## What changed
- Add `LocalThreadStore::migrate_rollouts` with dry-run and apply modes,
optional thread selection, throughput limiting, and per-rollout outcomes.
- Canonicalize legacy JSONL records into paginated history while preserving
model-visible conversation context, including compressed rollouts and copied
fork history.
- Publish replacements atomically and journal migrations so interrupted SQLite
projections can be recovered. Coordinate migration with rollout compression
and skip rollouts with active writers.
- Make paginated history a one-way SQLite promotion so stale metadata cannot
downgrade a migrated thread.
## Testing
- Cover legacy record normalization, dry runs, idempotency, malformed input,
compressed rollouts, active writers, interrupted migration recovery, and a
cold app-server resume after migration.
GitOrigin-RevId: b9991b659f28ebb52da39ce62e8b4e0bae2ba2bb
Owen Lin
6bb6e9045f