Fix #1307: split-created document docks are WorkspaceContentDock

Overrides `WorkspaceDockFactory.CreateDocumentDock` so Dock's
`NewHorizontalDocumentDock` / `NewVerticalDocumentDock` split paths mint
`WorkspaceContentDock` instances instead of plain `Dock.Model.Mvvm.Controls.DocumentDock`.
Previously the plain type matched only the generic `IDocumentDock` fallback
template in `DockDataTemplates.axaml`, which has no `HeaderTemplate`, so tabs
in split-created regions rendered with Dock.Avalonia's default header — no
favicon and no `MaxWidth=180` / `CharacterEllipsis` constraint. Assigns a
fresh GUID `Id` per instance to prevent `FactoryBase` from copying the source
dock's id on split.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: JoshuaRowePhantom

Phantom.Workspaces.Tests/MainWindowDockTemplateTests.cs

@@ -268,6 +268,62 @@ public void WorkspacePaneDockControl_InnerDockControl_HasDocumentDockTemplate()
         Assert.NotNull(matching);
     }
 
+    // ── Regression tests for #1307 ────────────────────────────────────────────
+    // Split-created document docks (via NewHorizontalDocumentDock / NewVerticalDocumentDock)
+    // must be WorkspaceContentDock so tabs they host match the rich header template
+    // (favicon + MaxWidth=180 + CharacterEllipsis) instead of the bare IDocumentDock fallback.
+
+    [AvaloniaFact(Timeout = 15_000)]
+    public async Task WorkspaceDockFactory_CreateDocumentDock_ReturnsWorkspaceContentDock()
+    {
+        await using var viewModel = CreateBootedMainWindowViewModel();
+        await viewModel.InitializeAsync();
+        var factory = GetDockFactory(viewModel);
+
+        var created = factory.CreateDocumentDock();
+
+        Assert.IsType<WorkspaceContentDock>(created);
+    }
+
+    [AvaloniaFact(Timeout = 15_000)]
+    public async Task WorkspaceDockFactory_CreateDocumentDock_AssignsFreshUniqueId()
+    {
+        await using var viewModel = CreateBootedMainWindowViewModel();
+        await viewModel.InitializeAsync();
+        var factory = GetDockFactory(viewModel);
+
+        var a = factory.CreateDocumentDock();
+        var b = factory.CreateDocumentDock();
+
+        Assert.False(string.IsNullOrEmpty(a.Id));
+        Assert.False(string.IsNullOrEmpty(b.Id));
+        Assert.NotEqual(a.Id, b.Id);
+    }
+
+    [AvaloniaFact(Timeout = 15_000)]
+    public async Task WorkspaceDockFactory_CreateDocumentDock_MatchesRichHeaderTemplate_InInnerPaneDockControl()
+    {
+        // #1307: the split-created dock must be picked up by the rich WorkspaceContentDock
+        // template ahead of the generic IDocumentDock fallback in the inner workspace-pane
+        // DockControl.DataTemplates scope.
+        await using var viewModel = CreateBootedMainWindowViewModel();
+        await viewModel.InitializeAsync();
+        var factory = GetDockFactory(viewModel);
+
+        var splitCreated = factory.CreateDocumentDock();
+        var innerDockControl = BuildInnerWorkspacePaneDockControl();
+
+        var matching = innerDockControl.DataTemplates
+            .OfType<IDataTemplate>()
+            .FirstOrDefault(t => t.Match(splitCreated));
+
+        Assert.NotNull(matching);
+        // Ensure it is the WorkspaceContentDock-specific template (matches WorkspaceContentDock
+        // but does NOT match a plain DocumentDock), not the generic IDocumentDock fallback.
+        Assert.True(matching!.Match(new WorkspaceContentDock()));
+        Assert.False(matching!.Match(new DocumentDock()));
+    }
+
     [AvaloniaFact(Timeout = 15_000)]
     public void DockDataTemplates_ProportionalDockSplitter_ResolvesProportionalStackPanelSplitter()
     {

Phantom.Workspaces/ViewModels/WorkspaceDockFactory.cs

@@ -107,6 +107,24 @@ public override IRootDock CreateLayout()
         return root;
     }
 
+    /// <summary>
+    /// #1307: split-created docks (via Dock's ``NewHorizontalDocumentDock`` /
+    /// ``NewVerticalDocumentDock`` paths) must be ``WorkspaceContentDock`` so tabs
+    /// they host match the rich header template in ``DockDataTemplates.axaml``
+    /// (favicon + ``MaxWidth=180`` + ``CharacterEllipsis``). A plain ``DocumentDock``
+    /// would fall through to the generic ``IDocumentDock`` template, which has no
+    /// ``HeaderTemplate`` and would render an unbounded, icon-less tab title.
+    /// A fresh ``Id`` is assigned to prevent ``FactoryBase`` from copying the source
+    /// dock's ``Id`` on split (which would create duplicate ids in the layout).
+    /// </summary>
+    public override IDocumentDock CreateDocumentDock()
+    {
+        return new WorkspaceContentDock
+        {
+            Id = Guid.NewGuid().ToString(),
+        };
+    }
+
     /// <summary>
     /// Creates a dock layout for workspace content (entity tabs, agent sessions, etc.)
     /// Uses ItemsSource wired to <see cref="WorkspacePaneViewModel.Tabs"/> so that