Numpad 1-9 hotkeys toggle Nth participant's ISO

Fast keyboard-driven ISO routing for operators with one hand on the keyboard during a show. Both NumPad1..9 and top-row 1..9 bind to ToggleByIndexCommand which resolves against the filtered+sorted ParticipantsView — index matches what's on screen, not the underlying storage order.

Press a digit again to toggle off. Plays nice with sort modes: LoudestFirst means '1' is always whoever's loudest right now; Alphabetical lets you build muscle memory for recurring guests.

Implementation:

- New generic RelayCommand<T> in RelayCommand.cs so XAML CommandParameter strings convert to the action's T (int / string / etc.).

- ToggleByIndexCommand on MainViewModel iterates ParticipantsView, finds the Nth ParticipantViewModel, fires its ToggleIsoCommand if CanExecute.

- 18 KeyBindings (9 NumPad + 9 D1-D9) in MainWindow.xaml's Window.InputBindings.

- F1 help cheat sheet updated to mention the new range.

src/TeamsISO.App/HelpWindow.xaml

@@ -120,12 +120,19 @@
                                            Text="Ctrl + R"
                                            Style="{StaticResource Wd.Text.Mono}"
                                            Foreground="{DynamicResource Wd.Accent.Cyan}"
-                                           Margin="0,0,16,0"/>
+                                           Margin="0,0,16,6"/>
                                 <TextBlock Grid.Row="3" Grid.Column="1"
                                            Text="Refresh NDI discovery (rebuild finder)"
                                            Style="{StaticResource Wd.Text.Body}"
-                                           FontSize="12"/>
+                                           FontSize="12"
+                                           Margin="0,0,0,6"/>
                             </Grid>
+                            <TextBlock Margin="0,12,0,0"
+                                       Style="{StaticResource Wd.Text.Body}"
+                                       FontSize="12"
+                                       Foreground="{DynamicResource Wd.Text.Secondary}"
+                                       TextWrapping="Wrap"
+                                       Text="Numpad 1-9 (or top-row 1-9) toggles the Nth visible participant's ISO. Sort + filter aware — the index matches what you see in the DataGrid, not the underlying storage order."/>
                         </StackPanel>
                     </Border>
 

src/TeamsISO.App/MainWindow.xaml

@@ -54,6 +54,26 @@
         <KeyBinding Key="M" Modifiers="Ctrl" Command="{Binding DropRecordingMarkerCommand}"/>
         <KeyBinding Key="S" Modifiers="Ctrl+Shift" Command="{Binding StopAllIsosCommand}"/>
         <KeyBinding Key="R" Modifiers="Ctrl" Command="{Binding RefreshDiscoveryCommand}"/>
+        <!-- NumPad 1-9 toggles ISO for the Nth visible participant (sort + filter aware).
+             Top-row digits 1-9 mirror this so laptop operators without a numpad still get them. -->
+        <KeyBinding Key="NumPad1" Command="{Binding ToggleByIndexCommand}" CommandParameter="1"/>
+        <KeyBinding Key="NumPad2" Command="{Binding ToggleByIndexCommand}" CommandParameter="2"/>
+        <KeyBinding Key="NumPad3" Command="{Binding ToggleByIndexCommand}" CommandParameter="3"/>
+        <KeyBinding Key="NumPad4" Command="{Binding ToggleByIndexCommand}" CommandParameter="4"/>
+        <KeyBinding Key="NumPad5" Command="{Binding ToggleByIndexCommand}" CommandParameter="5"/>
+        <KeyBinding Key="NumPad6" Command="{Binding ToggleByIndexCommand}" CommandParameter="6"/>
+        <KeyBinding Key="NumPad7" Command="{Binding ToggleByIndexCommand}" CommandParameter="7"/>
+        <KeyBinding Key="NumPad8" Command="{Binding ToggleByIndexCommand}" CommandParameter="8"/>
+        <KeyBinding Key="NumPad9" Command="{Binding ToggleByIndexCommand}" CommandParameter="9"/>
+        <KeyBinding Key="D1" Command="{Binding ToggleByIndexCommand}" CommandParameter="1"/>
+        <KeyBinding Key="D2" Command="{Binding ToggleByIndexCommand}" CommandParameter="2"/>
+        <KeyBinding Key="D3" Command="{Binding ToggleByIndexCommand}" CommandParameter="3"/>
+        <KeyBinding Key="D4" Command="{Binding ToggleByIndexCommand}" CommandParameter="4"/>
+        <KeyBinding Key="D5" Command="{Binding ToggleByIndexCommand}" CommandParameter="5"/>
+        <KeyBinding Key="D6" Command="{Binding ToggleByIndexCommand}" CommandParameter="6"/>
+        <KeyBinding Key="D7" Command="{Binding ToggleByIndexCommand}" CommandParameter="7"/>
+        <KeyBinding Key="D8" Command="{Binding ToggleByIndexCommand}" CommandParameter="8"/>
+        <KeyBinding Key="D9" Command="{Binding ToggleByIndexCommand}" CommandParameter="9"/>
     </Window.InputBindings>
 
     <Grid>

src/TeamsISO.App/ViewModels/MainViewModel.cs

@@ -181,6 +181,14 @@ public sealed class MainViewModel : ObservableObject, IDisposable
     /// <summary>Save a PNG snapshot of every enabled participant's current frame.</summary>
     public RelayCommand SnapshotAllCommand { get; }
 
+    /// <summary>
+    /// Toggle the ISO for the Nth visible participant (1-based, matches the
+    /// numpad layout). Used by the NumPad1..NumPad9 hotkeys; resolves
+    /// against ParticipantsView so the index matches what the operator
+    /// sees in the current sort + filter.
+    /// </summary>
+    public RelayCommand<string> ToggleByIndexCommand { get; }
+
     /// <summary>
     /// Two-way bound to the quick-join input. Whatever the operator pastes
     /// gets handed to <see cref="TeamsLauncher.TryJoinMeeting"/> when the
@@ -412,6 +420,25 @@ public sealed class MainViewModel : ObservableObject, IDisposable
 
         SnapshotAllCommand = new RelayCommand(SnapshotAll, () => Participants.Any(p => p.IsEnabled));
 
+        ToggleByIndexCommand = new RelayCommand<string>(s =>
+        {
+            // Numpad / digit hotkeys pass "1".."9" as a string. Resolve
+            // against the filtered/sorted view so the index matches what
+            // the operator sees on screen, not the underlying storage order.
+            if (!int.TryParse(s, out var idx) || idx < 1 || idx > 9) return;
+            var i = 0;
+            foreach (var item in ParticipantsView)
+            {
+                if (item is not ParticipantViewModel p) continue;
+                if (++i == idx)
+                {
+                    if (p.ToggleIsoCommand.CanExecute(null))
+                        p.ToggleIsoCommand.Execute(null);
+                    break;
+                }
+            }
+        });
+
         JoinMeetingCommand = new RelayCommand(() =>
         {
             // Trim + handle the operator pasting whitespace around the URL.

src/TeamsISO.App/ViewModels/RelayCommand.cs

@@ -23,6 +23,38 @@ public sealed class RelayCommand : ICommand
     public void RaiseCanExecuteChanged() => CanExecuteChanged?.Invoke(this, EventArgs.Empty);
 }
 
+/// <summary>
+/// Synchronous command that accepts a typed parameter. Used by hotkeys
+/// that need to pass an index (e.g. NumPad1..NumPad9 → 1..9). The
+/// parameter is converted from object via Convert.ChangeType so XAML
+/// CommandParameter="1" works for int T.
+/// </summary>
+public sealed class RelayCommand<T> : ICommand
+{
+    private readonly Action<T> _execute;
+    private readonly Func<T, bool>? _canExecute;
+
+    public RelayCommand(Action<T> execute, Func<T, bool>? canExecute = null)
+    {
+        _execute = execute;
+        _canExecute = canExecute;
+    }
+
+    public bool CanExecute(object? parameter) => _canExecute?.Invoke(Convert<T>(parameter)) ?? true;
+    public void Execute(object? parameter) => _execute(Convert<T>(parameter));
+
+    public event EventHandler? CanExecuteChanged;
+    public void RaiseCanExecuteChanged() => CanExecuteChanged?.Invoke(this, EventArgs.Empty);
+
+    private static TValue Convert<TValue>(object? value)
+    {
+        if (value is null) return default!;
+        if (value is TValue typed) return typed;
+        try { return (TValue)System.Convert.ChangeType(value, typeof(TValue)); }
+        catch { return default!; }
+    }
+}
+
 /// <summary>
 /// Async command that suppresses re-entrancy while running.
 /// </summary>