feat(render): Phase A8 R3 — wire stencil pipeline into render frame (WB order)

Replaces the pre-A8 single dispatcher call with the WB RenderInsideOut
order when cameraInsideCell:

  1. Terrain draws normally (color + depth)
  2. depth-clear-if-inside (depth = 1.0 globally)
  3. MarkAndPunch — stencil bit 1 at camera's-own-cell exit portals
  4. IndoorPass — cell mesh + cell statics + building shells, stencil OFF
  5. EnableOutdoorPass + re-draw terrain + OutdoorScenery, stencil-gated
  6. DisableStencil + LiveDynamic, depth-test only

Outdoor (cameraInsideCell == false) path unchanged: single Draw(set: All).

Step 5 (WB's 3-stencil-bit cross-cell-portal pipeline) is DEFERRED — we
mark only the camera's own cell's exit portals via [visibility.CameraCell],
not the BFS-extended VisibleCellIds. Trade-off documented in
docs/research/2026-05-26-a8-entity-taxonomy.md §"open questions".

Adds IndoorCellStencilPipeline field + ctor wiring + Dispose. Field types
the partition consumers from R2; the ParentCellId / IsBuildingShell /
ServerGuid distinctions are now consumed at runtime.

Visual verification at cottage interior / cottage cellar / inn interior /
dungeon is R4.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -36,6 +36,7 @@ public sealed class GameWindow : IDisposable
     private AcDream.App.Rendering.Wb.EntitySpawnAdapter? _wbEntitySpawnAdapter;
     private AcDream.App.Rendering.Vfx.EntityScriptActivator? _entityScriptActivator;
     private AcDream.App.Rendering.Wb.WbDrawDispatcher? _wbDrawDispatcher;
+    private IndoorCellStencilPipeline? _indoorStencilPipeline;
     /// <summary>Phase N.5: ARB_bindless_texture + ARB_shader_draw_parameters
     /// support. Required at startup — missing bindless throws
     /// <see cref="NotSupportedException"/> in <c>OnLoad</c>.</summary>
@@ -1752,6 +1753,15 @@ public sealed class GameWindow : IDisposable
                 _classificationCache);
             // A.5 T22.5: apply A2C gate from quality preset.
             _wbDrawDispatcher.AlphaToCoverage = _resolvedQuality.AlphaToCoverage;
+
+            // Phase A8 R3 — indoor visibility culling pipeline. Owns the
+            // portal_stencil shader pair and a dynamic VBO for per-frame
+            // portal triangle uploads. Stencil work runs only when the
+            // camera is inside an EnvCell; outside, the object is dormant.
+            _indoorStencilPipeline = new IndoorCellStencilPipeline(
+                _gl,
+                Path.Combine(shadersDir, "portal_stencil.vert"),
+                Path.Combine(shadersDir, "portal_stencil.frag"));
         }
 
         // Phase G.1 sky renderer — its own shader (sky.vert / sky.frag)
@@ -7119,14 +7129,10 @@ public sealed class GameWindow : IDisposable
             if (cameraInsideCell)
                 _gl!.Clear(ClearBufferMask.DepthBufferBit);
 
-            // L-fix1 (2026-04-28): pass the set of animated-entity ids so
+            // L-fix1 (2026-04-28): animated-entity id set. Required by both
-            // the renderer keeps remote players / NPCs / monsters
+            // the cameraInsideCell branch (to route them to LiveDynamic pass)
-            // visible even when their landblock rotates out of the
+            // and the outdoor path (where it preserves visibility across
-            // frustum. Without this, other characters wink in/out as
+            // landblock frustum culling).
-            // the camera turns. The set is rebuilt per-frame from
-            // _animatedEntities — it's small (<100 entities typically)
-            // so HashSet allocation is cheap. Static scenery still
-            // respects landblock-level cull.
             HashSet<uint>? animatedIds = null;
             if (_animatedEntities.Count > 0)
             {
@@ -7135,11 +7141,75 @@ public sealed class GameWindow : IDisposable
                     animatedIds.Add(k);
             }
 
-            // N.5: WbDrawDispatcher is always non-null (modern path mandatory).
+            if (cameraInsideCell && _indoorStencilPipeline is not null
+                && visibility?.CameraCell is not null)
+            {
+                // Phase A8 R3 — WB RenderInsideOut order.
+                //
+                // 1. Terrain has already drawn (color + depth) at line ~7104.
+                // 2. depth-clear-if-inside has already cleared depth to 1.0
+                //    (above this branch at line ~7118). The MarkAndPunch
+                //    below is a no-op against that baseline — left in for
+                //    symmetry with WB's reference pipeline and to handle
+                //    the unusual case where depth-clear is later dropped.
+                // 3. MarkAndPunch — stencil bit 1 at the camera's-own-cell
+                //    exit portals. Step 5 (cross-cell-portal visibility via
+                //    3-stencil-bit pipeline) is DEFERRED — we mark ONLY the
+                //    camera's own cell's portals, not the BFS-extended
+                //    VisibleCellIds. Trade-off: cross-cell visibility loss
+                //    (rare visually); correctness in the common case (no
+                //    see-through-wall to far-side portal openings).
+                var cameraCells = new[] { visibility.CameraCell };
+                _indoorStencilPipeline.UploadPortalMesh(cameraCells);
+
+                var viewProjection = camera.View * camera.Projection;
+                _indoorStencilPipeline.MarkAndPunch(viewProjection);
+
+                // 4. IndoorPass — cell mesh + cell statics + building shells
+                //    (R1's IsBuildingShell flag drives the partition).
+                //    Stencil OFF (MarkAndPunch's cleanup restored that).
+                //    Depth test normal; building shells write the wall depth
+                //    that protects the indoor from outdoor visibility.
+                _wbDrawDispatcher!.Draw(camera, _worldState.LandblockEntries, frustum,
+                    neverCullLandblockId: playerLb,
+                    visibleCellIds: visibility.VisibleCellIds,
+                    animatedEntityIds: animatedIds,
+                    set: AcDream.App.Rendering.Wb.WbDrawDispatcher.EntitySet.IndoorPass);
+
+                // 5. Stencil-gated outdoor pass.
+                _indoorStencilPipeline.EnableOutdoorPass();
+
+                // 5a. Re-draw terrain — at portal-silhouette pixels only,
+                //     terrain Z (with the f48c74a -0.01 nudge) wins over the
+                //     punched 1.0 depth. Color writes through window.
+                _terrain?.Draw(camera, frustum, neverCullLandblockId: playerLb);
+
+                // 5b. Outdoor scenery — same stencil gating.
+                _wbDrawDispatcher!.Draw(camera, _worldState.LandblockEntries, frustum,
+                    neverCullLandblockId: playerLb,
+                    visibleCellIds: visibility.VisibleCellIds,
+                    animatedEntityIds: animatedIds,
+                    set: AcDream.App.Rendering.Wb.WbDrawDispatcher.EntitySet.OutdoorScenery);
+
+                // 6. Stencil OFF — live dynamic entities draw freely with
+                //    depth test only (no stencil clipping).
+                _indoorStencilPipeline.DisableStencil();
+
+                _wbDrawDispatcher!.Draw(camera, _worldState.LandblockEntries, frustum,
+                    neverCullLandblockId: playerLb,
+                    visibleCellIds: visibility.VisibleCellIds,
+                    animatedEntityIds: animatedIds,
+                    set: AcDream.App.Rendering.Wb.WbDrawDispatcher.EntitySet.LiveDynamic);
+            }
+            else
+            {
+                // Outdoor path — unchanged from pre-A8: single dispatcher call
+                // walks every entity with default EntitySet.All partition.
                 _wbDrawDispatcher!.Draw(camera, _worldState.LandblockEntries, frustum,
                     neverCullLandblockId: playerLb,
                     visibleCellIds: visibility?.VisibleCellIds,
                     animatedEntityIds: animatedIds);
+            }
 
             // Phase G.1 / E.3: draw all live particles after opaque
             // scene geometry so alpha blending composites correctly.
@@ -10495,6 +10565,7 @@ public sealed class GameWindow : IDisposable
         _liveSession = null;
         _audioEngine?.Dispose();  // Phase E.2: stop all voices, close AL context
         _wbDrawDispatcher?.Dispose();
+        _indoorStencilPipeline?.Dispose();
         _skyRenderer?.Dispose();      // depends on sampler cache; dispose first
         _samplerCache?.Dispose();
         _textureCache?.Dispose();