Slim follow-up to the cherry-picked #111585 (@KoNit-K):
- tools/skill_usage.py: generalize the usage ledger's `_usage_file_lock()` into
`skill_file_lock(lock_path)` — same fcntl/msvcrt idiom, now thread-re-entrant
via a per-thread held set (flock is not re-entrant across separate fds; a
ContextVar would leak "held" into copy_context() timer threads).
- tools/skill_manager_tool.py: drop the third fcntl/msvcrt copy, hashlib and the
ContextVar; the per-skill lock is `<skills>/.locks/<skill-dir-name>.lock`
(readable, outside the skill dir so delete/recreate cannot unlink it under a
waiting writer). Batch locks sort by lock PATH, not name, so two batches
naming the same skills in different forms cannot deadlock.
- tools/skill_manager_batch.py: plain `with` around snapshot -> commit/rollback
instead of manual __enter__/__exit__ bookkeeping.
- tests: trimmed to two invariants — the two-writer lost-update test on
SKILL.md (from #111585) and a re-entrancy/exclusivity test on the helper.
Dropped: the edit/write_file/remove_file parametrization (same dispatcher
path as patch) and the category-dir cleanup test (lock files never lived in
category dirs here).
For each issue anchor present in BASE 63279301bc non-test .py and absent on HEAD, the BASE comment/docstring block was re-attached at the HEAD location of the code it explained (matched by the distinctive code line / enclosing def). Sentences already covered by an existing HEAD comment were deduped; the issue number always survives. Insert-only: no code lines changed.
teknium1