Reuse cached mention regex in parseMentions (#812)

bitchat/Nostr/GeoRelayDirectory.swift

@@ -33,13 +33,32 @@ final class GeoRelayDirectory {
 
     /// Returns up to `count` relay URLs (wss://) closest to the given coordinate.
     func closestRelays(toLat lat: Double, lon: Double, count: Int = 5) -> [String] {
-        guard !entries.isEmpty else { return [] }
-        let sorted = entries
-            .sorted { a, b in
-                haversineKm(lat, lon, a.lat, a.lon) < haversineKm(lat, lon, b.lat, b.lon)
+        guard !entries.isEmpty, count > 0 else { return [] }
+
+        if entries.count <= count {
+            return entries
+                .sorted { a, b in
+                    haversineKm(lat, lon, a.lat, a.lon) < haversineKm(lat, lon, b.lat, b.lon)
+                }
+                .map { "wss://\($0.host)" }
+        }
+
+        var best: [(entry: Entry, distance: Double)] = []
+        best.reserveCapacity(count)
+
+        for entry in entries {
+            let distance = haversineKm(lat, lon, entry.lat, entry.lon)
+            if best.count < count {
+                let idx = best.firstIndex { $0.distance > distance } ?? best.count
+                best.insert((entry, distance), at: idx)
+            } else if let worstDistance = best.last?.distance, distance < worstDistance {
+                let idx = best.firstIndex { $0.distance > distance } ?? best.count
+                best.insert((entry, distance), at: idx)
+                best.removeLast()
             }
-            .prefix(count)
-        return sorted.map { "wss://\($0.host)" }
+        }
+
+        return best.map { "wss://\($0.entry.host)" }
     }
 
     // MARK: - Remote Fetch