Keep stamped reservations a marker, and end a skipped turn degraded
Commit

- A stamped reservation is prepare-commit-msg's marker for its own commit only. It is never turned into a condensation attempt: an eager or doctor condensation starts a fresh attempt instead of adopting it, and a failed post-commit condensation records nothing, as before reservations existed. A table test covers every reservation state against matching and differing trailers.
- A step skipped because the session is homed in another worktree ends the turn degraded instead of as a clean capture.
- The restored guard ledger entry says why the git call stays.
Co-Authored-By: Claude Opus 5.5 (1M context) noreply@anthropic.com Entire-Checkpoint: 01M3YXRV1H86VAEFGZRRS4P01K
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