feat(finalmask): sync transport with upstream Xray core changes

Consolidate the eight legacy mKCP/header UDP mask types into a single mkcp-legacy type ({header, value}), simplify xicmp to {dgram, ips}, and add the new realm UDP mask type, matching the updated Xray-core wire format. Update the FinalMask schema enum, the transport form, the mKCP seeding default, and the backend KCP share-link translation. Refresh golden fixtures/snapshots and add backend coverage for the mapping.

sub/subService.go

@@ -1465,28 +1465,22 @@ func applyXhttpExtraParams(xhttp map[string]any, params map[string]string) {
 }
 
 var kcpMaskToHeaderType = map[string]string{
-	"header-dns":       "dns",
-	"header-dtls":      "dtls",
-	"header-srtp":      "srtp",
-	"header-utp":       "utp",
-	"header-wechat":    "wechat-video",
-	"header-wireguard": "wireguard",
+	"dns":       "dns",
+	"dtls":      "dtls",
+	"srtp":      "srtp",
+	"utp":       "utp",
+	"wechat":    "wechat-video",
+	"wireguard": "wireguard",
 }
 
 var validFinalMaskUDPTypes = map[string]struct{}{
-	"salamander":       {},
-	"mkcp-aes128gcm":   {},
-	"header-dns":       {},
-	"header-dtls":      {},
-	"header-srtp":      {},
-	"header-utp":       {},
-	"header-wechat":    {},
-	"header-wireguard": {},
-	"mkcp-original":    {},
-	"xdns":             {},
-	"xicmp":            {},
-	"noise":            {},
-	"header-custom":    {},
+	"salamander":    {},
+	"mkcp-legacy":   {},
+	"xdns":          {},
+	"xicmp":         {},
+	"noise":         {},
+	"header-custom": {},
+	"realm":         {},
 }
 
 var validFinalMaskTCPTypes = map[string]struct{}{
@@ -1557,21 +1551,19 @@ func extractKcpShareFields(stream map[string]any) kcpShareFields {
 		if mask == nil {
 			continue
 		}
-		maskType, _ := mask["type"].(string)
-		if mapped, ok := kcpMaskToHeaderType[maskType]; ok {
-			fields.headerType = mapped
+		if maskType, _ := mask["type"].(string); maskType != "mkcp-legacy" {
 			continue
 		}
 
-		switch maskType {
-		case "mkcp-original":
-			fields.seed = ""
-		case "mkcp-aes128gcm":
-			fields.seed = ""
-			settings, _ := mask["settings"].(map[string]any)
-			if value, ok := settings["password"].(string); ok && value != "" {
-				fields.seed = value
-			}
+		settings, _ := mask["settings"].(map[string]any)
+		header, _ := settings["header"].(string)
+		value, _ := settings["value"].(string)
+		if header == "" {
+			fields.seed = value
+			continue
+		}
+		if mapped, ok := kcpMaskToHeaderType[header]; ok {
+			fields.headerType = mapped
 		}
 	}