Gestures get stuck when the pointer is released outside the canvas (pan, marquee, box, rotation) — no pointer capture

[dompm]

onPointerUp is bound only to the Konva Stage (ResultPanel.tsx:1217-1294, SheetPanel.tsx:298-345); there is no setPointerCapture and no window-level fallback. Releasing the mouse button outside the panel means the gesture never ends:

1. Pan sticks "on": start panning (space / middle-click / pan tool), drag off the panel, release → vp.endPan() never runs → isPanning ref stays true (useViewport.ts:195-212) → when the cursor re-enters, the canvas pans with no button held until the user clicks again.
2. Marquee / box / pencil stick: drawingBox, marqueeBox, pencilPoints keep following the bare cursor after release.
3. Sheet rotation corrupts undo granularity: rotatingPieceId sticks — every subsequent move keeps writing skipHistory: true rotation updates, and the committing (history-recording) update at SheetPanel.tsx:341 never happens, so the undo history silently misses the rotation.

Fix: call setPointerCapture on the stage container on pointerdown (or register a one-shot window pointerup/pointercancel listener while a gesture is active).

Related stale-ref bug: useViewport.ts:224 returns isPanning: isPanning.current — a render-time ref read. endPan() mutates the ref without re-rendering, so after a middle-click pan with a piece selected, isInteracting stays true and the PieceProperties popover remains opacity: 0; pointer-events: none until some unrelated re-render (ResultPanel.tsx:2217-2228). Also the cursor doesn't switch to "grabbing" until the first move. Make isPanning state (or bump a render counter on start/end).

[dompm]

SheetPanel half fixed on branch worktree-agent-a4a9a3a5a0d883e50 (commit 13be332): pointer is captured on the stage content element at gesture start (background pointerdown for pan/marquee, and the rotation handle's pointerdown), so releasing the button outside the canvas now ends the gesture — pan no longer sticks on, the marquee stops following the bare cursor, and rotations always get their committing (history-recording) update.

Still open (pattern side): ResultPanel's pan/box/pencil gestures, and the related useViewport.ts stale isPanning: isPanning.current render-time ref read that keeps the PieceProperties popover hidden after a middle-click pan.

[dompm]

ResultPanel/useViewport half fixed on the worktree-agent branch (commit 9a083b8):

• Pointer capture is taken on the canvas when a drag gesture starts (pan / box / marquee / pencil), so pointermove/pointerup keep arriving after the pointer leaves the panel and gestures end on release instead of sticking to the bare cursor. A Stage onPointerCancel handler aborts in-progress gestures without committing.
• The related stale-ref bug is fixed: useViewport now mirrors isPanning into state, so after a pan ends the cursor returns to 'grab' and the PieceProperties popover regains pointer events immediately instead of waiting for an unrelated re-render.

SheetPanel's pan/marquee/rotation handlers were not touched here.