Function migrate_from_sqlite_once 

pub fn migrate_from_sqlite_once(
    home: &Path,
    registry: &Registry,
) -> Result<MigrateStats, RegistryError>

Scan every channel + dev objects.db under home and populate the shared registry. Skipped if the marker file exists. Never overwrites an existing registry record (idempotency + respect for newer-written data). The SQLite files are opened read-only — never modified.

On dedup conflicts (same instance_id in multiple versions/channels), the row with the latest started_at wins; any version expressing “forget” intent (display_hidden) is preserved as a tombstone.