## What changed
- Add a `thread_artifacts` SQLite table with per-thread typed identities,
JSON payloads, cascade deletion, uniqueness enforcement, and an index for
ordered per-thread reads.
- Export artifact records, attachment and removal outcomes, and paginated
result models from `codex-state`.
## Testing
- Add a migration test covering preservation of existing thread-section
metadata and compatibility with the previous migration set.
GitOrigin-RevId: 4e0a8e5bfa168ae2b8871970466e5055e142a4a6
