Desktop: drop the VAULT columns that had nothing in them, and the snippet buttons with nothing to act on

tests/DodoSSH.Client.App.Layout.Tests/ScreenLayoutTests.cs

@@ -2296,6 +2296,66 @@ public sealed class ScreenLayoutTests : IAsyncLifetime
             },
             Token);
 
+    /// <remarks>
+    /// Three greyed buttons under a list nobody has clicked in read as something broken rather than something
+    /// waiting. The row appears with a snippet to act on, and goes with it.
+    /// </remarks>
+    [Fact]
+    public async Task TheSnippetButtonsAppearWithASnippetToActOn()
+    {
+        await SeedSnippetsAsync();
+
+        var snippets = NewSnippetsScreen();
+
+        await LayoutHarness.OnTheUiThreadAsync(
+            () =>
+            {
+                var screen = new SnippetsScreen { DataContext = snippets };
+
+                var window = LayoutHarness.HostAtMinimumSize(
+                    screen, LayoutHarness.ScreenWidth, LayoutHarness.ScreenHeight);
+
+                try
+                {
+                    var edit = screen.GetVisualDescendants().OfType<Button>()
+                        .Single(button => button.Content is "Edit");
+
+                    snippets.Selected = null;
+                    LayoutHarness.Settle(window, LayoutHarness.ScreenWidth, LayoutHarness.ScreenHeight);
+                    edit.IsEffectivelyVisible.ShouldBeFalse("nothing is chosen for it to edit");
+
+                    snippets.Selected = snippets.Visible.First();
+                    LayoutHarness.Settle(window, LayoutHarness.ScreenWidth, LayoutHarness.ScreenHeight);
+                    edit.IsEffectivelyVisible.ShouldBeTrue();
+                }
+                finally
+                {
+                    window.Close();
+                }
+            },
+            Token);
+    }
+
+    /// <remarks>
+    /// With one vault no row names one, and a fixed VAULT column was a heading over a stripe of nothing
+    /// between TYPE and USED BY. It is sized to what its rows hold now, and its heading goes with them.
+    /// </remarks>
+    [Fact]
+    public async Task TheKeychainsVaultColumn_TakesNoRoomWithOneVault()
+    {
+        await OnTheVaultAsync((screen, _) =>
+        {
+            vault.HasVaultItems.ShouldBeTrue("an empty table has no columns to judge");
+            vault.ShowsVaultColumn.ShouldBeFalse("this suite's keychain has one vault");
+
+            var heading = screen.GetVisualDescendants().OfType<TextBlock>()
+                .Single(block => block.Text is "VAULT");
+
+            heading.IsEffectivelyVisible.ShouldBeFalse();
+            heading.Parent.ShouldBeOfType<Grid>().ColumnDefinitions[3].ActualWidth.ShouldBe(0);
+        });
+    }
+
     private SnippetsViewModel NewSnippetsScreen(InsertTarget? target = null) =>
         new(
             vault,