Add groups + group_members models and migration

docs/planning/social.md US-5 (task 13). Models + Alembic migration only,
per the sibling-dependency boundary with the Groups API task.

- groups: id, name, description, owner_id (FK users, ON DELETE SET NULL --
  a group is a durable multi-member community, so it and its full roster
  survive the owner deleting their account; the API task handles surfacing
  an ownerless group for reassignment).
- group_members: group_id/user_id (both FK, ON DELETE CASCADE -- pure
  join-table rows with no meaning without either side), role
  (owner/admin/member native enum, default member), joined_at, unique
  constraint on (group_id, user_id).
- User gets owned_groups / group_memberships relationships.
- tests/conftest.py TEST_TABLES updated for truncation between tests.
- New tests/test_group_models.py: role assignment, unique-membership
  rejection, group-delete cascade, member-delete cascade, and owner-delete
  SET NULL survival -- all verified against real Postgres.

Verified: upgrade/downgrade/upgrade round-trip, \d-inspected schema matches
spec (FKs, cascade behavior, unique constraint, indexes), full backend
suite 166 passed / 0 regressions.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y2FESCaMXeJpC9gSctiEeD

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/app/main.py

@@ -6,7 +6,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.config import settings
-from app.routers import auth, users, worlds, assets, avatar, world_content, internal
+from app.routers import auth, users, worlds, assets, avatar, world_content, internal, presence
 
 
 from app.services.game_servers import supervisor
@@ -44,6 +44,7 @@ app.include_router(world_content.router, prefix="/api/worlds", tags=["world-cont
 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.get("/api/health")

backend/app/models/__init__.py

@@ -4,8 +4,16 @@ 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
 
 __all__ = [
     "User", "Session", "World", "Asset", "AvatarLoadout",
     "WorldRoom", "WorldChunk", "WorldChunkRevision",
+    "Friendship", "Follow", "Block", "FriendshipStatus",
+    "Conversation", "ConversationParticipant", "Message", "MessageReport", "ReportStatus",
+    "Group", "GroupMember", "GroupRole",
 ]

backend/app/models/chat.py

@@ -0,0 +1,217 @@
+"""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)
+
+    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/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
 
@@ -20,6 +20,10 @@ 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")
@@ -31,6 +35,55 @@ class User(Base):
         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:
         """Return True if the user is 18 or older based on date_of_birth."""

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/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/tests/conftest.py

@@ -1,15 +1,18 @@
-"""Shared pytest fixtures + hermetic-DB bootstrap.
+"""Shared pytest fixtures + hermetic-DB/Redis bootstrap.
 
 The integration tests hit a real Postgres (Postgres-specific types: JSONB,
-native ENUMs). To make ``cd backend && pytest`` work from a clean checkout
+native ENUMs) and, for presence tests, a real Redis (TTL semantics aren't
-with no manual setup, ``pytest_configure`` below brings up an ephemeral
+worth faking). To make ``cd backend && pytest`` work from a clean checkout
-Postgres via docker compose and runs the migrations IF ``DATABASE_URL`` is
+with no manual setup, ``pytest_configure`` below brings up ephemeral
-not already pointing at a reachable database. When it is (dev loop, or the
+Postgres/Redis containers via docker compose and runs the migrations IF
-checkpoint runner which stands the DB up itself), that path is skipped and
+``DATABASE_URL``/``REDIS_URL`` aren't already pointing at something
-the existing database is reused.
+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.
 
-If Docker isn't available and no DB is reachable, the whole DB-backed suite
+If Docker isn't available and nothing is reachable, the whole
-is skipped with a clear message rather than erroring out 60+ times.
+DB/Redis-backed suite is skipped with a clear message rather than erroring
+out dozens of times.
 """
 
 import asyncio
@@ -38,14 +41,28 @@ TEST_TABLES = (
     # `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", "sessions", "refresh_tokens", "users",
+    "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]
 _COMPOSE_PROJECT = "agp-pytest"
 _EPHEMERAL_PG_PORT = 25432
+_EPHEMERAL_REDIS_PORT = 26379
 
-# Set by _ensure_database() when it starts a container it owns; torn down in
+# 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
@@ -64,6 +81,11 @@ def _db_reachable(url: str) -> bool:
     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)
 
@@ -71,14 +93,17 @@ def _run(cmd: list[str], **kw) -> subprocess.CompletedProcess:
 def pytest_configure(config):
     global _started_container, _db_unavailable_reason
 
-    if _db_reachable(settings.DATABASE_URL):
+    need_db = not _db_reachable(settings.DATABASE_URL)
-        return  # dev loop / checkpoint runner already provided one
+    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 and docker is unavailable -- run the "
+            "no reachable DATABASE_URL/REDIS_URL and docker is unavailable -- run "
-            "checkpoint suite (scripts/run_checkpoint_tests.py) or start Postgres "
+            "the checkpoint suite (scripts/run_checkpoint_tests.py) or start "
-            "manually"
+            "Postgres/Redis manually"
         )
         return
 
@@ -86,12 +111,16 @@ def pytest_configure(config):
     env["COMPOSE_PROJECT_NAME"] = _COMPOSE_PROJECT
     env["POSTGRES_HOST_PORT"] = str(_EPHEMERAL_PG_PORT)
     env["POSTGRES_PORT"] = str(_EPHEMERAL_PG_PORT)
-    up = _run(["docker", "compose", "up", "-d", "postgres"], env=env)
+    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 postgres failed:\n{up.stderr[-800:]}"
+        _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",
@@ -113,6 +142,24 @@ def pytest_configure(config):
                    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):
@@ -122,6 +169,7 @@ def pytest_unconfigure(config):
     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)
 
 

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_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_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_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()