Checkpoint web parity through Chromium input tasks

docs/status/M12-03G.md

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+# M12-03G Status
+
+status: done
+task: block every linked data writer before Main mutation
+updated: 2026-08-17 America/New_York
+enablingTask: false
+parityStateChange: false
+
+## Scope
+
+The schema-1 linked mutation gate covers object transforms, mesh geometry, mesh material slots,
+material properties, material image nodes, and packed image data. Every request must identify a
+`SOURCE_LIBRARY` owner with `linkedLibrary=true` and `readOnly=true`. A current linked request is
+blocked with `LINKED_DATA_MUTATION_BLOCKED` before any Main writer can run; stale revisions remain
+`REVISION_CONFLICT`, and malformed or ownership-substituted requests fail closed.
+
+This task does not claim a linked writer, reload, relocation, missing-library recovery, or full
+N-023 Link parity. The desktop linked ownership contract is the M12-03F input to this gate.
+
+## Evidence
+
+- `npm --prefix web run test:library-linked-mutation` passed 3/3 unit tests.
+- All six linked writer operations return `BLOCKED` with exactly
+  `LINKED_DATA_MUTATION_BLOCKED`, `recoverable=false`, and no Main mutation path. The test also
+  verifies the schema round-trip for each operation.
+- A stale revision returns `REVISION_CONFLICT`; an unknown field, unsupported operation, or owner /
+  read-only substitution returns `TASK_VALIDATION_FAILED` or `LINKED_DATA_MUTATION_BLOCKED` before
+  any writer invocation.
+
+## Artifact Hashes
+
+- protocol: `f629e0e7e04dc1f5437b6e2ca62fbe35484fc238830fa47e8358bcab46b7e104`
+- unit: `f19d47cefe89daf6123062e045ec717e6ffe60977e8a4b20c996dd62e49da211`
+- manifest: `890891fda5c91b08d157927170fb33190ae0d8a49f8962b88c8554307c0c06a8`
+- package commands: `cfb232baa494ff59f6c8d65514a08c86332ee9354350b2a0392b6f932a7ee42c`
+
+## Next Task
+
+`M12-03H`: library reload replaces only the matching linked generation snapshot.
+
+## Rollback
+
+Remove the linked mutation protocol, unit suite, manifest, package command, and this status entry.
+Restore M12-03F to pending and move the machine queue back to `M12-03F`. No parity ledger rollback
+is required.