docs(overhaul): bound nonempty geometry witness integration

Prepare the original unpinned witness with an explicit cathedral-shell non-vacuity gate. Write-only while the separate production bridge owns test execution; preserve the scratch and its failed diagnostics.

Co-Authored-By: OpenAI Codex <noreply@openai.com>

docs/research/2026-09-01-overhaul/c1a-geometry-witness-integration-contract.md

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+# C1a original geometry witness — guarded integration, write-only
+
+Lead bounded test-only contract,2026-09-05. The separate AP159 production
+bridge is in flight under its own contract; it owns all build/test execution.
+This work is independent file preparation only, not a fourth authored-input
+diagnostic fix. Do not change or rerun the preserved scratch diagnostics.
+
+Read `c1a-geometry-activation.md` and packet§37.3–37.4/§45. The original
+scratch witness remains unpinned because the production bridge was wrong.
+Its source SHA9894EC50BF40F732237E3249E5F7815FDC931DDC66F1D5D212D0CA717373A9C5
+has been independently reviewed and read by the lead. One actual pre-pin
+gap was found: shellF4180104 presence/nonzeroGeometryId is asserted, but its
+extracted mesh's nonzero vertex/subset/index content is not. An empty shell
+could become part of the initial golden. No other source blocker was found;
+mutation and full execution evidence remain owed.
+
+## Allowed change
+
+Work only in the canonical campaign worktree. Add exactly
+`tests/AcDream.App.Tests/Streaming/LandblockGeometryMembershipInstalledDatTests.cs`
+by copying the preserved original file from s5-c1a-geometry with apply_patch.
+Do not copy its AuthoredDiagnostic partial, any artifacts, package or old
+golden; do not alter the scratch. Retain the original partial declaration,
+all existing methods/serialization, original three-cell/21-entry semantics,
+and `REPLACE_AFTER_FIRST_VERIFIED_CAPTURE` placeholder.
+
+The only source addition is at the existing EnvCell mesh extraction before
+serialization: for the exact ShellCellIdF4180104, assert nonempty actual
+mesh.Vertices, nonempty ObjectMeshManager.OrderedUploadBatches(mesh), and
+positive total emitted index count from those real batches. A short comment
+may explain why the non-vacuity gate precedes first golden capture. Aggregate
+landblock totals, hard-coded mock geometry or a second extractor are forbidden.
+
+No production, existing tests, shaders, scripts, fixtures, register or docs
+edits by the implementer. No new agent, commit, build/test or client actions.
+Return code-ready with source hash and exact diff; lead releases execution
+only after the bridge implementer returns ownership and source is reviewed.
+
+## Later execution boundary (not authorized by this write-only contract)
+
+After the bridge passes focused review/tests, lead will activate the original
+semantic/deterministic capture on the integrated production code. Placeholder
+failure is expected until two fresh owner captures agree, all semantic facts
+including the now-explicit nonempty shell pass, and lead authorizes the exact
+combined hash. No four-cell update. Then run the required product mutations,
+two fresh processes and official full/canonical gates under§45 with exact
+hashes and nonpassing classifications. Keep C1c's existing25-frame consumer;
+do not copy its replay. Those steps need their explicit execution release.
+
+The fresh initialized0..6 part-order assertion is a production initialization
+witness, not a claim of universal equality with later live-retail retained
+part-list order0,1,6,5,2,4,3. AD117's source approximation and AP159's boundary
+ties remain explicit. C1a/G4 unpassed, FPS deferred, known retail leak unchanged.