feat(companion): add filtered runtime event subscription helper

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 optional `autoConnect` mode and `subscribeEvents()` for gateway stream events.
+- `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 optional `autoConnect` mode and event subscriptions (`subscribeEvents()`, `subscribeEvent()`).
 - `src/companion/platformClients.ts` provides platform-focused wrappers:
   - `MacOSCompanionClient` (`platform: "macos"`, APNs push registration)
   - `IOSCompanionClient` (`platform: "ios"`, APNs push registration)

docs/plans/state.json

@@ -313,6 +313,20 @@
       ],
       "test_status": "pnpm test:run src/companion/runtimeClient.test.ts src/companion/platformClients.test.ts src/companion/platformClients.integration.test.ts + pnpm typecheck passing"
     },
+    "companion-runtime-filtered-event-helper": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added typed `subscribeEvent(eventName, handler)` helper to `CompanionRuntimeClient` for filtered event consumption on top of generic `subscribeEvents`, including unsubscribe behavior tests.",
+      "files_modified": [
+        "src/companion/runtimeClient.ts",
+        "src/companion/runtimeClient.test.ts",
+        "src/companion/index.ts",
+        "README.md",
+        "docs/plans/state.json"
+      ],
+      "test_status": "pnpm test:run src/companion/runtimeClient.test.ts src/companion/platformClients.test.ts src/companion/platformClients.integration.test.ts src/companion/heartbeatLoop.test.ts + pnpm typecheck passing"
+    },
     "browser-tools-activation-clarity": {
       "status": "completed",
       "date": "2026-02-17",

src/companion/index.ts

@@ -12,6 +12,7 @@ export { CompanionHeartbeatLoop } from './heartbeatLoop.js';
 export type {
   CompanionRuntimeClientOptions,
   CompanionEventHandler,
+  CompanionTypedEventHandler,
   RegisterNodeInput,
   ListNodesInput,
   SetNodeStatusInput,

src/companion/runtimeClient.test.ts

@@ -151,6 +151,42 @@ describe('CompanionRuntimeClient', () => {
     expect(goodHandler).toHaveBeenCalledWith('agent.stream', { token: 'safe' });
   });
 
+  it('supports filtered subscribeEvent helper', () => {
+    const client = new CompanionRuntimeClient({
+      url: 'ws://127.0.0.1:1',
+    });
+    const streamHandler = vi.fn();
+    const unsubscribe = client.subscribeEvent<{ token: string }>('agent.stream', streamHandler);
+
+    (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
+      JSON.stringify({
+        id: 45,
+        event: 'agent.stream',
+        data: { token: 'first' },
+      }),
+    );
+    (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
+      JSON.stringify({
+        id: 46,
+        event: 'agent.typing',
+        data: { active: true },
+      }),
+    );
+
+    expect(streamHandler).toHaveBeenCalledTimes(1);
+    expect(streamHandler).toHaveBeenCalledWith({ token: 'first' });
+
+    unsubscribe();
+    (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
+      JSON.stringify({
+        id: 47,
+        event: 'agent.stream',
+        data: { token: 'second' },
+      }),
+    );
+    expect(streamHandler).toHaveBeenCalledTimes(1);
+  });
+
   it('connects and performs node registration + capability discovery', async () => {
     if (!LISTEN_ALLOWED) {
       return;

src/companion/runtimeClient.ts

@@ -42,6 +42,7 @@ export interface CompanionRuntimeClientOptions {
 }
 
 export type CompanionEventHandler = (event: string, data: unknown) => void;
+export type CompanionTypedEventHandler<TData = unknown> = (data: TData) => void;
 
 export interface RegisterNodeInput {
   nodeId: string;
@@ -352,6 +353,18 @@ export class CompanionRuntimeClient {
     };
   }
 
+  subscribeEvent<TData = unknown>(
+    eventName: string,
+    handler: CompanionTypedEventHandler<TData>,
+  ): () => void {
+    return this.subscribeEvents((event, data) => {
+      if (event !== eventName) {
+        return;
+      }
+      handler(data as TData);
+    });
+  }
+
   async call<T>(method: string, params?: Record<string, unknown>): Promise<T> {
     if (!this.connected) {
       if (!this.autoConnect) {