feat(render): Phase U.4 — unified gated draw pass (indoor root)

Wire the portal-visibility result through the clip pipeline: build a per-frame
ClipFrame (slot 0 no-clip, slot 1 OutsideView, slot 2..N per visible cell) +
cellIdToSlot from PortalVisibilityBuilder; call the (previously dormant)
EnvCellRenderer.Render for cell shells inside the clip bracket; assign per-instance
clip slots in WbDrawDispatcher (live-dynamic unclipped per retail, cell statics to
their cell slot, outdoor scenery to OutsideView, non-visible culled); gate/scissor/
skip terrain per OutsideView (empty ⇒ no terrain — the bleed fix). Emit ACDREAM_PROBE_VIS.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -237,6 +237,24 @@ public sealed unsafe class EnvCellRenderer : IDisposable
     public void SetClipRegionSsbo(uint sharedClipRegionSsbo)
         => _sharedClipRegionSsbo = sharedClipRegionSsbo;
 
+    // Phase U.4: per-frame cellId→CellClip-slot map for the cell shells. When
+    // non-null, RenderModernMDIInternal writes instanceClipSlot[i] =
+    // _cellIdToSlot[allInstances[i].CellId] so each cell's shell instances are
+    // gated to that cell's portal-clip region. When null (U.3 path), every
+    // instance maps to slot 0 (no-clip). A cell absent from the map writes slot 0
+    // (no-clip) — but the caller's Render filter already restricts the draw to the
+    // map's keys, so that fallback should not fire in practice.
+    private IReadOnlyDictionary<uint, int>? _cellIdToSlot;
+
+    /// <summary>
+    /// Phase U.4: install the per-frame cellId→slot map used to gate cell shells
+    /// to their portal-clip regions. Call once per frame BEFORE
+    /// <see cref="Render(WbRenderPass, HashSet{uint}?)"/>. Pass null to revert to
+    /// the U.3 no-clip behavior (every shell instance → slot 0).
+    /// </summary>
+    public void SetClipRouting(IReadOnlyDictionary<uint, int>? cellIdToSlot)
+        => _cellIdToSlot = cellIdToSlot;
+
     // ---------------------------------------------------------------------------
     // GetEnvCellGeomId
     // Verbatim copy of WB EnvCellRenderManager.cs:94-103.
@@ -1047,14 +1065,25 @@ public sealed unsafe class EnvCellRenderer : IDisposable
                 (nuint)(totalDraws * sizeof(ModernBatchData)), ptr);
         }
 
-        // Phase U.3: upload the per-instance clip-slot buffer (binding=3), all
-        // zeros ⇒ every instance maps to slot 0 ⇒ no-clip. Re-zero the reused head
-        // each frame so stale U.4 slot indices can't leak. Sized to
-        // uniqueInstanceCount; the buffer was already grown above with the
-        // instance buffer when capacity increased.
+        // Phase U.4: upload the per-instance clip-slot buffer (binding=3). When
+        // _cellIdToSlot is set (indoor routing), each cell shell instance is gated
+        // to its cell's CellClip slot via allInstances[i].CellId; cells absent from
+        // the map (shouldn't happen — the Render filter is the map's keys) and the
+        // U.3 path both map to slot 0 (no-clip). allInstances is laid out in the
+        // SAME order as the binding=0 transforms (_gpuInstanceTransforms below), so
+        // instanceClipSlot[i] tracks Instances[i] through the MDI BaseInstance.
         if (_clipSlotData.Length < uniqueInstanceCount)
             _clipSlotData = new uint[Math.Max(_clipSlotData.Length * 2, uniqueInstanceCount)];
-        Array.Clear(_clipSlotData, 0, uniqueInstanceCount);
+        if (_cellIdToSlot is null)
+        {
+            Array.Clear(_clipSlotData, 0, uniqueInstanceCount);
+        }
+        else
+        {
+            for (int i = 0; i < uniqueInstanceCount; i++)
+                _clipSlotData[i] = _cellIdToSlot.TryGetValue(allInstances[i].CellId, out int slot)
+                    ? (uint)slot : 0u;
+        }
         _gl.BindBuffer(GLEnum.ShaderStorageBuffer, _clipSlotBuffer);
         _gl.BufferData(GLEnum.ShaderStorageBuffer,
             (nuint)(uniqueInstanceCount * sizeof(uint)), null, GLEnum.DynamicDraw);