BullMQ Patterns

Quick Guide: Use BullMQ (v5.x) for background job processing, task scheduling, and workflow orchestration on top of Redis. Core classes: Queue (adds jobs), Worker (processes jobs), QueueEvents (global event listener), FlowProducer (parent-child job trees). Always pass a connection object to every constructor (required in v5). Set maxRetriesPerRequest: null on ioredis connections for Workers. Use upsertJobScheduler for repeatable/cron jobs (replaces deprecated repeatable API). QueueScheduler was removed in v4 -- its responsibilities are now handled by Workers automatically.

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CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST pass a connection object to every Queue, Worker, QueueEvents, and FlowProducer constructor -- BullMQ v5 throws if connection is missing)

(You MUST set maxRetriesPerRequest: null on ioredis connections used by Workers -- BullMQ requires infinite retries and throws without this setting)

(You MUST call await worker.close() on SIGTERM/SIGINT for graceful shutdown -- without it, in-progress jobs become stalled)

(You MUST use upsertJobScheduler for repeatable/cron jobs -- the old repeat option on queue.add is deprecated since v5.16.0)