stack/packages/mosaic/src/runtime/mcp-config.ts

import { readFileSync, writeFileSync, existsSync, mkdirSync } from 'node:fs';
import { join, dirname } from 'node:path';
import { homedir } from 'node:os';
import type { RuntimeName } from '../types.js';

const MCP_ENTRY = {
  command: 'npx',
  args: ['-y', '@modelcontextprotocol/server-sequential-thinking'],
};

export function configureMcpForRuntime(runtime: RuntimeName): void {
  switch (runtime) {
    case 'claude':
      return configureClaudeMcp();
    case 'codex':
      return configureCodexMcp();
    case 'opencode':
      return configureOpenCodeMcp();
  }
}

function ensureDir(filePath: string): void {
  mkdirSync(dirname(filePath), { recursive: true });
}

function configureClaudeMcp(): void {
  const settingsPath = join(homedir(), '.claude', 'settings.json');
  ensureDir(settingsPath);

  let data: Record<string, unknown> = {};
  if (existsSync(settingsPath)) {
    try {
      data = JSON.parse(readFileSync(settingsPath, 'utf-8')) as Record<string, unknown>;
    } catch {
      // Start fresh if corrupt
    }
  }

  if (
    !data['mcpServers'] ||
    typeof data['mcpServers'] !== 'object' ||
    Array.isArray(data['mcpServers'])
  ) {
    data['mcpServers'] = {};
  }
  (data['mcpServers'] as Record<string, unknown>)['sequential-thinking'] = MCP_ENTRY;

  writeFileSync(settingsPath, JSON.stringify(data, null, 2) + '\n', 'utf-8');
}

function configureCodexMcp(): void {
  const configPath = join(homedir(), '.codex', 'config.toml');
  ensureDir(configPath);

  let content = '';
  if (existsSync(configPath)) {
    content = readFileSync(configPath, 'utf-8');
    // Remove existing sequential-thinking section
    content = content
      .replace(/\[mcp_servers\.(sequential-thinking|sequential_thinking)\][\s\S]*?(?=\n\[|$)/g, '')
      .trim();
  }

  content +=
    '\n\n[mcp_servers.sequential-thinking]\n' +
    'command = "npx"\n' +
    'args = ["-y", "@modelcontextprotocol/server-sequential-thinking"]\n';

  writeFileSync(configPath, content, 'utf-8');
}

function configureOpenCodeMcp(): void {
  const configPath = join(homedir(), '.config', 'opencode', 'config.json');
  ensureDir(configPath);

  let data: Record<string, unknown> = {};
  if (existsSync(configPath)) {
    try {
      data = JSON.parse(readFileSync(configPath, 'utf-8')) as Record<string, unknown>;
    } catch {
      // Start fresh
    }
  }

  if (!data['mcp'] || typeof data['mcp'] !== 'object' || Array.isArray(data['mcp'])) {
    data['mcp'] = {};
  }
  (data['mcp'] as Record<string, unknown>)['sequential-thinking'] = {
    type: 'local',
    command: ['npx', '-y', '@modelcontextprotocol/server-sequential-thinking'],
    enabled: true,
  };

  writeFileSync(configPath, JSON.stringify(data, null, 2) + '\n', 'utf-8');
}