feat(clash): emit xhttp and httpupgrade transports in subscription (#4531)

applyTransport's switch only covered tcp/ws/grpc; xhttp and
httpupgrade inbounds fell through to the default branch and returned
false. buildProxy then returned a nil map and the inbound was dropped
from the Clash subscription. When the subscription only contained
xhttp/httpupgrade inbounds, the proxies list ended up empty and the
client saw a 404 (or an "Error!" body on older builds), then refused
to parse.

Add a case for each, mapping the inbound's stream settings onto the
Mihomo-format opts blocks:

  xhttp        -> xhttp-opts: { path, host, mode }
  httpupgrade  -> http-upgrade-opts: { path, headers: { Host } }

Host falls back to the headers map when the dedicated `host` field is
empty, matching the existing ws behavior.

Closes #4531

sub/subClashService.go

@@ -363,6 +363,53 @@ func (s *SubClashService) applyTransport(proxy map[string]any, network string, s
 			proxy["grpc-opts"] = grpcOpts
 		}
 		return true
+	case "httpupgrade":
+		proxy["network"] = "httpupgrade"
+		hu, _ := stream["httpupgradeSettings"].(map[string]any)
+		opts := map[string]any{}
+		if hu != nil {
+			if path, ok := hu["path"].(string); ok && path != "" {
+				opts["path"] = path
+			}
+			host := ""
+			if v, ok := hu["host"].(string); ok && v != "" {
+				host = v
+			} else if headers, ok := hu["headers"].(map[string]any); ok {
+				host = searchHost(headers)
+			}
+			if host != "" {
+				opts["headers"] = map[string]any{"Host": host}
+			}
+		}
+		if len(opts) > 0 {
+			proxy["http-upgrade-opts"] = opts
+		}
+		return true
+	case "xhttp":
+		proxy["network"] = "xhttp"
+		xhttp, _ := stream["xhttpSettings"].(map[string]any)
+		opts := map[string]any{}
+		if xhttp != nil {
+			if path, ok := xhttp["path"].(string); ok && path != "" {
+				opts["path"] = path
+			}
+			host := ""
+			if v, ok := xhttp["host"].(string); ok && v != "" {
+				host = v
+			} else if headers, ok := xhttp["headers"].(map[string]any); ok {
+				host = searchHost(headers)
+			}
+			if host != "" {
+				opts["host"] = host
+			}
+			if mode, ok := xhttp["mode"].(string); ok && mode != "" {
+				opts["mode"] = mode
+			}
+		}
+		if len(opts) > 0 {
+			proxy["xhttp-opts"] = opts
+		}
+		return true
 	default:
 		return false
 	}

sub/subClashService_test.go

@@ -0,0 +1,81 @@
+package sub
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestApplyTransport_XHTTP(t *testing.T) {
+	svc := &SubClashService{}
+	proxy := map[string]any{}
+	stream := map[string]any{
+		"xhttpSettings": map[string]any{
+			"path": "/xh",
+			"host": "example.com",
+			"mode": "auto",
+		},
+	}
+
+	if !svc.applyTransport(proxy, "xhttp", stream) {
+		t.Fatalf("applyTransport returned false for xhttp (#4531: would drop the inbound and yield an empty Clash YAML)")
+	}
+	if proxy["network"] != "xhttp" {
+		t.Fatalf("network = %v, want xhttp", proxy["network"])
+	}
+	opts, ok := proxy["xhttp-opts"].(map[string]any)
+	if !ok {
+		t.Fatalf("xhttp-opts missing or wrong type: %#v", proxy["xhttp-opts"])
+	}
+	want := map[string]any{"path": "/xh", "host": "example.com", "mode": "auto"}
+	if !reflect.DeepEqual(opts, want) {
+		t.Fatalf("xhttp-opts = %#v, want %#v", opts, want)
+	}
+}
+
+func TestApplyTransport_XHTTP_HostFromHeaders(t *testing.T) {
+	svc := &SubClashService{}
+	proxy := map[string]any{}
+	stream := map[string]any{
+		"xhttpSettings": map[string]any{
+			"path":    "/xh",
+			"headers": map[string]any{"Host": "via-header.example.com"},
+		},
+	}
+
+	if !svc.applyTransport(proxy, "xhttp", stream) {
+		t.Fatalf("applyTransport returned false for xhttp")
+	}
+	opts, _ := proxy["xhttp-opts"].(map[string]any)
+	if opts["host"] != "via-header.example.com" {
+		t.Fatalf("host should fall back to headers.Host, got %v", opts["host"])
+	}
+}
+
+func TestApplyTransport_HTTPUpgrade(t *testing.T) {
+	svc := &SubClashService{}
+	proxy := map[string]any{}
+	stream := map[string]any{
+		"httpupgradeSettings": map[string]any{
+			"path": "/hu",
+			"host": "example.com",
+		},
+	}
+
+	if !svc.applyTransport(proxy, "httpupgrade", stream) {
+		t.Fatalf("applyTransport returned false for httpupgrade")
+	}
+	if proxy["network"] != "httpupgrade" {
+		t.Fatalf("network = %v, want httpupgrade", proxy["network"])
+	}
+	opts, ok := proxy["http-upgrade-opts"].(map[string]any)
+	if !ok {
+		t.Fatalf("http-upgrade-opts missing: %#v", proxy["http-upgrade-opts"])
+	}
+	if opts["path"] != "/hu" {
+		t.Fatalf("path = %v, want /hu", opts["path"])
+	}
+	headers, _ := opts["headers"].(map[string]any)
+	if headers["Host"] != "example.com" {
+		t.Fatalf("headers.Host = %v, want example.com", headers["Host"])
+	}
+}