fix(render): FW4 slice 4 - straddler particles emit pre-clear, once

The cathedral falls survived slices 2 and 3; the [walk-dyn] dump then
pinned the real gate: the falls emitters are interior-parented
exit-plane STRADDLERS that pass BOTH the outside-stage predicate and
the viewcone (outside=1 cone=1) - they were in the pre-clear union all
along, and the deliberate ExceptRoute(DynamicLast) stripped them so
they emitted in the post-clear last pass instead ("straddlers emit
HERE"). That placement protects an indoor flame from interior repaint,
but a straddling emitter whose particles hang OUTSIDE the exit portal
has no depth left to occlude them after the clear - they splat across
terrain and water.

Retail submits an emitter''s polys at its object''s FIRST draw - the
landscape stage for anything overlapping outdoor shadow cells - and
drains them at the pre-clear boundary flush over true landscape depth.
Under an interior root the late-union now keeps the outside-stage
owners (straddlers included), records them, and BOTH last-pass arms
subtract the recorded set so every owner emits exactly once. Outdoor
roots keep the old except-at-union placement: both stages drain at the
same final flush there, so the last-pass emission is already correct
and a pre-emission would double-composite.

Hermetic 6,762/0.

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

src/AcDream.App/Rendering/RetailPViewRenderer.cs

@@ -71,6 +71,16 @@ public sealed class RetailPViewRenderer
     private readonly HashSet<uint> _cellParticleOwnerScratch = new();
     private readonly HashSet<uint> _dynamicParticleOwnerScratch = new();
 
+    // FW4 slice 4: owners whose particles ALREADY submitted in the
+    // pre-clear outside stage this frame (interior roots only). The last
+    // pass subtracts them — retail submits an emitter's polys at its
+    // object's FIRST draw (the landscape stage for anything overlapping
+    // outdoor shadow cells) and drains them at the pre-clear boundary
+    // flush over true landscape depth; a straddler re-emitted post-clear
+    // has no outdoor depth left to occlude it (the cathedral falls
+    // shine-through, fourth surface).
+    private readonly HashSet<uint> _preClearParticleOwnerScratch = new();
+
     // MP-Alloc (2026-07-05): the frame's entity partition (ByCell/OutdoorStatic/
     // Dynamics), reused across frames instead of `new`ing a Result (a Dictionary
     // + 2 Lists, plus one List<WorldEntity> per visible cell) every DrawInside
@@ -155,6 +165,7 @@ public sealed class RetailPViewRenderer
         passes.BeginFrame();
         RecycleLookInFrames();
         ResetBuildingGroups();
+        _preClearParticleOwnerScratch.Clear();
 
         var pvFrame = PortalVisibilityBuilder.Build(
             ctx.RootCell,
@@ -1493,13 +1504,26 @@ public sealed class RetailPViewRenderer
                 });
         }
 
-        // Late-particle union submission — DynamicLast owners excluded, same
-        // as DrawLandscapeThroughOutsideView's own final submission.
-        if (frameEntityPasses is not null)
+        // Late-particle union submission. OUTDOOR root: DynamicLast owners
+        // excluded (both stages drain at the same final flush there — a
+        // duplicate submission would double-composite), matching
+        // DrawLandscapeThroughOutsideView's own final submission. INTERIOR
+        // root (FW4 slice 4): the outside-stage owners — exit-plane
+        // STRADDLERS included — submit HERE, pre-clear, and the last pass
+        // subtracts them instead: retail submits an emitter's polys at its
+        // object's FIRST draw (the landscape stage) and drains them at the
+        // pre-clear boundary flush over true landscape depth; the former
+        // except-here/emit-last placement left a straddler's outside half
+        // with no depth to occlude it after the clear (the cathedral falls
+        // bleeding through terrain and water, probe-pinned:
+        // outside=1 cone=1 yet phase=post).
+        if (frameEntityPasses is not null && ctx.RootCell.IsOutdoorNode)
         {
             RenderFrameRouteOwnerSelector.ExceptRoute(
                 _staticParticleUnionScratch, in frameView, RenderFrameCandidateRoute.DynamicLast);
         }
+        if (!ctx.RootCell.IsOutdoorNode)
+            _preClearParticleOwnerScratch.UnionWith(_staticParticleUnionScratch);
         if (_staticParticleUnionScratch.Count > 0)
         {
             passes.DrawLandscapeStaticParticles(
@@ -2157,6 +2181,10 @@ public sealed class RetailPViewRenderer
                 RenderFrameCandidateRoute.DynamicLast,
                 0,
                 0);
+            // FW4 slice 4: owners already emitted pre-clear (the outside
+            // stage's late union — straddlers included) emit ONCE; see
+            // _preClearParticleOwnerScratch's field comment.
+            _dynamicParticleOwnerScratch.ExceptWith(_preClearParticleOwnerScratch);
 
             passes.UseIndoorMembershipOnlyRouting();
             DrawEntityRouteOrLegacy(
@@ -2291,6 +2319,9 @@ public sealed class RetailPViewRenderer
                 if (InteriorEntityPartition.IsIndoorCellId(e.ParentCellId))
                     _dynamicParticleOwnerScratch.Add(e.Id);
         }
+        // FW4 slice 4: pre-clear-emitted owners (straddlers) emit once —
+        // see _preClearParticleOwnerScratch's field comment.
+        _dynamicParticleOwnerScratch.ExceptWith(_preClearParticleOwnerScratch);
         if (_dynamicParticleOwnerScratch.Count > 0)
             passes.DrawDynamicsParticles(ctx, _dynamicParticleOwnerScratch);
     }