test: cover malformed hello runtime flow

tests/runtime-flow.test.ts

@@ -287,6 +287,44 @@ describe("Yonexus.Server runtime flow", () => {
     expect(recordAfterHeartbeat?.lastHeartbeatAt).toBe(now);
   });
 
+  it("returns MALFORMED_MESSAGE for hello without payload and keeps the connection open", async () => {
+    const store = createMockStore();
+    const transportState = createMockTransport();
+    const runtime = createYonexusServerRuntime({
+      config: {
+        followerIdentifiers: ["client-a"],
+        notifyBotToken: "stub-token",
+        adminUserId: "admin-user",
+        listenHost: "127.0.0.1",
+        listenPort: 8787
+      },
+      store,
+      transport: transportState.transport,
+      now: () => 1_710_000_000
+    });
+
+    await runtime.start();
+
+    const connection = createConnection();
+    await runtime.handleMessage(
+      connection,
+      encodeBuiltin({
+        type: "hello",
+        requestId: "req-bad-hello",
+        timestamp: 1_710_000_000
+      })
+    );
+
+    expect(transportState.sentToConnection).toHaveLength(1);
+    const errorResponse = decodeBuiltin(transportState.sentToConnection[0].message);
+    expect(errorResponse.type).toBe("error");
+    expect(errorResponse.payload).toMatchObject({
+      code: "MALFORMED_MESSAGE",
+      message: "hello payload is required"
+    });
+    expect((connection.ws.close as ReturnType<typeof vi.fn>)).not.toHaveBeenCalled();
+  });
+
   it("rejects unauthenticated rule messages by closing the connection", async () => {
     const store = createMockStore();
     const transportState = createMockTransport();