feat(companion): add runtime event subscription hooks

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 for one-shot RPC calls.
+- `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/platformClients.ts` provides platform-focused wrappers:
   - `MacOSCompanionClient` (`platform: "macos"`, APNs push registration)
   - `IOSCompanionClient` (`platform: "ios"`, APNs push registration)

docs/plans/state.json

@@ -299,6 +299,20 @@
       ],
       "test_status": "pnpm test:run src/companion/heartbeatLoop.test.ts src/companion/platformClients.test.ts + pnpm typecheck passing"
     },
+    "companion-runtime-event-subscriptions": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added event subscription support to `CompanionRuntimeClient` via `subscribeEvents()` so companion runtimes can receive gateway stream events with safe callback isolation and explicit unsubscribe flow.",
+      "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 + pnpm typecheck passing"
+    },
     "browser-tools-activation-clarity": {
       "status": "completed",
       "date": "2026-02-17",

src/companion/index.ts

@@ -11,6 +11,7 @@ export { CompanionHeartbeatLoop } from './heartbeatLoop.js';
 
 export type {
   CompanionRuntimeClientOptions,
+  CompanionEventHandler,
   RegisterNodeInput,
   ListNodesInput,
   SetNodeStatusInput,

src/companion/runtimeClient.test.ts

@@ -96,6 +96,61 @@ afterAll(async () => {
 });
 
 describe('CompanionRuntimeClient', () => {
+  it('dispatches gateway events to subscribed handlers and supports unsubscribe', () => {
+    const client = new CompanionRuntimeClient({
+      url: 'ws://127.0.0.1:1',
+    });
+    const handler = vi.fn();
+    const unsubscribe = client.subscribeEvents(handler);
+
+    (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
+      JSON.stringify({
+        id: 42,
+        event: 'agent.stream',
+        data: { token: 'hello' },
+      }),
+    );
+
+    expect(handler).toHaveBeenCalledWith('agent.stream', { token: 'hello' });
+
+    unsubscribe();
+
+    (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
+      JSON.stringify({
+        id: 43,
+        event: 'agent.stream',
+        data: { token: 'world' },
+      }),
+    );
+
+    expect(handler).toHaveBeenCalledTimes(1);
+  });
+
+  it('isolates subscriber callback failures', () => {
+    const client = new CompanionRuntimeClient({
+      url: 'ws://127.0.0.1:1',
+    });
+    const badHandler = vi.fn(() => {
+      throw new Error('subscriber failed');
+    });
+    const goodHandler = vi.fn();
+    client.subscribeEvents(badHandler);
+    client.subscribeEvents(goodHandler);
+
+    expect(() => {
+      (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
+        JSON.stringify({
+          id: 44,
+          event: 'agent.stream',
+          data: { token: 'safe' },
+        }),
+      );
+    }).not.toThrow();
+
+    expect(badHandler).toHaveBeenCalledOnce();
+    expect(goodHandler).toHaveBeenCalledWith('agent.stream', { token: 'safe' });
+  });
+
   it('connects and performs node registration + capability discovery', async () => {
     if (!LISTEN_ALLOWED) {
       return;

src/companion/runtimeClient.ts

@@ -41,6 +41,8 @@ export interface CompanionRuntimeClientOptions {
   websocketFactory?: (url: string) => WebSocket;
 }
 
+export type CompanionEventHandler = (event: string, data: unknown) => void;
+
 export interface RegisterNodeInput {
   nodeId: string;
   role: string;
@@ -257,6 +259,7 @@ export class CompanionRuntimeClient {
   private connectPromise: Promise<void> | null = null;
   private nextId = 1;
   private pending = new Map<number, PendingRequest>();
+  private readonly eventHandlers = new Set<CompanionEventHandler>();
 
   constructor(options: CompanionRuntimeClientOptions) {
     this.url = options.url;
@@ -342,6 +345,13 @@ export class CompanionRuntimeClient {
     ws.close(code, reason);
   }
 
+  subscribeEvents(handler: CompanionEventHandler): () => void {
+    this.eventHandlers.add(handler);
+    return () => {
+      this.eventHandlers.delete(handler);
+    };
+  }
+
   async call<T>(method: string, params?: Record<string, unknown>): Promise<T> {
     if (!this.connected) {
       if (!this.autoConnect) {
@@ -498,6 +508,13 @@ export class CompanionRuntimeClient {
     }
 
     if ('event' in parsed) {
+      for (const handler of this.eventHandlers) {
+        try {
+          handler(parsed.event, parsed.data);
+        } catch {
+          // Event subscribers are userland callbacks; isolate failures.
+        }
+      }
       return;
     }