Advance Blender 5.2 web parity through M12-03D

docs/status/M12-02G.md

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+# M12-02G Status
+
+status: done
+task: reclaim preview payload only after the final project-scoped reference is removed
+updated: 2026-08-17 America/New_York
+enablingTask: true
+parityStateChange: false
+
+## Scope
+
+Preview reference removal is a guarded catalog mutation: it validates the v2 row, checks the exact
+base revision, clears only the target asset's preview, advances revision, and commits a manifest
+hash receipt. Payload reclamation happens only after that reference transaction has completed and
+only when the committed manifest has zero remaining references to the content hash.
+
+OPFS payload ownership remains project-scoped (`projects/<projectId>/assets/sha256/...`). Therefore
+collection can target only the requested project's file and cannot delete an equal-hash payload
+owned and referenced by another project. Non-preview asset metadata is preserved.
+
+## Evidence
+
+- `WEB_TEST_PORT=5599 npm --prefix web run test:asset-preview-reference-gc` passed the artifact unit
+  test 1/1 and real Chromium OPFS/IndexedDB test 1/1.
+- Project A began with two references to one deduplicated payload. Removing the first at revision
+  9->10 returned `RETAINED`, one remaining reference, and kept the file.
+- Removing the final reference at revision 10->11 returned `COLLECTED` and removed project A's
+  payload. Project B's equal-hash payload remained present and its preview returned READY/513 bytes.
+- Reopening project A reproduced revision 11, two null preview references, and unchanged metadata.
+
+## Artifact Hashes
+
+- reference GC: `76b9d8ccd3e7992356f33adc694001f9b0ff364788234389eacdb09198d1415e`
+- Chromium suite: `2e9e9b47883997092c5afb0fb7859a484754764de19006e24a8ff2bdeb24f35a`
+- unit suite: `c5de3122b5d8aab17daf0179cb4f5bb0b5d299408818849cbe7b18e40a47706e`
+- manifest: `3449f2ea9488f66ea5e3f5f2423413e8e290d8ffed3b3d941bdeee3f76addd0a`
+- package commands: `7d1db0932fbe7405ffdbd44b770ce7bf9815b9dfb829c1906a06bfff635ae702`
+
+## Next Task
+
+`M12-02H`: compare desktop/browser preview pixels with explicit metrics and pass both main-thread
+and Offscreen display paths.
+
+## Rollback
+
+Remove the reference-GC protocol, Chromium/unit suites, M12-02G manifest, package command, and this
+status entry. Restore M12-02G to pending and `nextTask` to M12-02G. Catalog and parity ledger data
+do not require rollback.