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/ManagedGLTextureArray.cs

@@ -41,6 +41,16 @@ namespace AcDream.App.Rendering.Wb {
         public ulong BindlessClampHandle { get; private set; }
         public long TotalSizeInBytes => CalculateTotalSize();
 
+        /// <summary>
+        /// #105 diagnostic: staged layer updates (PBO writes + pending list) not yet
+        /// applied to the GL texture by <see cref="ProcessDirtyUpdates"/>. Layers with
+        /// a pending update sample UNDEFINED content (TexStorage3D contents) until the
+        /// flush runs — a stuck non-zero count at standstill is the white-walls mechanism.
+        /// </summary>
+        public int PendingUpdateCount {
+            get { lock (_mipmapLock) { return _pendingUpdates.Count; } }
+        }
+
         public ManagedGLTextureArray(OpenGLGraphicsDevice graphicsDevice, TextureFormat format, int width, int height,
             int size, ILogger logger, TextureParameters? texParams = null) {
             var p = texParams ?? TextureParameters.Default;