Fixes #2992
Fixes #2812

Description

Add a stateless Streamable HTTP transport endpoint at /mcp/{client_name}/http/{user_id} alongside the existing SSE transport. This enables MCP clients that only support Streamable HTTP (e.g. openclaw-mcp-adapter) to connect to the OpenMemory MCP server.

The existing SSE endpoint is untouched — this is purely additive.

What changed

• New import: StreamableHTTPServerTransport from mcp.server.streamable_http and anyio
• New route: /{client_name}/http/{user_id} accepting POST, GET, and DELETE
  • Extracts user_id and client_name from path params and sets context vars (same pattern as the SSE handler)
  • Creates a per-request stateless StreamableHTTPServerTransport with JSON responses enabled
  • Runs the MCP server in a scoped anyio task group, delegates to transport.handle_request(), then terminates
• Bug fix: The transport writes its response directly via the ASGI send callable. Without interception, FastAPI would also try to send its own response — a "double-response" bug that only worked because uvicorn silently dropped the second one. Fixed by capturing the transport's ASGI messages via capture_send and returning a proper starlette.responses.Response to FastAPI. A response_started guard ensures a transport crash returns 500 instead of an empty 200.

Why

The MCP spec defines two transports: SSE and Streamable HTTP. The OpenMemory MCP server currently only supports SSE. Some MCP client adapters (like openclaw-mcp-adapter) only speak Streamable HTTP. Adding this transport makes OpenMemory accessible to a wider set of MCP clients without changing existing behavior.

Type of change

• New feature (non-breaking change which adds functionality)
• Bug fix (double-response in Streamable HTTP handler)

Testing

Automated tests (21 tests)

New test suite at openmemory/api/tests/test_mcp_server.py using pytest-asyncio and httpx ASGI transport:

Run with:

cd openmemory/api && python -m pytest tests/test_mcp_server.py -v

Manual verification

Tested against a live uvicorn server (OPENAI_API_KEY=test-key uvicorn main:app):

1. Initialize:

   curl -X POST http://localhost:8765/mcp/testclient/http/user1 \
     -H 'Content-Type: application/json' \
     -H 'Accept: application/json, text/event-stream' \
     -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"test","version":"0.1.0"}}}'
   # → 200 OK with serverInfo, capabilities, protocolVersion

2. tools/list:

   curl -X POST http://localhost:8765/mcp/testclient/http/user1 \
     -H 'Content-Type: application/json' \
     -H 'Accept: application/json, text/event-stream' \
     -d '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}'
   # → 200 OK with all 5 tools

3. tools/call:

   curl -X POST http://localhost:8765/mcp/testclient/http/user1 \
     -H 'Content-Type: application/json' \
     -H 'Accept: application/json, text/event-stream' \
     -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"add_memories","arguments":{"text":"I like pizza"}}}'
   # → 200 OK with tool response (graceful error without vector store)

4. Error handling: DELETE → 405, missing Accept → 406, invalid JSON → 400

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• I have checked my code and corrected any misspellings