Update Watchlist

Workflow

Monthly (first weekly run of the month):
- [ ] Step 1: Read last 4-8 weekly digests' appendices
- [ ] Step 2: Identify sources with ≥3 consecutive fetch failures (remove candidates)
- [ ] Step 3: Identify external authors/URLs referenced by watchlist sources ≥3 times in a month (add candidates)
- [ ] Step 4: Parse any user-added markers in digest bodies (<!-- scout: drop-this-source --> / <!-- scout: add {url} -->)
- [ ] Step 5: WebFetch each proposed add to validate it returns content
- [ ] Step 6: Emit ops/trend-scout/watchlist-proposed-diff.md
- [ ] Step 7: On user approval (.approved file or explicit trigger), apply diff; append changelog to watchlist.md

Proposed diff format

# Watchlist changes proposed 2026-W17