Before: origin/main importer, identical synthetic v1 fixture.
[03:45:07.267] ERROR (#5481): server runtime startup failed
  {
    cause: 'SchemaError: Expected 1\n' +
      '  at ["version"]\n' +
      '    at server.startup.orchestration-v2.legacy-v1.import-shells (file:///home/ubuntu/wt/composer-chat-15/apps/server/src/serverRuntimeStartup.ts:382:12)\n' +
      '    at server.startup (file:///home/ubuntu/wt/composer-chat-15/apps/server/src/serverRuntimeStartup.ts:686:14)'
  }

After: rebuilt importer, shell import and hydration completed.
[03:47:11.572] INFO (#5477): Imported legacy v1 thread shells
  { importedThreadCount: 1, importedMessageCount: 1 }
[03:47:11.589] INFO (#5477): V2 orchestration recovery completed
  {
    terminalizedRuns: 0,
    stoppedSessions: 0,
    closedRequests: 0,
    retiredEffects: 0,
    requeuedEffects: 0
  }
[03:47:11.679] INFO (#5850): Hydrated legacy v1 thread transcripts
  { importedThreadCount: 1, importedMessageCount: 0 }

Database: message text preserved; unreadable context omitted; v1 source context unchanged.
Focused regression suite: 6/6 passing; dependency interruption preserves cancellation.
Linux web/Node24 verified. macOS, Windows, iOS, Android and Electron desktop unverified.