feat(content): POC deserter origin + world fixtures with id-resolution check

api/app/content.py

@@ -0,0 +1,50 @@
+"""Load authored world content and cross-check origin references.
+
+Language-neutral content integrity: every id an origin references (start
+location, start quest, granted items, seeded npc dispositions) must resolve in
+world content. New-game construction (client-side, Plan B) relies on this
+holding; catching it here fails a broken origin at authoring time, not three
+scenes into play.
+"""
+
+import json
+from pathlib import Path
+
+
+def _load_ids(dir_path: Path) -> set[str]:
+    ids: set[str] = set()
+    for f in dir_path.glob("*.json"):
+        with open(f) as fh:
+            ids.add(json.load(fh)["id"])
+    return ids
+
+
+def load_world(content_root: Path) -> dict[str, set[str]]:
+    world = content_root / "world"
+    return {
+        "locations": _load_ids(world / "locations"),
+        "npcs": _load_ids(world / "npcs"),
+        "quests": _load_ids(world / "quests"),
+        "items": _load_ids(world / "items"),
+    }
+
+
+def load_origin(path: Path) -> dict:
+    with open(path) as f:
+        return json.load(f)
+
+
+def unresolved_refs(origin: dict, world: dict[str, set[str]]) -> list[str]:
+    missing: list[str] = []
+    if origin["start_location_id"] not in world["locations"]:
+        missing.append(f"location:{origin['start_location_id']}")
+    quest = origin.get("start_quest_id")
+    if quest is not None and quest not in world["quests"]:
+        missing.append(f"quest:{quest}")
+    for grant in origin["inventory_grants"]:
+        if grant["item_id"] not in world["items"]:
+            missing.append(f"item:{grant['item_id']}")
+    for npc_id in origin["disposition_overrides"]:
+        if npc_id not in world["npcs"]:
+            missing.append(f"npc:{npc_id}")
+    return missing