Fix exponential backoff delay calculation in fetchWithRetry (#14159)

Author: graysonhicks

.changeset/proud-jeans-beg.md

@@ -0,0 +1,5 @@
+---
+'@mastra/core': patch
+---
+
+`fetchWithRetry` now backs off in sequence 2s → 4s → 8s and then caps at 10s.

packages/core/src/utils.test.ts

@@ -1,12 +1,12 @@
 import { jsonSchemaToZod } from '@mastra/schema-compat/json-to-zod';
-import { describe, expect, it, vi } from 'vitest';
+import { afterEach, describe, expect, it, vi } from 'vitest';
 import { z } from 'zod';
 import { MastraError } from './error';
 import { ConsoleLogger } from './logger';
 import { RequestContext } from './request-context';
 import { toStandardSchema } from './schema';
 import { createTool, isVercelTool } from './tools';
-import { makeCoreTool, maskStreamTags, resolveSerializedZodOutput } from './utils';
+import { fetchWithRetry, makeCoreTool, maskStreamTags, resolveSerializedZodOutput } from './utils';
 
 describe('maskStreamTags', () => {
   async function* makeStream(chunks: string[]) {
@@ -344,3 +344,39 @@ it('should log correctly for Vercel tool execution', async () => {
 
   debugSpy.mockRestore();
 });
+
+describe('fetchWithRetry', () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  it('should use exponential backoff delays capped at 10 seconds', async () => {
+    const delays: number[] = [];
+
+    vi.spyOn(globalThis, 'setTimeout').mockImplementation(((fn: () => void, delay?: number) => {
+      if (delay && delay > 100) {
+        delays.push(delay);
+      }
+      // Execute callback immediately so the test completes
+      if (typeof fn === 'function') fn();
+      return 0 as unknown as ReturnType<typeof setTimeout>;
+    }) as typeof setTimeout);
+
+    const mockFetch = vi.fn().mockRejectedValue(new Error('Network error'));
+    vi.stubGlobal('fetch', mockFetch);
+
+    // Use 5 retries so computed backoff 1000 * 2^4 = 16000 exceeds the 10000 cap
+    await expect(fetchWithRetry('https://example.com', {}, 5)).rejects.toThrow();
+
+    // Delays: 2000 (2^1), 4000 (2^2), 8000 (2^3), 10000 (2^4=16000 capped to 10000)
+    expect(delays.length).toBe(4); // 5 max retries = 4 retry delays
+    for (const delay of delays) {
+      expect(delay).toBeLessThanOrEqual(10000);
+    }
+    expect(delays[0]).toBe(2000); // 1000 * 2^1
+    expect(delays[1]).toBe(4000); // 1000 * 2^2
+    expect(delays[2]).toBe(8000); // 1000 * 2^3
+    expect(delays[3]).toBe(10000); // 1000 * 2^4 = 16000, capped at 10000
+  });
+});

packages/core/src/utils.ts

@@ -638,7 +638,7 @@ export async function fetchWithRetry(
         break;
       }
 
-      const delay = Math.min(1000 * Math.pow(2, retryCount) * 1000, 10000);
+      const delay = Math.min(1000 * Math.pow(2, retryCount), 10000);
       await new Promise(resolve => setTimeout(resolve, delay));
     }
   }