fix(render): repair particle CYpt preparation

Retain the GfxObj-authored SortCenter independently from the rendered AABB center and use its scaled, oriented world point for billboard/mode-2-5 CYpt. Keep the visual center unchanged.

Reserve prepared source payload only at Append, roll back the exact tail once on false or exception, cap retained preparation at 3000 CLIP plus 3000 ALPHA, preserve immediate duplicates, account the bounded scratch, and correct the static-record ordering comment. The lead-authorized plan edit records candidate 44e2bc227b's retail FAIL and this section 19 result.

Gates: Release solution build 0 warnings/0 errors; focused particle/driver/queue/order/bounds 95/95; register boundary/count 1/1; real allocations 2/2 at 0 B; shader/manifest 32/32; one-shot hermetic 16751/16751; InstalledDat 385 pass/10 documented fail/1 skip; diff-check pass. No graphical client.

Mutations: rendered pos first failed distance expected 40 actual 116; AABB center expected 40 actual 116; dropped size expected 40 actual 65; dropped orientation expected 40 actual 160; eager reservation first failed Assert.Empty with one payload; omitted false rollback first failed Assert.Single with two payloads; omitted exception rollback first failed Assert.Empty with one payload; removed caps first failed prepared count expected 6000 actual 6002.

Evidence note: the first ordinary InstalledDat filter produced 385 pass/2 expected fail/1 skip but excluded the eight required KnownFailure rows; the separate inclusive no-retry artifact produced the exact documented 10-failure set. Initial test fixture compilation/analyzer setup failures are recorded in packet section 19.5.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Rendering/ParticleRendererRouteTests.cs

@@ -190,6 +190,28 @@ public sealed class ParticleRendererRouteTests
         Assert.Equal(RetailAlphaList.Alpha, decision.List);
     }
 
+    [Fact]
+    public void PreparedCellCap_DropsOnlyRetentionAndPreservesRow2ImmediateDuplicate()
+    {
+        int retainedClip = RetailAlphaQueue.ListCapacity;
+        int retainedAlpha = 0;
+        var decision = new RetailAlphaMeshDecision(
+            RetailAlphaMeshAction.AppendClipAndImmediate,
+            RetailAlphaList.Clip,
+            OverrideClipmap: true);
+
+        ParticleRenderer.PreparedCellAlphaActions actions =
+            ParticleRenderer.ResolvePreparedCellAlphaActions(
+                decision,
+                ref retainedClip,
+                ref retainedAlpha);
+
+        Assert.False(actions.Retain);
+        Assert.True(actions.DrawImmediate);
+        Assert.Equal(RetailAlphaQueue.ListCapacity, retainedClip);
+        Assert.Equal(0, retainedAlpha);
+    }
+
     [Fact]
     public void ProductionImmediateMesh_WarmedDrawImmediateParticleSubmissionRhiDoesNotAllocate()
     {