docs(overhaul): start S4-c2 completion attempt 2

Record attempt 1's shader-source-hash contract conflict and permit only the deterministic manifest/paired vertex-SPIR-V closure needed by the required comment correction.

docs/research/2026-09-01-overhaul/2026-09-04-s4-handoff.md

@@ -97,18 +97,20 @@ every deviation gets a register row in the same commit.
   chamber; the zoomed-out FRONT view from the stairwell (hall arches + sky);
   #458's far-block admission (AD-118, 0.5 % edge-plane precision).
 
-## 3. S4 chunk 2 — owner attempt 1/5 ACTIVE, still UNLANDED
+## 3. S4 chunk 2 — owner attempt 2/5 ACTIVE, still UNLANDED
 
 **Binding current state (supersedes the historical procedure later in this
 section):** clean unlanded implementation `a094bf2b7` is behaviorally
 retail-faithful but failed its first review on the evidence/prose findings in
-packet §15. The owner has now authorized up to five more attempts. Packet §16
+packet §15. The owner authorized up to five more attempts. Attempt 1 produced
-is binding; attempt 1/5 corrects only the exact address, mutation-first-failure
+the correct five-file prose diff but its shader freshness gate failed 31/32:
-record, three source comments, one test comment, and the commit body. The
+the required `mesh_detail.vert` comment changes the manifest source hash, while
-implementation agent returns an uncommitted diff; the lead verifies and amends
+the contract forbade refreshing that artifact. Packet §16.2 records the stop
-the unlanded commit, then runs retail followed by production/gate review.
+and is attempt 2/5's binding contract: retain the prose diff, run the shader
-Nothing lands or graphically gates before dual PASS. The campaign renderer
+compiler once, permit only the manifest and paired vertex SPIR-V mechanical
-remains S4-c1 `766f9e749`; G3/G4 remain unpassed.
+closure, prove no shader instruction change, then let the lead amend and run
+both reviews sequentially. Nothing lands or graphically gates before dual
+PASS. The campaign renderer remains S4-c1 `766f9e749`; G3/G4 remain unpassed.
 
 **Historical state before the final round (kept for audit; do not execute its
 landing procedure):**

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

@@ -1070,3 +1070,39 @@ who writes the next bounded contract against that exact finding; up to four
 further attempts remain. Dual PASS authorizes landing the full S4-c2 stack,
 fresh campaign Release/hermetic/InstalledDat gates, then the graphical and
 stationary-soak gates. G3/G4 remain unpassed until those steps finish.
+
+### 16.2 Attempt 1/5 result; attempt 2/5 contract
+
+Attempt 1's five-file prose diff is correct and remains uncommitted on clean
+base `a094bf2b7`. Release passed with zero warnings/errors, the affected tests
+passed 37/37, both real allocation pins passed 2/2, and `git diff --check`
+passed. The shader lane correctly failed 31/32:
+`CommittedSpirvIsNotStaleAgainstItsGlslSource` reports that
+`mesh_detail.vert`'s source hash changed after its required comment correction.
+The attempt-1 contract allowed the GLSL comment but forbade the mechanically
+required manifest/SPIR-V refresh. The implementer stopped without weakening
+the freshness test or touching either artifact. This contract conflict
+consumes attempt 1; four attempts remain.
+
+Attempt 2/5 retains the exact five-file diff from §16.1 and permits only the
+mechanical shader-artifact closure:
+
+1. Run `tools/compile-shaders.ps1` once from `s4-c2-impl`.
+2. Permit changes only to
+   `src/AcDream.App/Rendering/Shaders/spv/shaders.manifest.json` and, if the
+   deterministic compiler rewrites it, the paired
+   `mesh_detail.vert.spv`. No other shader source or SPIR-V may change.
+3. Verify the vertex shader's executable instructions are unchanged: if the
+   SPIR-V bytes change, compare/disassemble the before/after modules and prove
+   the difference is non-semantic metadata only; otherwise stop instead of
+   accepting a shader behavior change.
+4. Run Release build, the complete shader/manifest lane (32/32), the 37
+   affected tests, both real allocation pins, `git diff --check`, and a strict
+   changed-file audit. The unchanged hermetic/InstalledDat evidence remains
+   reusable because the diff is prose plus deterministic shader metadata.
+
+The implementation agent still returns an uncommitted diff. The lead verifies
+the artifact closure and amends the unlanded implementation commit with all
+fourteen mutation names/first failures. Then review attempt 2 sequentially,
+retail/evidence first and production/gate second. A finding consumes attempt 2;
+three further attempts remain.