fix(render): retain surfaceless particle metadata

Preserve a successfully decoded GfxObj ParticleGfxInfo when SurfaceId is zero and condition only texture acquisition. Missing/no-Gfx descriptors retain Default behavior; material, additive, routing, and untextured drawing remain unchanged.

Add a production-path GfxObj-backed synthetic no-surface pin with distinct authored/AABB centers, non-unit size, nonidentity orientation, object/particle merge order, visual center, and unassigned texture-slot assertions. Correct the synthetic-DAT evidence wording and advance only the S4-c3a ledger row.

Final F2 source audit found no defect: preparation holds reconstruction inputs only; Append reserves once; false and exception roll back the exact tail once; first-use rejection remains registered; accepted tokens stay stable; independent 3000-entry caps preserve row-2 immediate duplicates; flush/end/abort/next-preparation cleanup converges; retained capacity/bytes remain bounded; warmed production paths remain 0 B.

Gates: no-surface target 1/1; unchanged section 19 baseline 95/95; AP boundary/count 1/1; real allocations 2/2 at 0 B; shader/manifest 32/32; Release solution 0 warnings/0 errors; diff-check pass. No graphical client.

Mutation: restoring eea5793d2's SurfaceId-zero-to-Default ternary first failed CellTurn_GfxObjBillboardWithoutSurfaceRetainsAuthoredSortCenterAndUntexturedFallback at the authored-distance assertion, expected 40 actual 100.

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

docs/research/2026-09-01-overhaul/s4-depth-alpha-packet.md

@@ -1702,3 +1702,69 @@ no-surface branch and evidence wording first. Only PASS unlocks the sequential
 production/gate-honesty lens over the complete c3a stack. Any further code,
 test, register, or evidence correction would be a third fix round: stop the
 chunk and write it up; do not land or graphically gate it.
+
+### 20.4 Final-fix implementation result (Sonnet, 2026-09-04)
+
+**IMPLEMENTED — FINAL RETAIL REVIEW REQUIRED.** A successfully decoded GfxObj
+now retains its complete `ParticleGfxInfo` when `SurfaceId == 0`; texture
+acquisition alone remains conditional on a nonzero Surface DID. Missing or
+unreadable GfxObjs and descriptors without a GfxObj retain the existing
+`Default` behavior. The production-path synthetic GfxObj test supplies no
+Surface DID or entry, a nonzero authored center distinct from its vertex-AABB
+center, size 2, and a nonidentity orientation. It proves authored distance²
+40, ordinary-object-then-particle merge order against distance² 49, the
+unchanged visual center `(10,4,0)`, and an unassigned texture slot. The
+evidence comment now calls both fixtures “production-path GfxObj-backed
+synthetic DAT records,” not real or installed DATs.
+
+Required §20.2 final-round source audit found no additional defect:
+
+- `PrepareForCellAlpha` clears and rebuilds only reconstruction records; it
+  does not add source payload to `_deferredAlpha`.
+- `PreparedParticleAlphaSubmission.Append` calls
+  `ReservePreparedDispatchDeferredParticle` exactly once at the visibility
+  edge, then calls `TryAppend` once.
+- A false return rolls back that exact tail once outside the `try`; an
+  exception rolls it back once in the `catch` and rethrows. The rollback
+  method rejects any non-tail token, so an accepted earlier token cannot be
+  renumbered or removed.
+- `RetailAlphaQueue.TryAppend` registers the source before its capacity
+  return. A rejected first-use source therefore still participates in the
+  next flush/end/abort reset while owning no rejected payload. Accepted token
+  indices remain stable.
+- Independent retained counters admit only the first 3,000 CLIP and first
+  3,000 ALPHA candidates from the already stable particle order. The row-2
+  immediate action is computed independently of retention, so candidate
+  3,001 still draws immediately.
+- Flush, EndFrame, and AbortFrame reset `_deferredAlpha`, prepared RHI count,
+  and `_preparedCellAlphaScratch`; the next preparation also clears the
+  scratch before any early return or rebuild. The immediate-exception path
+  holds no source payload and converges on that next preparation/abort.
+- The prepared list can retain at most 6,000 records and therefore at most the
+  8,192-slot `List<T>` geometric backing pinned by the diagnostic. Its bytes
+  remain included in `RetainedAlphaScratchBytes`.
+- The real warmed driver/particle/dispatcher merge and the immediate-particle
+  RHI path both still measure zero managed bytes.
+
+Mutation ledger: restoring candidate `eea5793d2`'s
+`SurfaceId == 0 ? ParticleGfxInfo.Default : ...` ternary made
+`CellTurn_GfxObjBillboardWithoutSurfaceRetainsAuthoredSortCenterAndUntexturedFallback`
+first fail its authored-distance assertion: expected `40`, actual `100`.
+The mutation was restored before the return matrix.
+
+Automated return:
+
+- targeted no-surface production path — PASS, 1/1 after mutation restore;
+- unchanged §19 focused baseline (excluding the separately executed new
+  target) — PASS, 95/95, 0 skipped;
+- AP-241/AP-242/AP-243 boundary/count pin — PASS, 1/1;
+- real production allocation pins — PASS, 2/2, both asserting 0 B;
+- shader/manifest/SPIR-V lane — PASS, 32/32;
+- Release solution build — PASS, 0 warnings / 0 errors;
+- `git diff --check` — PASS (only the repository's LF-to-CRLF working-copy
+  notices).
+
+Only `ParticleRenderer.cs`, `WalkFrameDriverTests.cs`, this packet, and the
+S4-c3a plan-ledger row changed. AP rows, queue/router/pipeline/shader/manifest/
+package behavior, and installed content remain unchanged. No graphical client
+was launched.