sq/todos/SQ-011-subscribe-endpoint.md

SQ-011: Subscribe Endpoint (Single Node)

Status: [ ] TODO 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