feat(companion): add heartbeat loop success callback

README.md

@@ -1200,7 +1200,7 @@ Companion runtime helper:
   - `createHeartbeatLoop()` convenience helper that returns a bound `CompanionHeartbeatLoop`
   - optional `defaultSessionId` for canvas helper calls so `sessionId` can be omitted per call
   - `dispose()` lifecycle helper for unified runtime teardown
-- `src/companion/heartbeatLoop.ts` provides `CompanionHeartbeatLoop` for periodic heartbeat scheduling (`publishHeartbeat`) with start/stop safety, optional interval jitter (`jitterRatio`) to spread load, `tickNow()` for manual sends, error hooks, failure observability (`failureCount`, `lastFailure`), and optional auto-stop after repeated failures.
+- `src/companion/heartbeatLoop.ts` provides `CompanionHeartbeatLoop` for periodic heartbeat scheduling (`publishHeartbeat`) with start/stop safety, optional interval jitter (`jitterRatio`) to spread load, `tickNow()` for manual sends, success/error hooks, failure observability (`failureCount`, `lastFailure`), and optional auto-stop after repeated failures.
 
 ## Canvas / A2UI Foundation
 

docs/plans/state.json

@@ -487,6 +487,19 @@
       ],
       "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-success-hook": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added `onSuccess` callback support to `CompanionHeartbeatLoop` so callers can observe successful heartbeat responses for telemetry and health instrumentation.",
+      "files_modified": [
+        "src/companion/heartbeatLoop.ts",
+        "src/companion/heartbeatLoop.test.ts",
+        "README.md",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/companion/heartbeatLoop.test.ts src/companion/runtimeClient.test.ts src/companion/platformClients.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

@@ -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 }));

src/companion/heartbeatLoop.ts

@@ -9,6 +9,7 @@ export interface CompanionHeartbeatLoopOptions {
   intervalMs?: number;
   jitterRatio?: number;
   buildHeartbeat?: () => HeartbeatStatusInput | Promise<HeartbeatStatusInput>;
+  onSuccess?: (result: NodeStatusSetResult) => void;
   onError?: (error: Error) => void;
   maxConsecutiveFailures?: number;
   onFailureLimitReached?: (error: Error, consecutiveFailures: number) => void;
@@ -24,6 +25,7 @@ export class CompanionHeartbeatLoop {
   private readonly intervalMs: number;
   private readonly jitterRatio: number;
   private readonly buildHeartbeat?: () => HeartbeatStatusInput | Promise<HeartbeatStatusInput>;
+  private readonly onSuccess?: (result: NodeStatusSetResult) => void;
   private readonly onError?: (error: Error) => void;
   private readonly maxConsecutiveFailures: number;
   private readonly onFailureLimitReached?: (error: Error, consecutiveFailures: number) => void;
@@ -56,6 +58,7 @@ export class CompanionHeartbeatLoop {
     this.intervalMs = intervalMs;
     this.jitterRatio = jitterRatio;
     this.buildHeartbeat = options.buildHeartbeat;
+    this.onSuccess = options.onSuccess;
     this.onError = options.onError;
     this.maxConsecutiveFailures = maxConsecutiveFailures;
     this.onFailureLimitReached = options.onFailureLimitReached;
@@ -129,9 +132,10 @@ export class CompanionHeartbeatLoop {
     this.inFlight = true;
     try {
       const payload = this.buildHeartbeat ? await this.buildHeartbeat() : undefined;
-      await this.publisher.publishHeartbeat(payload);
+      const result = await this.publisher.publishHeartbeat(payload);
       this.consecutiveFailures = 0;
       this.lastError = null;
+      this.onSuccess?.(result);
     } catch (error) {
       const err = error instanceof Error ? error : new Error(String(error));
       this.consecutiveFailures += 1;