Checkpoint web parity through Chromium input tasks

docs/status/M12-07F.md

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+# M12-07F Status
+
+status: done
+task: STL Web-to-desktop round-trip and material-loss report
+updated: 2026-08-18 America/New_York
+enablingTask: false
+parityStateChange: false
+
+## Scope
+
+The STL Web path now serializes the bounded parsed triangle result back to deterministic binary STL.
+The loss report explicitly records STL's lack of material slots as
+`STL_MATERIAL_UNSUPPORTED`; it never silently claims material preservation. A Chromium Worker output
+is imported by a fresh pinned Blender 5.2 process and compared by triangle count and facet normals.
+
+## Evidence
+
+- `node --test web/tests/unit/stl-export.test.mjs` passed 1/1 for binary header/table serialization
+  and explicit material-loss warning.
+- `CHROME_PATH=/usr/bin/google-chrome-stable WEB_TEST_PORT=5467 node_modules/.bin/playwright test
+  --config playwright.config.ts --workers=1 tests/e2e/stl-web-roundtrip.spec.ts` passed 1/1 in Chrome
+  150. Browser output is 184 bytes/2 triangles; Blender reopens 2 polygons/2 triangles with exact
+  normals; warning code is `STL_MATERIAL_UNSUPPORTED`.
+- `node tools/web/check-stl-web-roundtrip.mjs` passed:
+  `stl-web-roundtrip-ok triangles=2 normals=exact materialLoss=1 desktopExact=true next=M12-07G`.
+- Typecheck and `git diff --check` passed. The STL material loss remains machine-visible and STL UI
+  route/parity stays bounded.
+
+## Artifact Hashes
+
+- parent manifest: `19a9f460d1b939c9504dadd364cb87dab3b1769b0599035e2d2b51b47091e034`
+- protocol/Worker: `3b9c409de9fb3eaea34f82c1ddd466670d2b478845d8ff6af3c4e44cb4e04a52` /
+  `1da8b8281cf8ebf9ccf5fd2f42da8ed5886001ab83daba8d9fcd88980257af87`
+- desktop importer: `c4cbff52ff2e7cecba7aeab47e865975955da23a0e1e8ff885ece56b894558d5`
+- unit/Chromium/checker: `f06af242df80ec26d06e92b749449cfebaf909476198ff825207cdd4b9484102` /
+  `2e979dcd030f5316fcbe28e2c19b1c99fe5d111e849d3fc1d2ea316d2159032b` /
+  `093de04bf80b0909eee56ea590e04e7aa4749168e2e49615c62ab39ddc0d16cf`
+- report: `0495c645b4280f6e7821f0ba02010e25d4accbc552e3cd7c58e052607799040e`
+- source fixture: `50161172cd12e4240067064db6f80e74b2df69c475e3e34154e9d0523928c1ca`
+- package: `cfb232baa494ff59f6c8d65514a08c86332ee9354350b2a0392b6f932a7ee42c`
+- manifest: `3cbbcb541ee123da0ef8916ac2ca8805680d539bbf8db3b4a8d331aec418148c`
+
+## Next Task
+
+`M12-07G`: PLY ASCII/binary little-endian capability declarations.
+
+## Rollback
+
+Remove the STL export/loss protocol, Worker, desktop importer, tests, checker, report, manifest, and
+this status entry. Restore M12-07E as the queue tail and move the machine queue back to M12-07F. No
+parity ledger rollback is required.