feat(companion): add heartbeat success observability state

src/companion/heartbeatLoop.test.ts

@@ -96,6 +96,24 @@ describe('CompanionHeartbeatLoop', () => {
     loop.stop();
   });
 
+  it('tracks successCount and lastSuccessAt in loop state', async () => {
+    const publishHeartbeat = vi.fn(async () => buildStatusResult());
+    const loop = new CompanionHeartbeatLoop({ publishHeartbeat }, { intervalMs: 300 });
+
+    expect(loop.successCount).toBe(0);
+    expect(loop.lastSuccessAt).toBeNull();
+
+    loop.start();
+    await Promise.resolve();
+
+    expect(loop.successCount).toBe(1);
+    expect(loop.lastSuccessAt).not.toBeNull();
+    expect(loop.getState().successCount).toBe(1);
+    expect(loop.getState().lastSuccessAt).toBe(loop.lastSuccessAt);
+
+    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 }));
@@ -193,6 +211,8 @@ describe('CompanionHeartbeatLoop', () => {
     expect(loop.running).toBe(false);
     expect(loop.getState()).toEqual({
       running: false,
+      successCount: 1,
+      lastSuccessAt: expect.any(Number),
       failureCount: 0,
       lastFailure: null,
     });