Fence pointer capture ownership across node and edge gestures

src/lib/canvas-bindings/pointer-capture.ts

@@ -0,0 +1,5 @@
+/** Transport ownership only: document geometry and gesture tokens stay in the editor. */
+export type PointerCapturePort={setPointerCapture(id:number):void;hasPointerCapture(id:number):boolean;releasePointerCapture(id:number):void};
+export function ownsPointerCapture(owner:{pointerId:number;capture:unknown}|null|undefined,input:{pointerId:number;type?:string;target?:unknown}){if(!owner||owner.pointerId!==input.pointerId)return false;if(input.type!=='lostpointercapture')return true;if(input.target!==owner.capture)return false;const capture=owner.capture as Partial<PointerCapturePort>|undefined;try{if(capture?.hasPointerCapture?.(owner.pointerId))return false;}catch{/* A detached matching target may still need cancellation. */}return true;}
+export function acquirePointerCapture(target:PointerCapturePort,id:number){try{target.setPointerCapture(id);return true;}catch{return false;}}
+export function releasePointerCapture(target:PointerCapturePort,id:number){try{if(target.hasPointerCapture(id))target.releasePointerCapture(id);}catch{/* Detached DOM or an already released platform capture has no editor authority. */}}