inventions: resolve real creator ids for a room (creatorIds)

api/inventions/v1/creatorIds was a stub returning an empty list, so the
2020.03 watch's GetCreatorIdsOfInventionsInRoom never learned which
creators it must request invention permissions for before spawning a
room's invention-based geometry. Resolve the real set from
InventionEntity.CreationRoomId via a shared ResolveRoomInventionsAsync
helper: direct matches (created in-place) unioned with the imported
cluster (most-frequent non-local CreationRoomId among the room creator's
inventions, since zip-imported inventions keep their original Rec Room
room id). Returns List<int> of distinct creator account ids.

DorkNet.Server/Controllers/API/Inventions/InventionsController.cs

@@ -165,13 +165,58 @@ public class InventionsController(
         });
     }
 
+    /// <summary>GET <c>api/inventions/v1/creatorIds</c> — the distinct
+    /// creator account ids of every invention placed in a room
+    /// (<c>GetCreatorIdsOfInventionsInRoom</c>, called by the 2020.03
+    /// watch on room load). It uses these to resolve which creators it
+    /// must request invention permissions for before spawning a room's
+    /// invention-based geometry. Returns <c>List&lt;int&gt;</c> — empty
+    /// when the room has no tracked inventions.</summary>
     [HttpGet("api/inventions/v1/creatorIds")]
-    public IActionResult CreatorIdsInRoom([FromQuery] long roomId)
+    public async Task<IActionResult> CreatorIdsInRoom([FromQuery] long roomId)
     {
-        // We don't yet track per-room invention placements; return
-        // empty list (correct shape: List<int>).
-        _ = roomId;
-        return Ok(Array.Empty<int>());
+        var inventions = await ResolveRoomInventionsAsync(roomId);
+        var creatorIds = inventions
+            .Select(i => (int)i.CreatorPlayerId)
+            .Distinct()
+            .ToList();
+        return Ok(creatorIds);
+    }
+
+    /// <summary>Resolve the inventions that belong to a room. Direct
+    /// matches are inventions whose
+    /// <see cref="InventionEntity.CreationRoomId"/> equals the room's
+    /// local id (RR-Originals, dorms, anything created in-place).
+    /// Zip-imported rooms instead carry each invention's ORIGINAL Rec
+    /// Room CreationRoomId, which won't equal our local id and can't be
+    /// reverse-resolved without an OriginalRoomId column; we approximate
+    /// that cluster as the most-frequent non-local CreationRoomId among
+    /// the room creator's inventions. The two sets are unioned so a room
+    /// with both kinds resolves fully.</summary>
+    private async Task<List<InventionEntity>> ResolveRoomInventionsAsync(long roomId)
+    {
+        var creatorId = await db.Rooms
+            .Where(r => r.Id == roomId)
+            .Select(r => (long?)r.CreatorPlayerId)
+            .FirstOrDefaultAsync();
+
+        long? importedRoomId = null;
+        if (creatorId is long creator)
+        {
+            importedRoomId = await db.Inventions
+                .Where(i => !i.IsDeleted && i.CreatorPlayerId == creator
+                    && i.CreationRoomId != null && i.CreationRoomId != roomId)
+                .GroupBy(i => i.CreationRoomId)
+                .OrderByDescending(g => g.Count())
+                .Select(g => g.Key)
+                .FirstOrDefaultAsync();
+        }
+
+        return await db.Inventions
+            .Where(i => !i.IsDeleted
+                && (i.CreationRoomId == roomId
+                    || (importedRoomId != null && i.CreationRoomId == importedRoomId)))
+            .ToListAsync();
     }
 
     // ── Single fetch ─────────────────────────────────────────────────────