## Why
Guardian review needs the original user instructions alongside verified answers, even after compaction, resume, or rollback. A summarized or legacy checkpoint cannot establish a complete instruction history.
## What changed
- Capture text user messages in retained context when `guardian_thread_context` is enabled, preserving their message identity through compaction and replay.
- Keep retained instructions and verified answers in arrival order, with independent size and completeness tracking for each family.
- Roll back retained evidence at the exact user-message boundary, including steers that share a turn ID, and apply the same semantics during rollout migration.
- Treat checkpoints without retained user messages as incomplete while preserving their verified answers.
## Testing
- Cover capture, compaction, resume, rollback, child forks, legacy checkpoints, storage bounds, and rollout migration.
GitOrigin-RevId: 72706731b54e5ac8645db61b446d2401afb42235
felixxia-oai
80d7ca34bc