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

[christian-bromann]

Description

Fixes a bug where using MCP (Model Context Protocol) tools with ChatMistralAI would throw a TypeError: Cannot read properties of undefined (reading 'typeName') error.

fixes #8171

Problem

The _convertToolToMistralTool function was assuming all tool schemas were Zod schemas and unconditionally calling zodToJsonSchema() on them. However, MCP tools from @langchain/mcp-adapters provide tools with JSON schemas already, not Zod schemas. This mismatch caused the zodToJsonSchema function to fail when trying to access the typeName property on a plain JSON schema object.

Error Stack Trace:

TypeError: Cannot read properties of undefined (reading 'typeName')
    at parseDef (/node_modules/.pnpm/[email protected][email protected]/node_modules/zod-to-json-schema/dist/cjs/parseDef.js:22:77)
    at zodToJsonSchema (/node_modules/.pnpm/[email protected][email protected]/node_modules/zod-to-json-schema/dist/cjs/zodToJsonSchema.js:22:45)
    at _convertToolToMistralTool (/node_modules/.pnpm/@[email protected]_@[email protected][email protected][email protected][email protected]__/node_modules/@langchain/mistralai/dist/chat_models.cjs:261:70)

Solution

Modified the _convertToolToMistralTool function to:

1. Check if the tool schema is a Zod schema using the existing isZodSchema helper function
2. Only call zodToJsonSchema() if it's actually a Zod schema
3. Use the schema directly if it's already a JSON schema (like MCP tools)

Code Changes:

// Before
parameters: zodToJsonSchema(tool.schema),

// After  
const parameters = isZodSchema(tool.schema) 
  ? zodToJsonSchema(tool.schema)
  : tool.schema;

Testing

• ✅ Added unit test covering both Zod schema tools and JSON schema tools
• ✅ Verified existing unit tests still pass
• ✅ Test specifically covers DynamicStructuredTool with JSON schema (simulating MCP tools)
• ✅ Integration tests pass (where API keys are available)

Compatibility

This change maintains backward compatibility with existing Zod-based tools while adding support for JSON schema-based tools from MCP adapters.

Affected Packages:

• @langchain/mistralai (primary fix)
• @langchain/mcp-adapters (compatibility restored)

Related Issues

This resolves the compatibility issue reported between @langchain/mistralai and @langchain/mcp-adapters when using tools in agent workflows with the createReactAgent function.

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[christian-bromann]

Seems like there is a similar fix for it in #8257 so feel free to close this one.