fix(render): #105 white indoor walls — restore WB's per-frame staged-texture flush dropped in the N.4/O-T4 extraction

Root cause: TextureAtlasManager.AddTexture only STAGES texture content (PBO
write + ManagedGLTextureArray._pendingUpdates); the actual TexSubImage3D
copies + mipmap regeneration happen in ProcessDirtyUpdates, which WB drives
once per frame via ObjectMeshManager.GenerateMipmaps() from its render loop
(WB GameScene.cs:975, just before the opaque pass). GameScene is the file we
replaced with GameWindow, so the call site was silently dropped — staged
updates only reached the GPU as a side effect of PBO growth (UpdateLayerInternal
flushes pending updates before orphaning the PBO). Every layer staged after an
array's LAST growth kept undefined TexStorage3D content behind a valid,
resident bindless sampler handle: white/garbage walls, zh==0, dat tripwires
silent — exactly the #105 signature. Only ObjectRenderBatch.BindlessTextureHandle
consumers are affected (EnvCellRenderer cell shells = indoor walls); entities
resolve via TextureCache (immediate TexImage2D) and terrain via TerrainAtlas
(immediate GenerateMipmap), which is why only indoor walls ever struck.

Fix: WbMeshAdapter.Tick() now calls _meshManager.GenerateMipmaps() after the
staged-upload drain — Tick runs before all draw passes (GameWindow OnRender),
the exact WB-equivalent position.

Evidence (ACDREAM_PROBE_TEXFLUSH=1 apparatus, kept env-gated):
- pre-fix (texflush-prefix.log): pending updates climb 0->48->...->142 and
  park at 126 across 34/34 atlas arrays at standstill, forever (19 heartbeats);
  brief dips only at PBO-growth crossings — the broken contract live.
- post-fix (texflush-postfix.log): every line after=0 — staged updates drain
  the same frame, all 34 arrays clean.

Intermittency explained: background decode-completion order shuffles which
textures land in the never-flushed tail; whether a visible wall samples one is
per-run luck. Also explains the #110 correlation: znear=0.1 makes close-up
geometry newly visible -> more prepare/upload pressure indoors -> bigger tail
-> higher strike probability. The near plane is mechanism-innocent (re-land
follows as its own commit).

Baseline maintained: App 223 / UI 420 / Net 294 / Core 1377 green + 4
pre-existing #99-era failures + 1 skip; CornerFloodReplayTests (5) and
CameraCornerSealReplayTests (2) gates green.

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

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

@@ -301,6 +301,23 @@ namespace AcDream.App.Rendering.Wb {
             }
         }
 
+        /// <summary>
+        /// #105 diagnostic: counts staged-but-unflushed texture layer updates across all
+        /// shared atlases (see <see cref="ManagedGLTextureArray.PendingUpdateCount"/>).
+        /// Render thread only — <c>_globalAtlases</c> is render-thread-owned.
+        /// </summary>
+        public (int PendingUpdates, int ArraysWithPending, int TotalArrays) GetPendingTextureUpdateStats() {
+            int pending = 0, arraysWith = 0, total = 0;
+            foreach (var atlasList in _globalAtlases.Values) {
+                foreach (var atlas in atlasList) {
+                    total++;
+                    int p = atlas.TextureArray.PendingUpdateCount;
+                    if (p > 0) { arraysWith++; pending += p; }
+                }
+            }
+            return (pending, arraysWith, total);
+        }
+
         /// <summary>
         /// Decrement reference count and unload GPU resources if no longer needed.
         /// </summary>