At most two leases per group: a group's batches wait for each other, more workers only queue

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/services/leases.ts

@@ -17,6 +17,13 @@ export class LeaseLost extends Error {}
  * prefetched (LOG.md 2026-10-09). A lease whose worker went quiet for
  * LEASE_TTL_SECONDS is taken over and resumes at its resume point.
  */
+/**
+ * A group's batches wait for each other (the batch store locks the group): more workers than this on one group only
+ * queue. Eight on one picture group's gap ranges (priority -1, in id order) held the node API's batches for minutes
+ * (LOG.md 2026-10-16 (68)).
+ */
+const MAX_LEASES_PER_GROUP = 2
+
 class Leases {
   async lease(nodeId: number): Promise<Lease | null> {
     const rules = await RuleSets.current()
@@ -29,9 +36,12 @@ class Leases {
            SELECT id FROM ranges
            WHERE ${spooled ? 'spooled_chunks > 0' : 'true'} AND next_id <= end_id ${history}
              AND (status = 'planned' OR (status = 'leased' AND heartbeat_at < now() - make_interval(secs => ?)))
+             AND (SELECT count(*) FROM ranges l
+                  WHERE l.status = 'leased' AND l.group_id = ranges.group_id AND l.id <> ranges.id
+                    AND l.heartbeat_at >= now() - make_interval(secs => ?)) < ${MAX_LEASES_PER_GROUP}
            ORDER BY priority, id LIMIT 1 FOR UPDATE SKIP LOCKED)
          RETURNING r.id, r.group_id, r.start_id, r.end_id, r.next_id`,
-        [nodeId, rules.version, coordinatorConfig.leaseTtlSeconds]
+        [nodeId, rules.version, coordinatorConfig.leaseTtlSeconds, coordinatorConfig.leaseTtlSeconds]
       )
     let { rows } = await take(true)
     if (rows.length === 0) ({ rows } = await take(false))