Purge the edge after a repair, or verify answers per PoP (#89) (#90)

#89 asked for a decision. This is it, and it is the laziest of the three options listed there: **purge the whole pull zone by hand after a repair, one call, documented in the repair procedure.**

Why not the other two:

- Purging from `emit --verify` needs a CDN credential `emit` deliberately does not hold, and `emit` reports how many blobs it wrote, never which ones — so it could not target the keys anyway.
- Waiting out the TTL means 30 days.

Whole-zone rather than per-key costs a cold cache on a zone whose objects are mostly cold, and a repair scatters thousands of keys across the tree regardless.

Also answers the question #89 left open: **the zone does not negative-cache.** A missing key answers 404 with `cache-control: no-cache` and `cdn-cache: MISS`, still MISS on an immediate retry (checked credential-free, 2026-08-01).

Docs only — `docs/command-surface.md` and `nwsync`'s usage text. The procedure itself lives in sow-platform's NWSync runbook, next to the zone it acts on.

Closes #89.

🤖 Generated with [Claude Code](https://claude.com/claude-code)Reviewed-on: #90
Reviewed-by: xtul <mpiasecki720@protonmail.com>
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>

docs/command-surface.md

@@ -97,6 +97,18 @@ broken — is skipped by every later run forever and no backfill repairs it. Wit
 and replaced when it does not match. It costs a full GET per existing blob, so
 it is a repair pass, not the default.
 
+**After a repair, purge the pull zone before believing `verify`.** A repair is
+the one thing that makes a key serve different bytes than it did before, and the
+edge caches these objects for 30 days precisely because that normally cannot
+happen. The two commands therefore look at different copies on purpose: `emit
+--verify` repairs the **origin**, `verify` reads the **edge**, and in between a
+warm PoP still answers with the old bytes while a cold one answers with the new.
+Until the zone is purged `verify`'s verdict is per-PoP and settles nothing — a
+pass is not proof, and a failure is not the repair having failed. The purge is
+one call against the pull zone; it belongs in the repair procedure rather than
+in `emit`, which holds a storage credential and no CDN one (sow-tools#89, and
+the procedure itself is in sow-platform's NWSync runbook).
+
 `emit` uploads blobs first and the index last, so the presence of an index is
 the publication marker: an artifact whose emit died halfway leaves real blobs in
 the zone and no index. Blob names are content hashes, so re-running skips