- Add context_handoff operation 'validate' for continuation-readiness checks
- 4 probes: recall, continuation, artifact, decision
- ok = recall && continuation; artifact/decision gaps are warnings only
- Explanatory checks array with name/passed/reason per check
- Placeholder filtering: N/A, Not run excluded from evidence
- Tightened continuation: verification/blocker alone cannot pass
- All public output paths normalized to repo-relative
- 203 tests passing, 0 regressions