fix: properly mount StreamableHttpService as Tower service

The HTTP server was incorrectly using custom Axum handlers to wrap the
StreamableHttpService, when it should be mounted directly using nest_service().

Fixed:
- Use .nest_service("/mcp", http_service) to let the service handle its own routing
- Removed custom handle_mcp_request() and handle_sse_stream() handlers
- The StreamableHttpService handles POST/GET /mcp internally

This fixes the SSE connection issues where the MCP Python SDK couldn't connect.
The service now properly handles the MCP-over-HTTP protocol as designed by rmcp.

Also removed the separate health check from test_agentic_mcp.py since the MCP
session initialization serves as the connectivity test.

Author: jruokola

crates/codegraph-mcp/src/http_server.rs

@@ -35,12 +35,12 @@ pub async fn start_http_server(
         },
     );
 
-    // Build Axum router with MCP endpoints
+    // Build Axum router with MCP service mounted as Tower service
+    // IMPORTANT: Use nest_service to mount the StreamableHttpService directly
+    // This lets the service handle its own /mcp POST/GET routing internally
     let app = Router::new()
-        .route("/mcp", axum::routing::post(handle_mcp_request))
-        .route("/sse", axum::routing::get(handle_sse_stream))
-        .route("/health", axum::routing::get(health_check))
-        .with_state(http_service);
+        .nest_service("/mcp", http_service)
+        .route("/health", axum::routing::get(health_check));
 
     // Parse bind address
     let addr: SocketAddr = config
@@ -50,8 +50,8 @@ pub async fn start_http_server(
 
     info!("CodeGraph MCP HTTP server listening on http://{}", addr);
     info!("Endpoints:");
-    info!("  POST http://{}/mcp - Send MCP requests", addr);
-    info!("  GET  http://{}/sse - Connect to SSE stream (requires Mcp-Session-Id header)", addr);
+    info!("  POST http://{}/mcp - Initialize session and send MCP requests", addr);
+    info!("  GET  http://{}/mcp - Open SSE stream (requires Mcp-Session-Id header)", addr);
     info!("  GET  http://{}/health - Health check", addr);
 
     // Start server
@@ -65,131 +65,3 @@ pub async fn start_http_server(
 async fn health_check() -> &'static str {
     "OK"
 }
-
-/// Handle MCP POST requests
-async fn handle_mcp_request(
-    axum::extract::State(service): axum::extract::State<
-        StreamableHttpService<CodeGraphMCPServer, LocalSessionManager>,
-    >,
-    headers: axum::http::HeaderMap,
-    body: axum::body::Bytes,
-) -> axum::response::Response {
-    use axum::response::IntoResponse;
-    use http_body_util::Full;
-    use tower::ServiceExt;
-    use tracing::warn;
-
-    // Build HTTP request for Tower service
-    let mut builder = axum::http::Request::builder()
-        .method(axum::http::Method::POST)
-        .uri("/mcp")
-        .header(axum::http::header::CONTENT_TYPE, "application/json")
-        .header(
-            axum::http::header::ACCEPT,
-            "application/json, text/event-stream",
-        );
-
-    // Forward session ID header if present
-    if let Some(session_id) = headers.get("Mcp-Session-Id") {
-        builder = builder.header("Mcp-Session-Id", session_id);
-    }
-
-    // Create request with body
-    let http_request = match builder.body(Full::new(body)) {
-        Ok(req) => req,
-        Err(e) => {
-            warn!("Failed to build HTTP request: {}", e);
-            return (
-                axum::http::StatusCode::INTERNAL_SERVER_ERROR,
-                format!("Request build error: {}", e),
-            )
-                .into_response();
-        }
-    };
-
-    // Call Tower service using oneshot
-    match service.oneshot(http_request).await {
-        Ok(response) => {
-            // Response is already in the correct format (BoxBody)
-            // Just need to convert it to an Axum response
-            let (parts, body) = response.into_parts();
-            axum::http::Response::from_parts(parts, body).into_response()
-        }
-        Err(e) => {
-            warn!("Service call failed: {:?}", e);
-            (
-                axum::http::StatusCode::INTERNAL_SERVER_ERROR,
-                format!("Service error: {:?}", e),
-            )
-                .into_response()
-        }
-    }
-}
-
-/// Handle SSE streaming connections (reconnection support)
-async fn handle_sse_stream(
-    axum::extract::State(service): axum::extract::State<
-        StreamableHttpService<CodeGraphMCPServer, LocalSessionManager>,
-    >,
-    headers: axum::http::HeaderMap,
-) -> axum::response::Response {
-    use axum::response::IntoResponse;
-    use http_body_util::Empty;
-    use tower::ServiceExt;
-    use tracing::warn;
-
-    // Extract session ID (REQUIRED for SSE reconnection)
-    let session_id = match headers.get("Mcp-Session-Id").and_then(|v| v.to_str().ok()) {
-        Some(sid) => sid,
-        None => {
-            warn!("SSE connection missing Mcp-Session-Id header");
-            return (
-                axum::http::StatusCode::BAD_REQUEST,
-                "Missing Mcp-Session-Id header",
-            )
-                .into_response();
-        }
-    };
-
-    // Build HTTP request for Tower service
-    let mut builder = axum::http::Request::builder()
-        .method(axum::http::Method::GET)
-        .uri("/sse")
-        .header("Mcp-Session-Id", session_id);
-
-    // Extract Last-Event-Id for resumption (optional)
-    if let Some(last_event_id) = headers.get("Last-Event-Id") {
-        builder = builder.header("Last-Event-Id", last_event_id);
-    }
-
-    // Create request with empty body for GET
-    let http_request = match builder.body(Empty::<axum::body::Bytes>::new()) {
-        Ok(req) => req,
-        Err(e) => {
-            warn!("Failed to build SSE request: {}", e);
-            return (
-                axum::http::StatusCode::INTERNAL_SERVER_ERROR,
-                format!("Request build error: {}", e),
-            )
-                .into_response();
-        }
-    };
-
-    // Call Tower service using oneshot
-    match service.oneshot(http_request).await {
-        Ok(response) => {
-            // Response is already in the correct format (BoxBody)
-            // Just need to convert it to an Axum response
-            let (parts, body) = response.into_parts();
-            axum::http::Response::from_parts(parts, body).into_response()
-        }
-        Err(e) => {
-            warn!("SSE service call failed: {:?}", e);
-            (
-                axum::http::StatusCode::INTERNAL_SERVER_ERROR,
-                format!("Service error: {:?}", e),
-            )
-                .into_response()
-        }
-    }
-}