feat(sleep): add revert command to rollback adopted proposals

[RohithPariki]

Resolves #247

Implements the skillopt-sleep revert command to allow users to cleanly undo adopted proposals by restoring state from their immutable backups.

Changes

• CLI: Added revert subcommand to skillopt_sleep/__main__.py, matching the adopt interface (--staging, --skill, --all-skills, --legacy).
• Core: Added revert_skills and revert in skillopt_sleep/staging.py to restore original bytes safely.
• Safety:
  • Reversion refuses to run if the live file has been locally modified since adoption (protects user's work).
  • Automatically unlinks files that were originally created during the adoption, leaving no orphaned files.
• Testing: Added test_sleep_revert.py with idempotent behavior validation.

[Yifan Yang (Yif-Yang)]

Thank you for adding an explicit undo command; safe rollback is a useful missing capability.

Reviewed 312aaf7 against the current adoption machinery and the outstanding #248 review. The undo command is useful, but this implementation does not resolve that review's receipt-binding, history-ordering, and recovery requirements, and it omits adoption locking/recovery entirely. Please use validated, trusted receipt/destination bindings and a durable transaction before adding filesystem restoration or deletion. A matching content hash alone does not establish that an old night is the current adoption. Coordinate security-sensitive reproduction details privately under SECURITY.md.

Two additional functional regressions are reproducible with synthetic fixtures: adopt -> revert -> adopt fails because revert clears the receipt but leaves the immutable backup, and bare revert after a newer unadopted staging night reports success without undoing the earlier adoption. The default should select the current adopted history head, and backup/receipt cleanup should be recoverable.

The focused suite passes 104 tests, but these adverse paths are not covered by the two new happy-path tests. Please coordinate one coherent rollback implementation with #248 and keep #247 open until the safety contract is met.

[RohithPariki]

Thank you for the detailed review and guidance! I have updated the branch to address all the safety, transaction, and history-ordering requirements:

1. Adoption Locking & Recovery:

   • Revert operations for both legacy managed files and per-skill proposals now run under _adoption_locks across the staging directory and target live paths, and invoke _recover_before_manifest before transactions.
   • Receipt file ID, inode/dev identity, and file modes are validated against race conditions during lock acquisition.

2. Trusted Receipt & Manifest Binding:

   • Receipt live paths are strictly bound to and validated against the trusted staging manifest (_safe_live_path, _adopt_target_ok, _adopt_live_target_ok).
   • Tampered receipts attempting to target paths outside the project roots or containing unexpected schema fields are rejected.

3. LIFO History Ordering (Stack Model):

   • Added _assert_current_adopted_head: an older adopted night cannot be reverted if a subsequent night has also adopted the same target/skill. Newer adoptions must be rolled back first.

4. Resolved adopt -> revert -> adopt Regression:

   • Upon successful rollback, immutable backups and empty backup subdirectories in the staging directory are cleanly unlinked (_unlink_fsync and _clean_empty_backup_dir), allowing clean re-adoption.

5. Default Selection of Adopted History Head:

   • Bare skillopt-sleep revert now selects the target night via latest_adopted_staging(project), ensuring it skips newer staging nights that were never adopted.

6. Expanded Test Suite:

   • Expanded tests/test_sleep_revert.py to 20 comprehensive unit tests covering all adverse paths (tampered receipts, external target paths, stack-order enforcement, unadopted newer nights, and full adopt-revert-adopt cycles). All tests and ruff lint checks pass cleanly.