feat(companion): add filtered runtime event subscription helper

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) {