Three fixes for the image drop overlay interference:
1. Block handle clipping: Add padding (0 4px) to editor container so
BlockNote's side menu (42px) fits within the overflow clip edge.
overflow-y:auto forces overflow-x:auto (CSS spec), which was clipping
the menu 2px past the container's left boundary.
2. Block handle click interference: Extract isInteractiveTarget() to
exclude .bn-side-menu from handleContainerClick — prevents the
container from stealing focus when clicking drag handle or add button.
3. Internal drag isolation: Track document-level dragstart/dragend to
flag internal HTML5 drags (tabs, blocks). Tauri onDragDropEvent
handler skips entirely during internal drags to prevent interference.
Extract useInternalDragFlag() and handleTauriDrop() to keep
useImageDrop under CodeScene complexity threshold.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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