Configurable bind addresses + display host in Server Settings

ServerConfig grows two fields:
- BindAddresses: list of IPs Kestrel binds to (empty = all interfaces,
  current behavior). Listening only on a subset is useful when the host
  has multiple NICs and the webhook should not be reachable on all of
  them.
- DisplayHost: the hostname/IP the GUI splices into the URL column and
  Copy URL button. Cosmetic; doesn't affect what the server accepts.

Server Settings dialog gains a "Network" section: a checkbox for "all
interfaces" plus per-NIC checkboxes auto-detected via NetworkInterface.
GetAllNetworkInterfaces, and an editable ComboBox for the display host
pre-populated with detected IPs and the machine name.

Listener restart fires on BindAddresses change but not on DisplayHost
change (cosmetic).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/WebhookServer.Gui/ViewModels/MainViewModel.cs

@@ -57,8 +57,9 @@ public sealed partial class MainViewModel : ObservableObject
 
                 if (status is not null)
                 {
-                    HttpBaseUrl = $"http://localhost:{status.HttpPort}";
-                    HttpsBaseUrl = status.HttpsPort.HasValue ? $"https://localhost:{status.HttpsPort.Value}" : null;
+                    var host = string.IsNullOrEmpty(status.DisplayHost) ? "localhost" : status.DisplayHost;
+                    HttpBaseUrl = $"http://{host}:{status.HttpPort}";
+                    HttpsBaseUrl = status.HttpsPort.HasValue ? $"https://{host}:{status.HttpsPort.Value}" : null;
                 }
 
                 Endpoints.Clear();
@@ -202,6 +203,8 @@ public sealed partial class MainViewModel : ObservableObject
             ServerConfig.HttpPort = vm.HttpPort;
             ServerConfig.TrustedProxies = vm.TrustedProxiesList;
             ServerConfig.HttpsBinding = vm.BuildBinding();
+            ServerConfig.BindAddresses = vm.BindAddressesList;
+            ServerConfig.DisplayHost = vm.DisplayHostValue;
             await _client.InvokeAsync(AdminOps.UpdateConfig, ServerConfig).ConfigureAwait(false);
             await RefreshAsync().ConfigureAwait(false);
         }

src/WebhookServer.Gui/ViewModels/ServerSettingsViewModel.cs

@@ -1,3 +1,7 @@
+using System.Collections.ObjectModel;
+using System.Net;
+using System.Net.NetworkInformation;
+using System.Net.Sockets;
 using System.Runtime.Versioning;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
@@ -16,6 +20,14 @@ public sealed partial class ServerSettingsViewModel : ObservableObject
     [ObservableProperty] private string _pfxPassword = "";
     [ObservableProperty] private string _thumbprint = "";
     [ObservableProperty] private string _trustedProxiesText = "";
+    [ObservableProperty] private bool _listenAllInterfaces = true;
+    [ObservableProperty] private string _displayHost = "localhost";
+
+    /// <summary>One row per detected local IPv4/IPv6 address. Bound for "listen on" checkboxes.</summary>
+    public ObservableCollection<NetworkAddressRow> Addresses { get; } = new();
+
+    /// <summary>Suggestions for the Display URL host dropdown (detected IPs + localhost + machine name).</summary>
+    public ObservableCollection<string> DisplayHostChoices { get; } = new();
 
     public bool Accepted { get; private set; }
 
@@ -31,11 +43,48 @@ public sealed partial class ServerSettingsViewModel : ObservableObject
         PfxPath = b?.PfxPath ?? "";
         PfxPassword = b?.PfxPassword?.Plaintext ?? "";
         Thumbprint = b?.Thumbprint ?? "";
+
+        var detected = DetectLocalAddresses();
+        var alreadyBound = new HashSet<string>(config.BindAddresses, StringComparer.OrdinalIgnoreCase);
+
+        ListenAllInterfaces = config.BindAddresses.Count == 0;
+        foreach (var (addr, label) in detected)
+        {
+            Addresses.Add(new NetworkAddressRow
+            {
+                Address = addr,
+                Label = label,
+                IsBound = !ListenAllInterfaces && alreadyBound.Contains(addr),
+            });
+        }
+        // Surface any persisted address that isn't currently detected (e.g. a NIC unplugged
+        // since save) so the user can keep or remove it explicitly.
+        foreach (var entry in config.BindAddresses)
+        {
+            if (Addresses.Any(a => string.Equals(a.Address, entry, StringComparison.OrdinalIgnoreCase))) continue;
+            Addresses.Add(new NetworkAddressRow { Address = entry, Label = "(not currently present)", IsBound = true });
+        }
+
+        DisplayHostChoices.Add("localhost");
+        DisplayHostChoices.Add(Environment.MachineName);
+        foreach (var (addr, _) in detected)
+            if (!DisplayHostChoices.Contains(addr))
+                DisplayHostChoices.Add(addr);
+
+        DisplayHost = string.IsNullOrEmpty(config.DisplayHost) ? "localhost" : config.DisplayHost;
     }
 
     public List<string> TrustedProxiesList =>
         (TrustedProxiesText ?? "").Split(new[] { '\r', '\n', ',' }, StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries).ToList();
 
+    public List<string> BindAddressesList =>
+        ListenAllInterfaces
+            ? new List<string>()
+            : Addresses.Where(a => a.IsBound).Select(a => a.Address).ToList();
+
+    public string? DisplayHostValue =>
+        string.IsNullOrEmpty(DisplayHost) || DisplayHost == "localhost" ? null : DisplayHost.Trim();
+
     public HttpsBinding? BuildBinding()
     {
         if (!HttpsEnabled) return null;
@@ -58,4 +107,29 @@ public sealed partial class ServerSettingsViewModel : ObservableObject
 
     [RelayCommand]
     private void Save() => Accepted = true;
+
+    private static IEnumerable<(string Address, string Label)> DetectLocalAddresses()
+    {
+        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+        foreach (var ni in NetworkInterface.GetAllNetworkInterfaces())
+        {
+            if (ni.OperationalStatus != OperationalStatus.Up) continue;
+            if (ni.NetworkInterfaceType == NetworkInterfaceType.Tunnel) continue;
+            foreach (var ua in ni.GetIPProperties().UnicastAddresses)
+            {
+                if (ua.Address.AddressFamily != AddressFamily.InterNetwork &&
+                    ua.Address.AddressFamily != AddressFamily.InterNetworkV6) continue;
+                var key = ua.Address.ToString();
+                if (!seen.Add(key)) continue;
+                yield return (key, $"{ni.Name} ({ni.NetworkInterfaceType})");
+            }
+        }
+    }
+}
+
+public sealed partial class NetworkAddressRow : ObservableObject
+{
+    public required string Address { get; init; }
+    public required string Label { get; init; }
+    [ObservableProperty] private bool _isBound;
 }