Function writeMcpjsonFile

src/services/mcp/config.ts:88–131

* Internal utility: Write MCP config to .mcp.json file. * Preserves file permissions and flushes to disk before rename. * Uses the original path for rename (does not follow symlinks).

(config: McpJsonConfig)

 * Uses the original path for rename (does not follow symlinks).
 */
async function writeMcpjsonFile(config: McpJsonConfig): Promise<void> {
  const mcpJsonPath = join(getCwd(), '.mcp.json')

  // Read existing file permissions to preserve them
  let existingMode: number | undefined
  try {
    const stats = await stat(mcpJsonPath)
    existingMode = stats.mode
  } catch (e: unknown) {
    const code = getErrnoCode(e)
    if (code !== 'ENOENT') {
      throw e
    }
    // File doesn't exist yet -- no permissions to preserve
  }

  // Write to temp file, flush to disk, then atomic rename
  const tempPath = `${mcpJsonPath}.tmp.${process.pid}.${Date.now()}`
  const handle = await open(tempPath, 'w', existingMode ?? 0o644)
  try {
    await handle.writeFile(jsonStringify(config, null, 2), {
      encoding: 'utf8',
    })
    await handle.datasync()
  } finally {
    await handle.close()
  }

  try {
    // Restore original file permissions on the temp file before rename
    if (existingMode !== undefined) {
      await chmod(tempPath, existingMode)
    }
    await rename(tempPath, mcpJsonPath)
  } catch (e: unknown) {
    // Clean up temp file on failure
    try {
      await unlink(tempPath)
    } catch {
      // Best-effort cleanup
    }
    throw e
  }
}

/**
 * Extract command array from server config (stdio servers only)