feat(render) Campaign FW3.2b-2 step 1: the production leaf adapter

Additive, nothing invokes it yet (the cutover flip is step 2):

- WalkProductionLeafRenderer + RetailPViewPassExecutor.WalkLeaf: the
  walk driver's leaf turns over the SAME executor renderers the packed
  path uses today - DrawWalkSky (the per-slice sky block looped under
  one driver turn), DrawWalkTerrainSlice (the terrain block of
  DrawLandscapeSlice), per-cell shells via EnvCellRenderer,
  DrawWalkPunchFan (PortalDepthMaskRenderer far-Z, +ShellDrawLiftZ
  matching today's DrawPortalDepthWrite until FW3.3 retires it), the
  alpha barrier via FlushLandscapeAlphaFartherThan, and caller-supplied
  clear/seal actions (the renderer owns the pass scope). The cutover
  changes ORDER, never leaf mechanics.
- Punch fans now carry the ACTIVE VIEW INDEX end to end (retail pins
  building_view = Render::portal_view_num @0x0059f3bf for the whole
  two-pass walk; the fan clips by that view's slice planes):
  PortalPassSink.ActiveViewIndex -> IWalkEventSink.OnPunchGeometry ->
  IWalkFrameLeafRenderer.DrawPunchFan.
- The FW3.2b-2 rooting design is recorded in the plan (dual-compute
  split, LookInObject route filtered to dynamics, consumer
  re-pointing, gate list).

Suites: full Release build 0 warnings; Walk lane green; hermetic green.

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

src/AcDream.App/Rendering/Walk/RetailFrameWalk.cs

@@ -212,6 +212,10 @@ public sealed class RetailFrameWalk
         Vector3 viewpoint = ctx.ViewpointInBuilding(building);
         for (int v = 0; v < viewCount; v++)
         {
+            // Retail pins building_view = the CURRENT view for the whole
+            // two-pass walk (DrawMeshInternal @0x0059f3bf) — the punch fans
+            // it emits clip against THAT view, so the sink carries the index.
+            passSink.ActiveViewIndex = v;
             ctx.SetActiveView(activeViews, v);
             WalkBuildingPortals.BuildDrawPortalsOnly(
                 bsp, 1, viewpoint,
@@ -257,6 +261,11 @@ public sealed class RetailFrameWalk
     private sealed class PortalPassSink(WalkBuilding building, IWalkEventSink sink)
         : WalkBuildingPortals.IWalkPortalPassSink
     {
+        /// <summary>The view the two-pass walk is currently pinned to
+        /// (retail <c>building_view = Render::portal_view_num</c>
+        /// @0x0059f3bf) — punch fans clip against THIS view's slice.</summary>
+        public int ActiveViewIndex;
+
         public void OnPunch(WalkPolygon polygon)
         {
             // The far-Z punch is a depth-only GPU submission (FW2's ordered
@@ -264,7 +273,7 @@ public sealed class RetailFrameWalk
             // FW3.2b-1): forward to the richer sink so a driver can flush +
             // draw the punch fan — building-local space, world transform is
             // the driver's job (WalkProductionFrameContext-style lookup).
-            sink.OnPunchGeometry(building, polygon);
+            sink.OnPunchGeometry(building, polygon, ActiveViewIndex);
         }
 
         public void OnDrawCells(WalkPView pview)

src/AcDream.App/Rendering/Walk/WalkEvents.cs

@@ -124,7 +124,15 @@ public interface IWalkEventSink
     /// stayed a no-op through FW1/FW2 for exactly that reason). Default
     /// no-op.
     /// </summary>
-    void OnPunchGeometry(WalkBuilding building, WalkPolygon polygon) { }
+    /// <param name="building">The building whose portal walk emitted the
+    /// punch.</param>
+    /// <param name="polygon">The portal polygon, building-local.</param>
+    /// <param name="activeViewIndex">The active-view index the two-pass walk
+    /// is pinned to (retail <c>building_view</c> @0x0059f3bf) — the punch
+    /// fan clips against THIS view's slice planes in production.</param>
+    void OnPunchGeometry(
+        WalkBuilding building, WalkPolygon polygon, int activeViewIndex)
+    { }
 
     /// <summary>
     /// Fires once per interior root, at the point <c>PView::DrawCells</c>

src/AcDream.App/Rendering/Walk/WalkFrameDriver.cs

@@ -152,8 +152,11 @@ internal interface IWalkFrameLeafRenderer
     /// the punch (a preceding cell's/building's contents — never this
     /// building's OWN shell, which retail draws only after the whole portal
     /// walk completes; see <see cref="WalkFrameDriver"/>'s type doc comment)
-    /// reaches the GPU first.</summary>
-    void DrawPunchFan(WalkPolygon worldPolygon);
+    /// reaches the GPU first. <paramref name="activeViewIndex"/> is the view
+    /// the emitting two-pass walk was pinned to (retail
+    /// <c>building_view = Render::portal_view_num</c> @0x0059f3bf) —
+    /// production clips the fan by that view's slice planes.</summary>
+    void DrawPunchFan(WalkPolygon worldPolygon, int activeViewIndex);
 
     /// <summary><c>RetailAlphaQueue.FlushFartherThan</c>'s <c>DrawBuilding</c>
     /// barrier — retail's own call site is
@@ -424,7 +427,8 @@ internal sealed class WalkFrameDriver : IWalkEventSink
             shell.Records, shell.TupleLandblockId, _cameraWorldPosition, _viewProjection);
     }
 
-    void IWalkEventSink.OnPunchGeometry(WalkBuilding building, WalkPolygon polygon)
+    void IWalkEventSink.OnPunchGeometry(
+        WalkBuilding building, WalkPolygon polygon, int activeViewIndex)
     {
         ArgumentNullException.ThrowIfNull(building);
         ArgumentNullException.ThrowIfNull(polygon);
@@ -432,7 +436,8 @@ internal sealed class WalkFrameDriver : IWalkEventSink
 
         FlushIfNonEmpty();
         Matrix4x4 worldTransform = _worldData.GetBuildingWorldTransform(building);
-        _leafRenderer.DrawPunchFan(TransformToWorld(polygon, worldTransform));
+        _leafRenderer.DrawPunchFan(
+            TransformToWorld(polygon, worldTransform), activeViewIndex);
     }
 
     void IWalkEventSink.OnInteriorFloodDrawTurn(IReadOnlyList<uint> cells)