# SQ-010: Publish Endpoint (Single Node)

**Status:** `[ ] TODO`
**Blocked by:** SQ-007, SQ-009
**Priority:** High

## Description

Implement the Publish gRPC RPC. Clients send messages which are durably written to the local WAL via StorageEngine.

## Files to Create/Modify

- `crates/sq-server/src/grpc/data_plane.rs` - DataPlaneService Publish impl
- `crates/sq-server/src/state.rs` - add StorageEngine to State

## Behavior

1. Receive PublishRequest with batch of messages
2. For each message: call StorageEngine::append
3. Ack mode handling:
   - ACK_MODE_ALL: return after fsync (default single-node behavior)
   - ACK_MODE_LOCAL: same as ALL for single node
   - ACK_MODE_NONE: return immediately, write async
4. Return PublishResponse with offset assignments

## Acceptance Criteria

- [ ] Publish 1 message, verify WAL file exists and contains the message
- [ ] Publish batch of 100 messages, verify all acked with sequential offsets
- [ ] ACK_MODE_NONE: response is immediate (no waiting for fsync)
- [ ] Invalid request (empty topic): returns InvalidArgument gRPC status
- [ ] Auto-create topic on first publish (if topic doesn't exist)