Order brush selection by sweep direction

[theop-luma]

Summary

• During brush selection, selectedShapeIds are now ordered by when each shape first entered the brush rectangle
• Dragging left-to-right gives left-to-right order, and vice versa
• Accessible after brush completes via Brushing.selectionOrder map

Test plan

• Create several shapes in a row
• Brush select left-to-right, verify editor.getSelectedShapeIds() matches left-to-right order
• Brush select right-to-left, verify reverse order
• Shift+brush to add to existing selection, verify new shapes appended in sweep order
• Shrink brush so shapes leave, then re-expand — verify re-entered shapes get fresh order

🤖 Generated with Claude Code

[cursor]

PR Summary

Medium Risk
Changes the ordering semantics of editor.setSelectedShapes during brush selection, which may affect downstream behaviors that depend on selection order (e.g. grouping/alignment operations). Logic is localized to Brushing but touches core interaction UX.

Overview
Brush selection now preserves a deterministic sweep/entry order for selectedShapeIds instead of using an unordered set.

Brushing tracks when each shape first enters the brush rectangle via a new selectionOrder map and applies that ordering when calling editor.setSelectedShapes, including shift+brush additive selection and cases with no hit-test candidates.

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[kaznaan]

👍