fix(physics): restore retail cell availability semantics

tests/AcDream.Core.Tests/Physics/CellTransitFindCellSetTests.cs

@@ -315,10 +315,11 @@ public class CellTransitFindCellSetTests
     }
 
     [Fact]
-    public void IndoorSeed_CellWithoutBsp_CannotVerify_StaysCurrent()
+    public void IndoorSeed_LoadedNullRoot_IsUniversallyInside_StaysCurrent()
     {
-        // Stale-beats-null while streaming hydrates: a registered cell with
-        // no CellBSP yet cannot be verified — trust the claim (no demotion).
+        // Retail distinguishes a failed cell lookup from a loaded CellStruct
+        // whose containment root is null. The latter is the BSP query's
+        // universally-inside base case, so the current cell wins immediately.
         Matrix4x4.Invert(Matrix4x4.Identity, out var inv);
         var cellNoBsp = new CellPhysics
         {