Run a weekly competitor diff from one agent skill

Write SKILL.md for a weekly competitor diff job. This is not a general research digest — only deltas since the last saved diff.

Standing competitor list:
[names and the public pages we always check: changelog, pricing, blog, jobs, status]

Last diff file path in repo:
[e.g. research/competitor-diffs/2026-10-19.md or "none — first run"]

SKILL.md sections:
- Purpose: produce a replaceable weekly diff artifact.
- When to use: Monday AM or before roadmap review; when not to use: ad-hoc deep dives (different skill).
- Required inputs: today's date, path to last diff, max competitors per run.
- Steps:
  1. Read last diff if it exists; extract what was already reported per competitor.
  2. For each competitor, check only the standing URLs for changes since the date on the last diff (or last 7 days if first run).
  3. Output format — use exactly these headings:
     ## Changed (with links)
     One bullet per change: competitor — one sentence — URL
     ## Unchanged
     One line per competitor: name — unchanged since [date]
     ## Worth opening
     At most two links total across all competitors, or write "none"
     ## Ignore
     One headline that looks important but is not actionable, or "none"
  4. Save the output to research/competitor-diffs/YYYY-MM-DD.md and mention the path in done checklist.
- Pitfalls: re-reporting old news, summarizing company history, inventing pricing, treating job posts as launches without saying why.
- Done means: new file committed or pasted, every Changed bullet has a URL you could open, Unchanged is honest.

Also return one example user prompt that invokes this skill with the date and last-diff path filled in.

Rules:
- No revenue, traffic, or market-share estimates.
- If a page cannot be fetched, omit the claim.
- Do not add competitors not on the standing list without human approval.