file_keys: fill in the background, use it once complete

Copying all existing keys in the migration read the files rows from the
HDD for over half an hour and held up the deploy. gc:scheduler now copies
them in slices (FILE_KEYS_FILL_SECONDS per sweep) and FileStore checks
every partition until the fill is complete.

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

commands/GcScheduler.ts

@@ -10,6 +10,7 @@ import ReleaseMergeService from '#services/ReleaseMergeService'
 import StagingService from '#services/StagingService'
 import FilePartitions from '#services/FilePartitions'
 import ReleaseCompleteness from '#services/ReleaseCompleteness'
+import FileKeys from '#services/FileKeys'
 import Shutdown from '#services/Shutdown'
 
 const CLEAN_BATCH = 1000
@@ -51,6 +52,11 @@ export default class GcScheduler extends BaseCommand {
         } catch (err: any) {
           this.logger.error(`Release completeness failed: ${err.message}`)
         }
+        try {
+          await this.fillFileKeys()
+        } catch (err: any) {
+          this.logger.error(`file_keys fill failed: ${err.message}`)
+        }
         if (!this.once) await Shutdown.sleep(gcConfig.intervalMs)
       } while (!this.once && !Shutdown.requested)
     } finally {
@@ -117,6 +123,17 @@ export default class GcScheduler extends BaseCommand {
   }
 
   /** Rebuilds bloated indexes, at most every gcConfig.reindexIntervalMs (CONCEPT.md D33). */
+  /** The keys of files from before file_keys, a slice of time per sweep, until done. */
+  private async fillFileKeys() {
+    if (this.dryRun || (await FileKeys.complete())) return
+    const started = Date.now()
+    const { read, complete, nextId, untilId } = await FileKeys.fill(gcConfig.fileKeysFillMs)
+    this.logger.info(
+      `file_keys: ${read.toLocaleString('en')} keys copied in ${Math.round((Date.now() - started) / 1000)} s, ` +
+        (complete ? 'complete: file inserts use the filter now.' : `at file ${nextId.toLocaleString('en')} of ${untilId.toLocaleString('en')}.`)
+    )
+  }
+
   private async releaseCompleteness() {
     if (this.dryRun || (!this.once && Date.now() - this.completenessAt < gcConfig.releaseCompleteIntervalMs)) return
     this.completenessAt = Date.now()