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>

app/services/batch_store.ts

@@ -9,7 +9,7 @@ import { SIDECAR } from '#services/sidecar_folder'
 import { identityKey, releaseKey } from '#lib/release/keys'
 import { sourceCode } from '#lib/release/source'
 import { uploadTool } from '#lib/rules/index'
-import { byEffort } from '#services/pending_ladder'
+import { byEffort, lockOrder } from '#services/pending_ladder'
 import { TEXT_KINDS, TEXT_MAX, textsToStore } from '#lib/release/text_kind'
 
 /**
@@ -232,7 +232,8 @@ class BatchStore {
            target_bytes = coalesce(pending_releases.target_bytes, excluded.target_bytes)
          WHERE NOT pending_releases.finished
          RETURNING release_key, tool, klass, (xmax = 0) AS inserted`,
-        [groupId, JSON.stringify(rows)]
+        // In the record's lock order: the upsert locks a finished row too, before its WHERE passes it by.
+        [groupId, JSON.stringify(lockOrder(rows, (r) => r.release_key))]
       )
       written += done.length
       // Each class seen gets its row in the ladder's record, so the claim explores it (pending_classes).
@@ -248,7 +249,10 @@ class BatchStore {
           `INSERT INTO pending_classes (tool, group_id, klass, waiting)
            SELECT v.tool, ?, v.klass, v.waiting FROM jsonb_to_recordset(?::jsonb) AS v(tool text, klass int, waiting int)
            ON CONFLICT (tool, group_id, klass) DO UPDATE SET waiting = pending_classes.waiting + excluded.waiting`,
-          [groupId, JSON.stringify([...classes.values()])]
+          [
+            groupId,
+            JSON.stringify(lockOrder(classes.values(), (c) => `${c.tool}\t${groupId}\t${c.klass}`)),
+          ]
         )
       }
     }