test(companion): cover heartbeat loop state reset on restart

docs/plans/state.json

@@ -832,6 +832,17 @@
       ],
       "test_status": "pnpm test:run src/companion/runtimeClient.test.ts src/companion/platformClients.test.ts src/companion/heartbeatLoop.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
     },
+    "companion-heartbeat-loop-restart-state-reset-coverage": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added restart regression coverage for `CompanionHeartbeatLoop` to verify success/failure counters and timestamps are reset deterministically on restart.",
+      "files_modified": [
+        "src/companion/heartbeatLoop.test.ts",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/companion/heartbeatLoop.test.ts src/companion/platformClients.test.ts src/companion/runtimeClient.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
+    },
     "browser-tools-activation-clarity": {
       "status": "completed",
       "date": "2026-02-17",

src/companion/heartbeatLoop.test.ts

@@ -234,4 +234,36 @@ describe('CompanionHeartbeatLoop', () => {
 
     loop.stop();
   });
+
+  it('resets success and failure state when restarted', async () => {
+    const publishHeartbeat = vi
+      .fn<() => Promise<NodeStatusSetResult>>()
+      .mockResolvedValueOnce(buildStatusResult())
+      .mockRejectedValueOnce(new Error('transient'))
+      .mockResolvedValue(buildStatusResult());
+    const loop = new CompanionHeartbeatLoop({ publishHeartbeat }, { intervalMs: 500 });
+
+    loop.start();
+    await Promise.resolve();
+    expect(loop.successCount).toBe(1);
+    expect(loop.failureCount).toBe(0);
+
+    await vi.advanceTimersByTimeAsync(500);
+    expect(loop.failureCount).toBe(1);
+    expect(loop.lastFailure?.message).toBe('transient');
+
+    loop.stop();
+    loop.start(false);
+
+    expect(loop.successCount).toBe(0);
+    expect(loop.lastSuccessAt).toBeNull();
+    expect(loop.failureCount).toBe(0);
+    expect(loop.lastFailure).toBeNull();
+
+    await vi.advanceTimersByTimeAsync(500);
+    expect(loop.successCount).toBe(1);
+    expect(loop.failureCount).toBe(0);
+
+    loop.stop();
+  });
 });