Rebuild: the fragment merger

Files cut by a range's edge are put together once the ranges around them
are done (coordinator:run, every minute): a complete file is judged by the
rules and written as a release chunk with probe candidates; one still
missing parts while both neighbouring ranges are done is dropped and
counted (incomplete/edge). A neighbour not planned yet counts as not done,
except before the group's oldest article. BatchStore.writeReleases is the
shared write path.

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

commands/coordinator_run.ts

@@ -3,14 +3,17 @@ import type { CommandOptions } from '@adonisjs/core/types/ace'
 import { setTimeout as sleep } from 'node:timers/promises'
 import { Prefetcher } from '#services/prefetcher'
 import Planner from '#services/planner'
+import FragmentMerger from '#services/fragment_merger'
 import NntpPool from '#services/nntp_pool'
 
 const TICK_MS = 2000
 const PLAN_EVERY_MS = 60 * 60 * 1000
+const MERGE_EVERY_MS = 60 * 1000
 
 /**
  * The coordinator's background work (REBUILD.md, part 1): the prefetcher,
- * and planning ranges for new articles every hour. The API (leases, stream,
+ * merging fragments of finished ranges every minute, and planning ranges
+ * for new articles every hour. The API (leases, stream,
  * batches) runs in the web server.
  */
 export default class CoordinatorRun extends BaseCommand {
@@ -30,6 +33,7 @@ export default class CoordinatorRun extends BaseCommand {
       await done
     })
     let plannedAt = 0
+    let mergedAt = 0
     this.logger.info('Coordinator started.')
     while (!stopping) {
       try {
@@ -38,6 +42,11 @@ export default class CoordinatorRun extends BaseCommand {
           const { groups, ranges } = await Planner.planAll()
           if (ranges > 0) this.logger.info(`Planned ${ranges} ranges over ${groups} groups.`)
         }
+        if (Date.now() - mergedAt >= MERGE_EVERY_MS) {
+          mergedAt = Date.now()
+          const merged = await FragmentMerger.run()
+          if (merged.completed || merged.incomplete) this.logger.info(`Fragments: ${merged.completed} files completed, ${merged.incomplete} incomplete, ${merged.waiting} waiting.`)
+        }
         await prefetcher.tick()
       } catch (error: any) {
         this.logger.error(`Coordinator round failed: ${error.message}`)