feat(prior-art): edit-time record-sync nudge — the sync class (#2708)

A snippet recorded AT the exact file being edited is not a reuse
suggestion — it IS the record of the file being changed. The write-path
hint now renders those as their own SYNC class: 'snippet #N records this
file — updating the record is part of the edit (update_snippet /
verify_snippet)'. Nearby and semantic hits stay the reuse menu.

The two classes dedup on separate per-session channels (exclude_ids vs
exclude_sync_ids, .ids vs .sync.ids in the hook), so a reuse hint shown
early in a session can no longer silence the record-sync nudge when the
recorded file itself is edited later. Sync surfacing is measured under
its own note_usage source (write_path_sync) — its pull-through rate is
the scoreboard for whether edit-time sync actually happens, per decision
#2707 (no forge connection; records stay current in the session that has
the context). Plugin 0.1.31.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

plugin/README.md

@@ -50,6 +50,9 @@ On install you'll be asked for:
   (`hooks/scribe_prior_art.sh`) → `GET /api/plugin/prior-art`. Returns
   `additionalContext` with **no** permission decision, so it can inform the write
   but never stop it; silent when nothing is recorded, which is most of the time.
+  Two framings: a REUSE menu (similar/nearby records), and a SYNC nudge when a
+  snippet records the exact file being edited — "updating the record is part of
+  the edit" — each with its own once-per-session dedup.
   Toggle in **Settings → Knowledge auto-inject**.
 - `skills/` → the universal process-skills, surfaced by description match.
 - `hooks/scribe_sync_processes.sh` (a 2nd SessionStart hook) + the `/scribe:sync`