fix: support multiple concurrent MCP client connections

[dddabtc]

Summary

• The MCP Server (Protocol) instance was a singleton shared across all sessions. When a second client sent an initialize request to /mcp, Protocol.connect() threw "Already connected to a transport" because the singleton was already bound to the first client's transport.
• Replaced the singleton getMcpServer() with a factory function createMcpServer(), so each new transport (both /mcp StreamableHTTP and /sse SSE) gets its own independent MCP Server instance.

Steps to reproduce (before fix)

# First request succeeds
curl -X POST "http://127.0.0.1:12306/mcp" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":"1","method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}'

# Second request fails with 500: "Already connected to a transport"
curl -X POST "http://127.0.0.1:12306/mcp" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":"1","method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test2","version":"1.0"}}}'

Changes

File	Change
app/native-server/src/mcp/mcp-server.ts	Replace singleton getMcpServer() with factory createMcpServer()
app/native-server/src/server/index.ts	Use createMcpServer() for each new transport in /mcp and /sse endpoints

Test plan

• First MCP client initialize → succeeds
• Second MCP client initialize (without session ID) → succeeds (previously 500 error)
• Existing session reuse via mcp-session-id header → still works
• SSE endpoint /sse with multiple clients → works independently

[oshliaer]

@dddabtc, your solution is good and works great!

I've checked.

┌───────────────┬─────────────────────────────────────────┐
│ Component     │ Value                                   │
├───────────────┼─────────────────────────────────────────┤
│ OS            │ Linux 6.8.0-100-generic (Ubuntu) x86_64 │
│ Node.js       │ v22.14.0                                │
│ npm           │ 11.8.0                                  │
│ pnpm          │ 10.29.2                                 │
│ Google Chrome │ 145.0.7632.109                          │
└───────────────┴─────────────────────────────────────────┘

However, today @PyEL666 proposed a more elegant solution #301 that is backward-compatible which seems cleaner:

• Kept the getMcpServer() name (backward-compatible API)
• Changed only the implementation: removed caching, made it a factory function
• Added detailed comments explaining why this is safe
• Does not require changes in server/index.ts -- calls remain the same