fix(mistralai): handle both Zod and JSON schemas in tool conversion

The _convertToolToMistralTool function was attempting to convert all tool
schemas using zodToJsonSchema(), but MCP tools already provide JSON schemas.
This caused a "Cannot read properties of undefined (reading 'typeName')"
error when using MCP tools with ChatMistralAI.

Now checks if schema is a Zod schema before conversion, allowing both
Zod schemas (from standard LangChain tools) and JSON schemas (from MCP tools)
to work correctly.

Fixes compatibility issue between @langchain/mistralai and @langchain/mcp-adapters.

Author: christian-bromann

libs/langchain-mistralai/src/chat_models.ts

@@ -503,12 +503,17 @@ function _convertToolToMistralTool(
     }
 
     const description = tool.description ?? `Tool: ${tool.name}`;
+    // Check if schema is a Zod schema or already a JSON schema
+    const parameters = isZodSchema(tool.schema)
+      ? zodToJsonSchema(tool.schema)
+      : tool.schema;
+
     return {
       type: "function",
       function: {
         name: tool.name,
         description,
-        parameters: zodToJsonSchema(tool.schema),
+        parameters,
       },
     };
   });

libs/langchain-mistralai/src/tests/chat_models.test.ts

@@ -1,3 +1,5 @@
+import { z } from "zod";
+import { DynamicStructuredTool } from "@langchain/core/tools";
 import { ChatMistralAI } from "../chat_models.js";
 import {
   _isValidMistralToolCallId,
@@ -30,6 +32,55 @@ describe("Mistral Tool Call ID Conversion", () => {
   });
 });
 
+test("Tool conversion handles both Zod schemas and JSON schemas", () => {
+  const model = new ChatMistralAI({ apiKey: "test" });
+  const zodTool = {
+    name: "zodTool",
+    description: "A tool with Zod schema",
+    schema: z.object({
+      input: z.string().describe("Input parameter"),
+    }),
+  };
+  const jsonSchemaTool = {
+    name: "jsonSchemaTool",
+    description: "A tool with JSON schema",
+    schema: {
+      type: "object",
+      properties: {
+        input: {
+          type: "string",
+          description: "Input parameter"
+        }
+      },
+      required: ["input"]
+    },
+  };
+
+  expect(() => {
+    const modelWithTools = model.bindTools([zodTool, jsonSchemaTool]);
+    expect(modelWithTools).toBeDefined();
+  }).not.toThrow();
+
+  const mcpLikeTool = new DynamicStructuredTool({
+    name: "mcpLikeTool",
+    description: "Tool similar to MCP tools",
+    schema: {
+      type: "object",
+      properties: {
+        city: { type: "string" },
+      },
+      required: ["city"],
+    },
+    func: async () => "test result",
+  });
+
+  // This should also not throw an error
+  expect(() => {
+    const modelWithMcpTool = model.bindTools([mcpLikeTool]);
+    expect(modelWithMcpTool).toBeDefined();
+  }).not.toThrow();
+});
+
 test("Serialization", () => {
   const model = new ChatMistralAI({
     apiKey: "foo",