diag(render): tripwires on every silent dat-miss path (white-walls attribution, #105)

The intermittent white-cottage-walls failure has NEVER produced a log line:
every dat-read failure on the walls-relevant paths exits silently, and the
failed result is cached for the session (mesh batches build once). Today it
reproduced on a probe-free launch with a 35-line, zero-error log — so the
prior heavy-probes-starve-the-dat-reader framing is not the whole story.

Tripwires (print ONLY on anomaly; zero cost healthy; keep until #105 closes):
- [dat-miss]  DatDatabaseWrapper.TryGet — a miss for an id whose BTree entry
  EXISTS (re-probed under the same lock); legit not-found fallbacks stay quiet.
- [tex-miss]  TextureCache.DecodeFromDats x3 — render-thread decode fell back
  to magenta (Surface / SurfaceTexture / RenderSurface miss).
- [cell-miss] GameWindow interior hydration x2 — EnvCell or Environment read
  returned null, so a cell''s WALLS are silently never registered while its
  statics still draw (the exact observed geometry signature).

Color discriminates the layer on the next occurrence: magenta = TextureCache;
see-through + [tex-skip]/[dat-miss] = mesh build; see-through + [cell-miss] =
hydration; broken with NO tripwire output = GL-side upload/residency.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -5471,13 +5471,28 @@ public sealed class GameWindow : IDisposable
         {
             uint envCellId = firstCellId + offset;
             var envCell = _dats.Get<DatReaderWriter.DBObjs.EnvCell>(envCellId);
-            if (envCell is null) continue;
+            if (envCell is null)
+            {
+                // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix):
+                // every id in [0x0100, 0x0100+NumCells) is derived from LandBlockInfo and
+                // MUST exist in the cell dat — a null here is always a read anomaly.
+                Console.WriteLine($"[cell-miss] EnvCell 0x{envCellId:X8} null during interior hydration (NumCells={lbInfo.NumCells})");
+                continue;
+            }
 
             // Phase 7.1: build and register room geometry for this EnvCell.
             DatReaderWriter.Types.CellStruct? cellStruct = null;
             if (envCell.EnvironmentId != 0)
             {
                 var environment = _dats.Get<DatReaderWriter.DBObjs.Environment>(0x0D000000u | envCell.EnvironmentId);
+                if (environment is null)
+                {
+                    // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix):
+                    // a null Environment means this cell's WALLS are silently never
+                    // registered while its static objects still draw — the exact
+                    // white-walls geometry signature.
+                    Console.WriteLine($"[cell-miss] Environment 0x{0x0D000000u | envCell.EnvironmentId:X8} null for EnvCell 0x{envCellId:X8} -> walls not registered");
+                }
                 if (environment is not null
                     && environment.Cells.TryGetValue(envCell.CellStructure, out cellStruct))
                 {

src/AcDream.App/Rendering/TextureCache.cs

@@ -385,7 +385,11 @@ public sealed unsafe class TextureCache : Wb.ITextureCachePerInstance, IDisposab
     {
         var surface = _dats.Get<Surface>(surfaceId);
         if (surface is null)
+        {
+            // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix)
+            Console.WriteLine($"[tex-miss] Surface 0x{surfaceId:X8} -> magenta (thread={System.Environment.CurrentManagedThreadId})");
             return DecodedTexture.Magenta;
+        }
 
         // Base1Solid surfaces (and any with OrigTextureId==0) carry a ColorValue
         // instead of a texture chain. Overrides are irrelevant here — there's
@@ -401,12 +405,20 @@ public sealed unsafe class TextureCache : Wb.ITextureCachePerInstance, IDisposab
         uint surfaceTextureId = origTextureOverride ?? (uint)surface.OrigTextureId;
         var surfaceTexture = _dats.Get<SurfaceTexture>(surfaceTextureId);
         if (surfaceTexture is null || surfaceTexture.Textures.Count == 0)
+        {
+            // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix)
+            Console.WriteLine($"[tex-miss] SurfaceTexture 0x{surfaceTextureId:X8} (surface 0x{surfaceId:X8}) -> magenta (thread={System.Environment.CurrentManagedThreadId})");
             return DecodedTexture.Magenta;
+        }
 
         uint renderSurfaceId = (uint)surfaceTexture.Textures[0];
         if (!_dats.Portal.TryGet<RenderSurface>(renderSurfaceId, out var rs)
             && !_dats.HighRes.TryGet<RenderSurface>(renderSurfaceId, out rs))
+        {
+            // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix)
+            Console.WriteLine($"[tex-miss] RenderSurface 0x{renderSurfaceId:X8} (surface 0x{surfaceId:X8}) -> magenta (thread={System.Environment.CurrentManagedThreadId})");
             return DecodedTexture.Magenta;
+        }
 
         // Start with the texture's default palette, then apply overlays.
         // ACViewer's Render/TextureCache.IndexToColor does the same and never

src/AcDream.App/Rendering/Wb/DatCollectionAdapter.cs

@@ -149,6 +149,17 @@ internal sealed class DatDatabaseWrapper : IDatDatabase
                 _cache.TryAdd((typeof(T), fileId), value);
                 return true;
             }
+
+            // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix):
+            // a miss for an id whose BTree entry EXISTS is always an anomaly —
+            // either Unpack returned false or the lookup flickered transiently.
+            // Legit not-found probes (e.g. Portal→HighRes fallback) stay silent.
+            if (_db.Tree.TryGetFile(fileId, out _))
+            {
+                Console.WriteLine(
+                    $"[dat-miss] {typeof(T).Name} 0x{fileId:X8} entry EXISTS but TryGet failed " +
+                    $"(thread={Environment.CurrentManagedThreadId})");
+            }
         }
 
         return false;