Add Streamable HTTP transport for MCP (replaces SSE as primary)

- New /mcp endpoint with StreamableHTTPServerTransport (stateless per-request)
- SSE kept as /mcp/sse fallback
- Survives pod restarts — no persistent connection needed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agent/mcp_app.py

@@ -1,4 +1,4 @@
-"""Standalone MCP SSE app — proxies tool calls to assay-runtime."""
+"""Standalone MCP app — proxies tool calls to assay-runtime. Supports Streamable HTTP + SSE."""
 
 import json
 import logging
@@ -14,6 +14,7 @@ from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
 
 from mcp.server import Server
 from mcp.server.sse import SseServerTransport
+from mcp.server.streamable_http import StreamableHTTPServerTransport
 from mcp.types import TextContent, Tool
 
 logging.basicConfig(level=logging.INFO, format="%(asctime)s [%(name)s] %(message)s", datefmt="%H:%M:%S")
@@ -214,7 +215,29 @@ async def call_tool(name: str, arguments: dict):
         return [TextContent(type="text", text=f"Unknown tool: {name}")]
 
 
-# Mount MCP SSE endpoints
+# Mount MCP Streamable HTTP endpoint (primary — stateless, survives pod restarts)
+_http_transports: dict[str, StreamableHTTPServerTransport] = {}
+_http_tasks: dict[str, any] = {}
+
+@app.api_route("/mcp", methods=["GET", "POST", "DELETE"])
+async def mcp_http(request: Request, user=Depends(require_auth)):
+    import asyncio
+    # Get or create session-scoped transport
+    session_id = request.headers.get("mcp-session-id", "default")
+    if session_id not in _http_transports:
+        transport = StreamableHTTPServerTransport(mcp_session_id=session_id)
+        _http_transports[session_id] = transport
+
+        async def _run():
+            async with transport.connect() as streams:
+                await mcp_server.run(streams[0], streams[1], mcp_server.create_initialization_options())
+        _http_tasks[session_id] = asyncio.create_task(_run())
+
+    transport = _http_transports[session_id]
+    await transport.handle_request(request.scope, request.receive, request._send)
+
+
+# Mount MCP SSE endpoints (legacy fallback)
 @app.get("/mcp/sse")
 async def mcp_sse(request: Request, user=Depends(require_auth)):
     async with _mcp_transport.connect_sse(request.scope, request.receive, request._send) as streams: