Checkpoint web parity through Chromium input tasks

docs/status/M12-03K.md

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+# M12-03K Status
+
+status: done
+task: expose exactly one verified override writer property
+updated: 2026-08-17 America/New_York
+enablingTask: false
+parityStateChange: false
+
+## Scope
+
+Schema-1 override writer accepts exactly `SET_M12_OVERRIDE_VALUE` for the property path
+`["m12_override_value"]`. It requires `LOCAL_OVERRIDE`, `readOnly=false`,
+`referenceReadOnly=true`, matching local/reference/hierarchy IDs, and the current revision. A valid
+write updates only the verified value and advances the local revision by one.
+
+Linked ownership, a second property path, identity drift, stale revision, malformed fields, and values
+outside the bounded float range are blocked before any writer commit.
+
+## Evidence
+
+- `npm --prefix web run test:library-override-writer` passed 4/4 unit tests.
+- The valid request applies one property and increments revision exactly once while preserving local
+  override ownership and reference read-only semantics.
+- Stale, linked-owner, identity, alternate-operation, alternate-property, malformed, and out-of-range
+  requests fail closed.
+
+## Artifact Hashes
+
+- protocol: `dd181c7e9946b98334a5d1c686887afecfe3fc11d732beec246e40bf11a155aa`
+- unit: `e41bd32eb4ce4d331a20ecb91f3325a27f461b9ae85e98940d5afd482ec21c4c`
+- manifest: `9eeee93e4a806aa59b5c53a6485fe3a1b5e3972c1d2585cdc71b7cfc293afb70`
+- package commands: `cfb232baa494ff59f6c8d65514a08c86332ee9354350b2a0392b6f932a7ee42c`
+
+## Next Task
+
+`M12-03L`: block override stale source/revision before Main commit.
+
+## Rollback
+
+Remove the override writer protocol, unit suite, manifest, package command, and this status entry.
+Restore M12-03J to pending and move the machine queue back to `M12-03K`. No parity ledger rollback
+is required.