fix(desktop): enable drag-and-drop for single pane tabs

[Kitenite]

Summary

• Fixes single-pane tabs not being draggable to other tabs
• react-mosaic-component skips connecting the drag source for root panes (path=[]), which prevents cross-tab drag-and-drop when a tab has only one pane
• Uses MosaicWindowContext.connectDragSource to manually connect the drag source for root panes while preserving the library's default behavior for multi-pane layouts

Test plan

• Open a tab with a single pane and drag it to another tab — should work
• Open a tab with multiple panes and drag between panes — should still work as before
• Drag a pane from a multi-pane tab to another tab — should still work as before

Summary by CodeRabbit

• New Features
  • Workspace panes can now be dragged and dropped across tabs, enabling more flexible layout reorganization.

[coderabbitai]

Caution

Review failed

The pull request is closed.

📝 Walkthrough

Walkthrough

The change modifies BasePaneWindow component to enable cross-tab drag-and-drop for root panes by introducing a RootDraggable internal component that connects to the Mosaic drag source via MosaicWindowContext. Root panes are identified using an isRoot flag based on path.length === 0.

Changes

Cohort / File(s)	Summary
Root Pane Drag-and-Drop Support apps/desktop/src/renderer/.../BasePaneWindow/BasePaneWindow.tsx	Introduces RootDraggable wrapper component and isRoot flag to enable cross-tab drag-and-drop for root panes via MosaicWindowContext integration, while preserving existing behavior for non-root panes.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• refactor(desktop): update changes view #595: Directly modifies the same BasePaneWindow.tsx file, adding RootDraggable component and MosaicWindowContext usage for root pane drag support.
• feat(desktop): Add drag-and-drop panes to tab bar #856: Related drag behavior enhancement that handles drag start/end and drag-state management alongside the RootDraggable wrapper implementation.

Poem

🐰 Root panes now waltz with grace across the tabs,
MosaicWindowContext weaves their dragging dance,
No longer bound by borders, they gracefully prance,
RootDraggable's magic makes layouts expand! ✨

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch kitenite/single-pane-draggable

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[github-actions]

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