diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 18f1beb..10b6aba 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -10106,11 +10106,38 @@ public sealed class GameWindow : IDisposable
             _playerController.StepDownHeight = 0.4f;
             Console.WriteLine($"physics: player step heights — defaulting to 0.4 m (no setup dat)");
         }
-        int plbX = _liveCenterX + (int)MathF.Floor(playerEntity.Position.X / 192f);
-        int plbY = _liveCenterY + (int)MathF.Floor(playerEntity.Position.Y / 192f);
-        uint pinitCellId = ((uint)plbX << 24) | ((uint)plbY << 16) | 0x0001u;
+        // Issue #92 (2026-05-20): seed the resolver with the SERVER's
+        // authoritative cell id from the spawn message instead of a
+        // hardcoded outdoor sentinel (`landblockPrefix | 0x0001`). When
+        // the player logs in INSIDE a building (server reports an indoor
+        // cell like `0xA9B4015A`), the old sentinel forced the resolver
+        // into the outdoor seed branch — for the first several ticks
+        // CheckBuildingTransit hadn't yet picked up the interior cell,
+        // so the player was classified outdoor, indoor BSP queries
+        // didn't run, and exterior walls were passable until the player
+        // moved far enough INWARD that the sphere overlap eventually
+        // promoted them. Visible symptom: "logged in inside the inn,
+        // ran out through the exterior wall."
+        //
+        // Fall back to the old sentinel when no spawn record is cached
+        // (defensive — should never fire in live play because the
+        // _lastSpawnByGuid entry was written by OnLiveEntitySpawnedLocked
+        // before EnterPlayerModeNow could possibly be reached).
+        uint pinitCellId;
+        if (_lastSpawnByGuid.TryGetValue(_playerServerGuid, out var playerSpawn)
+            && playerSpawn.Position is { } spawnPos
+            && spawnPos.LandblockId != 0)
+        {
+            pinitCellId = spawnPos.LandblockId;
+        }
+        else
+        {
+            int plbX = _liveCenterX + (int)MathF.Floor(playerEntity.Position.X / 192f);
+            int plbY = _liveCenterY + (int)MathF.Floor(playerEntity.Position.Y / 192f);
+            pinitCellId = ((uint)plbX << 24) | ((uint)plbY << 16) | 0x0001u;
+        }
         var initResult = _physicsEngine.Resolve(
-            playerEntity.Position, pinitCellId & 0xFFFFu,
+            playerEntity.Position, pinitCellId,
             System.Numerics.Vector3.Zero, 100f);
         _playerController.SetPosition(initResult.Position, initResult.CellId);