fix(plugin-mcp): pass MCP request context through tool callbacks to fetch

[Copilot]

MCP-generated tool handlers were discarding the RequestHandlerExtra (2nd arg of server.tool() callbacks), so callers had no way to propagate auth headers or other request context to the underlying API fetch.

Changes

• plugin-client/src/components/Client.tsx — adds optional requestParam?: string prop; when set, appends , ${requestParam}?: unknown to the generated function signature and passes it as the second arg to fetch (non-configurable path only)
• plugin-mcp/src/generators/mcpGenerator.tsx — passes requestParam="request" to Client so every MCP handler accepts and forwards request context
• plugin-mcp/src/components/Server.tsx — updates server.tool() callback templates to capture and thread request through to handlers:
  • with params: async (params, request) => handler(params, request)
  • no params: async (_, request) => handler(request)

Generated output (before → after)

Before:

server.tool('getAll', 'Get all', { params }, async ({ params }) => {
  return getAllHandler({ params })
})

export async function getAllHandler({ params }: { params?: Params }): Promise<CallToolResult> {
  const res = await fetch({ method: 'GET', url: `/items`, params })
  // ...
}

After:

server.tool('getAll', 'Get all', { params }, async ({ params }, request) => {
  return getAllHandler({ params }, request)
})

export async function getAllHandler({ params }: { params?: Params }, request?: unknown): Promise<CallToolResult> {
  const res = await fetch({ method: 'GET', url: `/items`, params }, request)
  // ...
}

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested this code locally with pnpm run test.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is for the docs (no release).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>MCP is not passing down headers to fetch</issue_title>
<issue_description>### What version of kubb is running?

4.22.0

What kind of platform do you use?

None

Your kubb.config.ts config file?

import { defineConfig } from '@kubb/core';
import { pluginOas } from '@kubb/plugin-oas';
import { pluginTs } from '@kubb/plugin-ts';
import { pluginMcp } from '@kubb/plugin-mcp';
import { pluginZod } from '@kubb/plugin-zod';

export default defineConfig({
  input: {
    path: './swagger-v1.json',
  },
  output: {
    format: 'prettier',
    path: './src/generated/v1',
    extension: { '.ts': '' },
    clean: true,
  },
  plugins: [
    pluginOas(),
    pluginTs(),
    pluginZod(),
    pluginMcp({
      output: {
        path: './mcp',
        barrelType: false,
      },
      client: {
        importPath: '../../client',
      },
      group: {
        type: 'tag',
        name: ({ group }) => `${group}Handlers`,
      },
    }),
  ],
});

Swagger/OpenAPI file?

What version of external packages are you using(@tanstack-query, MSW, React, Vue, ...)

What steps can reproduce the bug?

kubb generates such MCP tool

server.tool(
  'Project_getAll',
  'Get all',
  { params },
  async ({ params }) => {
    return projectGetAllHandler({ params });
  },
);

ideally it should pass down request (2nd argument in tool) to client and then client can pull out headers (auth, traceId) and pass it down to API call

// MCP tool
server.tool(
  'Project_getAll',
  'Get all',
  { params },
  async ({ params }, request) => {
    return projectGetAllHandler({ params }, request);
  },
);

import fetch from '../../../../client';

// Handler
export async function projectGetAllHandler({
  params,
}: { params }, request): Promise<
  Promise<CallToolResult>
> {
  const res = await fetch({ method: 'GET', url: `/project`, params }, request);
  return {
    content: [
      {
        type: 'text',
        text: JSON.stringify(res.data),
      },
    ],
  };
}

How often does this bug happen?

None

What is the expected behavior?

No response

Additional information

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes MCP is not passing down headers to fetch #2501

---

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