feat(translator): add mixed-system-proxy extension field for sing-box set_system_proxy

Non-standard mihomo extension: when mixed-system-proxy is set to true
in Clash YAML config, translates to set_system_proxy on the mixed
inbound only (http inbound is not affected).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: mapleafgo

translator/general.go

@@ -20,6 +20,9 @@ func translateGeneral(cfg *RawConfig, result *singboxConfig) {
 			"listen":      listen,
 			"listen_port": cfg.MixedPort,
 		}
+		if cfg.MixedSystemProxy {
+			inbound["set_system_proxy"] = true
+		}
 		applyInboundAuth(cfg.Authentication, inbound)
 		result.Inbounds = append(result.Inbounds, inbound)
 	}

translator/general_test.go

@@ -152,6 +152,53 @@ func TestTranslateGeneralFindProcess(t *testing.T) {
 	}
 }
 
+func TestTranslateGeneralMixedSystemProxy(t *testing.T) {
+	tests := []struct {
+		name      string
+		enabled   bool
+		wantMixed bool
+	}{
+		{"enabled", true, true},
+		{"disabled", false, false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := &RawConfig{
+				MixedPort:        7890,
+				Port:             8080,
+				MixedSystemProxy: tt.enabled,
+			}
+			result := &singboxConfig{}
+
+			translateGeneral(cfg, result)
+
+			for _, ib := range result.Inbounds {
+				tag := ib["tag"].(string)
+				got, _ := ib["set_system_proxy"].(bool)
+				if tag == "mixed-in" && got != tt.wantMixed {
+					t.Errorf("mixed-in set_system_proxy = %v, want %v", got, tt.wantMixed)
+				}
+				if tag == "http-in" && got {
+					t.Error("http-in should never have set_system_proxy from MixedSystemProxy")
+				}
+			}
+		})
+	}
+}
+
+func TestTranslateGeneralMixedSystemProxyOmitted(t *testing.T) {
+	cfg := &RawConfig{MixedPort: 7890}
+	result := &singboxConfig{}
+
+	translateGeneral(cfg, result)
+
+	ib := result.Inbounds[0]
+	if _, ok := ib["set_system_proxy"]; ok {
+		t.Error("set_system_proxy should be absent when MixedSystemProxy is false")
+	}
+}
+
 func TestTranslateGeneralInterface(t *testing.T) {
 	cfg := &RawConfig{
 		Interface:   "eth0",

translator/types_mihomo.go

@@ -6,6 +6,8 @@ type RawConfig struct {
 	RedirPort          int                       `yaml:"redir-port" json:"redir-port"`
 	TProxyPort         int                       `yaml:"tproxy-port" json:"tproxy-port"`
 	MixedPort          int                       `yaml:"mixed-port" json:"mixed-port"`
+	// Extension: not a standard mihomo field. Translates to sing-box mixed inbound set_system_proxy.
+	MixedSystemProxy   bool                      `yaml:"mixed-system-proxy" json:"mixed-system-proxy"`
 	Authentication     []string                  `yaml:"authentication" json:"authentication"`
 	AllowLan           bool                      `yaml:"allow-lan" json:"allow-lan"`
 	BindAddress        string                    `yaml:"bind-address" json:"bind-address"`