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Schema migrations — vouch migrate

The .vouch/ layout is the durable contract: yaml claims, markdown pages with frontmatter, json sessions, the jsonl audit log. As the pydantic models in src/vouch/models.py evolve, a KB created against an older model would become a load-time error. vouch migrate gives that evolution a versioned, reversible, audit-logged upgrade path so a schema change never silently breaks a KB in the wild.

Two version axes

vouch tracks two independent versions, and vouch migrate covers both:

Stamp What it governs Reached by
Format (integer) config.yaml version the .vouch/ directory layout (subdirs, .gitignore) vouch migrate (no subcommand)
Schema (semver) .vouch/schema_version the model schema of each artifact vouch migrate <subcommand>

A KB with no .vouch/schema_version file is treated as the baseline (0.1.0), so existing KBs keep loading until their first migrate. vouch init stamps the current version on bootstrap.

Commands

vouch migrate status                 # current schema version, target, pending migrations
vouch migrate plan                   # dry-run: every file each pending migration would change
vouch migrate plan --to 0.3.0        # plan against a specific target
vouch migrate apply                  # apply pending migrations (audit-logged, atomic)
vouch migrate apply --yes            # skip the confirmation prompt (CI)
vouch migrate rollback               # reverse the most recently applied migration
vouch migrate verify                 # parse-load every artifact under the current version

Manifests

Migrations are data, not code: yaml manifests in the repo-root migrations/ directory, one consecutive version step each. See migrations/README.md for the full format and the transform verbs (rename, default, drop, split, merge). Only consecutive manifests apply — a 0.1 → 0.5 KB walks through 0.2, 0.3, 0.4 in order.

Safety model

  • Atomic per file. Each artifact is rewritten to a temp file, fsync-ed, then os.replace-d into place. A file is always its old bytes or its new bytes — never a torn mix.
  • Reversible. Before any rewrite, the prior content of every file the step touches is journalled to .vouch/migrations/rollback-<id>.jsonl. vouch migrate rollback replays it, restoring the exact prior bytes — so apply → rollback is byte-equivalent (modulo the audit-log entries recording the round trip).
  • Crash-safe. The journal is written and fsynced before the first rewrite, and .vouch/schema_version is bumped last. An interrupted apply therefore leaves the KB reporting its prior version, with a journal to recover from.
  • Precondition. Apply refuses if the KB has pending proposals — it won't rewrite a reviewer's in-flight queue out from under them. Resolve them with vouch list-pending first.
  • state.db is disposable. The runner does not migrate the FTS5 / embedding cache; the CLI rebuilds it after a successful apply.

Audit trail

Each applied manifest logs one kb.migrate.apply event (manifest id, file count, rollback-journal id); a rollback logs kb.migrate.rollback. The legacy format migration continues to log kb.migrate.

Out of scope (v1)

  • Cross-major jumps in a single manifest (consecutive only).
  • custom: path/to/migration.py script transforms (lands once the verb taxonomy stabilises).
  • Migrating state.db (disposable; rebuilt by vouch index).
  • Bundle version embedding / refusing mismatched imports — a follow-up.
  • Concurrent multi-process migrate runs (single-writer assumption).