diff --git a/src/AcDream.Core/Physics/PhysicsEngine.cs b/src/AcDream.Core/Physics/PhysicsEngine.cs
index 24edafac..437cb422 100644
--- a/src/AcDream.Core/Physics/PhysicsEngine.cs
+++ b/src/AcDream.Core/Physics/PhysicsEngine.cs
@@ -582,6 +582,13 @@ public sealed class PhysicsEngine
 
         var candidatePos = currentPos + new Vector3(delta.X, delta.Y, 0f);
 
+        // #111 apparatus: one [snap] line per Resolve call (entry + teleport
+        // arrival only — low volume, permanent). The gate-3/4/5 runs committed
+        // ACE's restored pair VERBATIM through this method while every read
+        // path should have changed Z or cell — this line answers which branch
+        // actually ran. Remove or demote to env-gate once #111 closes.
+        bool snapDiag = (delta.X == 0f && delta.Y == 0f);
+
         // Find the landblock this candidate position falls in.
         // #106 follow-up (2026-06-09): capture its high-16 prefix — every
         // computed cell id below is returned FULL (lbPrefix | low). The old
@@ -605,11 +612,47 @@ public sealed class PhysicsEngine
         }
 
         if (physics is null)
+        {
+            if (snapDiag)
+                Console.WriteLine(System.FormattableString.Invariant(
+                    $"[snap] claim=0x{cellId:X8} pos=({currentPos.X:F3},{currentPos.Y:F3},{currentPos.Z:F3}) branch=NO-LANDBLOCK (lbs={_landblocks.Count}) -> verbatim"));
             return new ResolveResult(candidatePos, cellId, IsOnGround: false);
+        }
 
         float localCandX = candidatePos.X - physics.WorldOffsetX;
         float localCandY = candidatePos.Y - physics.WorldOffsetY;
 
+        // #111 (2026-06-10): a VALIDATED indoor claim is AUTHORITATIVE for the
+        // cell — retail SetPositionInternal commits the AdjustPosition cell and
+        // only settles Z (CheckPositionInternal → find_valid_position, :283426);
+        // it never re-picks the cell from floor geometry. The legacy bestCell
+        // floor-pick below scans EVERY CellSurface in the landblock (123 at
+        // Holtburg) and breaks same-height ties by iteration order — on a live
+        // login it clobbered ACE's clean, validated claim 0xA9B40171 with
+        // 0xA9B4013F (issue111-snap1.log), putting the player in a wrong cell
+        // → outdoor demote on first movement → transparent interior (#111).
+        // Snap shape only (zero delta): ground Z onto the validated claim's own
+        // floor when it has one under this XY; cells without their own floor
+        // surface here (thresholds, stair lips) fall through to the legacy path.
+        if (snapDiag && adjustedFound && (cellId & 0xFFFFu) >= 0x0100u)
+        {
+            CellSurface? claimSurface = null;
+            foreach (var c in physics.Cells)
+            {
+                if ((c.CellId & 0xFFFFu) == (cellId & 0xFFFFu)) { claimSurface = c; break; }
+            }
+            float? claimFloorZ = claimSurface?.SampleFloorZ(candidatePos.X, candidatePos.Y);
+            if (claimFloorZ is not null)
+            {
+                Console.WriteLine(System.FormattableString.Invariant(
+                    $"[snap] claim=0x{cellId:X8} pos=({currentPos.X:F3},{currentPos.Y:F3},{currentPos.Z:F3}) VALIDATED -> grounded to its floor z={claimFloorZ.Value:F3}"));
+                return new ResolveResult(
+                    new Vector3(candidatePos.X, candidatePos.Y, claimFloorZ.Value),
+                    lbPrefix | (cellId & 0xFFFFu),
+                    IsOnGround: true);
+            }
+        }
+
         // Check if the candidate position falls on any indoor cell floor.
         // Pick the cell whose floor Z is closest to the entity's current Z.
         CellSurface? bestCell = null;
@@ -757,6 +800,9 @@ public sealed class PhysicsEngine
 
         // Step-height enforcement: block upward movement that exceeds the limit.
         float zDelta = targetZ - currentPos.Z;
+        if (snapDiag)
+            Console.WriteLine(System.FormattableString.Invariant(
+                $"[snap] claim=0x{cellId:X8} pos=({currentPos.X:F3},{currentPos.Y:F3},{currentPos.Z:F3}) cells={physics.Cells.Count} bestCell=0x{(bestCell?.CellId ?? 0u):X8} bestZ={(bestCellZ?.ToString("F3") ?? "none")} terrainZ={terrainZ:F3} indoor={currentlyIndoor} -> targetZ={targetZ:F3} targetCell=0x{(lbPrefix | (targetCellId & 0xFFFFu)):X8} stepReject={zDelta > stepUpHeight}"));
         if (zDelta > stepUpHeight)
         {
             // Too steep to step up — reject horizontal movement.