", headers=headers, json={"world_ids": [w1]})
+        cleared = client.put("/api/profile/me/favorites", headers=headers, json={"world_ids": []})
+        assert cleared.status_code == 200
+        assert cleared.json() == {"world_ids": []}
+
+    def test_rejects_nonexistent_world_id(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "fav_badworld")
+        resp = client.put("/api/profile/me/favorites", headers=headers, json={"world_ids": [999999]})
+        assert resp.status_code == 422
+
+    def test_rejects_nonexistent_world_id_mixed_with_valid(self):
+        client = TestClient(app)
+        headers = _auth_headers(client, "fav_mixed")
+        w1 = _make_world(client, headers, "W1")
+        resp = client.put("/api/profile/me/favorites", headers=headers, json={"world_ids": [w1, 999999]})
+        assert resp.status_code == 422
+        # nothing partially applied
+        got = client.get("/api/profile/me/favorites", headers=headers)
+        assert got.json()["world_ids"] == []
+
+    def test_favorites_isolated_per_user(self):
+        client = TestClient(app)
+        headers_a = _auth_headers(client, "fav_owner")
+        headers_b = _auth_headers(client, "fav_other")
+        w1 = _make_world(client, headers_a, "W1")
+
+        client.put("/api/profile/me/favorites", headers=headers_a, json={"world_ids": [w1]})
+        got_b = client.get("/api/profile/me/favorites", headers=headers_b)
+        assert got_b.json()["world_ids"] == []
+
+    def test_requires_auth(self):
+        client = TestClient(app)
+        assert client.get("/api/profile/me/favorites").status_code == 401
+        assert client.put("/api/profile/me/favorites", json={"world_ids": []}).status_code == 401
+
+
+class TestPublicProfile:
+    def test_public_profile_full_view(self):
+        client = TestClient(app)
+        h_alice = _auth_headers(client, "pub_alice")
+        alice_id = _me_id(client, h_alice)
+        h_bob = _auth_headers(client, "pub_bob")
+
+        w1 = _make_world(client, h_alice, "AliceWorld")
+        asset_id = _make_asset(client, h_alice, "AliceAsset")
+
+        client.put(
+            "/api/profile/me",
+            headers=h_alice,
+            json={"bio": "Hi, I am Alice", "avatar_asset_id": asset_id},
+        )
+        client.put("/api/profile/me/favorites", headers=h_alice, json={"world_ids": [w1]})
+
+        resp = client.get(f"/api/profile/{alice_id}", headers=h_bob)
+        assert resp.status_code == 200, resp.text
+        data = resp.json()
+        assert data["user_id"] == alice_id
+        assert data["username"] == "pub_alice"
+        assert data["bio"] == "Hi, I am Alice"
+        assert data["avatar_asset_id"] == asset_id
+        assert data["is_restricted"] is False
+        assert len(data["favorites"]) == 1
+        assert data["favorites"][0]["id"] == w1
+        assert data["favorites"][0]["name"] == "AliceWorld"
+        assert "email" not in data
+        assert "password" not in data
+
+    def test_public_profile_not_found(self):
+        client = TestClient(app)
+        h_bob = _auth_headers(client, "pub_nf_bob")
+        resp = client.get("/api/profile/999999", headers=h_bob)
+        assert resp.status_code == 404
+
+    def test_public_profile_requires_auth(self):
+        client = TestClient(app)
+        assert client.get("/api/profile/1").status_code == 401
+
+    def test_public_profile_private_visibility(self):
+        client = TestClient(app)
+        h_alice = _auth_headers(client, "pub_priv_a")
+        alice_id = _me_id(client, h_alice)
+        h_bob = _auth_headers(client, "pub_priv_b")
+
+        client.put(
+            "/api/profile/me",
+            headers=h_alice,
+            json={"bio": "Top secret bio", "privacy": {"profile_visibility": "private"}},
+        )
+
+        resp_bob = client.get(f"/api/profile/{alice_id}", headers=h_bob)
+        assert resp_bob.status_code == 200
+        data_bob = resp_bob.json()
+        assert data_bob["is_restricted"] is True
+        assert data_bob["bio"] is None
+        assert data_bob["favorites"] == []
+        assert data_bob["friends"] == []
+
+        # Alice viewing herself is not restricted
+        resp_alice = client.get(f"/api/profile/{alice_id}", headers=h_alice)
+        assert resp_alice.status_code == 200
+        assert resp_alice.json()["is_restricted"] is False
+        assert resp_alice.json()["bio"] == "Top secret bio"
+
+    def test_public_profile_friends_only_visibility(self):
+        client = TestClient(app)
+        h_alice = _auth_headers(client, "pub_fo_a")
+        alice_id = _me_id(client, h_alice)
+        h_bob = _auth_headers(client, "pub_fo_b")
+        bob_id = _me_id(client, h_bob)
+        h_charlie = _auth_headers(client, "pub_fo_c")
+
+        client.put(
+            "/api/profile/me",
+            headers=h_alice,
+            json={"bio": "Friends only bio", "privacy": {"profile_visibility": "friends"}},
+        )
+
+        # Charlie is not a friend -> restricted
+        resp_c = client.get(f"/api/profile/{alice_id}", headers=h_charlie)
+        assert resp_c.json()["is_restricted"] is True
+        assert resp_c.json()["bio"] is None
+
+        # Bob becomes friends with Alice
+        req = client.post("/api/friends/requests", headers=h_bob, json={"user_id": alice_id})
+        req_id = req.json()["id"]
+        client.post(f"/api/friends/requests/{req_id}/accept", headers=h_alice)
+
+        # Now Bob sees full profile and friends list contains Bob
+        resp_b = client.get(f"/api/profile/{alice_id}", headers=h_bob)
+        assert resp_b.json()["is_restricted"] is False
+        assert resp_b.json()["bio"] == "Friends only bio"
+        assert any(f["id"] == bob_id for f in resp_b.json()["friends"])
+
+    def test_public_profile_blocked_user_gets_restricted(self):
+        client = TestClient(app)
+        h_alice = _auth_headers(client, "pub_blk_a")
+        alice_id = _me_id(client, h_alice)
+        h_dan = _auth_headers(client, "pub_blk_d")
+        dan_id = _me_id(client, h_dan)
+
+        client.put("/api/profile/me", headers=h_alice, json={"bio": "Alice public bio"})
+        client.post(f"/api/friends/{dan_id}/block", headers=h_alice)
+
+        # Dan viewing Alice gets restricted view
+        resp_dan = client.get(f"/api/profile/{alice_id}", headers=h_dan)
+        assert resp_dan.status_code == 200
+        assert resp_dan.json()["is_restricted"] is True
+        assert resp_dan.json()["bio"] is None
+
+        # Alice viewing Dan gets restricted view
+        resp_alice = client.get(f"/api/profile/{dan_id}", headers=h_alice)
+        assert resp_alice.status_code == 200
+        assert resp_alice.json()["is_restricted"] is True
+
+    def test_public_profile_selective_favorites_and_friends_privacy(self):
+        client = TestClient(app)
+        h_alice = _auth_headers(client, "pub_sec_a")
+        alice_id = _me_id(client, h_alice)
+        h_bob = _auth_headers(client, "pub_sec_b")
+        bob_id = _me_id(client, h_bob)
+        w1 = _make_world(client, h_alice, "WorldSec")
+
+        client.put("/api/profile/me/favorites", headers=h_alice, json={"world_ids": [w1]})
+        req = client.post("/api/friends/requests", headers=h_bob, json={"user_id": alice_id})
+        req_id = req.json()["id"]
+        client.post(f"/api/friends/requests/{req_id}/accept", headers=h_alice)
+
+        client.put(
+            "/api/profile/me",
+            headers=h_alice,
+            json={
+                "bio": "Bio is public",
+                "privacy": {
+                    "profile_visibility": "public",
+                    "favorites_visibility": "private",
+                    "friends_list_visibility": "private",
+                },
+            },
+        )
+
+        resp = client.get(f"/api/profile/{alice_id}", headers=h_bob)
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["bio"] == "Bio is public"
+        assert data["favorites"] == []
+        assert data["friends"] == []
+

backend/tests/test_rate_limit.py

@@ -0,0 +1,124 @@
+"""The auth endpoints are rate-limited per client IP."""
+
+import pytest
+from fastapi import Depends, FastAPI
+from fastapi.testclient import TestClient
+
+from app import rate_limit
+from app.config import settings
+from app.main import app
+
+
+@pytest.fixture(autouse=True)
+def _clean_limiter():
+    # This module tests the limiter itself: force it on (the checkpoint
+    # runner disables it suite-wide via RATE_LIMIT_ENABLED) and start each
+    # test from an empty window.
+    prev = settings.RATE_LIMIT_ENABLED
+    settings.RATE_LIMIT_ENABLED = True
+    rate_limit.reset_all()
+    yield
+    rate_limit.reset_all()
+    settings.RATE_LIMIT_ENABLED = prev
+
+
+def test_login_is_limited_after_the_threshold():
+    client = TestClient(app)
+    codes = []
+    for i in range(15):
+        r = client.post("/api/auth/login", data={"username": f"nobody{i}", "password": "x"})
+        codes.append(r.status_code)
+    # First 10 get through to the (failing) auth check; the rest are 429.
+    assert codes[:10] == [401] * 10
+    assert 429 in codes[10:]
+    assert codes[-1] == 429
+
+
+def test_register_shares_the_same_bucket():
+    client = TestClient(app)
+    # Burn the budget on login...
+    for i in range(10):
+        client.post("/api/auth/login", data={"username": f"x{i}", "password": "y"})
+    # ...register from the same IP is now blocked too.
+    r = client.post("/api/auth/register", json={
+        "username": "rl_user", "email": "rl@e.com",
+        "password": "secret123", "date_of_birth": "1990-01-01",
+    })
+    assert r.status_code == 429
+    assert "Retry-After" in r.headers
+
+
+def test_limiter_window_is_per_key():
+    limiter = rate_limit.SlidingWindowLimiter(max_hits=2, window_seconds=60)
+    limiter.check("a")
+    limiter.check("a")
+    with pytest.raises(Exception):
+        limiter.check("a")
+    limiter.check("b")  # different key, unaffected
+
+
+def _make_named_limit_app():
+    """A tiny standalone app exercising two independent named limits, so
+    these tests don't depend on any sibling endpoint existing yet."""
+    limit_a = rate_limit.rate_limit("test_named_a", max_hits=2, window_seconds=60)
+    limit_b = rate_limit.rate_limit("test_named_b", max_hits=2, window_seconds=60)
+
+    app = FastAPI()
+
+    @app.post("/a", dependencies=[Depends(limit_a)])
+    def _a():
+        return {"ok": True}
+
+    @app.post("/b", dependencies=[Depends(limit_b)])
+    def _b():
+        return {"ok": True}
+
+    return TestClient(app)
+
+
+def test_named_limits_do_not_share_counters():
+    client = _make_named_limit_app()
+
+    # Burn out limit "a" entirely.
+    assert client.post("/a").status_code == 200
+    assert client.post("/a").status_code == 200
+    r = client.post("/a")
+    assert r.status_code == 429
+    assert "Retry-After" in r.headers
+
+    # Limit "b" is untouched -- same process, same client IP, different name.
+    assert client.post("/b").status_code == 200
+    assert client.post("/b").status_code == 200
+    assert client.post("/b").status_code == 429
+
+
+def test_named_limit_returns_429_with_retry_after_once_exhausted():
+    client = _make_named_limit_app()
+    client.post("/a")
+    client.post("/a")
+    r = client.post("/a")
+    assert r.status_code == 429
+    retry_after = r.headers["Retry-After"]
+    assert int(retry_after) >= 1
+
+
+def test_named_limit_is_a_noop_when_rate_limiting_disabled():
+    prev = settings.RATE_LIMIT_ENABLED
+    settings.RATE_LIMIT_ENABLED = False
+    try:
+        client = _make_named_limit_app()
+        codes = [client.post("/a").status_code for _ in range(10)]
+        assert codes == [200] * 10
+    finally:
+        settings.RATE_LIMIT_ENABLED = prev
+
+
+def test_reset_all_clears_named_limiters_too():
+    client = _make_named_limit_app()
+    client.post("/a")
+    client.post("/a")
+    assert client.post("/a").status_code == 429
+
+    rate_limit.reset_all()
+
+    assert client.post("/a").status_code == 200

backend/tests/test_refresh_endpoint.py

@@ -59,7 +59,7 @@ class TestRefresh:
                 "username": username,
                 "email": email,
                 "password": password,
-                "date_of_birth": "2000-01-01",
+                "date_of_birth": "1990-01-01",
             },
         )
         assert resp.status_code == 201
@@ -143,7 +143,7 @@ class TestRefresh:
                 "username": "refep_loginrefuser",
                 "email": "loginref@example.com",
                 "password": "secret123",
-                "date_of_birth": "2000-01-01",
+                "date_of_birth": "1990-01-01",
             },
         )
         # Login to get a refresh token

backend/tests/test_social_friends.py

@@ -0,0 +1,317 @@
+"""Integration tests for the friends/follow/block API:
+
+- POST   /api/friends/requests
+- GET    /api/friends/requests
+- POST   /api/friends/requests/{id}/accept
+- POST   /api/friends/requests/{id}/decline
+- DELETE /api/friends/{user_id}
+- POST   /api/friends/{user_id}/follow
+- DELETE /api/friends/{user_id}/follow
+- POST   /api/friends/{user_id}/block
+- DELETE /api/friends/{user_id}/block
+- GET    /api/friends
+- GET    /api/friends/following
+- GET    /api/friends/blocked
+
+app/routers/social_friends.py, built on the merged models in
+app/models/social.py (Friendship/Follow/Block).
+"""
+
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+def _register(client: TestClient, username: str) -> dict:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    token = resp.json()["access_token"]
+    headers = {"Authorization": f"Bearer {token}"}
+    me = client.get("/api/users/me", headers=headers)
+    assert me.status_code == 200, me.text
+    return {"headers": headers, "id": me.json()["id"]}
+
+
+class TestFriendRequestFlow:
+    def test_send_list_accept_makes_mutual_friendship(self):
+        client = TestClient(app)
+        a = _register(client, "fr_flow_a")
+        b = _register(client, "fr_flow_b")
+
+        resp = client.post("/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"])
+        assert resp.status_code == 201, resp.text
+        request_id = resp.json()["id"]
+        assert resp.json()["status"] == "pending"
+
+        incoming = client.get("/api/friends/requests", headers=b["headers"])
+        assert incoming.status_code == 200
+        ids = [r["id"] for r in incoming.json()["requests"]]
+        assert request_id in ids
+
+        # Requester doesn't see it in their own incoming list.
+        a_incoming = client.get("/api/friends/requests", headers=a["headers"])
+        assert a_incoming.json()["requests"] == []
+
+        accept = client.post(f"/api/friends/requests/{request_id}/accept", headers=b["headers"])
+        assert accept.status_code == 200, accept.text
+        assert accept.json()["status"] == "accepted"
+
+        # Mutual: shows up in both users' friend lists.
+        a_friends = client.get("/api/friends", headers=a["headers"]).json()["friends"]
+        b_friends = client.get("/api/friends", headers=b["headers"]).json()["friends"]
+        assert any(u["id"] == b["id"] for u in a_friends)
+        assert any(u["id"] == a["id"] for u in b_friends)
+
+    def test_decline_removes_request_and_allows_re_request(self):
+        client = TestClient(app)
+        a = _register(client, "fr_decl_a")
+        b = _register(client, "fr_decl_b")
+
+        resp = client.post("/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"])
+        request_id = resp.json()["id"]
+
+        decline = client.post(f"/api/friends/requests/{request_id}/decline", headers=b["headers"])
+        assert decline.status_code == 200, decline.text
+
+        assert client.get("/api/friends/requests", headers=b["headers"]).json()["requests"] == []
+
+        # A can send a new request now that the old one is gone.
+        resp2 = client.post("/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"])
+        assert resp2.status_code == 201, resp2.text
+
+    def test_accept_or_decline_of_others_request_is_404_not_403(self):
+        client = TestClient(app)
+        a = _register(client, "fr_enum_a")
+        b = _register(client, "fr_enum_b")
+        c = _register(client, "fr_enum_c")
+
+        resp = client.post("/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"])
+        request_id = resp.json()["id"]
+
+        # c is neither requester nor addressee -- must not be able to act on it,
+        # and must not be able to distinguish "not yours" from "doesn't exist".
+        accept = client.post(f"/api/friends/requests/{request_id}/accept", headers=c["headers"])
+        assert accept.status_code == 404
+
+        decline = client.post(f"/api/friends/requests/{request_id}/decline", headers=c["headers"])
+        assert decline.status_code == 404
+
+        nonexistent = client.post("/api/friends/requests/999999999/accept", headers=c["headers"])
+        assert nonexistent.status_code == 404
+
+    def test_unfriend_removes_mutual_friendship(self):
+        client = TestClient(app)
+        a = _register(client, "fr_unfr_a")
+        b = _register(client, "fr_unfr_b")
+
+        request_id = client.post(
+            "/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"]
+        ).json()["id"]
+        client.post(f"/api/friends/requests/{request_id}/accept", headers=b["headers"])
+
+        unfriend = client.delete(f"/api/friends/{a['id']}", headers=b["headers"])
+        assert unfriend.status_code == 200, unfriend.text
+
+        assert client.get("/api/friends", headers=a["headers"]).json()["friends"] == []
+        assert client.get("/api/friends", headers=b["headers"]).json()["friends"] == []
+
+        # Idempotency / no dangling state: unfriending again is a clean 404, not 500.
+        again = client.delete(f"/api/friends/{a['id']}", headers=b["headers"])
+        assert again.status_code == 404
+
+
+class TestSelfAndDuplicateRejection:
+    def test_self_request_rejected(self):
+        client = TestClient(app)
+        a = _register(client, "self_req_a")
+        resp = client.post("/api/friends/requests", json={"user_id": a["id"]}, headers=a["headers"])
+        assert resp.status_code == 400
+
+    def test_self_follow_rejected(self):
+        client = TestClient(app)
+        a = _register(client, "self_follow_a")
+        resp = client.post(f"/api/friends/{a['id']}/follow", headers=a["headers"])
+        assert resp.status_code == 400
+
+    def test_self_block_rejected(self):
+        client = TestClient(app)
+        a = _register(client, "self_block_a")
+        resp = client.post(f"/api/friends/{a['id']}/block", headers=a["headers"])
+        assert resp.status_code == 400
+
+    def test_duplicate_friend_request_is_conflict_not_500(self):
+        client = TestClient(app)
+        a = _register(client, "dup_req_a")
+        b = _register(client, "dup_req_b")
+        assert client.post("/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"]).status_code == 201
+        dup = client.post("/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"])
+        assert dup.status_code == 409
+
+    def test_reverse_duplicate_friend_request_is_conflict(self):
+        """b requesting a while a's request to b is still pending is treated
+        as a duplicate of the same pair, not a second independent request."""
+        client = TestClient(app)
+        a = _register(client, "dup_rev_a")
+        b = _register(client, "dup_rev_b")
+        assert client.post("/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"]).status_code == 201
+        reverse = client.post("/api/friends/requests", json={"user_id": a["id"]}, headers=b["headers"])
+        assert reverse.status_code == 409
+
+    def test_duplicate_follow_is_conflict_not_500(self):
+        client = TestClient(app)
+        a = _register(client, "dup_follow_a")
+        b = _register(client, "dup_follow_b")
+        assert client.post(f"/api/friends/{b['id']}/follow", headers=a["headers"]).status_code == 201
+        dup = client.post(f"/api/friends/{b['id']}/follow", headers=a["headers"])
+        assert dup.status_code == 409
+
+    def test_duplicate_block_is_conflict_not_500(self):
+        client = TestClient(app)
+        a = _register(client, "dup_block_a")
+        b = _register(client, "dup_block_b")
+        assert client.post(f"/api/friends/{b['id']}/block", headers=a["headers"]).status_code == 201
+        dup = client.post(f"/api/friends/{b['id']}/block", headers=a["headers"])
+        assert dup.status_code == 409
+
+    def test_friend_request_to_nonexistent_user_is_404(self):
+        client = TestClient(app)
+        a = _register(client, "req_missing_a")
+        resp = client.post("/api/friends/requests", json={"user_id": 999999999}, headers=a["headers"])
+        assert resp.status_code == 404
+
+
+class TestFollow:
+    def test_follow_unfollow_and_list(self):
+        client = TestClient(app)
+        a = _register(client, "follow_flow_a")
+        b = _register(client, "follow_flow_b")
+
+        follow = client.post(f"/api/friends/{b['id']}/follow", headers=a["headers"])
+        assert follow.status_code == 201, follow.text
+
+        following = client.get("/api/friends/following", headers=a["headers"]).json()["following"]
+        assert any(u["id"] == b["id"] for u in following)
+
+        # One-way: b does not follow a.
+        b_following = client.get("/api/friends/following", headers=b["headers"]).json()["following"]
+        assert b_following == []
+
+        unfollow = client.delete(f"/api/friends/{b['id']}/follow", headers=a["headers"])
+        assert unfollow.status_code == 200, unfollow.text
+
+        following_after = client.get("/api/friends/following", headers=a["headers"]).json()["following"]
+        assert following_after == []
+
+        # Unfollowing again is a clean 404, not 500.
+        again = client.delete(f"/api/friends/{b['id']}/follow", headers=a["headers"])
+        assert again.status_code == 404
+
+    def test_follow_requires_auth(self):
+        client = TestClient(app)
+        b = _register(client, "follow_noauth_b")
+        resp = client.post(f"/api/friends/{b['id']}/follow", json={})
+        assert resp.status_code == 401
+
+
+class TestBlock:
+    def test_block_clears_existing_friendship_and_follow(self):
+        client = TestClient(app)
+        a = _register(client, "block_clear_a")
+        b = _register(client, "block_clear_b")
+
+        request_id = client.post(
+            "/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"]
+        ).json()["id"]
+        client.post(f"/api/friends/requests/{request_id}/accept", headers=b["headers"])
+        client.post(f"/api/friends/{a['id']}/follow", headers=b["headers"])
+
+        assert any(
+            u["id"] == b["id"] for u in client.get("/api/friends", headers=a["headers"]).json()["friends"]
+        )
+        assert any(
+            u["id"] == a["id"]
+            for u in client.get("/api/friends/following", headers=b["headers"]).json()["following"]
+        )
+
+        block = client.post(f"/api/friends/{b['id']}/block", headers=a["headers"])
+        assert block.status_code == 201, block.text
+
+        assert client.get("/api/friends", headers=a["headers"]).json()["friends"] == []
+        assert client.get("/api/friends", headers=b["headers"]).json()["friends"] == []
+        assert client.get("/api/friends/following", headers=b["headers"]).json()["following"] == []
+
+        blocked_list = client.get("/api/friends/blocked", headers=a["headers"]).json()["blocked"]
+        assert any(u["id"] == b["id"] for u in blocked_list)
+
+    def test_block_prevents_new_friend_request_and_follow(self):
+        client = TestClient(app)
+        a = _register(client, "block_prevent_a")
+        b = _register(client, "block_prevent_b")
+
+        client.post(f"/api/friends/{b['id']}/block", headers=a["headers"])
+
+        req = client.post("/api/friends/requests", json={"user_id": a["id"]}, headers=b["headers"])
+        assert req.status_code == 403
+
+        follow = client.post(f"/api/friends/{a['id']}/follow", headers=b["headers"])
+        assert follow.status_code == 403
+
+    def test_unblock_removes_block(self):
+        client = TestClient(app)
+        a = _register(client, "unblock_a")
+        b = _register(client, "unblock_b")
+
+        client.post(f"/api/friends/{b['id']}/block", headers=a["headers"])
+        unblock = client.delete(f"/api/friends/{b['id']}/block", headers=a["headers"])
+        assert unblock.status_code == 200, unblock.text
+
+        assert client.get("/api/friends/blocked", headers=a["headers"]).json()["blocked"] == []
+
+        # Idempotency: unblocking again is a clean 404, not 500.
+        again = client.delete(f"/api/friends/{b['id']}/block", headers=a["headers"])
+        assert again.status_code == 404
+
+        # After unblock, a fresh follow/request works again.
+        assert client.post(f"/api/friends/{a['id']}/follow", headers=b["headers"]).status_code == 201
+
+
+class TestDataIsolation:
+    def test_list_endpoints_are_scoped_to_caller(self):
+        """A third party's friends/following/blocked lists must never leak
+        into another user's response."""
+        client = TestClient(app)
+        a = _register(client, "iso_a")
+        b = _register(client, "iso_b")
+        c = _register(client, "iso_c")
+
+        request_id = client.post(
+            "/api/friends/requests", json={"user_id": b["id"]}, headers=a["headers"]
+        ).json()["id"]
+        client.post(f"/api/friends/requests/{request_id}/accept", headers=b["headers"])
+        client.post(f"/api/friends/{b['id']}/follow", headers=a["headers"])
+        client.post(f"/api/friends/{b['id']}/block", headers=c["headers"])
+
+        c_friends = client.get("/api/friends", headers=c["headers"]).json()["friends"]
+        c_following = client.get("/api/friends/following", headers=c["headers"]).json()["following"]
+        assert c_friends == []
+        assert c_following == []
+
+        # c's block of b must not appear in a's or b's blocked list.
+        a_blocked = client.get("/api/friends/blocked", headers=a["headers"]).json()["blocked"]
+        assert a_blocked == []
+
+    def test_requires_auth_on_all_endpoints(self):
+        client = TestClient(app)
+        assert client.get("/api/friends").status_code == 401
+        assert client.get("/api/friends/requests").status_code == 401
+        assert client.get("/api/friends/following").status_code == 401
+        assert client.get("/api/friends/blocked").status_code == 401
+        assert client.post("/api/friends/requests", json={"user_id": 1}).status_code == 401

backend/tests/test_social_models.py

@@ -0,0 +1,240 @@
+"""Model-level tests for the social graph: friendships, follows, blocks.
+
+app/models/social.py / alembic/versions/0007_add_social_graph_tables.py
+(docs/planning/social.md US-1). This is the models+migration task only --
+there are no API endpoints yet (a sibling task owns the router), so these
+tests exercise the ORM models and the real Postgres constraints directly
+rather than going through HTTP.
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+from sqlalchemy import delete, select
+from sqlalchemy.exc import IntegrityError
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+
+from app.config import settings
+from app.main import app
+from app.models.social import Friendship, Follow, Block, FriendshipStatus
+from app.models.user import User
+
+
+def _register(client: TestClient, username: str) -> int:
+    resp = client.post(
+        "/api/auth/register",
+        json={
+            "username": username,
+            "email": f"{username}@example.com",
+            "password": "secret123",
+            "date_of_birth": "1990-01-01",
+        },
+    )
+    assert resp.status_code == 201, resp.text
+    headers = {"Authorization": f"Bearer {resp.json()['access_token']}"}
+    me = client.get("/api/users/me", headers=headers)
+    assert me.status_code == 200, me.text
+    return me.json()["id"]
+
+
+def _session_factory():
+    engine = create_async_engine(settings.DATABASE_URL, poolclass=NullPool)
+    return engine, async_sessionmaker(engine, expire_on_commit=False)
+
+
+class TestFriendshipRequestAccept:
+    async def test_request_defaults_to_pending(self):
+        client = TestClient(app)
+        a = _register(client, "sg_fr_a1")
+        b = _register(client, "sg_fr_b1")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                fr = Friendship(requester_id=a, addressee_id=b)
+                session.add(fr)
+                await session.commit()
+                await session.refresh(fr)
+                assert fr.status == FriendshipStatus.PENDING
+                assert fr.requester_id == a
+                assert fr.addressee_id == b
+        finally:
+            await engine.dispose()
+
+    async def test_accept_updates_status(self):
+        client = TestClient(app)
+        a = _register(client, "sg_fr_a2")
+        b = _register(client, "sg_fr_b2")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                fr = Friendship(requester_id=a, addressee_id=b)
+                session.add(fr)
+                await session.commit()
+                fr_id = fr.id
+
+            async with factory() as session:
+                fr = await session.get(Friendship, fr_id)
+                fr.status = FriendshipStatus.ACCEPTED
+                await session.commit()
+
+            async with factory() as session:
+                fr = await session.get(Friendship, fr_id)
+                assert fr.status == FriendshipStatus.ACCEPTED
+        finally:
+            await engine.dispose()
+
+
+class TestUniquePairConstraints:
+    async def test_duplicate_friendship_pair_rejected(self):
+        client = TestClient(app)
+        a = _register(client, "sg_uq_fr_a")
+        b = _register(client, "sg_uq_fr_b")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                session.add(Friendship(requester_id=a, addressee_id=b))
+                await session.commit()
+
+            async with factory() as session:
+                session.add(Friendship(requester_id=a, addressee_id=b))
+                with pytest.raises(IntegrityError):
+                    await session.commit()
+        finally:
+            await engine.dispose()
+
+    async def test_duplicate_follow_pair_rejected(self):
+        client = TestClient(app)
+        a = _register(client, "sg_uq_fw_a")
+        b = _register(client, "sg_uq_fw_b")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                session.add(Follow(follower_id=a, followed_id=b))
+                await session.commit()
+
+            async with factory() as session:
+                session.add(Follow(follower_id=a, followed_id=b))
+                with pytest.raises(IntegrityError):
+                    await session.commit()
+        finally:
+            await engine.dispose()
+
+    async def test_duplicate_block_pair_rejected(self):
+        client = TestClient(app)
+        a = _register(client, "sg_uq_bl_a")
+        b = _register(client, "sg_uq_bl_b")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                session.add(Block(blocker_id=a, blocked_id=b))
+                await session.commit()
+
+            async with factory() as session:
+                session.add(Block(blocker_id=a, blocked_id=b))
+                with pytest.raises(IntegrityError):
+                    await session.commit()
+        finally:
+            await engine.dispose()
+
+
+class TestFollow:
+    async def test_create_follow(self):
+        client = TestClient(app)
+        a = _register(client, "sg_follow_a")
+        b = _register(client, "sg_follow_b")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                session.add(Follow(follower_id=a, followed_id=b))
+                await session.commit()
+
+            async with factory() as session:
+                rows = (await session.execute(
+                    select(Follow).where(Follow.follower_id == a, Follow.followed_id == b)
+                )).scalars().all()
+                assert len(rows) == 1
+        finally:
+            await engine.dispose()
+
+
+class TestBlock:
+    async def test_create_block(self):
+        client = TestClient(app)
+        a = _register(client, "sg_block_a")
+        b = _register(client, "sg_block_b")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                session.add(Block(blocker_id=a, blocked_id=b))
+                await session.commit()
+
+            async with factory() as session:
+                rows = (await session.execute(
+                    select(Block).where(Block.blocker_id == a, Block.blocked_id == b)
+                )).scalars().all()
+                assert len(rows) == 1
+        finally:
+            await engine.dispose()
+
+
+class TestCascadeDelete:
+    async def test_deleting_user_removes_rows_in_all_three_tables(self):
+        """Deleting a user removes friendships/follows/blocks referencing them
+        in *either* FK column, via the real DB ON DELETE CASCADE (deleted with
+        a Core statement, bypassing any ORM-level cascade, to prove the
+        database constraint itself does the job)."""
+        client = TestClient(app)
+        a = _register(client, "sg_cascade_a")
+        b = _register(client, "sg_cascade_b")
+        c = _register(client, "sg_cascade_c")
+
+        engine, factory = _session_factory()
+        try:
+            async with factory() as session:
+                # a as requester/follower/blocker, and also as addressee (c -> a)
+                session.add(Friendship(requester_id=a, addressee_id=b))
+                session.add(Friendship(requester_id=c, addressee_id=a))
+                session.add(Follow(follower_id=a, followed_id=b))
+                session.add(Follow(follower_id=c, followed_id=a))
+                session.add(Block(blocker_id=a, blocked_id=b))
+                session.add(Block(blocker_id=c, blocked_id=a))
+                await session.commit()
+
+            async with factory() as session:
+                await session.execute(delete(User).where(User.id == a))
+                await session.commit()
+
+            async with factory() as session:
+                friendships = (await session.execute(
+                    select(Friendship).where(
+                        (Friendship.requester_id == a) | (Friendship.addressee_id == a)
+                    )
+                )).scalars().all()
+                follows = (await session.execute(
+                    select(Follow).where(
+                        (Follow.follower_id == a) | (Follow.followed_id == a)
+                    )
+                )).scalars().all()
+                blocks = (await session.execute(
+                    select(Block).where(
+                        (Block.blocker_id == a) | (Block.blocked_id == a)
+                    )
+                )).scalars().all()
+                assert friendships == []
+                assert follows == []
+                assert blocks == []
+
+                # Unrelated rows (b, c only) survive.
+                remaining_users = (await session.execute(
+                    select(User.id).where(User.id.in_([b, c]))
+                )).scalars().all()
+                assert set(remaining_users) == {b, c}
+        finally:
+            await engine.dispose()

backend/tests/test_text_filter.py

@@ -0,0 +1,194 @@
+"""Unit tests for app.services.text_filter (docs/planning/social.md §4/§5 US-4).
+
+Pure, side-effect-free service -- no DB/Redis fixtures needed.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from app.services.text_filter import (
+    DEFAULT_TERMS_PATH,
+    FilterAction,
+    FilterMode,
+    FilterResult,
+    ListBasedTextFilter,
+    TextFilter,
+    default_text_filter,
+    load_terms,
+)
+
+
+@pytest.fixture
+def redact_filter() -> ListBasedTextFilter:
+    return ListBasedTextFilter(terms=["badword", "shoot"], mode=FilterMode.REDACT)
+
+
+@pytest.fixture
+def reject_filter() -> ListBasedTextFilter:
+    return ListBasedTextFilter(terms=["badword", "shoot"], mode=FilterMode.REJECT)
+
+
+class TestAllowPath:
+    def test_clean_text_is_allowed_unchanged(self, redact_filter: ListBasedTextFilter) -> None:
+        result = redact_filter.check("hello there, how are you today?")
+        assert result.action is FilterAction.ALLOW
+        assert result.filtered_text == "hello there, how are you today?"
+        assert result.matched_terms == ()
+
+    def test_message_with_no_matches(self, reject_filter: ListBasedTextFilter) -> None:
+        # Distinct from the clean-text case above: exercises the reject-mode
+        # filter's no-match path specifically (mode should not matter when
+        # nothing matches).
+        text = "let's meet at the plaza around noon"
+        result = reject_filter.check(text)
+        assert result.action is FilterAction.ALLOW
+        assert result.filtered_text == text
+        assert result.matched_terms == ()
+
+
+class TestRedactPath:
+    def test_exact_match_is_redacted(self, redact_filter: ListBasedTextFilter) -> None:
+        result = redact_filter.check("don't be a badword about it")
+        assert result.action is FilterAction.REDACT
+        assert result.matched_terms == ("badword",)
+        assert "badword" not in result.filtered_text
+        assert result.filtered_text == "don't be a ******* about it"
+
+    def test_multiple_distinct_matches(self, redact_filter: ListBasedTextFilter) -> None:
+        result = redact_filter.check("badword, don't shoot!")
+        assert result.action is FilterAction.REDACT
+        assert set(result.matched_terms) == {"badword", "shoot"}
+        assert "badword" not in result.filtered_text
+        assert "shoot" not in result.filtered_text
+        # Length is preserved (asterisks replace matched spans 1:1).
+        assert len(result.filtered_text) == len("badword, don't shoot!")
+
+    def test_redaction_char_is_configurable(self) -> None:
+        f = ListBasedTextFilter(terms=["badword"], mode=FilterMode.REDACT, redaction_char="#")
+        result = f.check("that's a badword thing to say")
+        assert result.filtered_text == "that's a ####### thing to say"
+
+
+class TestRejectPath:
+    def test_match_is_rejected_and_text_left_intact(self, reject_filter: ListBasedTextFilter) -> None:
+        text = "stop, badword!"
+        result = reject_filter.check(text)
+        assert result.action is FilterAction.REJECT
+        assert result.matched_terms == ("badword",)
+        # Reject mode does not mutate the text -- callers are expected to
+        # not store/deliver it at all, based on `action`.
+        assert result.filtered_text == text
+
+
+class TestNormalization:
+    def test_leetspeak_variant_is_caught(self, redact_filter: ListBasedTextFilter) -> None:
+        # "b4dw0rd" -> normalizes to "badword" via the leet map (4->a, 0->o).
+        result = redact_filter.check("you're being a b4dw0rd right now")
+        assert result.action is FilterAction.REDACT
+        assert result.matched_terms == ("badword",)
+
+    def test_separators_between_letters_are_stripped(self, redact_filter: ListBasedTextFilter) -> None:
+        result = redact_filter.check("that is b.a.d.w.o.r.d behavior")
+        assert result.action is FilterAction.REDACT
+        assert result.matched_terms == ("badword",)
+
+    def test_spacing_between_letters_is_stripped(self, redact_filter: ListBasedTextFilter) -> None:
+        result = redact_filter.check("b a d w o r d, seriously")
+        assert result.action is FilterAction.REDACT
+        assert result.matched_terms == ("badword",)
+
+    def test_case_folding(self, redact_filter: ListBasedTextFilter) -> None:
+        result = redact_filter.check("BADWORD in all caps")
+        assert result.action is FilterAction.REDACT
+        assert result.matched_terms == ("badword",)
+
+    def test_symbol_lookalikes(self) -> None:
+        # @ -> a, $ -> s: "@ss" should normalize to "ass".
+        f = ListBasedTextFilter(terms=["ass"], mode=FilterMode.REDACT)
+        result = f.check("what an @$$ move")
+        assert result.action is FilterAction.REDACT
+        assert result.matched_terms == ("ass",)
+
+
+class TestEmptyAndWhitespace:
+    def test_empty_string(self, redact_filter: ListBasedTextFilter) -> None:
+        result = redact_filter.check("")
+        assert result.action is FilterAction.ALLOW
+        assert result.filtered_text == ""
+        assert result.matched_terms == ()
+
+    def test_whitespace_only_string(self, redact_filter: ListBasedTextFilter) -> None:
+        text = "   \t\n  "
+        result = redact_filter.check(text)
+        assert result.action is FilterAction.ALLOW
+        assert result.filtered_text == text
+        assert result.matched_terms == ()
+
+    def test_punctuation_only_string_has_nothing_to_normalize(self, redact_filter: ListBasedTextFilter) -> None:
+        # No alnum characters survive normalization at all -- must not
+        # crash on an empty normalized string / empty index_map.
+        result = redact_filter.check("...!!!???")
+        assert result.action is FilterAction.ALLOW
+        assert result.matched_terms == ()
+
+
+class TestConfigurability:
+    def test_custom_term_list_is_used_instead_of_default(self) -> None:
+        f = ListBasedTextFilter(terms=["zzzcustomzzz"], mode=FilterMode.REDACT)
+        result = f.check("this contains zzzcustomzzz right here")
+        assert result.action is FilterAction.REDACT
+        assert result.matched_terms == ("zzzcustomzzz",)
+        # Default list terms should NOT match since we overrode the list.
+        result2 = f.check("this is fucking unrelated")
+        assert result2.action is FilterAction.ALLOW
+
+    def test_duplicate_and_blank_terms_are_deduped(self) -> None:
+        f = ListBasedTextFilter(terms=["badword", "badword", "  ", ""], mode=FilterMode.REDACT)
+        assert f._terms == ("badword",)
+
+    def test_default_terms_file_loads_and_is_nonempty(self) -> None:
+        terms = load_terms()
+        assert isinstance(terms, list)
+        assert len(terms) > 0
+        assert all(isinstance(t, str) and t for t in terms)
+
+    def test_default_terms_path_exists(self) -> None:
+        assert DEFAULT_TERMS_PATH.exists()
+        assert DEFAULT_TERMS_PATH.suffix == ".json"
+
+    def test_load_terms_from_explicit_path(self, tmp_path: Path) -> None:
+        custom = tmp_path / "custom_terms.json"
+        custom.write_text('{"terms": ["foo", "bar"]}', encoding="utf-8")
+        assert load_terms(custom) == ["foo", "bar"]
+
+    def test_default_text_filter_factory_matches_default_list(self) -> None:
+        f = default_text_filter(mode=FilterMode.REJECT)
+        result = f.check("that's fucking ridiculous")
+        assert result.action is FilterAction.REJECT
+        assert "fuck" in result.matched_terms
+
+
+class TestProtocol:
+    def test_list_based_filter_satisfies_text_filter_protocol(self, redact_filter: ListBasedTextFilter) -> None:
+        assert isinstance(redact_filter, TextFilter)
+
+    def test_check_returns_filter_result(self, redact_filter: ListBasedTextFilter) -> None:
+        result = redact_filter.check("hi")
+        assert isinstance(result, FilterResult)
+
+    def test_a_third_party_style_implementation_satisfies_the_protocol(self) -> None:
+        # Demonstrates the extension point: any object with a matching
+        # `check` method satisfies TextFilter without inheriting from
+        # anything -- this is how a future third-party provider would plug
+        # in without touching this module.
+        class AlwaysAllow:
+            def check(self, text: str) -> FilterResult:
+                return FilterResult(action=FilterAction.ALLOW, filtered_text=text, matched_terms=())
+
+        provider: TextFilter = AlwaysAllow()
+        assert isinstance(provider, TextFilter)
+        result = provider.check("anything at all, even fuck")
+        assert result.action is FilterAction.ALLOW

backend/tests/test_world_content.py

@@ -0,0 +1,490 @@
+"""Integration tests for the world content API: rooms + chunks.
+
+Covers docs/architecture/world_persistence_impl.md §8.1 (public router,
+app/routers/world_content.py) and §8.3 (internal router,
+app/routers/internal.py), plus the create_world -> auto "main" room
+behaviour (§4.1).
+
+Runs against the real ephemeral Postgres the hermetic conftest.py stands
+up -- these are full HTTP round trips through TestClient, not mocked.
+"""
+
+import base64
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.main import app
+from app.services import chunk_codec as cc
+from app.services.game_servers import supervisor
+
+GRID_32 = (32, 32, 1)
+
+
+def _auth(client: TestClient, name: str) -> tuple[dict, int]:
+    r = client.post("/api/auth/register", json={
+        "username": name, "email": f"{name}@e.com", "password": "secret123",
+        "date_of_birth": "1990-01-01",
+    })
+    assert r.status_code == 201, r.text
+    headers = {"Authorization": f"Bearer {r.json()['access_token']}"}
+    me = client.get("/api/users/me", headers=headers)
+    return headers, me.json()["id"]
+
+
+def _make_world(client: TestClient, headers: dict, visibility: str = "public") -> int:
+    r = client.post("/api/worlds/", headers=headers, json={"name": "W", "visibility": visibility})
+    assert r.status_code == 201, r.text
+    return r.json()["id"]
+
+
+def _build_chunk(world_id: int, slug: str, cx: int, cy: int, cz: int, *,
+                  grid=GRID_32, revision: int = 1, extra_tag: str = "") -> bytes:
+    """A small but structurally-real chunk payload for `world_id`/`slug`/coord,
+    sized to match the room's default 32x32x1 grid."""
+    w, h, d = grid
+    layer = cc.TileLayer(
+        name="ground", layer_id=0, width=w, height=h, depth=d,
+        palette=[cc.TileDef(id=0, asset_id="", solid=False, flags=0, variants=1)],
+        tiles=[0] * (w * h * d),
+    )
+    obj = cc.WorldObject(
+        id=f"obj_{extra_tag or '1'}", type="prop", asset_id="props/rock",
+        pos=(1.0, 1.0, 0.0), properties={"tag": extra_tag},
+    )
+    payload = cc.ChunkPayload(
+        world_id=str(world_id), room_id=slug, coord=(cx, cy, cz),
+        bounds=cc.ChunkBounds(min=(0.0, 0.0, 0.0), size=(float(w), float(h), float(d))),
+        tile_layers=[layer], objects=[obj], revision=revision, author="pytest",
+        created_at=1_700_000_000, updated_at=1_700_000_000,
+    )
+    return cc.encode_binary(payload)
+
+
+class TestCreateWorldMainRoom:
+    def test_create_world_auto_creates_main_room(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "cw_main")
+        wid = _make_world(client, headers)
+
+        r = client.get(f"/api/worlds/{wid}/rooms", headers=headers)
+        assert r.status_code == 200, r.text
+        rooms = r.json()
+        assert len(rooms) == 1
+        assert rooms[0]["slug"] == "main"
+        assert rooms[0]["name"] == "Main"
+        assert rooms[0]["chunk_count"] == 0
+        assert rooms[0]["grid"]["size"] == [32, 32, 1]
+
+
+class TestRoomAuth:
+    def test_create_room_requires_owner(self):
+        client = TestClient(app)
+        owner_headers, _ = _auth(client, "room_owner")
+        wid = _make_world(client, owner_headers)
+        other_headers, _ = _auth(client, "room_other")
+        r = client.post(f"/api/worlds/{wid}/rooms", headers=other_headers,
+                         json={"slug": "annex", "name": "Annex"})
+        assert r.status_code == 403
+
+    def test_list_rooms_of_private_world_is_404_for_non_owner(self):
+        client = TestClient(app)
+        owner_headers, _ = _auth(client, "room_priv_owner")
+        wid = _make_world(client, owner_headers, "private")
+        other_headers, _ = _auth(client, "room_priv_other")
+        r = client.get(f"/api/worlds/{wid}/rooms", headers=other_headers)
+        assert r.status_code == 404
+
+
+class TestChunkPutGetRoundTrip:
+    def test_binary_put_then_binary_get_round_trips(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_rt")
+        wid = _make_world(client, headers)
+        payload = _build_chunk(wid, "main", 0, 0, 0)
+
+        r = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/0/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        assert r.status_code == 200, r.text
+        body = r.json()
+        assert body["revision"] == 1
+        assert body["payload_len"] == len(payload)
+        assert body["checksum"] == cc.checksum(payload[cc.HEADER_SIZE:])
+        assert body["live_session"] is False
+
+        g = client.get(
+            f"/api/worlds/{wid}/rooms/main/chunks/0/0/0",
+            headers={**headers, "Accept": "application/octet-stream"},
+        )
+        assert g.status_code == 200
+        assert g.content == payload
+        assert g.headers["ETag"] == f'"{body["checksum"]}"'
+        assert g.headers["X-Chunk-Revision"] == "1"
+
+    def test_json_accept_returns_decoded_shape(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_json")
+        wid = _make_world(client, headers)
+        payload = _build_chunk(wid, "main", 1, 1, 0)
+        client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/1/1/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        g = client.get(
+            f"/api/worlds/{wid}/rooms/main/chunks/1/1/0",
+            headers={**headers, "Accept": "application/json"},
+        )
+        assert g.status_code == 200
+        data = g.json()
+        assert data["coord"] == {"cx": 1, "cy": 1, "cz": 0}
+        assert data["world_id"] == str(wid)
+        assert data["room_id"] == "main"
+        assert len(data["objects"]) == 1
+
+    def test_json_put_with_base64_payload(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_json_put")
+        wid = _make_world(client, headers)
+        payload = _build_chunk(wid, "main", 2, 2, 0)
+        r = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/2/2/0", headers=headers,
+            json={"base_revision": 0, "payload_b64": base64.b64encode(payload).decode()},
+        )
+        assert r.status_code == 200, r.text
+        assert r.json()["revision"] == 1
+
+    def test_if_none_match_returns_304(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_304")
+        wid = _make_world(client, headers)
+        payload = _build_chunk(wid, "main", 3, 3, 0)
+        put = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/3/3/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        checksum = put.json()["checksum"]
+        g = client.get(
+            f"/api/worlds/{wid}/rooms/main/chunks/3/3/0",
+            headers={**headers, "If-None-Match": f'"{checksum}"'},
+        )
+        assert g.status_code == 304
+
+    def test_unwritten_coordinate_is_404(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_404")
+        wid = _make_world(client, headers)
+        g = client.get(f"/api/worlds/{wid}/rooms/main/chunks/9/9/0", headers=headers)
+        assert g.status_code == 404
+
+
+class TestRevisionConflict:
+    def test_create_conflict_when_chunk_already_exists(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "conflict_create")
+        wid = _make_world(client, headers)
+        payload = _build_chunk(wid, "main", 4, 4, 0)
+        first = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/4/4/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        assert first.status_code == 200
+
+        second = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/4/4/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        assert second.status_code == 409
+        body = second.json()
+        assert body["detail"] == "revision conflict"
+        assert body["current_revision"] == 1
+
+    def test_stale_base_revision_conflict_reports_current_state(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "conflict_stale")
+        wid = _make_world(client, headers)
+        payload_v1 = _build_chunk(wid, "main", 5, 5, 0, revision=1)
+        client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/5/5/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload_v1,
+        )
+        payload_v2 = _build_chunk(wid, "main", 5, 5, 0, revision=2, extra_tag="v2")
+        r2 = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/5/5/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "1"},
+            content=payload_v2,
+        )
+        assert r2.status_code == 200
+        assert r2.json()["revision"] == 2
+
+        # Now retry with the now-stale base_revision=1 again.
+        payload_v3 = _build_chunk(wid, "main", 5, 5, 0, revision=3, extra_tag="v3")
+        stale = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/5/5/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "1"},
+            content=payload_v3,
+        )
+        assert stale.status_code == 409
+        body = stale.json()
+        assert body["current_revision"] == 2
+        assert body["current_checksum"] == r2.json()["checksum"]
+
+
+class TestBatchWrite:
+    def test_batch_put_all_succeed(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "batch_ok")
+        wid = _make_world(client, headers)
+        chunks = [
+            {"cx": cx, "cy": 0, "cz": 0, "base_revision": 0,
+             "payload_b64": base64.b64encode(_build_chunk(wid, "main", cx, 0, 0)).decode()}
+            for cx in (10, 11)
+        ]
+        r = client.put(f"/api/worlds/{wid}/rooms/main/chunks", headers=headers, json={"chunks": chunks})
+        assert r.status_code == 200, r.text
+        body = r.json()
+        assert len(body["chunks"]) == 2
+        assert all(c["revision"] == 1 for c in body["chunks"])
+
+        idx = client.get(f"/api/worlds/{wid}/rooms/main/chunks", headers=headers)
+        keys = {c["key"] for c in idx.json()["chunks"]}
+        assert f"{wid}:main:10:0:0" in keys
+        assert f"{wid}:main:11:0:0" in keys
+
+    def test_batch_put_is_all_or_nothing_on_conflict(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "batch_conflict")
+        wid = _make_world(client, headers)
+
+        # Pre-create one of the two coordinates so the batch's base_revision=0
+        # for it will conflict.
+        pre = _build_chunk(wid, "main", 20, 0, 0)
+        client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/20/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=pre,
+        )
+
+        chunks = [
+            {"cx": 21, "cy": 0, "cz": 0, "base_revision": 0,
+             "payload_b64": base64.b64encode(_build_chunk(wid, "main", 21, 0, 0)).decode()},
+            {"cx": 20, "cy": 0, "cz": 0, "base_revision": 0,  # conflicts: already exists at revision 1
+             "payload_b64": base64.b64encode(_build_chunk(wid, "main", 20, 0, 0, extra_tag="v2")).decode()},
+        ]
+        r = client.put(f"/api/worlds/{wid}/rooms/main/chunks", headers=headers, json={"chunks": chunks})
+        assert r.status_code == 409
+
+        # Nothing from this batch should have been persisted -- (21,0,0)
+        # must NOT exist even though it was valid and came first.
+        g = client.get(f"/api/worlds/{wid}/rooms/main/chunks/21/0/0", headers=headers)
+        assert g.status_code == 404
+
+
+class TestDelete:
+    def test_delete_then_get_is_404(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_delete")
+        wid = _make_world(client, headers)
+        payload = _build_chunk(wid, "main", 30, 0, 0)
+        client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/30/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        d = client.delete(f"/api/worlds/{wid}/rooms/main/chunks/30/0/0", headers=headers)
+        assert d.status_code == 204
+        g = client.get(f"/api/worlds/{wid}/rooms/main/chunks/30/0/0", headers=headers)
+        assert g.status_code == 404
+
+
+class TestRevisionsAndRollback:
+    def test_revisions_then_rollback(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_rollback")
+        wid = _make_world(client, headers)
+        v1 = _build_chunk(wid, "main", 40, 0, 0, revision=1)
+        r1 = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/40/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=v1,
+        )
+        v2 = _build_chunk(wid, "main", 40, 0, 0, revision=2, extra_tag="v2")
+        r2 = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/40/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "1"},
+            content=v2,
+        )
+        assert r2.status_code == 200
+
+        revs = client.get(f"/api/worlds/{wid}/rooms/main/chunks/40/0/0/revisions", headers=headers)
+        assert revs.status_code == 200
+        rev_numbers = [row["revision"] for row in revs.json()]
+        assert 1 in rev_numbers and 2 in rev_numbers
+
+        rb = client.post(
+            f"/api/worlds/{wid}/rooms/main/chunks/40/0/0/rollback",
+            headers=headers, json={"revision": 1},
+        )
+        assert rb.status_code == 200, rb.text
+        assert rb.json()["revision"] == 3  # a new revision, restoring v1's content
+        assert rb.json()["checksum"] == r1.json()["checksum"]
+
+    def test_revisions_requires_owner(self):
+        client = TestClient(app)
+        owner_headers, _ = _auth(client, "revisions_owner")
+        wid = _make_world(client, owner_headers)
+        payload = _build_chunk(wid, "main", 41, 0, 0)
+        client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/41/0/0",
+            headers={**owner_headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        other_headers, _ = _auth(client, "revisions_other")
+        r = client.get(f"/api/worlds/{wid}/rooms/main/chunks/41/0/0/revisions", headers=other_headers)
+        assert r.status_code == 403
+
+
+class TestValidationErrors:
+    def test_malformed_payload_is_422(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_malformed")
+        wid = _make_world(client, headers)
+        r = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/0/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=b"not a real chunk",
+        )
+        assert r.status_code == 422
+        assert r.json()["reason"] == "malformed"
+
+    def test_wrong_grid_size_is_422_layer_dims(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_layerdims")
+        wid = _make_world(client, headers)
+        # Room's default grid is 32x32x1; build a chunk sized for 4x4x1.
+        payload = _build_chunk(wid, "main", 0, 0, 0, grid=(4, 4, 1))
+        r = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/0/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        assert r.status_code == 422
+        assert r.json()["reason"] == "layer_dims"
+
+    def test_oversized_payload_is_413(self, monkeypatch):
+        from app.config import settings
+        monkeypatch.setattr(settings, "WORLD_CHUNK_MAX_PAYLOAD_BYTES", 10)
+        client = TestClient(app)
+        headers, _ = _auth(client, "chunk_413")
+        wid = _make_world(client, headers)
+        payload = _build_chunk(wid, "main", 0, 0, 0)
+        r = client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/0/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+        assert r.status_code == 413
+
+
+class TestInternalApi:
+    """docs/architecture/world_persistence_impl.md §7/§8.3. No real Godot
+    process is spawned in this test env (GAME_SERVERS_ENABLED=False); we
+    register a fake in-memory server entry with a known token to exercise
+    require_game_server without needing a live process."""
+
+    @pytest.fixture
+    def fake_server_token(self):
+        # NB: a class body can't read a same-named local from the
+        # enclosing function via `token = token` (class bodies use LOAD_NAME,
+        # which skips enclosing function scopes) -- use a literal instead.
+        world_id_str = "internal-test-world"
+
+        class _FakeSrv:
+            def alive(self_inner):
+                return True
+            token = "test-internal-token-12345"
+
+        supervisor._servers[world_id_str] = _FakeSrv()
+        yield _FakeSrv.token
+        supervisor._servers.pop(world_id_str, None)
+
+    def test_missing_token_is_401(self):
+        client = TestClient(app)
+        r = client.get("/api/internal/worlds/1/manifest")
+        assert r.status_code == 401
+
+    def test_wrong_token_is_403(self):
+        client = TestClient(app)
+        r = client.get(
+            "/api/internal/worlds/1/manifest",
+            headers={"Authorization": "Bearer not-the-real-token"},
+        )
+        assert r.status_code == 403
+
+    def test_valid_token_but_wrong_world_id_is_403(self, fake_server_token):
+        # The fake token is registered under world_id "internal-test-world";
+        # a request for a different world_id must not authenticate.
+        client = TestClient(app)
+        r = client.get(
+            "/api/internal/worlds/999999/manifest",
+            headers={"Authorization": f"Bearer {fake_server_token}"},
+        )
+        assert r.status_code == 403
+
+    def test_valid_token_reaches_manifest_for_real_world(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "internal_manifest")
+        wid = _make_world(client, headers)
+
+        class _FakeSrv:
+            def alive(self_inner):
+                return True
+            token = "another-real-token"
+
+        supervisor._servers[str(wid)] = _FakeSrv()
+        try:
+            r = client.get(
+                f"/api/internal/worlds/{wid}/manifest",
+                headers={"Authorization": "Bearer another-real-token"},
+            )
+            assert r.status_code == 200, r.text
+            body = r.json()
+            assert body["world_id"] == wid
+            assert len(body["rooms"]) == 1
+            assert body["rooms"][0]["slug"] == "main"
+        finally:
+            supervisor._servers.pop(str(wid), None)
+
+    def test_internal_chunk_fetch_returns_binary(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "internal_chunk")
+        wid = _make_world(client, headers)
+        payload = _build_chunk(wid, "main", 0, 0, 0)
+        client.put(
+            f"/api/worlds/{wid}/rooms/main/chunks/0/0/0",
+            headers={**headers, "Content-Type": "application/octet-stream", "X-Base-Revision": "0"},
+            content=payload,
+        )
+
+        class _FakeSrv:
+            def alive(self_inner):
+                return True
+            token = "internal-chunk-token"
+
+        supervisor._servers[str(wid)] = _FakeSrv()
+        try:
+            r = client.get(
+                f"/api/internal/worlds/{wid}/rooms/main/chunks/0/0/0",
+                headers={"Authorization": "Bearer internal-chunk-token"},
+            )
+            assert r.status_code == 200
+            assert r.content == payload
+        finally:
+            supervisor._servers.pop(str(wid), None)

backend/tests/test_world_join.py

@@ -0,0 +1,54 @@
+"""Tests for POST /api/worlds/{id}/join.
+
+The happy path spawns a real Godot process, so it's covered by a manual /
+checkpoint integration test, not here. These cover the envelope: auth,
+visibility, and the 503 when orchestration is disabled (the default).
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+def _auth(client: TestClient, name: str) -> tuple[dict, int]:
+    r = client.post("/api/auth/register", json={
+        "username": name, "email": f"{name}@e.com", "password": "secret123", "date_of_birth": "1990-01-01",
+    })
+    assert r.status_code == 201, r.text
+    headers = {"Authorization": f"Bearer {r.json()['access_token']}"}
+    me = client.get("/api/users/me", headers=headers)
+    return headers, me.json()["id"]
+
+
+def _make_world(client: TestClient, headers: dict, visibility: str = "public") -> int:
+    r = client.post("/api/worlds/", headers=headers, json={"name": "W", "visibility": visibility})
+    assert r.status_code == 201, r.text
+    return r.json()["id"]
+
+
+class TestJoinWorld:
+    def test_requires_auth(self):
+        client = TestClient(app)
+        assert client.post("/api/worlds/1/join").status_code == 401
+
+    def test_unknown_world_is_404(self):
+        client = TestClient(app)
+        headers, _ = _auth(client, "join_404")
+        assert client.post("/api/worlds/999999/join", headers=headers).status_code == 404
+
+    def test_private_world_of_another_user_is_404(self):
+        client = TestClient(app)
+        owner_headers, _ = _auth(client, "join_owner")
+        wid = _make_world(client, owner_headers, "private")
+        other_headers, _ = _auth(client, "join_other")
+        assert client.post(f"/api/worlds/{wid}/join", headers=other_headers).status_code == 404
+
+    def test_disabled_orchestration_returns_503(self):
+        # GAME_SERVERS_ENABLED defaults to False in tests.
+        client = TestClient(app)
+        headers, _ = _auth(client, "join_503")
+        wid = _make_world(client, headers, "public")
+        r = client.post(f"/api/worlds/{wid}/join", headers=headers)
+        assert r.status_code == 503
+        assert "not enabled" in r.json()["detail"]

docs/architecture/avatar.md

@@ -449,6 +449,37 @@ The catalog is a JSON manifest mapping asset ids to metadata and resource paths:
 
 ---
 
+## 9a. Loadout Persistence (implemented, PC3 Phase 1)
+
+**Storage.** One row per user in `avatar_loadouts` (`user_id` PK/FK,
+`data` JSONB, timestamps). The entire loadout is stored as a single JSON
+document in the exact shape the client's `AvatarLoadout.to_json()` emits
+(`{"base_body": str, "slots": {...}, "skin_tone"?: {r,g,b,a}}`) rather than
+exploded into columns.
+
+**Why one JSON blob, not columns.** The server has no copy of the asset
+catalog (`assets/avatars/catalog.json` ships with the client). It therefore
+cannot meaningfully validate *which* asset belongs in *which* slot, whether
+an asset exists, or slot-exclusivity rules — that validation stays on the
+client (`AvatarLoadout.validate()` against the loaded `AvatarCatalog`). The
+server enforces only the envelope: a JSON object with a non-empty string
+`base_body`, an object `slots`, and a sane size cap. Keeping the schema
+opaque to the server also means catalog/loadout-shape changes don't need a
+migration.
+
+**Endpoints** (`/api/avatar`, bearer auth):
+
+| Method | Path | Behaviour |
+|---|---|---|
+| `GET` | `/loadout` | The user's saved loadout, or the server default (`{"base_body": "base_human_male_01", "slots": {}}`, `is_default: true`) if they have never saved one. |
+| `PUT` | `/loadout` | Replace the user's loadout (full document, not a patch). |
+
+**Defaults.** A brand-new account has no row; `GET` returns
+`models.avatar_loadout.DEFAULT_LOADOUT` with `is_default: true` so the client
+can distinguish "never customised" from "customised back to the base look".
+
+---
+
 ## 10. Summary
 
 | Concern                | Decision                                              |

docs/architecture/content_moderation.md

@@ -227,18 +227,33 @@ An account has an **age verification status**:
 
 ### 5.2 Tier 1 — Self-Declaration Flow
 
+> **Implemented, PC3 Phase 3.** `POST /api/auth/register` now takes a real
+> `date_of_birth` (ISO `YYYY-MM-DD`), not the throwaway `over_18` boolean it
+> had before. The server computes age (`auth.calculate_age`) and rejects
+> anyone under `auth.MIN_AGE` (18) with a **403** — this platform is
+> adults-only, so there is no "minor, restricted" tier here (the 13+ rows
+> below are the general design, not the current gate). A future-in-the-past
+> or nonsensical date is a **400**. The DOB is stored on the user row and
+> surfaced only back to that user (`/api/auth/me`), never to other players.
+>
+> **Limitation, stated plainly:** this is still self-attested — a determined
+> user can enter a false DOB. It is a concrete, stored, legally-meaningful
+> data point (matching how most platforms gate before adding hard checks)
+> and the seam for Tier 2. Encryption-at-rest for the DOB column and the
+> Tier 2 ID-check hook below are **not yet implemented**.
+
 ```
 User submits { date_of_birth }
         │
         ▼
-Server validates format & plausibility (age 13–120, not in future)
+Server validates format & plausibility (real date, not in future)
         │
         ▼
 Compute age from DOB
         │
         ▼
-age >= 18 ──► status = self_declared (adult)
+age >= 18 ──► status = self_declared (adult)   ← the current gate
-age >= 13 ──► status = self_declared (minor, restricted)
+age >= 13 ──► status = self_declared (minor, restricted)   ← design only
 age <  13 ──► status = rejected (below minimum platform age)
 ```
 

docs/architecture/editor.md

@@ -4,6 +4,11 @@
 > **Owner:** Platform team
 > **Related:** World chunk data format & persistence, server authority + client
 > prediction, content moderation & age verification, avatar component system
+> **Note:** the recommendation here stands, but edits do **not** ride the
+> `request_chunk_edit` ENet RPC (§4.2, §7.4). Per
+> [`world_persistence_impl.md`](world_persistence_impl.md) the editor saves
+> chunks over HTTP to the FastAPI backend, which is the sole writer; the
+> validation/moderation boundary moves with it.
 > **Godot version:** 4.6.2 stable
 
 ## 1. Overview

docs/architecture/networking.md

@@ -237,6 +237,62 @@ snapshot_state:
 
 ---
 
+## 7a. Server Orchestration (implemented, PC3 Phase 2)
+
+**One dedicated server process per world**, spawned on demand.
+
+```
+client                    backend (single worker)              host
+  │  POST /api/worlds/{id}/join  (bearer JWT)                    │
+  │ ───────────────────────────▶ GameServerSupervisor           │
+  │                              ensure_server(world_id):        │
+  │                                if none running for world ─── spawn:
+  │                                                              godot --headless
+  │                                                              res://scenes/server.tscn --
+  │                                                              --port <p> --world <id>
+  │                                                              --status-file <path>
+  │  ◀─────────────────────────── { host, port, world_id }       │
+  │                                                              │
+  │  ENet connect  host:port ───────────────────────────────────▶ dedicated server
+```
+
+- **Supervisor** (`backend/app/services/game_servers.py`): in-process singleton,
+  so the backend MUST run single-worker. Keys servers by `world_id`. Allocates
+  ports from `GAME_SERVER_PORT_MIN..MAX`. A background reaper kills a world's
+  server once its **status file** (`{players, tick, updated}`, rewritten by the
+  server ~1×/s) reports `players == 0` for `GAME_SERVER_IDLE_TIMEOUT_SECONDS`.
+  No crash-restart — the next join respawns.
+- **Enable flag:** `GAME_SERVERS_ENABLED` (default off). The checkpoint/playtest
+  launcher (`pm/checkpoint_ops.py`) turns it on, passes `GODOT_BIN`,
+  `GAME_PROJECT_DIR`, and `GAME_SERVER_HOST` (the LAN IP baked into the `.exe`).
+  A backend with it off returns **503** from `/join`, and the client falls back
+  to local single-player.
+- **Per-world content:** all worlds currently load the same test level (M2/M7
+  work). `world_id` still scopes a distinct process + session.
+
+### 7b. Client play path
+
+`world_list.gd` → `POST /join` → `Session.begin(world_id, host, port)` →
+load `game.tscn`. `game.gd` sees `Session.active` and connects a
+`NetworkClient`:
+
+- **Local player** keeps predicting with its own collision-aware
+  `CharacterBody3D` (`player.gd`) — that *is* the prediction. Its input frame
+  (`player.net_input`) is forwarded to the server every physics tick.
+- **Correction backstop:** if the local position drifts from the server's by
+  more than `CORRECTION_THRESHOLD` (1.5 m — generous; catches teleport / a wall
+  walked through / real desync, not prediction noise) it snaps.
+- **Remote players:** rendered from snapshots, position lerped. *Appearance sync
+  is a follow-up* — remotes currently show as labelled capsules; the server
+  does not yet replicate avatar loadouts.
+- **Disconnect** → status message → back to the world list.
+
+The `NetworkClient`'s own flat-plane prediction + input-replay reconciliation
+(§5) is exercised by `smoke_test_network_client.gd`; the collision-aware game
+path above uses the lighter `send_input()` + drift-snap instead.
+
+---
+
 ## 8. Security & Anti-Cheat
 
 - **No client-authoritative gameplay values.** Clients only send *inputs* and