[servicememeai]

Scope

• Treat only actual Branch HEAD conflicts as retryable; Guard/ACL/SQL 1176 and other storage errors fail immediately.
• Verify the full current V2 Guard column/index signature at fileserver startup, not merely table existence. A historical 029_editing_core Guard becomes an explicit CF_EDIT_SCHEMA_MISMATCH rather than ten repeated upload attempts.
• Align native C file-lock and final Branch checks with current V2 single-table Guard (no cf_resource joins or lease_until), and automatically enforce the Guard when installed.
• Add focused Go tests for contract shape and deterministic error classification.

Safety

No Guard bypass, no schema mutation, no new tables. An existing legacy Guard requires a separately reviewed offline data migration. No DEV/PROD database changes or deployments in this PR.

Validation

Lightweight PR source CI only by default; targeted Go+C build and actual MariaDB upload E2E remain a release gate. Companion Hub and Docker schema-owner PRs should be delivered with this.