Plain-click mutex chip = single-select, Shift+click = add

Default click on a value chip in a flags-filter mutex group now collapses the
selection to {value} — the file-manager / Excel intuition. Shift+click keeps
the existing additive multi-toggle behaviour. Plain click on the <Any> chip
clears the filter for the group.

Assisted-by: Claude:claude-opus-4-7:Claude Code

ILSpy/Controls/FlagsFilterPopup.cs

@@ -65,6 +65,17 @@ namespace ILSpy.Views.Filters
 				stack.Children.Add(independentGroup);
 			}
 
+			// Hint text in the same style as the live filter summary below — just a quiet
+			// italic line explaining the chip click semantics so users don't have to guess.
+			var chipHint = new TextBlock {
+				Text = "Click a chip to select only that value · Shift+Click to add to / remove from the selection · Click <Any> to clear",
+				FontStyle = FontStyle.Italic,
+				Foreground = Brushes.Gray,
+				TextWrapping = TextWrapping.Wrap,
+				Margin = new Thickness(0, 6, 0, 0),
+			};
+			stack.Children.Add(chipHint);
+
 			summary = new TextBlock {
 				FontStyle = FontStyle.Italic,
 				Foreground = Brushes.Gray,

ILSpy/Controls/MutexChipGroup.cs

@@ -24,6 +24,8 @@ using System.Linq;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Controls.Primitives;
+using Avalonia.Input;
+using Avalonia.Interactivity;
 using Avalonia.Layout;
 using Avalonia.Media;
 
@@ -67,6 +69,16 @@ namespace ILSpy.Views.Filters
 				// the synthetic zero entry "(none)" so its purpose stays obvious.
 				var chip = MakeChip(v.Label);
 				chip.IsCheckedChanged += (_, _) => OnValueToggled(v.Value);
+				// Plain click → "select only this" (single-select). Shift+Click falls through
+				// to the ToggleButton's default toggle, which feeds OnValueToggled and lets
+				// the user build / trim an additive multi-select set.
+				var capturedValue = v.Value;
+				chip.AddHandler(InputElement.PointerPressedEvent, (_, e) => {
+					if ((e.KeyModifiers & KeyModifiers.Shift) != 0)
+						return; // additive: keep ToggleButton's default toggle behaviour
+					SelectOnly(capturedValue);
+					e.Handled = true;
+				}, RoutingStrategies.Tunnel);
 				valueChips[v.Value] = chip;
 				wrap.Children.Add(chip);
 			}
@@ -122,6 +134,24 @@ namespace ILSpy.Views.Filters
 			state.SetMutexSelection(group.Name, selection);
 		}
 
+		void SelectOnly(uint value)
+		{
+			// Single-chip selection — collapse the group to {value}. We bypass the
+			// "all checked == any" / "none checked == any" collapse rules in
+			// OnValueToggled because Ctrl/Shift+click is an explicit narrow-down
+			// gesture; the user picked exactly one chip and wants exactly one.
+			suppress = true;
+			try
+			{
+				anyChip.IsChecked = false;
+				foreach (var (v, chip) in valueChips)
+					chip.IsChecked = v == value;
+			}
+			finally
+			{ suppress = false; }
+			state.SetMutexSelection(group.Name, ImmutableHashSet.Create(value));
+		}
+
 		void ResetToAny()
 		{
 			suppress = true;