🧰 fix: Convert const to enum in MCP Schemas for Gemini Compatibility (#11784)

* fix: Convert `const` to `enum` in MCP tool schemas for Gemini/Vertex AI compatibility

  Gemini/Vertex AI rejects the JSON Schema `const` keyword in function declarations
  with a 400 error. Previously, the Zod conversion layer accidentally stripped `const`,
  but after migrating to pass raw JSON schemas directly to providers, the unsupported
  keyword now reaches Gemini verbatim.

  Add `normalizeJsonSchema` to recursively convert `const: X` → `enum: [X]`, which is
  semantically equivalent per the JSON Schema spec and supported by all providers.

* fix: Update secure cookie handling in AuthService to use dynamic secure flag

Replaced the static `secure: isProduction` with a call to `shouldUseSecureCookie()` in the `setOpenIDAuthTokens` function. This change ensures that the secure cookie setting is evaluated at runtime, improving cookie handling in development environments while maintaining security in production.

* refactor: Simplify MCP tool key formatting and remove unused mocks in tests

- Updated MCP test suite to replace static tool key formatting with a dynamic delimiter from Constants, enhancing consistency and maintainability.
- Removed unused mock implementations for `@langchain/core/tools` and `@librechat/agents`, streamlining the test setup.
- Adjusted related test cases to reflect the new tool key format, ensuring all tests remain functional.

* chore: import order

packages/api/src/mcp/__tests__/zod.spec.ts

@@ -2,7 +2,12 @@
 // zod.spec.ts
 import { z } from 'zod';
 import type { JsonSchemaType } from '@librechat/data-schemas';
-import { resolveJsonSchemaRefs, convertJsonSchemaToZod, convertWithResolvedRefs } from '../zod';
+import {
+  convertWithResolvedRefs,
+  convertJsonSchemaToZod,
+  resolveJsonSchemaRefs,
+  normalizeJsonSchema,
+} from '../zod';
 
 describe('convertJsonSchemaToZod', () => {
   describe('integer type handling', () => {
@@ -206,7 +211,7 @@ describe('convertJsonSchemaToZod', () => {
         type: 'number' as const,
         enum: [1, 2, 3, 5, 8, 13],
       };
-      const zodSchema = convertWithResolvedRefs(schema as JsonSchemaType);
+      const zodSchema = convertWithResolvedRefs(schema as unknown as JsonSchemaType);
 
       expect(zodSchema?.parse(1)).toBe(1);
       expect(zodSchema?.parse(13)).toBe(13);
@@ -2002,3 +2007,189 @@ describe('convertJsonSchemaToZod', () => {
     });
   });
 });
+
+describe('normalizeJsonSchema', () => {
+  it('should convert const to enum', () => {
+    const schema = { type: 'string', const: 'hello' } as any;
+    const result = normalizeJsonSchema(schema);
+    expect(result).toEqual({ type: 'string', enum: ['hello'] });
+    expect(result).not.toHaveProperty('const');
+  });
+
+  it('should preserve existing enum when const is also present', () => {
+    const schema = { type: 'string', const: 'hello', enum: ['hello', 'world'] } as any;
+    const result = normalizeJsonSchema(schema);
+    expect(result).toEqual({ type: 'string', enum: ['hello', 'world'] });
+    expect(result).not.toHaveProperty('const');
+  });
+
+  it('should handle non-string const values (number, boolean, null)', () => {
+    expect(normalizeJsonSchema({ type: 'number', const: 42 } as any)).toEqual({
+      type: 'number',
+      enum: [42],
+    });
+    expect(normalizeJsonSchema({ type: 'boolean', const: true } as any)).toEqual({
+      type: 'boolean',
+      enum: [true],
+    });
+    expect(normalizeJsonSchema({ type: 'string', const: null } as any)).toEqual({
+      type: 'string',
+      enum: [null],
+    });
+  });
+
+  it('should recursively normalize nested object properties', () => {
+    const schema = {
+      type: 'object',
+      properties: {
+        mode: { type: 'string', const: 'advanced' },
+        count: { type: 'number', const: 5 },
+        name: { type: 'string', description: 'A name' },
+      },
+    } as any;
+
+    const result = normalizeJsonSchema(schema);
+    expect(result.properties.mode).toEqual({ type: 'string', enum: ['advanced'] });
+    expect(result.properties.count).toEqual({ type: 'number', enum: [5] });
+    expect(result.properties.name).toEqual({ type: 'string', description: 'A name' });
+  });
+
+  it('should normalize inside oneOf/anyOf/allOf arrays', () => {
+    const schema = {
+      type: 'object',
+      oneOf: [
+        { type: 'object', properties: { kind: { type: 'string', const: 'A' } } },
+        { type: 'object', properties: { kind: { type: 'string', const: 'B' } } },
+      ],
+      anyOf: [{ type: 'string', const: 'x' }],
+      allOf: [{ type: 'number', const: 1 }],
+    } as any;
+
+    const result = normalizeJsonSchema(schema);
+    expect(result.oneOf[0].properties.kind).toEqual({ type: 'string', enum: ['A'] });
+    expect(result.oneOf[1].properties.kind).toEqual({ type: 'string', enum: ['B'] });
+    expect(result.anyOf[0]).toEqual({ type: 'string', enum: ['x'] });
+    expect(result.allOf[0]).toEqual({ type: 'number', enum: [1] });
+  });
+
+  it('should normalize array items with const', () => {
+    const schema = {
+      type: 'array',
+      items: { type: 'string', const: 'fixed' },
+    } as any;
+
+    const result = normalizeJsonSchema(schema);
+    expect(result.items).toEqual({ type: 'string', enum: ['fixed'] });
+  });
+
+  it('should normalize additionalProperties with const', () => {
+    const schema = {
+      type: 'object',
+      additionalProperties: { type: 'string', const: 'val' },
+    } as any;
+
+    const result = normalizeJsonSchema(schema);
+    expect(result.additionalProperties).toEqual({ type: 'string', enum: ['val'] });
+  });
+
+  it('should handle null, undefined, and primitive inputs safely', () => {
+    expect(normalizeJsonSchema(null as any)).toBeNull();
+    expect(normalizeJsonSchema(undefined as any)).toBeUndefined();
+    expect(normalizeJsonSchema('string' as any)).toBe('string');
+    expect(normalizeJsonSchema(42 as any)).toBe(42);
+    expect(normalizeJsonSchema(true as any)).toBe(true);
+  });
+
+  it('should be a no-op when no const is present', () => {
+    const schema = {
+      type: 'object',
+      properties: {
+        name: { type: 'string', description: 'Name' },
+        age: { type: 'number' },
+        tags: { type: 'array', items: { type: 'string' } },
+      },
+      required: ['name'],
+    } as any;
+
+    const result = normalizeJsonSchema(schema);
+    expect(result).toEqual(schema);
+  });
+
+  it('should handle a Tavily-like schema pattern with const', () => {
+    const schema = {
+      type: 'object',
+      properties: {
+        query: {
+          type: 'string',
+          description: 'The search query',
+        },
+        search_depth: {
+          type: 'string',
+          const: 'advanced',
+          description: 'The depth of the search',
+        },
+        topic: {
+          type: 'string',
+          enum: ['general', 'news'],
+          description: 'The search topic',
+        },
+        include_answer: {
+          type: 'boolean',
+          const: true,
+        },
+        max_results: {
+          type: 'number',
+          const: 5,
+        },
+      },
+      required: ['query'],
+    } as any;
+
+    const result = normalizeJsonSchema(schema);
+
+    // const fields should be converted to enum
+    expect(result.properties.search_depth).toEqual({
+      type: 'string',
+      enum: ['advanced'],
+      description: 'The depth of the search',
+    });
+    expect(result.properties.include_answer).toEqual({
+      type: 'boolean',
+      enum: [true],
+    });
+    expect(result.properties.max_results).toEqual({
+      type: 'number',
+      enum: [5],
+    });
+
+    // Existing enum should be preserved
+    expect(result.properties.topic).toEqual({
+      type: 'string',
+      enum: ['general', 'news'],
+      description: 'The search topic',
+    });
+
+    // Non-const fields should be unchanged
+    expect(result.properties.query).toEqual({
+      type: 'string',
+      description: 'The search query',
+    });
+
+    // Top-level fields preserved
+    expect(result.required).toEqual(['query']);
+    expect(result.type).toBe('object');
+  });
+
+  it('should handle arrays at the top level', () => {
+    const schemas = [
+      { type: 'string', const: 'a' },
+      { type: 'number', const: 1 },
+    ] as any;
+
+    const result = normalizeJsonSchema(schemas);
+    expect(result).toEqual([
+      { type: 'string', enum: ['a'] },
+      { type: 'number', enum: [1] },
+    ]);
+  });
+});

packages/api/src/mcp/zod.ts

@@ -248,6 +248,65 @@ export function resolveJsonSchemaRefs<T extends Record<string, unknown>>(
   return result as T;
 }
 
+/**
+ * Recursively normalizes a JSON schema by converting `const` values to `enum` arrays.
+ * Gemini/Vertex AI does not support the `const` keyword in function declarations,
+ * but `const: X` is semantically equivalent to `enum: [X]` per the JSON Schema spec.
+ *
+ * @param schema - The JSON schema to normalize
+ * @returns The normalized schema with `const` converted to `enum`
+ */
+export function normalizeJsonSchema<T extends Record<string, unknown>>(schema: T): T {
+  if (!schema || typeof schema !== 'object') {
+    return schema;
+  }
+
+  if (Array.isArray(schema)) {
+    return schema.map((item) =>
+      item && typeof item === 'object' ? normalizeJsonSchema(item) : item,
+    ) as unknown as T;
+  }
+
+  const result: Record<string, unknown> = {};
+
+  for (const [key, value] of Object.entries(schema)) {
+    if (key === 'const' && !('enum' in schema)) {
+      result['enum'] = [value];
+      continue;
+    }
+
+    if (key === 'const' && 'enum' in schema) {
+      // Skip `const` when `enum` already exists
+      continue;
+    }
+
+    if (key === 'properties' && value && typeof value === 'object' && !Array.isArray(value)) {
+      const newProps: Record<string, unknown> = {};
+      for (const [propKey, propValue] of Object.entries(value as Record<string, unknown>)) {
+        newProps[propKey] =
+          propValue && typeof propValue === 'object'
+            ? normalizeJsonSchema(propValue as Record<string, unknown>)
+            : propValue;
+      }
+      result[key] = newProps;
+    } else if (
+      (key === 'items' || key === 'additionalProperties') &&
+      value &&
+      typeof value === 'object'
+    ) {
+      result[key] = normalizeJsonSchema(value as Record<string, unknown>);
+    } else if ((key === 'oneOf' || key === 'anyOf' || key === 'allOf') && Array.isArray(value)) {
+      result[key] = value.map((item) =>
+        item && typeof item === 'object' ? normalizeJsonSchema(item) : item,
+      );
+    } else {
+      result[key] = value;
+    }
+  }
+
+  return result as T;
+}
+
 /**
  * Converts a JSON Schema to a Zod schema.
  *

packages/api/src/tools/definitions.ts

@@ -8,9 +8,10 @@
 import { Constants, actionDelimiter } from 'librechat-data-provider';
 import type { AgentToolOptions } from 'librechat-data-provider';
 import type { LCToolRegistry, JsonSchemaType, LCTool, GenericTool } from '@librechat/agents';
-import { buildToolClassification, type ToolDefinition } from './classification';
+import type { ToolDefinition } from './classification';
+import { resolveJsonSchemaRefs, normalizeJsonSchema } from '~/mcp/zod';
+import { buildToolClassification } from './classification';
 import { getToolDefinition } from './registry/definitions';
-import { resolveJsonSchemaRefs } from '~/mcp/zod';
 
 export interface MCPServerTool {
   function?: {
@@ -138,7 +139,7 @@ export async function loadToolDefinitions(
             name: actualToolName,
             description: toolDef.function.description,
             parameters: toolDef.function.parameters
-              ? resolveJsonSchemaRefs(toolDef.function.parameters)
+              ? normalizeJsonSchema(resolveJsonSchemaRefs(toolDef.function.parameters))
               : undefined,
             serverName,
           });
@@ -153,7 +154,7 @@ export async function loadToolDefinitions(
         name: toolName,
         description: toolDef.function.description,
         parameters: toolDef.function.parameters
-          ? resolveJsonSchemaRefs(toolDef.function.parameters)
+          ? normalizeJsonSchema(resolveJsonSchemaRefs(toolDef.function.parameters))
           : undefined,
         serverName,
       });