baseline: api+gui traffic mode + candidates picker

Snapshot before app-launcher (cgroup/mark) work; ignore binaries/backups.

selective-vpn-api/app/routes_units.go

@@ -0,0 +1,52 @@
+package app
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+// ---------------------------------------------------------------------
+// routes systemd unit name resolution
+// ---------------------------------------------------------------------
+
+// EN: Resolve routes service/timer unit names from preferred/active iface.
+// EN: Env overrides still have top priority for custom deployments.
+// RU: Вычисление имен unit для routes service/timer по preferred/active iface.
+// RU: Для кастомных окружений сохраняется приоритет переменных окружения.
+
+func resolveRoutesUnitIface() (string, string) {
+	st := loadTrafficModeState()
+	if pref := normalizePreferredIface(st.PreferredIface); pref != "" {
+		return pref, "preferred"
+	}
+	if statusIface := statusIfaceFromFile(); statusIface != "" && statusIface != "-" {
+		return statusIface, "status"
+	}
+	if active, reason := resolveTrafficIface(""); active != "" {
+		return active, reason
+	}
+	return "", "iface-not-found"
+}
+
+func routesServiceUnitName() string {
+	if forced := strings.TrimSpace(os.Getenv(routesServiceEnv)); forced != "" {
+		return forced
+	}
+	iface, _ := resolveRoutesUnitIface()
+	if iface == "" {
+		return ""
+	}
+	return fmt.Sprintf(routesServiceTemplate, iface)
+}
+
+func routesTimerUnitName() string {
+	if forced := strings.TrimSpace(os.Getenv(routesTimerEnv)); forced != "" {
+		return forced
+	}
+	iface, _ := resolveRoutesUnitIface()
+	if iface == "" {
+		return ""
+	}
+	return fmt.Sprintf(routesTimerTemplate, iface)
+}