- sync_changes gains schema_version column (default 1, idempotent ADD)
- Change/Changeset carry schemaVersion; server refuses > MaxSupported
- server->client changes now carry eventId + schemaVersion so the
restore path can dedup via eventId and route through a migration
chain keyed on schemaVersion
- backup JSONL gains schemaVersion per line
Pre-M2 clients (omit the field) are treated as v1 for compatibility.
This is the stability contract we commit to before launch: once v1
events are in the wild, all future builds must replay them forward.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>