Add a handle to the curved connector to change its trajectory

[formicoidea]

Summary

• Add a draggable handle on Curve connectors at t=0.5 on the Bézier curve, allowing users to adjust the curve trajectory by dragging
• The handle stores a curveControlPoint (absolute IVec) on ConnectorElementModel via @field(), persisted through Yjs/CRDT
• The Bézier is recalculated so the curve passes exactly through the control point (WYSIWYG point de passage)
• The control point transforms proportionally on resize/rotate and translates on move
• Cleared automatically when connector mode changes

Changes

File	Change
connector/connector.ts (model)	New @field() curveControlPoint: IVec | null, handled in moveTo() and resize()
connector-handle.ts	New _renderCurveMidpointHandle(), _startCurveMidpointDrag(), _bindCurveMidpointEvents()
connector-manager.ts	New _applyCurveControlPoint() — recalculates Bézier control vectors so curve passes through point at t=0.5
connector-watcher.ts	Watch curveControlPoint changes, clear on mode change
view.ts	Stash/pop curveControlPoint during resize and rotate

Design decisions

• Single handle at t=0.5 — keeps the UX simple, one draggable point per curve
• Point de passage (WYSIWYG) — the curve passes exactly through the handle position, not a traditional Bézier control point that "pulls" the curve
• Semi-persistent — stored in absolute coordinates, proportionally transformed via matrix when endpoints move (consistent with resizePath)
• Drag in component — follows existing endpoint handle pattern (pointerdown/pointermove/pointerup directly in connector-handle.ts)
• Single undo entry per drag (mousedown → mouseup grouped via captureSync())

Test plan

• Select a Curve connector → handle appears at midpoint of the curve
• Drag the handle → curve reshapes to pass through the dragged position
• Move a connected block → curve control point transforms proportionally
• Resize selection containing a curve connector → control point scales correctly
• Change connector mode (Curve → Straight → Curve) → control point is cleared
• Undo/redo after dragging → reverts correctly
• Multi-select connectors → handle does NOT appear (only on single selection)

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Project	Deployment	Actions	Updated (UTC)
blocksuite	Ready	Preview, Comment	Mar 22, 2026 6:23pm

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