Turn a Linear or GitHub issue into a skill brief

Turn this issue into an agent skill brief we can check into the repo. The brief becomes a SKILL.md section or a full SKILL.md if the work will repeat.

Issue paste (Linear, GitHub Issues, or Jira export):
[paste title, description, comments with decisions, links]

Repository context:
[test command, lint command, paths likely touched]

Output SKILL.md (or ## Skill brief section if you recommend nesting inside a larger skill) with:
1. Purpose — tie to the issue title in one sentence.
2. When to use / when not to use — include ticket id and branch naming pattern if the issue specifies one.
3. Acceptance criteria — copy from the issue; add [missing from ticket] bullets only where the issue is silent and the gap blocks verification.
4. Fixtures and test data — files, env names (not values), seed commands, or URLs to staging; write [human must provide] if absent.
5. Out of scope — explicit list from issue comments; if none, infer only from labels like “won’t do” in the paste or ask in one bracketed line.
6. Verification commands — ordered list using our real scripts; write [confirm command] for unknowns.
7. Steps for the agent — numbered, each ending with Verify:.
8. Two example prompts that invoke this brief with the ticket id filled in.
9. Pitfalls: scope creep, skipping tests mentioned in the issue, editing unrelated modules, closing without running verification commands.
10. Done means: checklist mapped to acceptance criteria (checkbox per criterion).

Rules:
- Do not invent product requirements not in the issue paste.
- Do not paste secrets from the ticket; replace with env var names.
- Markdown only.