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.

.gitignore

@@ -0,0 +1,4 @@
+*.exe
+*.dll
+*.so
+*.dylib

main.go

@@ -69,10 +69,11 @@ func main() {
 	debugLog("Connecting to: %s", giteaURL)
 
 	// Read JSON-RPC messages from stdin, forward to Gitea, write responses to stdout
+	// Supports both raw JSON lines and Content-Length framed messages (Claude Code uses framing)
 	reader := bufio.NewReader(os.Stdin)
 
 	for {
-		line, err := reader.ReadBytes('\n')
+		line, err := readMessage(reader)
 		if err != nil {
 			if err == io.EOF {
 				debugLog("EOF received, exiting")
@@ -89,10 +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",
@@ -109,11 +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"
 
@@ -147,9 +179,74 @@ func forwardToGitea(request []byte) ([]byte, error) {
 	return body, nil
 }
 
+// readMessage reads a JSON-RPC message from stdin.
+// Handles both raw JSON lines and Content-Length framed messages.
+// Claude Code sends: Content-Length: N\r\n\r\n{json}
+func readMessage(reader *bufio.Reader) ([]byte, error) {
+	// Peek at first bytes to detect format
+	for {
+		line, err := reader.ReadBytes('\n')
+		if err != nil {
+			return nil, err
+		}
+
+		trimmed := bytes.TrimSpace(line)
+		if len(trimmed) == 0 {
+			continue
+		}
+
+		// If it starts with '{', it's a raw JSON line
+		if trimmed[0] == '{' {
+			return trimmed, nil
+		}
+
+		// If it starts with "Content-Length:", read the framed message
+		if bytes.HasPrefix(bytes.ToLower(trimmed), []byte("content-length:")) {
+			// Parse content length
+			parts := bytes.SplitN(trimmed, []byte(":"), 2)
+			if len(parts) != 2 {
+				continue
+			}
+			lengthStr := bytes.TrimSpace(parts[1])
+			var contentLength int
+			fmt.Sscanf(string(lengthStr), "%d", &contentLength)
+			if contentLength <= 0 {
+				continue
+			}
+
+			// Read until empty line (end of headers)
+			for {
+				headerLine, err := reader.ReadBytes('\n')
+				if err != nil {
+					return nil, err
+				}
+				if len(bytes.TrimSpace(headerLine)) == 0 {
+					break
+				}
+			}
+
+			// Read exactly contentLength bytes
+			body := make([]byte, contentLength)
+			_, err := io.ReadFull(reader, body)
+			if err != nil {
+				return nil, fmt.Errorf("read body: %w", err)
+			}
+
+			return body, nil
+		}
+
+		// Unknown line, skip
+		debugLog("Skipping unknown line: %s", string(trimmed))
+	}
+}
+
 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{}) {