feat(godot): discovery & home UI with search, categories, sorting, pagination, and world entry

backend/app/routers/discovery.py

@@ -10,18 +10,49 @@ from fastapi import APIRouter, Depends, Header, HTTPException, Query, Request, s
 from pydantic import BaseModel
 from sqlalchemy import func, select, update
 from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
 
 from app.database import get_db
 from app.dependencies import OptionalUser
 from app.models.world import World, WorldVisibility
 from app.models.world_visit import WorldVisit
+from app.services.trending import get_trending_subquery
+
 
 router = APIRouter()
 
 DbDep = Annotated[AsyncSession, Depends(get_db)]
 
 
+class WorldOwnerSummary(BaseModel):
+    id: int
+    username: str
+
+    model_config = {"from_attributes": True}
+
+
+class DiscoveredWorld(BaseModel):
+    id: int
+    name: str
+    description: str | None = None
+    category: str | None = None
+    tags: list[str] = []
+    play_count: int = 0
+    created_at: datetime | None = None
+    owner: WorldOwnerSummary
+
+    model_config = {"from_attributes": True}
+
+
+class DiscoveryListResponse(BaseModel):
+    items: list[DiscoveredWorld]
+    total: int
+    skip: int
+    limit: int
+
+
 class VisitRequest(BaseModel):
+
     anonymous_token: str | None = None
     idempotency_key: str | None = None
 
@@ -132,3 +163,98 @@ async def record_world_visit(
         play_count=world.play_count,
         last_played_at=world.last_played_at,
     )
+
+
+@router.get("/categories", response_model=list[str])
+async def list_categories(
+    db: DbDep,
+):
+    """List distinct categories of public worlds."""
+    res = await db.execute(
+        select(World.category)
+        .where(World.category.is_not(None), World.visibility == WorldVisibility.PUBLIC)
+        .distinct()
+        .order_by(World.category)
+    )
+    categories = [c for c in res.scalars().all() if c]
+    return categories
+
+
+@router.get("/worlds", response_model=DiscoveryListResponse)
+async def list_discovery_worlds(
+    db: DbDep,
+    current_user: OptionalUser = None,
+    q: str | None = Query(None, description="Substring search on world name"),
+    tags: list[str] | None = Query(None, description="Filter by tags"),
+    category: str | None = Query(None, description="Exact category filter"),
+    sort: str = Query("newest", description="Sort order (newest, most_played)"),
+    skip: int = Query(0, ge=0),
+    limit: int = Query(50, ge=1, le=100),
+):
+    """List public worlds for discovery with search, category/tag filters, and pagination."""
+    base_query = select(World).where(World.visibility == WorldVisibility.PUBLIC)
+
+    if q:
+        base_query = base_query.where(World.name.ilike(f"%{q}%"))
+
+    if category:
+        base_query = base_query.where(func.lower(World.category) == category.lower())
+
+    if tags:
+        parsed_tags = [t.strip() for item in tags for t in item.split(",") if t.strip()]
+        if parsed_tags:
+            base_query = base_query.where(World.tags.overlap(parsed_tags))
+
+    # Count total matching worlds
+    count_query = select(func.count()).select_from(base_query.subquery())
+    total = (await db.execute(count_query)).scalar_one()
+
+    # Sort
+    if sort == "trending":
+        trending_subq = get_trending_subquery()
+        base_query = (
+            base_query
+            .outerjoin(trending_subq, World.id == trending_subq.c.trending_world_id)
+            .order_by(
+                func.coalesce(trending_subq.c.trending_score, 0.0).desc(),
+                World.play_count.desc(),
+                World.created_at.desc(),
+            )
+        )
+    elif sort == "most_played":
+        base_query = base_query.order_by(World.play_count.desc(), World.created_at.desc())
+    else:  # default: newest
+        base_query = base_query.order_by(World.created_at.desc())
+
+
+    # Pagination & load owner
+    query = (
+        base_query
+        .offset(skip)
+        .limit(limit)
+        .options(selectinload(World.owner))
+    )
+    result = await db.execute(query)
+    worlds = result.scalars().all()
+
+    items = [
+        DiscoveredWorld(
+            id=w.id,
+            name=w.name,
+            description=w.description,
+            category=w.category,
+            tags=w.tags or [],
+            play_count=w.play_count,
+            created_at=w.created_at,
+            owner=WorldOwnerSummary(id=w.owner.id, username=w.owner.username),
+        )
+        for w in worlds
+    ]
+
+    return DiscoveryListResponse(
+        items=items,
+        total=total,
+        skip=skip,
+        limit=limit,
+    )
+

backend/app/services/trending.py

@@ -0,0 +1,34 @@
+"""Trending recommendation heuristic service.
+
+docs/planning/discovery.md (task 33706f401ad9).
+"""
+
+from sqlalchemy import case, func, select, text
+from app.models.world_visit import WorldVisit
+
+
+def get_trending_subquery(days: int = 7):
+    """Build a subquery that computes a decay-weighted trending score per world_id.
+
+    Decay weights:
+    - Visited within 24 hours: weight 3.0
+    - Visited within 3 days: weight 2.0
+    - Visited within 7 days: weight 1.0
+    """
+    trending_weight = case(
+        (WorldVisit.visited_at >= func.now() - text("interval '1 day'"), 3.0),
+        (WorldVisit.visited_at >= func.now() - text("interval '3 days'"), 2.0),
+        else_=1.0,
+    )
+
+    interval_str = f"interval '{days} days'"
+    subq = (
+        select(
+            WorldVisit.world_id.label("trending_world_id"),
+            func.coalesce(func.sum(trending_weight), 0.0).label("trending_score"),
+        )
+        .where(WorldVisit.visited_at >= func.now() - text(interval_str))
+        .group_by(WorldVisit.world_id)
+        .subquery("trending_scores")
+    )
+    return subq

backend/tests/test_discovery_browse_api.py

@@ -0,0 +1,188 @@
+"""API tests for discovery browse & search endpoints.
+
+docs/planning/discovery.md (task 300da1dcddf3).
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+def _register(client: TestClient, username: str) -> tuple[int, dict[str, str]]:
+    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 me.json()["id"], headers
+
+
+@pytest.mark.asyncio
+async def test_discovery_public_worlds_only_and_fields():
+    client = TestClient(app)
+    uid, headers = _register(client, "creator_browse_1")
+
+    # Create public world
+    pub_resp = client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={
+            "name": "Fantasy Kingdom",
+            "description": "A magical realm",
+            "visibility": "public",
+            "category": "RPG",
+            "tags": ["magic", "dragons"],
+        },
+    )
+    assert pub_resp.status_code == 201, pub_resp.text
+    pub_id = pub_resp.json()["id"]
+
+    # Create private world
+    priv_resp = client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={
+            "name": "Secret Base",
+            "description": "Classified",
+            "visibility": "private",
+            "category": "RPG",
+            "tags": ["secret"],
+        },
+    )
+    assert priv_resp.status_code == 201, priv_resp.text
+
+    # 1. Anonymous listing: only public world is returned
+    anon_resp = client.get("/api/discovery/worlds")
+    assert anon_resp.status_code == 200, anon_resp.text
+    data = anon_resp.json()
+    assert data["total"] >= 1
+    items = data["items"]
+    ids = [w["id"] for w in items]
+    assert pub_id in ids
+    assert priv_resp.json()["id"] not in ids
+
+    # Check fields of returned item
+    pub_item = next(w for w in items if w["id"] == pub_id)
+    assert pub_item["name"] == "Fantasy Kingdom"
+    assert pub_item["description"] == "A magical realm"
+    assert pub_item["category"] == "RPG"
+    assert "magic" in pub_item["tags"]
+    assert pub_item["play_count"] == 0
+    assert pub_item["owner"]["id"] == uid
+    assert pub_item["owner"]["username"] == "creator_browse_1"
+
+    # 2. Authenticated caller also does NOT see private worlds in discovery
+    auth_resp = client.get("/api/discovery/worlds", headers=headers)
+    assert auth_resp.status_code == 200
+    auth_ids = [w["id"] for w in auth_resp.json()["items"]]
+    assert priv_resp.json()["id"] not in auth_ids
+
+
+@pytest.mark.asyncio
+async def test_discovery_filtering_and_categories():
+    client = TestClient(app)
+    uid, headers = _register(client, "creator_filter_2")
+
+    # Create distinct worlds
+    client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={"name": "Cyber Arena", "visibility": "public", "category": "Action", "tags": ["pvp", "fps"]},
+    )
+    client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={"name": "Peaceful Meadow", "visibility": "public", "category": "Social", "tags": ["relax", "hangout"]},
+    )
+    client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={"name": "Cyber Hangout", "visibility": "public", "category": "Social", "tags": ["cyberpunk", "chat"]},
+    )
+
+    # Search by q
+    res_q = client.get("/api/discovery/worlds?q=cyber")
+    assert res_q.status_code == 200
+    names = [w["name"] for w in res_q.json()["items"]]
+    assert "Cyber Arena" in names
+    assert "Cyber Hangout" in names
+    assert "Peaceful Meadow" not in names
+
+    # Filter by category (case-insensitive)
+    res_cat = client.get("/api/discovery/worlds?category=action")
+    assert res_cat.status_code == 200
+    names = [w["name"] for w in res_cat.json()["items"]]
+    assert "Cyber Arena" in names
+    assert "Peaceful Meadow" not in names
+
+    # Filter by tags (overlap)
+    res_tags = client.get("/api/discovery/worlds?tags=relax,pvp")
+    assert res_tags.status_code == 200
+    names = [w["name"] for w in res_tags.json()["items"]]
+    assert "Peaceful Meadow" in names
+    assert "Cyber Arena" in names
+    assert "Cyber Hangout" not in names
+
+    # Get distinct categories
+    res_cats = client.get("/api/discovery/categories")
+    assert res_cats.status_code == 200
+    cats = res_cats.json()
+    assert "Action" in cats
+    assert "Social" in cats
+
+
+@pytest.mark.asyncio
+async def test_discovery_sorting_and_pagination():
+    client = TestClient(app)
+    uid, headers = _register(client, "creator_sort_3")
+
+    w1 = client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={"name": "Sort World 1", "visibility": "public"},
+    ).json()
+    w2 = client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={"name": "Sort World 2", "visibility": "public"},
+    ).json()
+
+    # Record visits on w1 so play_count = 1
+    v_res = client.post(f"/api/discovery/worlds/{w1['id']}/visit")
+    assert v_res.status_code == 200
+
+    # Sort by most_played
+    res_mp = client.get("/api/discovery/worlds?sort=most_played")
+    assert res_mp.status_code == 200
+    items = res_mp.json()["items"]
+    # w1 should come before w2
+    idx_w1 = next(i for i, w in enumerate(items) if w["id"] == w1["id"])
+    idx_w2 = next(i for i, w in enumerate(items) if w["id"] == w2["id"])
+    assert idx_w1 < idx_w2
+
+    # Sort by newest (default)
+    res_new = client.get("/api/discovery/worlds?sort=newest")
+    assert res_new.status_code == 200
+    items_new = res_new.json()["items"]
+    idx_w1_n = next(i for i, w in enumerate(items_new) if w["id"] == w1["id"])
+    idx_w2_n = next(i for i, w in enumerate(items_new) if w["id"] == w2["id"])
+    # w2 was created after w1, so w2 is newer
+    assert idx_w2_n < idx_w1_n
+
+    # Pagination: limit 1, skip 0
+    p1 = client.get("/api/discovery/worlds?limit=1&skip=0")
+    assert p1.status_code == 200
+    assert len(p1.json()["items"]) == 1
+    assert p1.json()["total"] >= 2
+    assert p1.json()["skip"] == 0
+    assert p1.json()["limit"] == 1

backend/tests/test_discovery_trending.py

@@ -0,0 +1,103 @@
+"""API and heuristic tests for trending discovery sort.
+
+docs/planning/discovery.md (task 33706f401ad9).
+"""
+
+from datetime import datetime, timedelta, timezone
+import pytest
+from fastapi.testclient import TestClient
+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.world_visit import WorldVisit
+
+
+def _register(client: TestClient, username: str) -> tuple[int, dict[str, str]]:
+    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 me.json()["id"], headers
+
+
+def _session_factory():
+    engine = create_async_engine(settings.DATABASE_URL, poolclass=NullPool)
+    return engine, async_sessionmaker(engine, expire_on_commit=False)
+
+
+@pytest.mark.asyncio
+async def test_trending_sort_heuristic_and_zero_visits():
+    client = TestClient(app)
+    uid, headers = _register(client, "creator_trending_1")
+
+    # Create 3 worlds
+    wA = client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={"name": "Trending Hot World", "visibility": "public", "category": "Action"},
+    ).json()
+    wB = client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={"name": "Older Mild World", "visibility": "public", "category": "Action"},
+    ).json()
+    wC = client.post(
+        "/api/worlds/",
+        headers=headers,
+        json={"name": "Zero Visit World", "visibility": "public", "category": "Action"},
+    ).json()
+
+    engine, sf = _session_factory()
+    now = datetime.now(timezone.utc)
+    try:
+        async with sf() as session:
+            # World A: 3 visits within last 2 hours (weight 3 each = score 9)
+            for i in range(3):
+                session.add(
+                    WorldVisit(
+                        world_id=wA["id"],
+                        anonymous_token=f"hot_visitor_{i}",
+                        visited_at=now - timedelta(hours=1, minutes=i),
+                    )
+                )
+            # World B: 1 visit 5 days ago (weight 1 = score 1)
+            session.add(
+                WorldVisit(
+                    world_id=wB["id"],
+                    anonymous_token="old_visitor",
+                    visited_at=now - timedelta(days=5),
+                )
+            )
+            # World C: zero visits
+            await session.commit()
+    finally:
+        await engine.dispose()
+
+    # Query with sort=trending
+    resp = client.get("/api/discovery/worlds?sort=trending&category=Action")
+    assert resp.status_code == 200, resp.text
+    items = resp.json()["items"]
+
+    # Verify order: wA should be first, wB second, wC third
+    ids = [item["id"] for item in items]
+    assert wA["id"] in ids
+    assert wB["id"] in ids
+    assert wC["id"] in ids
+
+    idxA = ids.index(wA["id"])
+    idxB = ids.index(wB["id"])
+    idxC = ids.index(wC["id"])
+
+    assert idxA < idxB < idxC, f"Expected order A ({idxA}) < B ({idxB}) < C ({idxC})"

scenes/discovery_ui.tscn

@@ -0,0 +1,150 @@
+[gd_scene load_steps=2 format=3]
+
+[ext_resource type="Script" path="res://scripts/discovery_ui.gd" id="1_disc"]
+
+[node name="DiscoveryUI" type="Control"]
+layout_mode = 3
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+script = ExtResource("1_disc")
+
+[node name="VBox" type="VBoxContainer" parent="."]
+layout_mode = 1
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+offset_left = 32.0
+offset_top = 24.0
+offset_right = -32.0
+offset_bottom = -24.0
+grow_horizontal = 2
+grow_vertical = 2
+theme_override_constants/separation = 12
+
+[node name="Header" type="HBoxContainer" parent="VBox"]
+layout_mode = 2
+theme_override_constants/separation = 16
+
+[node name="BackButton" type="Button" parent="VBox/Header"]
+custom_minimum_size = Vector2(100, 36)
+layout_mode = 2
+text = "< Back"
+
+[node name="TitleLabel" type="Label" parent="VBox/Header"]
+layout_mode = 2
+size_flags_horizontal = 3
+theme_override_font_sizes/font_size = 26
+text = "Discover Experiences"
+horizontal_alignment = 1
+
+[node name="RefreshButton" type="Button" parent="VBox/Header"]
+custom_minimum_size = Vector2(100, 36)
+layout_mode = 2
+text = "Refresh"
+
+[node name="StatusLabel" type="Label" parent="VBox"]
+visible = false
+layout_mode = 2
+theme_override_colors/font_color = Color(1, 0.3, 0.3, 1)
+text = ""
+
+[node name="Filters" type="HBoxContainer" parent="VBox"]
+layout_mode = 2
+theme_override_constants/separation = 10
+
+[node name="SearchEdit" type="LineEdit" parent="VBox/Filters"]
+custom_minimum_size = Vector2(240, 36)
+layout_mode = 2
+placeholder_text = "Search by name or tag..."
+
+[node name="CategoryOption" type="OptionButton" parent="VBox/Filters"]
+custom_minimum_size = Vector2(160, 36)
+layout_mode = 2
+
+[node name="SortOption" type="OptionButton" parent="VBox/Filters"]
+custom_minimum_size = Vector2(140, 36)
+layout_mode = 2
+
+[node name="FilterButton" type="Button" parent="VBox/Filters"]
+custom_minimum_size = Vector2(90, 36)
+layout_mode = 2
+text = "Filter"
+
+[node name="Content" type="Control" parent="VBox"]
+layout_mode = 2
+size_flags_vertical = 3
+
+[node name="LoadingLabel" type="Label" parent="VBox/Content"]
+visible = false
+layout_mode = 1
+anchors_preset = 14
+anchor_top = 0.5
+anchor_right = 1.0
+anchor_bottom = 0.5
+offset_top = -12.0
+offset_bottom = 12.0
+text = "Loading experiences..."
+horizontal_alignment = 1
+
+[node name="ErrorLabel" type="Label" parent="VBox/Content"]
+visible = false
+layout_mode = 1
+anchors_preset = 14
+anchor_top = 0.5
+anchor_right = 1.0
+anchor_bottom = 0.5
+offset_top = -12.0
+offset_bottom = 12.0
+theme_override_colors/font_color = Color(1, 0.4, 0.4, 1)
+text = ""
+horizontal_alignment = 1
+
+[node name="EmptyLabel" type="Label" parent="VBox/Content"]
+visible = false
+layout_mode = 1
+anchors_preset = 14
+anchor_top = 0.5
+anchor_right = 1.0
+anchor_bottom = 0.5
+offset_top = -12.0
+offset_bottom = 12.0
+theme_override_colors/font_color = Color(0.7, 0.7, 0.7, 1)
+text = "No experiences found."
+horizontal_alignment = 1
+
+[node name="Scroll" type="ScrollContainer" parent="VBox/Content"]
+layout_mode = 1
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+
+[node name="WorldsVBox" type="VBoxContainer" parent="VBox/Content/Scroll"]
+layout_mode = 2
+size_flags_horizontal = 3
+size_flags_vertical = 3
+theme_override_constants/separation = 10
+
+[node name="Pagination" type="HBoxContainer" parent="VBox"]
+layout_mode = 2
+theme_override_constants/separation = 16
+alignment = 1
+
+[node name="PrevButton" type="Button" parent="VBox/Pagination"]
+custom_minimum_size = Vector2(90, 32)
+layout_mode = 2
+text = "< Prev"
+
+[node name="PageLabel" type="Label" parent="VBox/Pagination"]
+layout_mode = 2
+text = "Page 1 of 1"
+horizontal_alignment = 1
+
+[node name="NextButton" type="Button" parent="VBox/Pagination"]
+custom_minimum_size = Vector2(90, 32)
+layout_mode = 2
+text = "Next >"

scripts/api_client.gd

@@ -456,6 +456,31 @@ func report_message(message_id: int, conversation_type: String, reason: String,
 	return await SocialApiClient.report_message(self, message_id, conversation_type, reason, context_text)
 
 
+# ---------------------------------------------------------------------------
+# Discovery Features
+# ---------------------------------------------------------------------------
+
+## List public worlds for discovery with optional search, tags, category, and sort.
+func get_discovery_worlds(
+	q: String = "",
+	tags: Array = [],
+	category: String = "",
+	sort: String = "newest",
+	skip: int = 0,
+	limit: int = 50
+) -> Dictionary:
+	return await DiscoveryApiClient.get_worlds(self, q, tags, category, sort, skip, limit)
+
+## Get distinct categories of public worlds.
+func get_discovery_categories() -> Dictionary:
+	return await DiscoveryApiClient.get_categories(self)
+
+## Record a visit to a world.
+func record_world_visit(world_id: int, anonymous_token: String = "") -> Dictionary:
+	return await DiscoveryApiClient.record_visit(self, world_id, anonymous_token)
+
+
+
 
 # ---------------------------------------------------------------------------
 # Internals

scripts/discovery_api_client.gd

@@ -0,0 +1,140 @@
+extends RefCounted
+class_name DiscoveryApiClient
+## Helper client for AGP Discovery REST endpoints (Browse, Search, Categories, Visit tracking).
+##
+## docs/planning/discovery.md (task 56c49440d0a6).
+
+class WorldSummary extends RefCounted:
+	var id: int = 0
+	var name: String = ""
+	var description: String = ""
+	var category: String = ""
+	var tags: Array = []
+	var play_count: int = 0
+	var created_at: String = ""
+	var owner_id: int = 0
+	var owner_username: String = ""
+
+	static func from_dict(d: Dictionary) -> WorldSummary:
+		var w := WorldSummary.new()
+		w.id = int(d.get("id", 0))
+		w.name = str(d.get("name", ""))
+		w.description = str(d.get("description", "")) if d.get("description") != null else ""
+		w.category = str(d.get("category", "")) if d.get("category") != null else ""
+		var raw_tags = d.get("tags", [])
+		w.tags = raw_tags if raw_tags is Array else []
+		w.play_count = int(d.get("play_count", 0))
+		w.created_at = str(d.get("created_at", "")) if d.get("created_at") != null else ""
+		var owner: Dictionary = d.get("owner", {}) if d.get("owner") is Dictionary else {}
+		w.owner_id = int(owner.get("id", 0))
+		w.owner_username = str(owner.get("username", ""))
+		return w
+
+
+class DiscoveryResult extends RefCounted:
+	var items: Array[WorldSummary] = []
+	var total: int = 0
+	var skip: int = 0
+	var limit: int = 50
+
+	static func from_dict(d: Dictionary) -> DiscoveryResult:
+		var res := DiscoveryResult.new()
+		res.total = int(d.get("total", 0))
+		res.skip = int(d.get("skip", 0))
+		res.limit = int(d.get("limit", 50))
+		var raw_items = d.get("items", [])
+		if raw_items is Array:
+			for item in raw_items:
+				if item is Dictionary:
+					res.items.append(WorldSummary.from_dict(item))
+		return res
+
+
+static func get_api_client(node: Node) -> Node:
+	if node.has_node("/root/ApiClient"):
+		return node.get_node("/root/ApiClient")
+	return null
+
+
+## Fetch worlds with search, tags, category filter, sort, and pagination.
+## Attaches JWT token if client has one; works anonymously without token.
+## Surfaces transport/HTTP errors in the standard result dictionary.
+static func get_worlds(
+	api: Node,
+	q: String = "",
+	tags: Array = [],
+	category: String = "",
+	sort: String = "newest",
+	skip: int = 0,
+	limit: int = 50
+) -> Dictionary:
+	var params: Array[String] = []
+	if q != "":
+		params.append("q=" + q.uri_encode())
+	if tags.size() > 0:
+		var tag_strs: Array[String] = []
+		for t in tags:
+			tag_strs.append(str(t))
+		params.append("tags=" + ",".join(tag_strs).uri_encode())
+	if category != "":
+		params.append("category=" + category.uri_encode())
+	if sort != "":
+		params.append("sort=" + sort.uri_encode())
+	params.append("skip=%d" % skip)
+	params.append("limit=%d" % limit)
+
+	var url := "/api/discovery/worlds"
+	if params.size() > 0:
+		url += "?" + "&".join(params)
+
+	var custom_headers := PackedStringArray()
+	if api != null and api.has_method("has_token") and api.has_token():
+		custom_headers.append("Authorization: " + api.bearer_token)
+
+	var res: Dictionary = await api.request(
+		HTTPClient.METHOD_GET,
+		url,
+		"",
+		"application/json",
+		false,
+		custom_headers
+	)
+	if res.ok and res.data is Dictionary:
+		res["parsed"] = DiscoveryResult.from_dict(res.data)
+	return res
+
+
+## Fetch distinct categories of public worlds.
+static func get_categories(api: Node) -> Dictionary:
+	var custom_headers := PackedStringArray()
+	if api != null and api.has_method("has_token") and api.has_token():
+		custom_headers.append("Authorization: " + api.bearer_token)
+
+	return await api.request(
+		HTTPClient.METHOD_GET,
+		"/api/discovery/categories",
+		"",
+		"application/json",
+		false,
+		custom_headers
+	)
+
+
+## Record a visit to a world. Supports optional anonymous token or logged in user.
+static func record_visit(api: Node, world_id: int, anonymous_token: String = "") -> Dictionary:
+	var custom_headers := PackedStringArray()
+	if api != null and api.has_method("has_token") and api.has_token():
+		custom_headers.append("Authorization: " + api.bearer_token)
+
+	var payload := {}
+	if anonymous_token != "":
+		payload["anonymous_token"] = anonymous_token
+
+	return await api.request(
+		HTTPClient.METHOD_POST,
+		"/api/discovery/worlds/%d/visit" % world_id,
+		JSON.stringify(payload) if payload.size() > 0 else "",
+		"application/json",
+		false,
+		custom_headers
+	)

scripts/discovery_ui.gd

@@ -0,0 +1,376 @@
+extends Control
+class_name DiscoveryUI
+## Discovery & Home Screen for browsing, searching, and entering experiences.
+##
+## docs/planning/discovery.md (task b77bddf31ba5).
+
+signal back_requested
+signal world_selected(world_id: int)
+signal worlds_loaded(count: int)
+
+@onready var back_button: Button = $VBox/Header/BackButton
+@onready var refresh_button: Button = $VBox/Header/RefreshButton
+@onready var status_label: Label = $VBox/StatusLabel
+
+# Filter Controls
+@onready var search_edit: LineEdit = $VBox/Filters/SearchEdit
+@onready var category_option: OptionButton = $VBox/Filters/CategoryOption
+@onready var sort_option: OptionButton = $VBox/Filters/SortOption
+@onready var filter_button: Button = $VBox/Filters/FilterButton
+
+# Content
+@onready var loading_label: Label = $VBox/Content/LoadingLabel
+@onready var error_label: Label = $VBox/Content/ErrorLabel
+@onready var empty_label: Label = $VBox/Content/EmptyLabel
+@onready var worlds_container: VBoxContainer = $VBox/Content/Scroll/WorldsVBox
+
+# Pagination
+@onready var prev_button: Button = $VBox/Pagination/PrevButton
+@onready var next_button: Button = $VBox/Pagination/NextButton
+@onready var page_label: Label = $VBox/Pagination/PageLabel
+
+var _api_client: Node = null
+var _current_page: int = 0
+var _page_size: int = 10
+var _total_count: int = 0
+var _loaded_worlds: Array[DiscoveryApiClient.WorldSummary] = []
+
+
+func _ready() -> void:
+	_api_client = _get_api()
+	_wire_signals()
+	_setup_sort_options()
+	_setup_initial_ui_state()
+
+	# Populate categories then load initial worlds feed
+	await load_categories()
+	await load_worlds(0)
+
+
+func _get_api() -> Node:
+	if has_node("/root/ApiClient"):
+		return get_node("/root/ApiClient")
+	var api_script = load("res://scripts/api_client.gd")
+	if api_script:
+		var api = api_script.new()
+		add_child(api)
+		return api
+	return null
+
+
+func _setup_initial_ui_state() -> void:
+	if loading_label: loading_label.visible = false
+	if error_label: error_label.visible = false
+	if empty_label: empty_label.visible = false
+	if prev_button: prev_button.disabled = true
+	if next_button: next_button.disabled = true
+	if page_label: page_label.text = "Page 1"
+
+
+func _setup_sort_options() -> void:
+	if not sort_option:
+		return
+	sort_option.clear()
+	sort_option.add_item("Newest", 0)
+	sort_option.add_item("Most Played", 1)
+	sort_option.add_item("Trending", 2)
+	sort_option.selected = 0
+
+
+func _wire_signals() -> void:
+	if back_button and not back_button.pressed.is_connected(_on_back_pressed):
+		back_button.pressed.connect(_on_back_pressed)
+	if refresh_button and not refresh_button.pressed.is_connected(_on_refresh_pressed):
+		refresh_button.pressed.connect(_on_refresh_pressed)
+	if filter_button and not filter_button.pressed.is_connected(_on_filter_pressed):
+		filter_button.pressed.connect(_on_filter_pressed)
+	if search_edit and not search_edit.text_submitted.is_connected(_on_search_submitted):
+		search_edit.text_submitted.connect(_on_search_submitted)
+	if category_option and not category_option.item_selected.is_connected(_on_category_selected):
+		category_option.item_selected.connect(_on_category_selected)
+	if sort_option and not sort_option.item_selected.is_connected(_on_sort_selected):
+		sort_option.item_selected.connect(_on_sort_selected)
+	if prev_button and not prev_button.pressed.is_connected(_on_prev_page_pressed):
+		prev_button.pressed.connect(_on_prev_page_pressed)
+	if next_button and not next_button.pressed.is_connected(_on_next_page_pressed):
+		next_button.pressed.connect(_on_next_page_pressed)
+
+
+func load_categories() -> void:
+	if not category_option:
+		return
+	category_option.clear()
+	category_option.add_item("All Categories", 0)
+
+	if _api_client == null:
+		return
+
+	var res: Dictionary = await DiscoveryApiClient.get_categories(_api_client)
+	if res.ok and res.data is Array:
+		var idx := 1
+		for cat in res.data:
+			var cat_str := str(cat).strip_edges()
+			if cat_str != "":
+				category_option.add_item(cat_str, idx)
+				idx += 1
+
+
+func load_worlds(page: int = 0) -> void:
+	_current_page = page
+	if loading_label: loading_label.visible = true
+	if error_label: error_label.visible = false
+	if empty_label: empty_label.visible = false
+
+	var q := search_edit.text.strip_edges() if search_edit else ""
+	var category := ""
+	if category_option and category_option.selected > 0:
+		category = category_option.get_item_text(category_option.selected)
+
+	var sort := "newest"
+	if sort_option:
+		match sort_option.selected:
+			0: sort = "newest"
+			1: sort = "most_played"
+			2: sort = "trending"
+
+	var skip := _current_page * _page_size
+	var res: Dictionary = await DiscoveryApiClient.get_worlds(
+		_api_client,
+		q,
+		[],
+		category,
+		sort,
+		skip,
+		_page_size
+	)
+
+	if loading_label: loading_label.visible = false
+
+	if not res.ok:
+		if error_label:
+			error_label.text = "Error: %s" % res.detail
+			error_label.visible = true
+		_clear_container()
+		return
+
+	var parsed: DiscoveryApiClient.DiscoveryResult = res.get("parsed")
+	if parsed == null and res.data is Dictionary:
+		parsed = DiscoveryApiClient.DiscoveryResult.from_dict(res.data)
+
+	if parsed == null:
+		if error_label:
+			error_label.text = "Invalid discovery response"
+			error_label.visible = true
+		_clear_container()
+		return
+
+	_total_count = parsed.total
+	_loaded_worlds = parsed.items
+
+	_render_worlds(_loaded_worlds)
+	_update_pagination()
+	worlds_loaded.emit(_loaded_worlds.size())
+
+
+func _clear_container() -> void:
+	if not worlds_container:
+		return
+	for c in worlds_container.get_children():
+		worlds_container.remove_child(c)
+		c.queue_free()
+
+
+func _render_worlds(worlds: Array[DiscoveryApiClient.WorldSummary]) -> void:
+	_clear_container()
+
+	if worlds.is_empty():
+		if empty_label:
+			empty_label.text = "No experiences found matching your criteria."
+			empty_label.visible = true
+		return
+
+	if empty_label: empty_label.visible = false
+
+	for world in worlds:
+		var card := _create_world_card(world)
+		worlds_container.add_child(card)
+
+
+func _create_world_card(world: DiscoveryApiClient.WorldSummary) -> Control:
+	var panel := PanelContainer.new()
+	panel.size_flags_horizontal = Control.SIZE_EXPAND_FILL
+	panel.custom_minimum_size = Vector2(0, 90)
+
+	var style := StyleBoxFlat.new()
+	style.bg_color = Color(0.14, 0.16, 0.20, 1.0)
+	style.corner_radius_top_left = 6
+	style.corner_radius_top_right = 6
+	style.corner_radius_bottom_left = 6
+	style.corner_radius_bottom_right = 6
+	style.content_margin_left = 16
+	style.content_margin_right = 16
+	style.content_margin_top = 10
+	style.content_margin_bottom = 10
+	panel.add_theme_stylebox_override("panel", style)
+
+	var vbox := VBoxContainer.new()
+	vbox.size_flags_horizontal = Control.SIZE_EXPAND_FILL
+	vbox.add_theme_constant_override("separation", 4)
+	panel.add_child(vbox)
+
+	# Title & Category Row
+	var title_row := HBoxContainer.new()
+	var name_label := Label.new()
+	name_label.text = world.name
+	name_label.add_theme_font_size_override("font_size", 18)
+	name_label.add_theme_color_override("font_color", Color(1.0, 1.0, 1.0, 1.0))
+	title_row.add_child(name_label)
+
+	if world.category != "":
+		var cat_label := Label.new()
+		cat_label.text = "  [%s]" % world.category
+		cat_label.add_theme_font_size_override("font_size", 14)
+		cat_label.add_theme_color_override("font_color", Color(0.4, 0.7, 1.0, 1.0))
+		title_row.add_child(cat_label)
+
+	var spacer := Control.new()
+	spacer.size_flags_horizontal = Control.SIZE_EXPAND_FILL
+	title_row.add_child(spacer)
+
+	# Enter World Button
+	var enter_button := Button.new()
+	enter_button.text = "Enter World"
+	enter_button.custom_minimum_size = Vector2(110, 30)
+	enter_button.pressed.connect(_on_enter_world_pressed.bind(world.id, enter_button))
+	title_row.add_child(enter_button)
+	vbox.add_child(title_row)
+
+	# Description
+	var desc_label := Label.new()
+	desc_label.text = world.description if world.description != "" else "No description provided."
+	desc_label.autowrap_mode = TextServer.AUTOWRAP_WORD
+	desc_label.add_theme_font_size_override("font_size", 13)
+	desc_label.add_theme_color_override("font_color", Color(0.75, 0.75, 0.75, 1.0))
+	vbox.add_child(desc_label)
+
+	# Metadata Row: Tags, Plays, Owner
+	var meta_row := HBoxContainer.new()
+	meta_row.add_theme_constant_override("separation", 16)
+
+	var play_label := Label.new()
+	play_label.text = "%d plays" % world.play_count
+	play_label.add_theme_font_size_override("font_size", 12)
+	play_label.add_theme_color_override("font_color", Color(0.6, 0.9, 0.6, 1.0))
+	meta_row.add_child(play_label)
+
+	if world.tags.size() > 0:
+		var tags_str: String = ""
+		for t in world.tags:
+			tags_str += "#" + str(t) + " "
+		var tags_label := Label.new()
+		tags_label.text = tags_str.strip_edges()
+		tags_label.add_theme_font_size_override("font_size", 12)
+		tags_label.add_theme_color_override("font_color", Color(0.8, 0.7, 0.4, 1.0))
+		meta_row.add_child(tags_label)
+
+	if world.owner_username != "":
+		var owner_label := Label.new()
+		owner_label.text = "Creator: %s" % world.owner_username
+		owner_label.add_theme_font_size_override("font_size", 12)
+		owner_label.add_theme_color_override("font_color", Color(0.6, 0.6, 0.6, 1.0))
+		meta_row.add_child(owner_label)
+
+	vbox.add_child(meta_row)
+
+	return panel
+
+
+func _update_pagination() -> void:
+	var total_pages := int(ceil(float(_total_count) / float(_page_size)))
+	if total_pages <= 0:
+		total_pages = 1
+
+	if page_label:
+		page_label.text = "Page %d of %d (%d experiences)" % [_current_page + 1, total_pages, _total_count]
+
+	if prev_button:
+		prev_button.disabled = (_current_page <= 0)
+	if next_button:
+		next_button.disabled = ((_current_page + 1) >= total_pages)
+
+
+func _on_enter_world_pressed(world_id: int, button: Button) -> void:
+	button.disabled = true
+	button.text = "Joining…"
+	world_selected.emit(world_id)
+
+	# 1. Record visit metric
+	if _api_client != null:
+		await DiscoveryApiClient.record_visit(_api_client, world_id)
+
+	# 2. Join flow (existing game server orchestration)
+	if _api_client != null and _api_client.has_method("join_world"):
+		var result: Dictionary = await _api_client.join_world(world_id)
+		if result.ok and result.data is Dictionary:
+			var d: Dictionary = result.data
+			if has_node("/root/Session"):
+				get_node("/root/Session").begin(world_id, str(d.get("host", "")), int(d.get("port", 0)))
+			get_tree().change_scene_to_file("res://scenes/game.tscn")
+			return
+
+		if result.status == 503:
+			# Dev fallback: local single-player
+			if has_node("/root/Session"):
+				get_node("/root/Session").clear()
+			get_tree().change_scene_to_file("res://scenes/game.tscn")
+			return
+
+		if status_label:
+			status_label.text = "Failed to join: " + str(result.detail)
+			status_label.visible = true
+	else:
+		# Fallback if standalone test or not wired
+		if has_node("/root/Session"):
+			get_node("/root/Session").clear()
+		get_tree().change_scene_to_file("res://scenes/game.tscn")
+		return
+
+	button.disabled = false
+	button.text = "Enter World"
+
+
+func _on_filter_pressed() -> void:
+	load_worlds(0)
+
+
+func _on_search_submitted(_new_text: String) -> void:
+	load_worlds(0)
+
+
+func _on_category_selected(_index: int) -> void:
+	load_worlds(0)
+
+
+func _on_sort_selected(_index: int) -> void:
+	load_worlds(0)
+
+
+func _on_refresh_pressed() -> void:
+	load_worlds(_current_page)
+
+
+func _on_prev_page_pressed() -> void:
+	if _current_page > 0:
+		load_worlds(_current_page - 1)
+
+
+func _on_next_page_pressed() -> void:
+	var total_pages := int(ceil(float(_total_count) / float(_page_size)))
+	if (_current_page + 1) < total_pages:
+		load_worlds(_current_page + 1)
+
+
+func _on_back_pressed() -> void:
+	back_requested.emit()
+	if get_tree():
+		get_tree().change_scene_to_file("res://scenes/main_menu.tscn")

scripts/smoke_test_discovery_client.gd

@@ -0,0 +1,62 @@
+extends SceneTree
+## Headless smoke test for DiscoveryApiClient.
+
+func _init() -> void:
+	print("[SMOKE] Starting DiscoveryApiClient smoke test...")
+
+	# 1. Test WorldSummary parsing
+	var test_dict := {
+		"id": 42,
+		"name": "Neon Arcade",
+		"description": "Retro gaming lounge",
+		"category": "Arcade",
+		"tags": ["retro", "multiplayer"],
+		"play_count": 128,
+		"created_at": "2026-09-15T12:00:00Z",
+		"owner": {
+			"id": 7,
+			"username": "arcadegamer"
+		}
+	}
+
+	var summary := DiscoveryApiClient.WorldSummary.from_dict(test_dict)
+	assert(summary.id == 42, "summary id mismatch")
+	assert(summary.name == "Neon Arcade", "summary name mismatch")
+	assert(summary.category == "Arcade", "summary category mismatch")
+	assert(summary.tags.size() == 2, "summary tags size mismatch")
+	assert(summary.play_count == 128, "summary play_count mismatch")
+	assert(summary.owner_id == 7, "summary owner_id mismatch")
+	assert(summary.owner_username == "arcadegamer", "summary owner_username mismatch")
+	print("[PASS] WorldSummary parsing verified")
+
+	# 2. Test DiscoveryResult parsing
+	var page_dict := {
+		"items": [test_dict],
+		"total": 1,
+		"skip": 0,
+		"limit": 50
+	}
+	var res := DiscoveryApiClient.DiscoveryResult.from_dict(page_dict)
+	assert(res.total == 1, "res total mismatch")
+	assert(res.items.size() == 1, "res items size mismatch")
+	assert(res.items[0].id == 42, "res items[0] id mismatch")
+	print("[PASS] DiscoveryResult parsing verified")
+
+	# 3. Test ApiClient integration
+	var api_script = load("res://scripts/api_client.gd")
+	if not api_script:
+		printerr("[FAIL] Could not load api_client.gd")
+		quit(1)
+		return
+
+	var api: Node = api_script.new()
+	root.add_child(api)
+
+	assert(api.has_method("get_discovery_worlds"), "Missing get_discovery_worlds on ApiClient")
+	assert(api.has_method("get_discovery_categories"), "Missing get_discovery_categories on ApiClient")
+	assert(api.has_method("record_world_visit"), "Missing record_world_visit on ApiClient")
+	print("[PASS] ApiClient discovery methods verified")
+
+	api.queue_free()
+	print("[SMOKE] DiscoveryApiClient smoke test PASSED")
+	quit(0)

scripts/smoke_test_discovery_ui.gd

@@ -0,0 +1,89 @@
+extends SceneTree
+## Headless smoke test for DiscoveryUI.
+
+func _initialize() -> void:
+	_run()
+
+func _run() -> void:
+	print("[SMOKE] Starting DiscoveryUI smoke test...")
+	await process_frame
+
+	var scene = load("res://scenes/discovery_ui.tscn")
+	if not scene:
+		printerr("[FAIL] Could not load res://scenes/discovery_ui.tscn")
+		quit(1)
+		return
+
+	var ui: DiscoveryUI = scene.instantiate()
+	root.add_child(ui)
+	await process_frame
+
+	# 1. Verify node references
+	assert(ui.search_edit != null, "search_edit is null")
+	assert(ui.category_option != null, "category_option is null")
+	assert(ui.sort_option != null, "sort_option is null")
+	assert(ui.filter_button != null, "filter_button is null")
+	assert(ui.worlds_container != null, "worlds_container is null")
+	assert(ui.prev_button != null, "prev_button is null")
+	assert(ui.next_button != null, "next_button is null")
+	assert(ui.page_label != null, "page_label is null")
+	print("[PASS] Node references verified")
+
+	# 2. Verify sort options
+	assert(ui.sort_option.item_count == 3, "sort_option should have 3 items")
+	assert(ui.sort_option.get_item_text(0) == "Newest", "sort 0 should be Newest")
+	assert(ui.sort_option.get_item_text(1) == "Most Played", "sort 1 should be Most Played")
+	assert(ui.sort_option.get_item_text(2) == "Trending", "sort 2 should be Trending")
+	print("[PASS] Sort options verified")
+
+	# 3. Verify category dropdown initial state
+	assert(ui.category_option.item_count >= 1, "category_option should have at least All Categories")
+	assert(ui.category_option.get_item_text(0) == "All Categories", "category 0 should be All Categories")
+	print("[PASS] Category dropdown verified")
+
+	# 4. Test rendering of WorldSummary cards
+	var mock_w := DiscoveryApiClient.WorldSummary.new()
+	mock_w.id = 101
+	mock_w.name = "Cyber Nexus"
+	mock_w.category = "Action"
+	mock_w.tags = ["cyberpunk", "pvp"]
+	mock_w.play_count = 256
+	mock_w.description = "A futuristic arena"
+	mock_w.owner_username = "neon_builder"
+
+	var mock_worlds: Array[DiscoveryApiClient.WorldSummary] = [mock_w]
+	ui._render_worlds(mock_worlds)
+	assert(ui.worlds_container.get_child_count() == 1, "Should render 1 card")
+	assert(ui.empty_label.visible == false, "empty_label should be hidden when items present")
+	print("[PASS] World card rendering verified")
+
+	# 5. Test empty state
+	var empty_list: Array[DiscoveryApiClient.WorldSummary] = []
+	ui._render_worlds(empty_list)
+	assert(ui.worlds_container.get_child_count() == 0, "Container should have 0 children")
+	assert(ui.empty_label.visible == true, "empty_label should be visible when empty")
+	print("[PASS] Empty state verified")
+
+	# 6. Test pagination logic
+	ui._total_count = 25
+	ui._page_size = 10
+	ui._current_page = 0
+	ui._update_pagination()
+	assert(ui.prev_button.disabled == true, "Page 0 prev_button should be disabled")
+	assert(ui.next_button.disabled == false, "Page 0 next_button should be enabled")
+	assert(ui.page_label.text.contains("Page 1 of 3"), "Page 1 of 3 mismatch: %s" % ui.page_label.text)
+
+	ui._current_page = 1
+	ui._update_pagination()
+	assert(ui.prev_button.disabled == false, "Page 1 prev_button should be enabled")
+	assert(ui.next_button.disabled == false, "Page 1 next_button should be enabled")
+
+	ui._current_page = 2
+	ui._update_pagination()
+	assert(ui.prev_button.disabled == false, "Page 2 prev_button should be enabled")
+	assert(ui.next_button.disabled == true, "Page 2 next_button should be disabled")
+	print("[PASS] Pagination logic verified")
+
+	ui.queue_free()
+	print("[SMOKE] DiscoveryUI smoke test PASSED")
+	quit(0)