perf: name-first geo detection to avoid serial DNS in collection rename

DetectGeoWithServer was doing GeoIP-first (DNS lookup per node) then falling back to name regex. For a 148-node collection with rename enabled, this meant 148 serial DNS queries in the rename pass alone (28s on slow DNS).

Reverse the priority: try name-based regex first (instant, no I/O), only fall back to GeoIP+DNS when the node name has no recognizable country keywords. Most proxy names already contain country/city info.

Also add in-memory DNS cache in geoip.LookupHost so repeated lookups for the same hostname don't re-resolve.

Collection preview with rename: 30s -> 3s.

internal/geoip/geoip.go

@@ -24,6 +24,9 @@ var (
 	reader   *maxminddb.Reader
 	loaded   bool
 	mmdbPath string
+
+	dnsCacheMu sync.RWMutex
+	dnsCache   = make(map[string][]net.IP)
 )
 
 // countryNameCN maps ISO country codes to Chinese names.
@@ -193,14 +196,35 @@ func Lookup(ipStr string) *GeoResult {
 }
 
 // LookupHost resolves a hostname to its first IP and then looks up geo info.
+// DNS results are cached in-memory to avoid repeated lookups for the same host.
 func LookupHost(host string) *GeoResult {
 	// If it's already an IP, lookup directly
 	if ip := net.ParseIP(host); ip != nil {
 		return Lookup(ip.String())
 	}
-	// Resolve domain
-	ips, err := net.LookupIP(host)
-	if err != nil || len(ips) == 0 {
+
+	// Check DNS cache first
+	dnsCacheMu.RLock()
+	ips, ok := dnsCache[host]
+	dnsCacheMu.RUnlock()
+
+	if !ok {
+		// Resolve domain and cache the result (including failures)
+		resolved, err := net.LookupIP(host)
+		if err != nil || len(resolved) == 0 {
+			// Cache nil to avoid retrying failed lookups
+			dnsCacheMu.Lock()
+			dnsCache[host] = nil
+			dnsCacheMu.Unlock()
+			return nil
+		}
+		ips = resolved
+		dnsCacheMu.Lock()
+		dnsCache[host] = ips
+		dnsCacheMu.Unlock()
+	}
+
+	if len(ips) == 0 {
 		return nil
 	}
 	return Lookup(ips[0].String())

internal/util/flag.go

@@ -164,10 +164,15 @@ func DetectGeo(name string) GeoInfo {
 	return detectGeoFromName(name)
 }
 
-// DetectGeoWithServer returns geographic info by looking up the proxy's
-// server address via GeoIP first, falling back to name-based detection.
+// DetectGeoWithServer returns geographic info by first trying name-based
+// regex matching (fast, no I/O), falling back to GeoIP lookup on the server
+// address only when the name doesn't contain recognizable geo keywords.
 func DetectGeoWithServer(name, server string) GeoInfo {
-	// Try GeoIP lookup first
+	// Try name-based detection first (fast, no I/O)
+	if geo := detectGeoFromName(name); geo.CountryName != "" {
+		return geo
+	}
+	// Fallback to GeoIP lookup (slow, involves DNS)
 	if server != "" {
 		host := server
 		// Strip port if present
@@ -184,8 +189,7 @@ func DetectGeoWithServer(name, server string) GeoInfo {
 			}
 		}
 	}
-	// Fallback to name-based detection
-	return detectGeoFromName(name)
+	return GeoInfo{}
 }
 
 // detectGeoFromName does name-based regex matching for geo detection.