Fix/preserve editor selection state

src/TextForge.Core/Documents/Document.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using TextForge.Core.Modules;
 
 namespace TextForge.Core.Documents;
@@ -12,7 +13,7 @@ public class Document
     public Guid Id { get; init; } = Guid.NewGuid();
     public DocumentMetadata Metadata { get; set; } = new();
     public string TemplateName { get; set; } = "Default";
-    public List<Module> Modules { get; init; } = [];
+    public ObservableCollection<Module> Modules { get; init; } = [];
 
     /// <summary>
     /// Currently selected module in the active editing session, if any.
@@ -39,7 +40,10 @@ public Document(DocumentMetadata metadata, IEnumerable<Module>? modules = null,
         TemplateName = templateName;
         if (modules is not null)
         {
-            Modules.AddRange(modules);
+            foreach (var module in modules)
+            {
+                Modules.Add(module);
+            }
         }
     }
 
@@ -55,7 +59,8 @@ public void NotifyChanged()
 
     /// <summary>
     /// Adds a module to the document hierarchy.
-    /// If parent is provided, appends to parent.SubModules; otherwise appends to root Modules.
+    /// If parent is provided, appends to parent.SubModules, expands parent, and keeps parent selected.
+    /// If parent is null, appends to root Modules and selects the new module.
     /// </summary>
     /// <param name="newModule">The module to insert.</param>
     /// <param name="parent">The target parent module, or null to append to the document root.</param>
@@ -66,19 +71,23 @@ public Document AddModule(Module newModule, Module? parent = null)
 
         if (parent is not null)
         {
+            // Auto-expand the parent so the newly added child is visible
+            parent.IsExpanded = true;
             parent.SubModules.Add(newModule);
+
+            // Retain selection on the existing parent
+            SelectModule(parent);
         }
         else
         {
             Modules.Add(newModule);
+            // Root addition: select the newly created root module
+            SelectModule(newModule);
         }
 
-        // Keep the newly added module active for selection/toolbar
-        SelectModule(newModule);
         NotifyChanged();
         return this;
     }
-
     /// <summary>
     /// Updates the active module selection, updating all node flags across the tree.
     /// </summary>

src/TextForge.Core/Modules/Module.cs

@@ -1,47 +1,73 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
 
 namespace TextForge.Core.Modules;
 
 /// <summary>
 /// Represents an independent content element within a document.
 /// Modules can be nested hierarchically to form compound structures.
 /// </summary>
-public class Module
+public class Module : INotifyPropertyChanged
 {
+    private string _content = string.Empty;
+    private bool _isSelected;
+    private bool _isExpanded;
+
+    public event PropertyChangedEventHandler? PropertyChanged;
+
     public Guid Id { get; init; } = Guid.NewGuid();
 
-    /// <summary>
-    /// Archetype identifier used for preset styling and UI representation (e.g., "default-title").
-    /// </summary>
     public string Name { get; set; } = "default-text";
 
-    /// <summary>
-    /// Optional key corresponding to a template style rule (e.g., "Title", "Heading", "Body").
-    /// </summary>
     public string? StyleKey { get; init; }
 
     public ModuleType Type { get; init; } = ModuleType.Text;
 
-    public string Content { get; set; } = string.Empty;
-
+    public string Content
+    {
+        get => _content;
+        set
+        {
+            if (_content != value)
+            {
+                _content = value;
+                OnPropertyChanged();
+            }
+        }
+    }
 
-    /// <summary>
-    /// Direct visual overrides that take precedence over the template style.
-    /// </summary>
     public ModuleFeatures Features { get; set; } = ModuleFeatures.Default;
 
-    /// <summary>
-    /// Nested child modules (e.g., list items under a section heading).
-    /// </summary>
     public ObservableCollection<Module> SubModules { get; set; } = [];
 
+    public bool IsSelected
+    {
+        get => _isSelected;
+        set
+        {
+            if (_isSelected != value)
+            {
+                _isSelected = value;
+                OnPropertyChanged();
+            }
+        }
+    }
 
-    /// <summary>
-    /// Ephemeral UI selection state. Retained in-memory during active sessions.
-    /// </summary>
-    public bool IsSelected { get; set; }
+    public bool IsExpanded
+    {
+        get => _isExpanded;
+        set
+        {
+            if (_isExpanded != value)
+            {
+                _isExpanded = value;
+                OnPropertyChanged();
+            }
+        }
+    }
 
     public Module() { }
 
@@ -59,41 +85,28 @@ public Module(
         Name = name;
     }
 
+    protected void OnPropertyChanged([CallerMemberName] string? propertyName = null)
+    {
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+    }
+
     #region Archetype Presets
 
-    /// <summary>
-    /// Creates a top-level document title module.
-    /// </summary>
     public static Module CreateTitle(string text) =>
         new(text, ModuleType.Section, styleKey: "Title", name: "default-title");
 
-    /// <summary>
-    /// Creates a section header module.
-    /// </summary>
     public static Module CreateHeading(string text) =>
         new(text, ModuleType.Section, styleKey: "Heading", name: "default-heading");
 
-    /// <summary>
-    /// Creates a standard body paragraph module.
-    /// </summary>
     public static Module CreateParagraph(string text) =>
         new(text, ModuleType.Text, styleKey: "Body", name: "default-paragraph");
 
-    /// <summary>
-    /// Creates a bullet item module with prefixed bullet character.
-    /// </summary>
     public static Module CreateBulletItem(string text) =>
         new($"• {text.TrimStart('•', ' ')}", ModuleType.Text, styleKey: "Body", name: "default-bullet");
 
-    /// <summary>
-    /// Creates an accent callout banner module.
-    /// </summary>
     public static Module CreateCallout(string text) =>
         new(text, ModuleType.Text, styleKey: "Callout", name: "default-callout");
 
-    /// <summary>
-    /// Creates an alert module with explicit color and weight overrides.
-    /// </summary>
     public static Module CreateAlert(string text, string color = "#DC2626") =>
         new(text, ModuleType.Text, features: new ModuleFeatures
         {