Prober: claim only candidates of settled releases, without the join

The settler marks a settled release's candidates ready (and unreadable when
it had no readable name). Claims took the candidates by joining releases
from random points of the queue; in its newer half nothing had settled, so
a slice scanned to the end (0.3 s each, 20 slices and 5 tiers a claim) and
the prober stood still: 2.4M waiting, 0 probed a minute. Now an index over
the claimable rows only, the slices drawn within them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/services/settler.ts

@@ -21,14 +21,20 @@ class Settler {
   async run(): Promise<number> {
     let settled = 0
     while (true) {
-      const { rowCount } = await db.rawQuery(
-        `UPDATE releases SET settled_at = now(), complete = CASE WHEN file_total IS NULL THEN NULL ELSE files >= file_total END
-         WHERE id IN (SELECT id FROM releases WHERE settled_at IS NULL AND last_seen_at < now() - make_interval(mins => ?)
-           AND (last_seen_at < now() - make_interval(hours => ?) OR coalesce(last_posted_at, posted_at) < now() - make_interval(hours => ?)) LIMIT ?)`,
+      // Their probe candidates become claimable (Prober.claim), the unreadable ones first.
+      const { rows } = await db.rawQuery(
+        `WITH settled AS (
+           UPDATE releases SET settled_at = now(), complete = CASE WHEN file_total IS NULL THEN NULL ELSE files >= file_total END
+           WHERE id IN (SELECT id FROM releases WHERE settled_at IS NULL AND last_seen_at < now() - make_interval(mins => ?)
+             AND (last_seen_at < now() - make_interval(hours => ?) OR coalesce(last_posted_at, posted_at) < now() - make_interval(hours => ?)) LIMIT ?)
+           RETURNING id, readable),
+         marked AS (UPDATE probe_candidates pc SET ready = true, unreadable = NOT s.readable FROM settled s WHERE pc.release_id = s.id)
+         SELECT count(*)::int AS n FROM settled`,
         [QUIET_HISTORY_MINUTES, QUIET_HOURS, QUIET_HOURS, BATCH]
       )
-      settled += rowCount ?? 0
-      if ((rowCount ?? 0) < BATCH) return settled
+      const n = rows[0].n
+      settled += n
+      if (n < BATCH) return settled
     }
   }
 }