fix(sleep): confine legacy SKILL.md and CLAUDE.md adoption to staged roots

[RohithPariki]

Problem

Issue #288 identified an inconsistency between per-skill adoption (adopt_skills()) and legacy adoption (adopt()):
While adopt_skills() confines live skill targets to the recorded skills roots via _live_target_within_roots() and fails closed if targets escape, legacy adopt() performed no root containment checks on either live_skill_path or live_memory_path.
Furthermore, _planned_live_directories() would create any missing parent directory tree and write staged proposals to arbitrary paths outside the project or skills roots (such as ~/.bashrc or system files) if a manifest was retargeted or tampered with.
In addition, write_staging() did not record skill_roots in the manifest when staging pure legacy proposals, leaving legacy adoptions without a recorded root boundary.

Root Cause

1. write_staging() omitted project_root from manifest.json and only recorded manifest["skill_roots"] when skill_rows (per-skill proposals) was non-empty.
2. adopt() validated basename, canonical realpath, and symlink/junction presence, but never validated target containment against skill_roots or project_root.

Solution

1. Record roots in staging:
   • In write_staging(): Always record manifest["project_root"] = os.path.abspath(project) and populate manifest["skill_roots"] even for legacy proposals (deriving the root from live_skill_path and skill_search_roots).
   • In run_sleep_cycle(): Pass skill_search_roots(cfg) unconditionally to write_staging().
2. Read and validate staged project root:
   • Added staged_project_root(staging_dir: str) -> str to mirror staged_skill_roots(), requiring an absolute project_root in manifest.json and failing closed with an informative StagingError if missing or invalid.
3. Enforce containment in adopt():
   • For label == "skill": Ensure _live_target_within_roots(live, skill_roots) holds; otherwise raise StagingError ("live target for legacy skill is outside the skills roots recorded when this night was staged: ...").
   • For label == "memory": Ensure _live_target_within_roots(live, [project_root]) holds; otherwise raise StagingError ("live target for legacy memory is outside the project root: ...").
   • This containment check executes before any directory creation or adoption transaction targets are appended.

Testing

• Executed python -m pytest tests/test_sleep_adopt_skill_subset.py:
  • 106 tests passed (4 skipped due to platform-specific symlink support).
• Added TestLegacyAdoptionIsConfinedToTheStagedRoots with 8 focused regression tests:
  • test_legacy_skill_retargeted_onto_an_outside_file_is_refused (victim untouched)
  • test_legacy_skill_retargeted_to_create_a_new_outside_file_is_refused (no directories or files created)
  • test_legacy_memory_retargeted_onto_an_outside_file_is_refused (victim untouched)
  • test_legacy_memory_retargeted_to_create_a_new_outside_file_is_refused (no directory or file created)
  • test_legacy_manifest_without_recorded_skill_roots_is_refused (fails closed)
  • test_legacy_manifest_without_recorded_project_root_is_refused (fails closed)
  • test_staged_project_root_reads_and_validates
  • test_ordinary_legacy_adoption_still_succeeds
• Executed full cycle and adopt tests in tests/test_sleep_engine.py: all 5 tests passed.

Risk

Low. Valid legacy in-root adoption behavior is fully preserved. Staged nights written with unconfined or missing root manifests fail closed with an explicit error to restage.

Issue

Fixes #288