feat(ui): add sessionStorage persistence for TreeView expansion state (R11)

tests/ScadaLink.CentralUI.Tests/TreeViewTests.cs

@@ -33,7 +33,8 @@ public class TreeViewTests : BunitContext
         bool selectable = false,
         object? selectedKey = null,
         Action<object?>? onSelectedKeyChanged = null,
-        string? selectedCssClass = null)
+        string? selectedCssClass = null,
+        string? storageKey = null)
     {
         return Render<TreeView<TestNode>>(parameters =>
         {
@@ -61,6 +62,11 @@ public class TreeViewTests : BunitContext
             {
                 parameters.Add(p => p.SelectedCssClass, selectedCssClass);
             }
+
+            if (storageKey != null)
+            {
+                parameters.Add(p => p.StorageKey, storageKey);
+            }
         });
     }
 
@@ -317,4 +323,64 @@ public class TreeViewTests : BunitContext
         var alphaLi = cut.FindAll("li[role='treeitem']")[0];
         Assert.Equal("true", alphaLi.GetAttribute("aria-selected"));
     }
+
+    [Fact]
+    public void SessionStorage_NullKey_NoJsInteropCalls()
+    {
+        var cut = RenderTreeView();
+
+        // Expand Alpha
+        cut.Find(".tv-toggle").Click();
+
+        // No JS interop calls should have been made
+        Assert.Empty(JSInterop.Invocations);
+    }
+
+    [Fact]
+    public void SessionStorage_Set_ExpandWritesToStorage()
+    {
+        JSInterop.Setup<string?>("treeviewStorage.load", _ => true).SetResult(null);
+        JSInterop.SetupVoid("treeviewStorage.save", _ => true);
+
+        var cut = RenderTreeView(storageKey: "test-tree");
+
+        // Expand Alpha
+        cut.Find(".tv-toggle").Click();
+
+        // Verify save was called
+        var saveInvocations = JSInterop.Invocations
+            .Where(i => i.Identifier == "treeviewStorage.save")
+            .ToList();
+        Assert.Single(saveInvocations);
+    }
+
+    [Fact]
+    public void SessionStorage_RestoresExpandedOnMount()
+    {
+        JSInterop.Setup<string?>("treeviewStorage.load", _ => true).SetResult("[\"a\"]");
+        JSInterop.SetupVoid("treeviewStorage.save", _ => true);
+
+        var cut = RenderTreeView(storageKey: "test-tree");
+
+        // Alpha's children should be visible because "a" was restored from storage
+        var labels = cut.FindAll(".node-label");
+        Assert.Contains(labels, l => l.TextContent == "Alpha-1");
+        Assert.Contains(labels, l => l.TextContent == "Alpha-2");
+    }
+
+    [Fact]
+    public void SessionStorage_TakesPrecedenceOverInitiallyExpanded()
+    {
+        // Storage returns empty array — meaning user explicitly collapsed everything
+        JSInterop.Setup<string?>("treeviewStorage.load", _ => true).SetResult("[]");
+        JSInterop.SetupVoid("treeviewStorage.save", _ => true);
+
+        var cut = RenderTreeView(
+            storageKey: "test-tree",
+            initiallyExpanded: n => n.Key == "a");
+
+        // Alpha should NOT be expanded — storage (empty) wins over InitiallyExpanded
+        var labels = cut.FindAll(".node-label");
+        Assert.DoesNotContain(labels, l => l.TextContent == "Alpha-1");
+    }
 }