Prober: the signature index by the poster's md5

A poster of 2.7 kB broke the index build (a btree key is at most a third of a page) and left an invalid index
that IF NOT EXISTS would have taken for the real one: the migration drops it first and indexes md5(poster), and
the sweep asks by it.

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

app/services/pending_ladder.ts

@@ -438,8 +438,9 @@ class PendingLadder {
     for (const s of signatures) {
       let rows: any[]
       do {
-        // The poster's rows by the signature index, a tool's and group's by the ladder's: never a test on the rows,
-        // which was a scan of the whole table per signature on the HDD (LOG.md (134)).
+        // The poster's rows by the signature index (on the poster's md5: a poster can be longer than a btree
+        // key), a tool's and group's by the ladder's: never a test on the rows, which was a scan of the whole
+        // table per signature on the HDD (LOG.md (134)).
         ;({ rows } =
           s.poster === ''
             ? await db.rawQuery(
@@ -449,8 +450,8 @@ class PendingLadder {
               )
             : await db.rawQuery(
                 `SELECT encode(release_key, 'hex') AS release_key FROM pending_releases
-                 WHERE status = ? AND group_id = ? AND tool = ? AND poster = ? LIMIT ?`,
-                [PENDING.waiting, s.group_id, s.tool, s.poster, limit]
+                 WHERE status = ? AND group_id = ? AND tool = ? AND md5(poster) = md5(?::text) AND poster = ? LIMIT ?`,
+                [PENDING.waiting, s.group_id, s.tool, s.poster, s.poster, limit]
               ))
         discarded += await this.discardKeys(rows, samplePercent)
       } while (rows.length === limit && rows.some((r) => !explored(r.release_key, samplePercent)))