Update Section Map

Workflow

After writer confirms review proposals:
- [ ] Step 1: Snapshot current section-map.md to ops/curator/snapshots/YYYY-MM-DD-section-map.md
- [ ] Step 2: Apply confirmed changes: add / rename / merge / retire / reassign
- [ ] Step 3: Sort sections by `Established` date (oldest first for stable ordering)
- [ ] Step 4: Validate schema (every post in exactly one section or unassigned; every section has promise; retired sections preserved)
- [ ] Step 5: Write new section-map.md
- [ ] Step 6: Update the last_updated timestamp + changelog entry

Schema validation rules

• Every post appears in exactly one section OR in unassigned. No double-assignment.
• Every section has: slug, promise, fit_confidence, established, posts.
• Retired sections stay in map under ## Retired sections with retired: YYYY-MM-DD and reason.
• Max 5 non-retired sections. If >5, abort and flag.

Guardrails

1. Snapshot before every write.
2. Validate schema before writing. If invalid, bubble error; don't write partial.
3. Never delete retired-section entries.
4. Changelog entry on every write (single line with YYYY-MM-DD + summary of changes).
5. Atomic: read → snapshot → validate → write. Single operation.