test(companion): add platform event subscription lifecycle integration

docs/plans/state.json

@@ -772,6 +772,17 @@
       ],
       "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"
     },
+    "companion-platform-event-subscription-observability-integration": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added integration coverage for platform event subscription observability lifecycle, verifying `eventSubscriptionCount` behavior across subscribe, unsubscribe, and `clearEventSubscriptions()` operations.",
+      "files_modified": [
+        "src/companion/platformClients.integration.test.ts",
+        "docs/plans/state.json"
+      ],
+      "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-runtime-socket-close-waiter-rejection": {
       "status": "completed",
       "date": "2026-02-17",

src/companion/platformClients.integration.test.ts

@@ -108,6 +108,29 @@ function createRuntime(): CompanionRuntimeClient {
 }
 
 describe('platform clients integration', () => {
+  it('platform event subscription helpers track subscription count lifecycle', async () => {
+    if (!LISTEN_ALLOWED) {
+      return;
+    }
+
+    const runtime = createRuntime();
+    const client = new MacOSCompanionClient({ runtime, nodeId: 'macos-events-e2e' });
+
+    expect(client.eventSubscriptionCount).toBe(0);
+    const unsubscribeA = client.subscribeEvents(() => undefined);
+    const unsubscribeB = client.subscribeEvent('agent.stream', () => undefined);
+    expect(client.eventSubscriptionCount).toBe(2);
+
+    unsubscribeA();
+    expect(client.eventSubscriptionCount).toBe(1);
+
+    client.clearEventSubscriptions();
+    expect(client.eventSubscriptionCount).toBe(0);
+
+    unsubscribeB();
+    expect(client.eventSubscriptionCount).toBe(0);
+  });
+
   it('platform connected reflects runtime connection lifecycle', async () => {
     if (!LISTEN_ALLOWED) {
       return;