refactor: simplify detach() guard and add regression test for touch scroll

- Replace empty if block with optional chaining guard
- Add test verifying touchState survives detach/attach cycle

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ohah

packages/react-wasm-table/src/adapter/__tests__/event-manager.test.ts

@@ -866,6 +866,26 @@ describe("EventManager", () => {
       expect(onCellClick).not.toHaveBeenCalled();
     });
 
+    it("touchState survives detach/attach cycle during active scroll", () => {
+      const onScroll = mock(() => {});
+      em.setLayouts([], []);
+      em.attach(canvas, { onScroll });
+
+      // Start touch and begin scrolling
+      canvas.dispatchEvent(createTouchEvent("touchstart", [{ clientX: 100, clientY: 100 }]));
+      canvas.dispatchEvent(createTouchEvent("touchmove", [{ clientX: 100, clientY: 80 }]));
+      expect(onScroll).toHaveBeenCalled();
+      onScroll.mockClear();
+
+      // Simulate React effect re-run: detach then re-attach
+      em.detach();
+      em.attach(canvas, { onScroll });
+
+      // Continue scrolling — touchmove should still work
+      canvas.dispatchEvent(createTouchEvent("touchmove", [{ clientX: 100, clientY: 60 }]));
+      expect(onScroll).toHaveBeenCalled();
+    });
+
     it("multi-touch is ignored", () => {
       const onScroll = mock(() => {});
       const onCellClick = mock(() => {});

packages/react-wasm-table/src/adapter/event-manager.ts

@@ -874,10 +874,7 @@ export class EventManager {
   detach(): void {
     // Preserve touchState across detach/attach cycles so that an in-progress
     // touch gesture (e.g. scroll) survives React effect re-runs.
-    // Only clear touchState if there is no active gesture.
-    if (!this.touchState) {
-      // no active touch — safe to clear everything
-    } else if (this.touchState.longPressTimer) {
+    if (this.touchState?.longPressTimer) {
       clearTimeout(this.touchState.longPressTimer);
       this.touchState.longPressTimer = null;
     }