Add --prune flag to seed command to remove stale data

Without --prune, seeds continue to only upsert (add/update).
With --prune, routes, encounters, and bosses not present in the
seed JSON files are deleted from the database.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/app/seeds/loader.py

@@ -124,11 +124,14 @@ async def upsert_routes(
     session: AsyncSession,
     version_group_id: int,
     routes: list[dict],
+    *,
+    prune: bool = False,
 ) -> dict[str, int]:
     """Upsert route records for a version group, return {name: id} mapping.
 
     Handles hierarchical routes: routes with 'children' are parent routes,
     and their children get parent_route_id set accordingly.
+    When prune is True, deletes routes not present in the seed data.
     """
     # First pass: upsert all parent routes (without parent_route_id)
     for route in routes:
@@ -185,6 +188,27 @@ async def upsert_routes(
 
     await session.flush()
 
+    if prune:
+        seed_names: set[str] = set()
+        for route in routes:
+            seed_names.add(route["name"])
+            for child in route.get("children", []):
+                seed_names.add(child["name"])
+
+        pruned = await session.execute(
+            delete(Route)
+            .where(
+                Route.version_group_id == version_group_id,
+                Route.name.not_in(seed_names),
+            )
+            .returning(Route.id)
+        )
+        pruned_count = len(pruned.all())
+        if pruned_count:
+            print(f"    Pruned {pruned_count} stale route(s)")
+
+        await session.flush()
+
     # Return full mapping including children
     result = await session.execute(
         select(Route.name, Route.id).where(Route.version_group_id == version_group_id)
@@ -233,8 +257,15 @@ async def upsert_route_encounters(
     encounters: list[dict],
     dex_to_id: dict[int, int],
     game_id: int,
+    *,
+    prune: bool = False,
 ) -> int:
-    """Upsert encounters for a route and game, return count of upserted rows."""
+    """Upsert encounters for a route and game, return count of upserted rows.
+
+    When prune is True, deletes encounters not present in the seed data.
+    """
+    seed_keys: set[tuple[int, str, str]] = set()
+
     count = 0
     for enc in encounters:
         pokemon_id = dex_to_id.get(enc["pokeapi_id"])
@@ -245,6 +276,7 @@ async def upsert_route_encounters(
         conditions = enc.get("conditions")
         if conditions:
             for condition_name, rate in conditions.items():
+                seed_keys.add((pokemon_id, enc["method"], condition_name))
                 await _upsert_single_encounter(
                     session,
                     route_id,
@@ -258,6 +290,7 @@ async def upsert_route_encounters(
                 )
                 count += 1
         else:
+            seed_keys.add((pokemon_id, enc["method"], ""))
             await _upsert_single_encounter(
                 session,
                 route_id,
@@ -270,6 +303,23 @@ async def upsert_route_encounters(
             )
             count += 1
 
+    if prune:
+        existing = await session.execute(
+            select(RouteEncounter).where(
+                RouteEncounter.route_id == route_id,
+                RouteEncounter.game_id == game_id,
+            )
+        )
+        stale_ids = [
+            row.id
+            for row in existing.scalars()
+            if (row.pokemon_id, row.encounter_method, row.condition) not in seed_keys
+        ]
+        if stale_ids:
+            await session.execute(
+                delete(RouteEncounter).where(RouteEncounter.id.in_(stale_ids))
+            )
+
     return count
 
 
@@ -280,8 +330,13 @@ async def upsert_bosses(
     dex_to_id: dict[int, int],
     route_name_to_id: dict[str, int] | None = None,
     slug_to_game_id: dict[str, int] | None = None,
+    *,
+    prune: bool = False,
 ) -> int:
-    """Upsert boss battles for a version group, return count of bosses upserted."""
+    """Upsert boss battles for a version group, return count of bosses upserted.
+
+    When prune is True, deletes boss battles not present in the seed data.
+    """
     count = 0
     for boss in bosses:
         # Resolve after_route_name to an ID
@@ -364,6 +419,20 @@ async def upsert_bosses(
 
         count += 1
 
+    if prune:
+        seed_orders = {boss["order"] for boss in bosses}
+        pruned = await session.execute(
+            delete(BossBattle)
+            .where(
+                BossBattle.version_group_id == version_group_id,
+                BossBattle.order.not_in(seed_orders),
+            )
+            .returning(BossBattle.id)
+        )
+        pruned_count = len(pruned.all())
+        if pruned_count:
+            print(f"    Pruned {pruned_count} stale boss battle(s)")
+
     await session.flush()
     return count