Python: Add MCP hosting adapter package

[hashwnath]

Summary

Addresses #321

Introduces a new microsoft-agents-hosting-mcp package that exposes an M365 Agent as an MCP (Model Context Protocol) server, enabling MCP clients to discover and invoke agent capabilities through the standard MCP protocol.

Architecture

The adapter follows the established hosting adapter pattern used by hosting-aiohttp and hosting-fastapi:

• Subclasses ChannelAdapter and implements send_activities to buffer responses
• Translates MCP tool calls into Activity-based turns routed through the standard middleware → agent pipeline
• Uses FastMCP from the mcp Python SDK for protocol handling and transport
• Supports streamable HTTP transport for production deployment

Key Components

• MCPAdapter — Core adapter bridging MCP protocol to the Agents SDK pipeline
  • Built-in message tool for text-based agent interaction
  • Custom tool registration for exposing multiple agent capabilities
  • Full middleware pipeline support
  • Response buffering via TurnContext.turn_state
• MCP_CHANNEL_ID — Channel identifier ("mcp") for MCP-originated activities

Usage

from microsoft_agents.hosting.mcp import MCPAdapter

adapter = MCPAdapter(agent=my_agent, server_name="my-agent-mcp")

# Mount on FastAPI
app.mount("/mcp", adapter.streamable_http_app())

Test plan

• 14 unit tests covering:
  • Adapter initialization (default/custom server names, ASGI app creation)
  • Turn processing (echo, multi-response, silent agent, tool name propagation, channel ID)
  • send_activities response buffering
  • Unsupported operations (update_activity, delete_activity)
  • Middleware pipeline integration (invocation and activity modification)
  • Custom tool registration
• black formatted (88 char line length)
• flake8 clean (127 max line length)
• All tests pass on Python 3.11

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