feat: add initial

Signed-off-by: kjuulh <contact@kjuulh.io>

todos/SQ-010-publish-endpoint.md

@@ -0,0 +1,32 @@
+# 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)