Prober: the sweep by a signature index, pending rows locked in one order, deadlocked flushes kept

The discard sweep of a dropped signature read the whole pending_releases table per signature (a parallel seq
scan over the poster test, four minutes on the HDD that starved the lanes' claims): a partial index on
(group_id, tool, poster) WHERE status = 0 makes it a range, and the sweep queries a poster's rows by it and a
tool's and group's by the ladder index.

The batch store's pending upsert, the record, and the sweep deadlocked on pending_releases and pending_classes
rows locked in different orders, and a deadlocked flush dropped its outcomes: lockOrder() sorts every
multi-row statement's set the same way, and a flush that deadlocks anyway keeps its outcomes for the next.

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

REBUILD.md

@@ -936,10 +936,15 @@ f. **Nothing enters the catalog without a usable name** (amended
    `pending_signatures` for (tool, group, poster) and (tool, group), and a
    signature with PENDING_MIN_PROBES (100) climbs and at most
    PENDING_MAX_NAMED (0.5%) named is dropped: a sweep beside the lanes
-   (every five minutes, in its own loop: a signature's rows are minutes
-   of HDD) discards the waiting releases of each dropped signature and
-   class once (`swept_at`; the edge drops their new releases itself), the
-   rules' `samplePercent` of them left to climb (LOG.md (133)). The namer
+   (every five minutes, in its own loop) discards the waiting releases
+   of each dropped signature and class once (`swept_at`; the edge drops
+   their new releases itself), the rules' `samplePercent` of them left to
+   climb, each by an index (`pending_releases_signature_idx` for a
+   poster's rows: tested on the rows, a signature was a scan of the whole
+   table; LOG.md (133), (134)). The batch store, the record, the claim
+   and the sweep lock pending rows in one order (`lockOrder`), and a
+   flush that deadlocks anyway keeps its outcomes for the next (LOG.md
+   (134)). The namer
    (`app/services/pending_namer.ts`, in the prober's process): a named
    release's article span read again from the corpus (the stored range's
    chunks) or by XOVER on a connection of its own, a chunk of articles