Seed batches take file ids from the insert; merge split uploads hourly

SeedService looked up every file of a batch across all files partitions
after inserting it (15% of Postgres' active time); the merge job read
every release on each GC sweep.

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

commands/GcScheduler.ts

@@ -34,6 +34,8 @@ export default class GcScheduler extends BaseCommand {
 
   /** When release completeness was last recomputed (it runs less often than the sweep). */
   private completenessAt = 0
+  /** When split uploads were last merged. */
+  private mergedAt = 0
 
   public async run() {
     this.logger.info(
@@ -115,9 +117,13 @@ export default class GcScheduler extends BaseCommand {
       )
     }
 
-    // Uploads split per poster (CONCEPT.md D35); the releases this empties go in a later sweep.
-    const merged = await ReleaseMergeService.mergeSplitPosts({ dryRun: this.dryRun })
-    if (merged.releases) this.logger.info(`Split uploads: ${this.verb('merge', 'merged')} ${merged.releases} releases into ${merged.names}.`)
+    // Uploads split per poster (CONCEPT.md D35); the releases this empties go in a later sweep. It reads
+    // every release and its files: hourly, not every sweep (LOG.md 2026-10-06 (12)).
+    if (this.once || Date.now() - this.mergedAt >= gcConfig.mergeIntervalMs) {
+      this.mergedAt = Date.now()
+      const merged = await ReleaseMergeService.mergeSplitPosts({ dryRun: this.dryRun })
+      if (merged.releases) this.logger.info(`Split uploads: ${this.verb('merge', 'merged')} ${merged.releases} releases into ${merged.names}.`)
+    }
 
     await this.rebuildIndexes()
   }