feat(companion): add context warning stream helpers

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()`, `waitForEvent()` with timeout/predicate/abort support, `waitForAgentStream()`, `waitForAgentTyping()`, `clearEventSubscriptions()`).
+- `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, `waitForAgentStream()`, `waitForAgentTyping()`, `waitForContextWarning()`, `clearEventSubscriptions()`).
 - `src/companion/platformClients.ts` provides platform-focused wrappers:
   - `MacOSCompanionClient` (`platform: "macos"`, APNs push registration)
   - `IOSCompanionClient` (`platform: "ios"`, APNs push registration)

docs/plans/state.json

@@ -527,6 +527,19 @@
       ],
       "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"
     },
+    "companion-runtime-context-warning-helpers": {
+      "status": "completed",
+      "date": "2026-02-17",
+      "updated": "2026-02-17",
+      "summary": "Added dedicated context-warning event helpers on `CompanionRuntimeClient` (`subscribeContextWarning`, `waitForContextWarning`) for proactive context-pressure handling flows.",
+      "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

@@ -224,6 +224,24 @@ describe('CompanionRuntimeClient', () => {
     expect(typingHandler).toHaveBeenCalledWith({ active: true });
   });
 
+  it('supports subscribeContextWarning helper', () => {
+    const client = new CompanionRuntimeClient({
+      url: 'ws://127.0.0.1:1',
+    });
+    const warningHandler = vi.fn();
+    client.subscribeContextWarning(warningHandler);
+
+    (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
+      JSON.stringify({
+        id: 56,
+        event: 'context_warning',
+        data: { thresholdPct: 80, estimatedPct: 92 },
+      }),
+    );
+
+    expect(warningHandler).toHaveBeenCalledWith({ thresholdPct: 80, estimatedPct: 92 });
+  });
+
   it('clears all event subscriptions', () => {
     const client = new CompanionRuntimeClient({
       url: 'ws://127.0.0.1:1',
@@ -355,6 +373,25 @@ describe('CompanionRuntimeClient', () => {
     await expect(awaited).resolves.toEqual({ active: true });
   });
 
+  it('waitForContextWarning resolves on context_warning events', async () => {
+    const client = new CompanionRuntimeClient({
+      url: 'ws://127.0.0.1:1',
+    });
+
+    const awaited = client.waitForContextWarning<{ thresholdPct: number; estimatedPct: number }>({
+      timeoutMs: 2000,
+    });
+    (client as unknown as { handleMessage: (raw: string) => void }).handleMessage(
+      JSON.stringify({
+        id: 57,
+        event: 'context_warning',
+        data: { thresholdPct: 75, estimatedPct: 88 },
+      }),
+    );
+
+    await expect(awaited).resolves.toEqual({ thresholdPct: 75, estimatedPct: 88 });
+  });
+
   it('connects and performs node registration + capability discovery', async () => {
     if (!LISTEN_ALLOWED) {
       return;

src/companion/runtimeClient.ts

@@ -403,6 +403,12 @@ export class CompanionRuntimeClient {
     return this.subscribeEvent<TData>(COMPANION_EVENT_NAMES.agentTyping, handler);
   }
 
+  subscribeContextWarning<TData = unknown>(
+    handler: CompanionTypedEventHandler<TData>,
+  ): () => void {
+    return this.subscribeEvent<TData>(COMPANION_EVENT_NAMES.contextWarning, handler);
+  }
+
   waitForEvent<TData = unknown>(
     eventName: string,
     options?: {
@@ -475,6 +481,14 @@ export class CompanionRuntimeClient {
     return this.waitForEvent<TData>(COMPANION_EVENT_NAMES.agentTyping, options);
   }
 
+  waitForContextWarning<TData = unknown>(options?: {
+    timeoutMs?: number;
+    predicate?: CompanionEventPredicate<TData>;
+    signal?: AbortSignal;
+  }): Promise<TData> {
+    return this.waitForEvent<TData>(COMPANION_EVENT_NAMES.contextWarning, options);
+  }
+
   async call<T>(method: string, params?: Record<string, unknown>): Promise<T> {
     if (!this.connected) {
       if (!this.autoConnect) {