Add thread fork lineage and lazy context transfer

- Add context transfer IDs, schemas, and projections
- Support cheap fork creation and Codex native fork rollback
- Cover fork idempotency and replay behavior in tests
18fa4f3aa3Julius Marminge committed on 9/1/2026, 4:23:51 AMparent1b02d2b
26 files changedLine totals unavailable