The discard sweep beside the lanes, each dropped signature swept once

After aa40222 the prober still idled: a dropped signature's range of the
ladder index is minutes of HDD (309 dropped, 242 with a poster tested on
the rows) and the sweep read the same ranges again every five minutes
inside the claim. Now each dropped class and signature is swept once
(swept_at, migration 7100; null again when the record drops it anew),
20 of each per sweep in rounds of 10k rows, in a loop of its own in the
prober beside the lanes and the namer (LOG.md (133)).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

commands/pending_classes.ts

@@ -47,7 +47,7 @@ export default class PendingClasses extends BaseCommand {
     )
     const { pendingMinProbes, pendingMaxNamed } = coordinatorConfig.probe
     await db.rawQuery(
-      `UPDATE pending_classes SET dropped = true WHERE NOT dropped AND probed >= ?::int AND named::float <= probed * ?::float`,
+      `UPDATE pending_classes SET dropped = true, swept_at = NULL WHERE NOT dropped AND probed >= ?::int AND named::float <= probed * ?::float`,
       [pendingMinProbes, pendingMaxNamed]
     )
     // The waiting rows by windows of created_at (pending_releases_waiting_idx reaches them).