Normalize maintenance error classification, redaction, and recovery hints

[Widthdom]

Summary

Maintenance commands disagree on missing/corrupt/locked DB failures: vacuum --json emits human stderr, backfill uses a basename, optimize/integrity expose absolute paths, and SQLite error 26 (“file is not a database”) recommends retrying a writer lock.

Audit IDs: O-02, O-03, O-26. Reproduced on v1.40.3.

Existing issue relationship

Residual/follow-up to closed #1526 and #4338, which established error/status/maintenance diagnostics.

Expected behavior

All maintenance commands share a versioned DB error classifier, support-safe redaction, and condition-specific recovery guidance.

PR scope

Keep this to missing/not-a-database/corrupt/locked classification across maintenance commands.

Implementation guide for Codex 5.6 sol xhigh

• Classify using SQLite result/extended codes and validated file state, not message substring alone.
• Route vacuum, backfill, optimize, and integrity through one error DTO/writer.
• Apply the shared redaction policy while preserving an explicit diagnostic mode.
• Recommend create/rebuild/import/integrity actions for missing/corrupt data and retry/owner diagnostics only for real locks.
• Test JSON/human, relative/absolute paths, invalid header, corruption, locks, and platform differences.
• Run full tests and add a bilingual changelog fragment referencing Error messages lack stable machine-readable error codes #1526/Audit SQLite maintenance, migration, WAL, and prune boundaries #4338.

Acceptance criteria

• JSON mode always returns valid structured errors.
• Equivalent failures have equivalent codes/categories/redaction.
• Corruption never receives lock-retry guidance.
• Sensitive absolute paths are not leaked by default.

[Widthdom]

Work started on branch fix-issue4856.

[Widthdom]

Draft PR #4949 is open with the fix. The maintenance error classifier, path-redaction contract, structured validation failures, lock-holder diagnostics, tests, bilingual documentation, and changelog fragment are included.