Consume Redis Streams with a consumer group using XREADGROUP and XACK

Documented steps

1. Create a consumer group on the stream: `XGROUP CREATE mystream mygroup 0` (0 = deliver from the beginning; use `$` to only deliver new messages). MKSTREAM option auto-creates the stream.
2. Read as a consumer: `XREADGROUP GROUP mygroup consumer1 COUNT 10 STREAMS mystream >`. The `>` ID returns only messages never delivered to any other consumer (partitioned across the group).
3. Each consumer name is auto-created on first use and can see only the messages delivered to it - each message has a single owner.
4. After successfully processing, acknowledge: `XACK mystream mygroup <id> [id ...]` to remove the message from the Pending Entries List (PEL).
5. Block for new messages: `XREADGROUP GROUP mygroup consumer1 BLOCK 5000 COUNT 10 STREAMS mystream >` - blocks up to 5000 ms (0 = forever).
6. Inspect unacknowledged work: `XPENDING mystream mygroup`.
7. Pick up another consumer's stalled messages: `XREADGROUP GROUP mygroup consumer2 STREAMS mystream 0` reads this consumer's own pending entries; or use XCLAIM/XAUTOCLAIM to explicitly take over.
8. Skip PEL tracking entirely with `NOACK` if at-least-once is not required.