# SQ-011: Subscribe Endpoint (Single Node)

**Status:** `[x] DONE`
**Blocked by:** SQ-010
**Priority:** High

## Description

Implement the Subscribe gRPC RPC with server-streaming. Server pushes messages to the client as they become available.

## Files to Create/Modify

- `crates/sq-server/src/grpc/data_plane.rs` - DataPlaneService Subscribe impl

## Behavior

1. Client sends SubscribeRequest with topic, partition, optional start_offset
2. Server reads from StorageEngine starting at the given offset
3. Server streams batches of ConsumedMessage to the client
4. When caught up, server polls for new messages at a configurable interval (e.g. 100ms)
5. Stream continues until client disconnects or cancellation

## Acceptance Criteria

- [ ] Publish 10 messages, then subscribe from offset 0, receive all 10
- [ ] Subscribe from offset 5, receive messages 5-9 only
- [ ] Subscribe to empty topic from offset 0, then publish, receive new messages
- [ ] Client disconnect: server-side stream cleans up without error
- [ ] Subscribe to nonexistent topic: returns NotFound gRPC status