3 files changed, 108 insertions, 14 deletions
diff --git a/packages/core/src/utils/quotaErrorDetection.ts b/packages/core/src/utils/quotaErrorDetection.ts
index a8e87a5d..b07309cd 100644
--- a/packages/core/src/utils/quotaErrorDetection.ts
+++ b/packages/core/src/utils/quotaErrorDetection.ts
@@ -44,20 +44,9 @@ export function isProQuotaExceededError(error: unknown): boolean {
   // - "Quota exceeded for quota metric 'Gemini 2.5-preview Pro Requests'"
   // We use string methods instead of regex to avoid ReDoS vulnerabilities
 
-  const checkMessage = (message: string): boolean => {
-    console.log('[DEBUG] isProQuotaExceededError checking message:', message);
-    const result =
-      message.includes("Quota exceeded for quota metric 'Gemini") &&
-      message.includes("Pro Requests'");
-    console.log('[DEBUG] isProQuotaExceededError result:', result);
-    return result;
-  };
-
-  // Log the full error object to understand its structure
-  console.log(
-    '[DEBUG] isProQuotaExceededError - full error object:',
-    JSON.stringify(error, null, 2),
-  );
+  const checkMessage = (message: string): boolean =>
+    message.includes("Quota exceeded for quota metric 'Gemini") &&
+    message.includes("Pro Requests'");
 
   if (typeof error === 'string') {
     return checkMessage(error);
diff --git a/packages/core/src/utils/safeJsonStringify.test.ts b/packages/core/src/utils/safeJsonStringify.test.ts
new file mode 100644
index 00000000..9a38c048
--- /dev/null
+++ b/packages/core/src/utils/safeJsonStringify.test.ts
@@ -0,0 +1,73 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { safeJsonStringify } from './safeJsonStringify.js';
+
+describe('safeJsonStringify', () => {
+  it('should stringify normal objects without issues', () => {
+    const obj = { name: 'test', value: 42 };
+    const result = safeJsonStringify(obj);
+    expect(result).toBe('{"name":"test","value":42}');
+  });
+
+  it('should handle circular references by replacing them with [Circular]', () => {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const obj: any = { name: 'test' };
+    obj.circular = obj; // Create circular reference
+
+    const result = safeJsonStringify(obj);
+    expect(result).toBe('{"name":"test","circular":"[Circular]"}');
+  });
+
+  it('should handle complex circular structures like HttpsProxyAgent', () => {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const agent: any = {
+      sockets: {},
+      options: { host: 'example.com' },
+    };
+    agent.sockets['example.com'] = [{ agent }];
+
+    const result = safeJsonStringify(agent);
+    expect(result).toContain('[Circular]');
+    expect(result).toContain('example.com');
+  });
+
+  it('should respect the space parameter for formatting', () => {
+    const obj = { name: 'test', value: 42 };
+    const result = safeJsonStringify(obj, 2);
+    expect(result).toBe('{\n  "name": "test",\n  "value": 42\n}');
+  });
+
+  it('should handle circular references with formatting', () => {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const obj: any = { name: 'test' };
+    obj.circular = obj;
+
+    const result = safeJsonStringify(obj, 2);
+    expect(result).toBe('{\n  "name": "test",\n  "circular": "[Circular]"\n}');
+  });
+
+  it('should handle arrays with circular references', () => {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const arr: any[] = [{ id: 1 }];
+    arr[0].parent = arr; // Create circular reference
+
+    const result = safeJsonStringify(arr);
+    expect(result).toBe('[{"id":1,"parent":"[Circular]"}]');
+  });
+
+  it('should handle null and undefined values', () => {
+    expect(safeJsonStringify(null)).toBe('null');
+    expect(safeJsonStringify(undefined)).toBe(undefined);
+  });
+
+  it('should handle primitive values', () => {
+    expect(safeJsonStringify('test')).toBe('"test"');
+    expect(safeJsonStringify(42)).toBe('42');
+    expect(safeJsonStringify(true)).toBe('true');
+  });
+});
diff --git a/packages/core/src/utils/safeJsonStringify.ts b/packages/core/src/utils/safeJsonStringify.ts
new file mode 100644
index 00000000..f439bcea
--- /dev/null
+++ b/packages/core/src/utils/safeJsonStringify.ts
@@ -0,0 +1,32 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Safely stringifies an object to JSON, handling circular references by replacing them with [Circular].
+ *
+ * @param obj - The object to stringify
+ * @param space - Optional space parameter for formatting (defaults to no formatting)
+ * @returns JSON string with circular references replaced by [Circular]
+ */
+export function safeJsonStringify(
+  obj: unknown,
+  space?: string | number,
+): string {
+  const seen = new WeakSet();
+  return JSON.stringify(
+    obj,
+    (key, value) => {
+      if (typeof value === 'object' && value !== null) {
+        if (seen.has(value)) {
+          return '[Circular]';
+        }
+        seen.add(value);
+      }
+      return value;
+    },
+    space,
+  );
+}