Improve Startup Logging and 404 Response for MCP Session Initialization

[sojournerdev]

Following up on the other discussion about session initialization, I propose two small improvements to help users avoid confusion when using MCP over Streamable HTTP:

1. Startup Logging — When the server starts, explicitly show the HTTP endpoint (/mcp) used to initialize and obtain the Mcp-Session-Id for session management.

2. 404 Response Hint — Update the /404 Page Not Found response to return a minimal JSON message explaining that the MCP server expects an initialize request to /mcp before other calls.

Current Startup Log Example:

2025/08/15 13:25:24 Streamable HTTP server listening on 0.0.0.0:8000

[sojournerdev]

Moving to issues