collaboration skill's mistake-recording step uses capture-event's retired --type flag

[williamthorsen]

Problem

The "Skill improvement" step in the collaboration skill instructs the agent to invoke capture-event with --type mistake. capture-event retired --type in favor of --tags, and its CLI now rejects --type as an unknown flag. An agent that follows the instruction literally gets an invalid-args error and records nothing. The step fires exactly when a skill has just caused a mistake, so the correction is lost at the worst possible moment for the guidance to fail.

Context

The instruction was rewritten in #714 — the commit that introduced capture-event and deleted the older record-skill-mistake skill it replaced. --type was valid then; it was later retired in favor of --tags (the capture-event CLI test now asserts --type is rejected as "the retired --type flag"), but the collaboration instruction was never updated to match.

The original report asked whether the step should instead point at record-skill-mistake. It should not: that skill was deliberately removed in #714 and no longer exists in the source — only a stale installed copy lingers on machines that haven't synced since. capture-event is the intended home for agent mistakes under the project's unified-substrate direction.

Beyond the broken flag, the instruction records an unattributed event: it names no offending skill and no detail, so a recalled mistake event isn't actionable. And mistake is not yet an established tag convention — only --tags fix is documented in capture-event.

Proposed solution

Correct the collaboration step to invoke capture-event with the current flags: tag the event mistake, attribute it to the skill at fault via --skill, and capture what went wrong and what the skill should have said. The --skill attribution is the substrate-native equivalent of what record-skill-mistake did by colocating a mistakes.md with the offending skill — it preserves the "which skill needs revising" linkage so a recalled event is actionable.

Document mistake as a tag convention in capture-event alongside the existing fix convention, so the group-recall rationale that justifies tagging holds for mistakes too.

No CLI change is needed: --tags already accepts arbitrary values and --skill already exists, so mistake is just data. The existing test that asserts --type is rejected stays as-is.

Acceptance criteria

Must have

• The collaboration skill's mistake-recording step invokes capture-event with --tags mistake (not --type) and references no retired flag.
• The step attributes the event to the offending skill via --skill and directs the agent to capture what went wrong and what the skill should have said.
• capture-event documents mistake as a tag convention alongside fix.
• The agents test suite passes, including the existing --type-rejection test and the content-path-conventions checks.

Should have

• The two documents use parallel wording for the mistake capture — the collaboration instruction and the capture-event convention agree on the flags and on what goes in the body.