Manual Trigger with Redis-based Concurrency Control

### 📥 Input Buffer

1. **Save incoming message**

   * Push the new message into Redis list `buffer_in:{{context_id}}`.
2. **Update metadata**

   * Set `last_seen:{{context_id}}` to the current timestamp (with a TTL of `waitSeconds + 60`).
   * INCR the counter key `buffer_count:{{context_id}}` (also expiring after `waitSeconds + 60`).
3. **Check “waiting” flag**

   * GET `waiting_reply:{{context_id}}`.
   * If it’s null (no batch in flight), SET it to `true` with TTL `waitSeconds` to block concurrent triggers.