Default Environment should be appended with custom env's passed to client (instead of replacing)

[Pdash-exceeds]

Describe the bug
In this line

typescript-sdk/src/client/stdio.ts

Line 119 in 0fa2397

env: this._serverParams.env ?? getDefaultEnvironment(),

To Reproduce
Steps to reproduce the behavior:

1. Connect a stdio client without custom env (works)
2. Connect the same client with custom env (fails because HOME, PATH and other default envs are missing when spawning the process)

Expected behavior
Both cases should pass.
env: { ...getDefaultEnvironment(), ...(this._serverParams.env ?? {}) },

Logs
file:///Users/pradeeptadash/langchain_mcp/node_modules/@langchain/mcp-adapters/dist/src/client.js:407
throw new MCPClientError(Failed to connect to stdio server "${serverName}": ${error}, serverName);
^

MCPClientError: Failed to connect to stdio server "linear-server": Error: spawn npx ENOENT
at MultiServerMCPClient.initializeStdioConnection (file:///Users/pradeeptadash/langchain_mcp/node_modules/@langchain/mcp-adapters/dist/src/client.js:407:19)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
at async MultiServerMCPClient.initializeConnections (file:///Users/pradeeptadash/langchain_mcp/node_modules/@langchain/mcp-adapters/dist/src/client.js:371:17)

Additional context
Add any other context about the problem here.

[jiashengguo]

@Pdash-exceeds, thanks for filing this!

Does no one use 'env'? 😂

[Pdash-exceeds]

I think most people use a remote MCP so they don't use env

[xianminx]

I think most people use a remote MCP so they don't use env

this is for stdio, and I am struggling with env config for testing various local mcp servers.
#242 this is wanted.

[zerogu]

To use the Notion MCP, which requires certain environment variables, I worked around the original design by merging getDefaultEnvironment() with my own env like this:

{
  "command": "npx",
  "args": ["-y", "@suekou/mcp-notion-server"],
  "env": {
    "NOTION_API_TOKEN": "your-integration-token",
    "NOTION_MARKDOWN_CONVERSION": "true"
  }
}

import { StdioClientTransport, StdioServerParameters, getDefaultEnvironment } from '@modelcontextprotocol/sdk/client/stdio.js'

...

serverParams.env = {
    ...getDefaultEnvironment(),
    ...serverParams.env
}

this.transport = new StdioClientTransport(serverParams as StdioServerParameters)