# Raft Service Contract (gRPC)

## Overview

Single RPC entrypoint for Raft message exchange; uses raft-rs `Message` protobuf encoding (prost).

## Service

```
service RaftService {
  rpc Send(RaftMessage) returns (RaftResponse);
}
```

## Messages

- **RaftMessage**
  - `message: bytes` (serialized `raft::eraftpb::Message` via prost)

- **RaftResponse**
  - Empty payload; errors conveyed via gRPC status

## Expectations

- Client (peer) wraps raft-rs `Message` and posts to remote peer via `Send`.
- Receivers decode and feed into `RawNode::step`, then drive `on_ready` to persist/apply.
- Transport must retry/transient-handle UNAVAILABLE; fail fast on INVALID_ARGUMENT decode errors.

## Test Hooks

- Integration harness should:
  - Start 3 peers with distinct addresses.
  - Wire RaftService between peers.
  - Propose on leader; verify followers receive and persist entries.
  - Simulate follower stop/restart and verify catch-up via `Send`.