feat(mcp): add progress bar, throttling, and input validation for MCP tool progress (#19772)

packages/core/src/utils/events.test.ts

@@ -1,16 +1,22 @@
 /**
  * @license
- * Copyright 2025 Google LLC
+ * Copyright 2026 Google LLC
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 import {
   CoreEventEmitter,
   CoreEvent,
+  coreEvents,
   type UserFeedbackPayload,
+  type McpProgressPayload,
 } from './events.js';
 
+vi.mock('./debugLogger.js', () => ({
+  debugLogger: { log: vi.fn() },
+}));
+
 describe('CoreEventEmitter', () => {
   let events: CoreEventEmitter;
 
@@ -360,4 +366,63 @@ describe('CoreEventEmitter', () => {
       expect(listener.mock.calls[0][0]).toMatchObject({ prompt: 'Consent 10' });
     });
   });
+
+  describe('emitMcpProgress validation', () => {
+    const basePayload: McpProgressPayload = {
+      serverName: 'test-server',
+      callId: 'call-1',
+      progressToken: 'token-1',
+      progress: 0,
+    };
+
+    let listener: ReturnType<typeof vi.fn>;
+
+    afterEach(() => {
+      if (listener) {
+        coreEvents.off(CoreEvent.McpProgress, listener);
+      }
+    });
+
+    it('rejects NaN progress', () => {
+      listener = vi.fn();
+      coreEvents.on(CoreEvent.McpProgress, listener);
+
+      coreEvents.emitMcpProgress({ ...basePayload, progress: NaN });
+
+      expect(listener).not.toHaveBeenCalled();
+    });
+
+    it('rejects negative progress', () => {
+      listener = vi.fn();
+      coreEvents.on(CoreEvent.McpProgress, listener);
+
+      coreEvents.emitMcpProgress({ ...basePayload, progress: -1 });
+
+      expect(listener).not.toHaveBeenCalled();
+    });
+
+    it('rejects Infinity progress', () => {
+      listener = vi.fn();
+      coreEvents.on(CoreEvent.McpProgress, listener);
+
+      coreEvents.emitMcpProgress({ ...basePayload, progress: Infinity });
+
+      expect(listener).not.toHaveBeenCalled();
+    });
+
+    it('emits valid progress payload', () => {
+      listener = vi.fn();
+      coreEvents.on(CoreEvent.McpProgress, listener);
+
+      const payload: McpProgressPayload = {
+        ...basePayload,
+        progress: 5,
+        total: 10,
+        message: 'test',
+      };
+      coreEvents.emitMcpProgress(payload);
+
+      expect(listener).toHaveBeenCalledExactlyOnceWith(payload);
+    });
+  });
 });

packages/core/src/utils/events.ts

@@ -13,6 +13,7 @@ import type {
   TokenStorageInitializationEvent,
   KeychainAvailabilityEvent,
 } from '../telemetry/types.js';
+import { debugLogger } from './debugLogger.js';
 
 /**
  * Defines the severity level for user-facing feedback.
@@ -353,6 +354,10 @@ export class CoreEventEmitter extends EventEmitter<CoreEvents> {
    * Notifies subscribers that progress has been made on an MCP tool call.
    */
   emitMcpProgress(payload: McpProgressPayload): void {
+    if (!Number.isFinite(payload.progress) || payload.progress < 0) {
+      debugLogger.log(`Invalid progress value: ${payload.progress}`);
+      return;
+    }
     this.emit(CoreEvent.McpProgress, payload);
   }