fix(core): Ensure zero-quota limits fail fast to prevent retry loop hang (#27698)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

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

@@ -806,4 +806,123 @@ describe('classifyGoogleError', () => {
     const result = classifyGoogleError(new Error());
     expect(result).toBeInstanceOf(ValidationRequiredError);
   });
+
+  it('should return TerminalQuotaError when limit is 0 even if message contains "Please retry in Xs"', () => {
+    const complexError = {
+      error: {
+        message:
+          '{"error": {"code": 429, "status": 429, "message": "You exceeded your current quota, please check your plan and billing details. For more information on this error, head to: https://ai.google.dev/gemini-api/docs/rate-limits. To monitor your current usage, head to: https://ai.dev/usage?tab=rate-limit. \\n* Quota exceeded for metric: generativelanguage.googleapis.com/generate_content_free_tier_requests, limit: 0\\nPlease retry in 59.906331105s.", "details": [{"detail": "??? to (unknown) : APP_ERROR(8) You exceeded your current quota, please check your plan and billing details. For more information on this error, head to: https://ai.google.dev/gemini-api/docs/rate-limits. To monitor your current usage, head to: https://ai.dev/usage?tab=rate-limit. \\n* Quota exceeded for metric: generativelanguage.googleapis.com/generate_content_free_tier_requests, limit: 0\\nPlease retry in 59.906331105s."}]}}',
+        code: 429,
+        status: 'Too Many Requests',
+      },
+    };
+    const rawError = new Error(JSON.stringify(complexError)) as Error & {
+      status?: number;
+    };
+    rawError.status = 429;
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(null);
+
+    const result = classifyGoogleError(rawError);
+
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+  });
+
+  it('should return TerminalQuotaError when limit is 0 even if structured RetryInfo is present', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message: 'Quota exceeded for limit: 0',
+      details: [
+        {
+          '@type': 'type.googleapis.com/google.rpc.RetryInfo',
+          retryDelay: '59s',
+        },
+      ],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(
+      new Error('Quota exceeded for limit: 0'),
+    );
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+  });
+
+  it('should return TerminalQuotaError when limit is 0 and message contains actual newlines', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message: 'Quota exceeded for metric: ...\nlimit: 0, model: gemini-3-pro',
+      details: [],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(
+      new Error(
+        'Quota exceeded for metric: ...\nlimit: 0, model: gemini-3-pro',
+      ),
+    );
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+  });
+
+  it('should return TerminalQuotaError when limit is 0 followed by a period', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message: 'Quota exceeded for metric: ...\nlimit: 0. Please retry in 59s.',
+      details: [],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(
+      new Error(
+        'Quota exceeded for metric: ...\nlimit: 0. Please retry in 59s.',
+      ),
+    );
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+  });
+
+  it('should return RetryableQuotaError when limit is fractional (e.g., 0.5)', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message:
+        'Quota exceeded for metric: ...\nlimit: 0.5. Please retry in 59s.',
+      details: [],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(
+      new Error(
+        'Quota exceeded for metric: ...\nlimit: 0.5. Please retry in 59s.',
+      ),
+    );
+    expect(result).toBeInstanceOf(RetryableQuotaError);
+  });
+
+  it('should fall back to "Model not found" for 404 error with plain object', () => {
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(null);
+    const result = classifyGoogleError({ status: 404 });
+    expect(result).toBeInstanceOf(ModelNotFoundError);
+    expect((result as ModelNotFoundError).message).toBe('Model not found');
+  });
+
+  it('should parse custom 404 message from plain object correctly', () => {
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(null);
+    const result = classifyGoogleError({
+      status: 404,
+      message: 'Custom 404 message',
+    });
+    expect(result).toBeInstanceOf(ModelNotFoundError);
+    expect((result as ModelNotFoundError).message).toBe('Custom 404 message');
+  });
+
+  it('should classify plain object with limit: 0 message as TerminalQuotaError correctly', () => {
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(null);
+    const result = classifyGoogleError({
+      status: 429,
+      message: 'Quota exceeded, limit: 0',
+    });
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+  });
+
+  it('should handle Error instances with undefined message gracefully', () => {
+    const malformedError = new Error();
+    delete (malformedError as { message?: string }).message;
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(null);
+
+    const result = classifyGoogleError(malformedError);
+    expect(result).toBe(malformedError); // Should return the original error without crashing
+  });
 });

packages/core/src/utils/googleQuotaErrors.ts

@@ -219,11 +219,10 @@ function classifyValidationRequiredError(
 export function classifyGoogleError(error: unknown): unknown {
   const googleApiError = parseGoogleApiError(error);
   const status = googleApiError?.code ?? getErrorStatus(error);
+  const errorMessage = googleApiError?.message || extractErrorMessage(error);
 
   if (status === 404) {
-    const message =
-      googleApiError?.message ||
-      (error instanceof Error ? error.message : 'Model not found');
+    const message = errorMessage.trim() || 'Model not found';
     return new ModelNotFoundError(message, status);
   }
 
@@ -235,6 +234,20 @@ export function classifyGoogleError(error: unknown): unknown {
     }
   }
 
+  // Universal limit: 0 check (moved outside and before the fallback block)
+  const lowerMessage = errorMessage.toLowerCase();
+  if (
+    (status === 429 || status === 499 || status === 503) &&
+    /limit:\s*0(?!\d|\.\d)/.test(lowerMessage)
+  ) {
+    const cause = googleApiError ?? {
+      code: status ?? 429,
+      message: errorMessage,
+      details: [],
+    };
+    return new TerminalQuotaError(errorMessage, cause);
+  }
+
   if (
     !googleApiError ||
     (googleApiError.code !== 429 &&
@@ -243,9 +256,6 @@ export function classifyGoogleError(error: unknown): unknown {
     googleApiError.details.length === 0
   ) {
     // Fallback: try to parse the error message for a retry delay
-    const errorMessage =
-      googleApiError?.message ||
-      (error instanceof Error ? error.message : String(error));
     const match = errorMessage.match(/Please retry in ([0-9.]+(?:ms|s))/);
     if (match?.[1]) {
       const retryDelaySeconds = parseDurationInSeconds(match[1]);
@@ -394,8 +404,18 @@ export function classifyGoogleError(error: unknown): unknown {
 
   // If we reached this point, the status is 429, 499, or 503 and we have details,
   // but no specific violation was matched. We return a generic retryable error.
-  const errorMessage =
-    googleApiError.message ||
-    (error instanceof Error ? error.message : String(error));
   return new RetryableQuotaError(errorMessage, googleApiError);
 }
+
+function extractErrorMessage(error: unknown): string {
+  if (typeof error === 'string') {
+    return error;
+  }
+  if (typeof error === 'object' && error !== null && 'message' in error) {
+    const msg = (error as { message: unknown }).message;
+    if (typeof msg === 'string') {
+      return msg;
+    }
+  }
+  return '';
+}