fix(companion): dedupe heartbeat loop scheduled timers

docs/plans/state.json

@@ -760,6 +760,18 @@
       ],
       "test_status": "pnpm test:run src/companion/platformClients.integration.test.ts src/companion/platformClients.test.ts src/companion/runtimeClient.test.ts src/companion/heartbeatLoop.test.ts + pnpm typecheck passing"
     },
+    "companion-heartbeat-loop-timer-dedup": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Prevented duplicate pending timers in `CompanionHeartbeatLoop` by clearing any existing scheduled timeout before re-scheduling, with regression coverage for `tickNow()` during active loops.",
+      "files_modified": [
+        "src/companion/heartbeatLoop.ts",
+        "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

@@ -217,4 +217,21 @@ describe('CompanionHeartbeatLoop', () => {
       lastFailure: null,
     });
   });
+
+  it('tickNow while running does not accumulate duplicate scheduled timers', async () => {
+    const publishHeartbeat = vi.fn(async () => buildStatusResult());
+    const loop = new CompanionHeartbeatLoop({ publishHeartbeat }, { intervalMs: 1000 });
+
+    loop.start(false);
+    expect(vi.getTimerCount()).toBe(1);
+
+    await loop.tickNow();
+    expect(vi.getTimerCount()).toBe(1);
+    expect(publishHeartbeat).toHaveBeenCalledTimes(1);
+
+    await vi.advanceTimersByTimeAsync(1000);
+    expect(publishHeartbeat).toHaveBeenCalledTimes(2);
+
+    loop.stop();
+  });
 });

src/companion/heartbeatLoop.ts

@@ -138,6 +138,10 @@ export class CompanionHeartbeatLoop {
     if (!this.started) {
       return;
     }
+    if (this.timer) {
+      clearTimeout(this.timer);
+      this.timer = null;
+    }
     const delay = this.computeDelayMs();
     this.timer = setTimeout(() => {
       void this.tick();