fix: respect explicit model selection after Flash quota exhaustion (#26759) (#26872)

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

@@ -0,0 +1,32 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { normalizeModelId } from './modelUtils.js';
+
+describe('modelUtils', () => {
+  describe('normalizeModelId', () => {
+    it('should strip "models/" prefix if present', () => {
+      expect(normalizeModelId('models/gemini-3.1-pro-preview')).toBe(
+        'gemini-3.1-pro-preview',
+      );
+      expect(normalizeModelId('models/gemini-1.5-flash')).toBe(
+        'gemini-1.5-flash',
+      );
+    });
+
+    it('should leave model ID untouched if prefix is not present', () => {
+      expect(normalizeModelId('gemini-3.1-pro-preview')).toBe(
+        'gemini-3.1-pro-preview',
+      );
+      expect(normalizeModelId('auto')).toBe('auto');
+    });
+
+    it('should handle empty string', () => {
+      expect(normalizeModelId('')).toBe('');
+    });
+  });
+});

packages/core/src/utils/modelUtils.ts

@@ -0,0 +1,17 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Strips the 'models/' prefix from a model ID if present.
+ * This ensures internal logic (like family matching) works correctly
+ * even when receiving formal resource names from the API.
+ *
+ * @param modelId The model identifier to normalize.
+ * @returns The model ID without the 'models/' prefix.
+ */
+export function normalizeModelId(modelId: string): string {
+  return modelId.startsWith('models/') ? modelId.slice(7) : modelId;
+}