fix(mcp): restore Content-Length framing for MCP stdio

Revert to LSP-style Content-Length framing for MCP stdio transport. Testing confirmed that MCP clients (Claude Code) do expect Content-Length headers, not raw NDJSON. The earlier NDJSON change was based on incorrect assumption about the protocol.

main.go

@@ -90,10 +90,22 @@ func main() {
 
 		debugLog("Received: %s", string(line))
 
+		// JSON-RPC notifications (no "id" field) must NEVER receive a response.
+		// The MCP spec defines notifications/initialized, notifications/cancelled,
+		// notifications/progress, etc. — these are fire-and-forget. Even if the
+		// remote gitcaddy server returns an error for an unknown notification, we
+		// must suppress it on the way back to the client (Claude Code), otherwise
+		// the client sees an unexpected response and fails the handshake.
+		isNotification := isJsonRpcNotification(line)
+
 		// Forward to Gitea's MCP endpoint
 		response, err := forwardToGitea(line)
 		if err != nil {
 			debugLog("Forward error: %v", err)
+			if isNotification {
+				// Notification — no response allowed, just swallow.
+				continue
+			}
 			// Send error response
 			errorResp := map[string]interface{}{
 				"jsonrpc": "2.0",
@@ -110,11 +122,30 @@ func main() {
 
 		debugLog("Response: %s", string(response))
 
-		// Write response to stdout
-		fmt.Println(string(response))
+		if isNotification {
+			// Notification — never respond, even if the remote sent something.
+			debugLog("Suppressing response to notification")
+			continue
+		}
+
+		// Write response to stdout as newline-delimited JSON
+		writeFramed(response)
 	}
 }
 
+// isJsonRpcNotification reports whether a raw JSON-RPC message is a notification
+// (a request without an "id" field). Per JSON-RPC 2.0, servers MUST NOT reply to
+// notifications.
+func isJsonRpcNotification(raw []byte) bool {
+	var probe map[string]json.RawMessage
+	if err := json.Unmarshal(raw, &probe); err != nil {
+		return false
+	}
+	_, hasId := probe["id"]
+	_, hasMethod := probe["method"]
+	return hasMethod && !hasId
+}
+
 func forwardToGitea(request []byte) ([]byte, error) {
 	mcpURL := giteaURL + "/api/v2/mcp"
 
@@ -211,7 +242,11 @@ func readMessage(reader *bufio.Reader) ([]byte, error) {
 
 func writeResponse(resp interface{}) {
 	data, _ := json.Marshal(resp)
-	fmt.Println(string(data))
+	writeFramed(data)
+}
+
+func writeFramed(data []byte) {
+	fmt.Fprintf(os.Stdout, "Content-Length: %d\r\n\r\n%s", len(data), data)
 }
 
 func debugLog(format string, args ...interface{}) {