* fix(skills): rollback reads its history off the event loop
rollback_custom_skill constructed the user-scoped storage, probed whether the
skill exists and parsed custom/.history/<name>.jsonl inline, while the sibling
get_custom_skill_history two lines above already offloads exactly those three
steps and documents them as "blocking filesystem IO that must stay off the
event loop". The history file grows one entry per edit carrying full previous
and new content, so a rollback request parsed the whole edit history on the
Gateway loop; the strict Blockbuster gate catches the construction as a blocking
os.getcwd() through SkillsConfig.get_skills_path() -> project_root().
Offload the three steps through the same worker-thread closure and anchor both
pre-scan branches under tests/blocking_io/.
* test(skills): address rollback anchor review feedback
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
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