feat(companion): add heartbeat loop success callback

src/companion/heartbeatLoop.test.ts

@@ -81,6 +81,21 @@ describe('CompanionHeartbeatLoop', () => {
     loop.stop();
   });
 
+  it('calls onSuccess with heartbeat result payload', async () => {
+    const result = buildStatusResult();
+    const publishHeartbeat = vi.fn(async () => result);
+    const onSuccess = vi.fn();
+    const loop = new CompanionHeartbeatLoop(
+      { publishHeartbeat },
+      { intervalMs: 200, onSuccess },
+    );
+
+    loop.start();
+    await Promise.resolve();
+    expect(onSuccess).toHaveBeenCalledWith(result);
+    loop.stop();
+  });
+
   it('passes buildHeartbeat payload into publishHeartbeat', async () => {
     const publishHeartbeat = vi.fn(async () => buildStatusResult());
     const buildHeartbeat = vi.fn(() => ({ statusText: 'loop', powerSource: 'ac' as const }));