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>

app/services/prober.ts

@@ -97,7 +97,6 @@ export class Prober {
   }
   /** The pending ladder's namer: named pending releases into the catalog, alongside the lanes. */
   private namer = new PendingNamer()
-  private sweptAt = 0
 
   async run() {
     // A previous run's claims: one prober at a time.
@@ -106,6 +105,17 @@ export class Prober {
     const released = await PendingLadder.release()
     if (released) logger.info(`Probing: ${released} pending releases from a previous run back on the ladder.`)
     const namer = this.namer.run(() => this.stopped).catch((error) => logger.error(`Naming failed: ${error.message}`))
+    // The ladder's discard sweep beside the lanes: a dropped signature's rows take minutes on the HDD (LOG.md (133)).
+    const sweeper = (async () => {
+      while (!this.stopped) {
+        try {
+          this.stats.discarded += await PendingLadder.discard()
+        } catch (error: any) {
+          logger.error(`Probing: the discard sweep failed: ${error.message}`)
+        }
+        for (let waited = 0; waited < SWEEP_MS && !this.stopped; waited += 1000) await sleep(1000)
+      }
+    })()
     logger.info(`Probing with ${this.share.min}–${this.share.max} connections (its share of the account's).`)
     const flusher = (async () => {
       while (!this.stopped || this.outcomes.length > 0) {
@@ -136,6 +146,7 @@ export class Prober {
     }
     await Promise.all(this.lanes)
     await namer
+    await sweeper
     await this.share.leave().catch(() => {})
     // What was claimed and not probed goes back.
     for (const candidate of this.queue.splice(0)) this.outcomes.push({ candidate, status: 'waiting' })
@@ -266,10 +277,6 @@ export class Prober {
 
   /** The pending ladder's share of a claim: at least pendingShare of the batch, and whatever the catalog's tiers left. */
   private async claimPending() {
-    if (Date.now() - this.sweptAt > SWEEP_MS) {
-      this.sweptAt = Date.now()
-      this.stats.discarded += await PendingLadder.discard()
-    }
     const want = Math.max(Math.floor(this.batch * coordinatorConfig.probe.pendingShare), this.batch - this.queue.length)
     const probes = await PendingLadder.claim(want)
     if (probes.length === 0) return