# v2.0.0-alpha.0 — Artifact schema migration checks

This alpha opens the v2.0 stability line. relay-baton stays local-first,
subprocess-only, and deterministic; v2.0 work hardens the contracts and the
desktop workflow. First item: read-only upgrade/migration detection for
`.ai-session` artifacts.

## Added

- **Artifact schema registry** — `ARTIFACT_SCHEMA_VERSIONS` is the single source
  of truth for the current on-disk schema version of each versioned artifact
  (`session.json`, `checkpoints.jsonl`).
- **Migration checks** — `relay-baton migrate [--check] [--json]` reports each
  versioned artifact's schema status: `ok`, `outdated` (older than current),
  `ahead` (written by a newer CLI), `legacy` (no `schemaVersion` field — treated
  as v1), or `unreadable`, with guidance.
- **`doctor --deep` integration** — extended diagnostics now include a `schema:`
  line per artifact plus a migration hint when anything is migratable.

## Constraints

- Read-only this release: detection and guidance only. In-place migration apply
  is intentionally deferred to the first real schema-version bump, when a
  migrator plugs into the registry — so no artifact is ever rewritten yet.
- Deterministic, no model calls.

## Next in v2.0

- Stable artifact schema v2 (bump + migrators).
- Stable desktop contract with i18n parity.
- Installer/update story finalized, public docs pass, hard constraints reaffirmed.