5acaeba2bb
When the 'mcp' Python SDK isn't installed, _run_stdio leaked a bare 'NameError: name StdioServerParameters is not defined' because the top-level 'from mcp import ...' fails inside try/except ImportError, leaving the names unbound at module scope. Mirror the _MCP_HTTP_AVAILABLE gate that _run_http already had: raise a clear ImportError with install instructions instead. Fixes #30904