fix(sub): include xhttp mode in extra JSON for karing compatibility (#4365)

- Add mode to buildXhttpExtra() so clients reading xtra param
  (karing, etc.) receive the xhttp mode alongside other bidirectional
  SplitHTTP fields. Previously mode was only a flat URL param and was
  silently dropped when xtra was present.
- Add xhttp case to streamData() to strip acceptProxyProtocol and
  server-only fields (noSSEHeader, scMaxBufferedPosts,
  scStreamUpServerSecs, serverMaxHeaderBytes) from JSON sub configs.
- Sync frontend buildXhttpExtra() with the same mode addition.

Closes #4364

frontend/src/models/inbound.js

@@ -1595,6 +1595,10 @@ export class Inbound extends XrayCommonClass {
             });
         }
 
+        if (typeof xhttp.mode === 'string' && xhttp.mode.length > 0) {
+            extra.mode = xhttp.mode;
+        }
+
         const stringFields = [
             "sessionPlacement", "sessionKey",
             "seqPlacement", "seqKey",

sub/subJsonService.go

@@ -265,6 +265,14 @@ func (s *SubJsonService) streamData(stream string) map[string]any {
 		streamSettings["wsSettings"] = s.removeAcceptProxy(streamSettings["wsSettings"])
 	case "httpupgrade":
 		streamSettings["httpupgradeSettings"] = s.removeAcceptProxy(streamSettings["httpupgradeSettings"])
+	case "xhttp":
+		streamSettings["xhttpSettings"] = s.removeAcceptProxy(streamSettings["xhttpSettings"])
+		if xhttp, ok := streamSettings["xhttpSettings"].(map[string]any); ok {
+			delete(xhttp, "noSSEHeader")
+			delete(xhttp, "scMaxBufferedPosts")
+			delete(xhttp, "scStreamUpServerSecs")
+			delete(xhttp, "serverMaxHeaderBytes")
+		}
 	}
 	return streamSettings
 }

sub/subService.go

@@ -1025,6 +1025,10 @@ func buildXhttpExtra(xhttp map[string]any) map[string]any {
 		}
 	}
 
+	if mode, ok := xhttp["mode"].(string); ok && len(mode) > 0 {
+		extra["mode"] = mode
+	}
+
 	stringFields := []string{
 		"sessionPlacement", "sessionKey",
 		"seqPlacement", "seqKey",