A skill's SKILL.md frontmatter may declare session-start (output into
<skill_session_context>, at session start, /new, resume and after compaction),
turn-end (after every run, in the background; output or a failure reaches the
next run as a hidden notice, repeats suppressed until a clean run) and
protected-paths (write/edit refused inside them). Hooks run from the skill
directory with VOLCANIC_WORKSPACE, VOLCANIC_SKILL_DIR and the chat's TZ; waits
are bounded by each hook's timeout and failures never break a run. /skills
shows declared hooks and broken fields.
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