Bun/Node one-shot script hangs after main() returns when sharing imports with a long-running service

Operator-triggered backfill scripts (run_phase3_message_requests_backfill.ts, run_phase3_messages_backfill.ts) hang indefinitely on --dry-run and silently hang at the end of real backfills too. Symptom: main() resolves, the final JSONL event prints, but the process never exits. CI/operator scripts kill it with SIGINT or timeout.