feat(companion): expose runtime event subscription count

README.md

@@ -1190,7 +1190,7 @@ Methods:
 - `system.capabilities` returns gateway protocol and node policy snapshot.
 
 Companion runtime helper:
-- `src/companion/runtimeClient.ts` provides a typed Node/WebSocket client for companion runtimes (macOS/iOS/Android workers) with wrappers for `node.register`, `node.capabilities.get`, `node.location.set/get`, `node.status.set`, `node.push_token.set`, `system.capabilities`, `system.nodes`, and canvas artifact RPCs (`canvas.put/get/list/delete/clear`), plus convenience helpers (`bootstrapNode`, optional `autoConnect`, `dispose()`) and event helpers (`subscribeEvents()`, `subscribeEvent()`, `subscribeAgentStream()`, `subscribeAgentTyping()`, `subscribeContextWarning()`, `waitForEvent()` with timeout/predicate/abort support and deterministic teardown cancellation, `waitForAnyEvent()`, `waitForAgentStream()`, `waitForAgentTyping()`, `waitForContextWarning()`, `clearEventSubscriptions()`, `listKnownEventNames()`).
+- `src/companion/runtimeClient.ts` provides a typed Node/WebSocket client for companion runtimes (macOS/iOS/Android workers) with wrappers for `node.register`, `node.capabilities.get`, `node.location.set/get`, `node.status.set`, `node.push_token.set`, `system.capabilities`, `system.nodes`, and canvas artifact RPCs (`canvas.put/get/list/delete/clear`), plus convenience helpers (`bootstrapNode`, optional `autoConnect`, `dispose()`) and event helpers (`subscribeEvents()`, `subscribeEvent()`, `subscribeAgentStream()`, `subscribeAgentTyping()`, `subscribeContextWarning()`, `waitForEvent()` with timeout/predicate/abort support and deterministic teardown cancellation, `waitForAnyEvent()`, `waitForAgentStream()`, `waitForAgentTyping()`, `waitForContextWarning()`, `clearEventSubscriptions()`, `listKnownEventNames()`, `eventSubscriptionCount`).
 - `src/companion/platformClients.ts` provides platform-focused wrappers:
   - `MacOSCompanionClient` (`platform: "macos"`, APNs push registration)
   - `IOSCompanionClient` (`platform: "ios"`, APNs push registration)

docs/plans/state.json

@@ -660,6 +660,19 @@
       ],
       "test_status": "pnpm test:run src/companion/platformClients.test.ts src/companion/runtimeClient.test.ts src/companion/heartbeatLoop.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
     },
+    "companion-runtime-event-subscription-count": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added `eventSubscriptionCount` on `CompanionRuntimeClient` to expose active event-listener cardinality for runtime observability and debugging.",
+      "files_modified": [
+        "src/companion/runtimeClient.ts",
+        "src/companion/runtimeClient.test.ts",
+        "README.md",
+        "docs/plans/state.json"
+      ],
+      "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"
+    },
     "browser-tools-activation-clarity": {
       "status": "completed",
       "date": "2026-02-17",

src/companion/runtimeClient.test.ts

@@ -110,7 +110,9 @@ describe('CompanionRuntimeClient', () => {
       url: 'ws://127.0.0.1:1',
     });
     const handler = vi.fn();
+    expect(client.eventSubscriptionCount).toBe(0);
     const unsubscribe = client.subscribeEvents(handler);
+    expect(client.eventSubscriptionCount).toBe(1);
 
     (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
       JSON.stringify({
@@ -133,6 +135,7 @@ describe('CompanionRuntimeClient', () => {
     );
 
     expect(handler).toHaveBeenCalledTimes(1);
+    expect(client.eventSubscriptionCount).toBe(0);
   });
 
   it('isolates subscriber callback failures', () => {

src/companion/runtimeClient.ts

@@ -298,6 +298,10 @@ export class CompanionRuntimeClient {
     return this.ws?.readyState === WebSocket.OPEN;
   }
 
+  get eventSubscriptionCount(): number {
+    return this.eventHandlers.size;
+  }
+
   async connect(): Promise<void> {
     if (this.connected) {
       return;