refactor(web): extract timeline touch helpers

apps/web/src/hooks/timelineTouch.ts

@@ -0,0 +1,50 @@
+export type TouchPoint = {
+  clientX: number;
+  clientY: number;
+};
+
+export type TouchDecisionState = {
+  x: number;
+  y: number;
+  decided: boolean;
+};
+
+type TouchLike = {
+  clientX: number;
+  clientY: number;
+};
+
+type TouchEventLike = {
+  touches: ArrayLike<TouchLike>;
+  changedTouches: ArrayLike<TouchLike>;
+};
+
+export function getTouchPoint(event: TouchEventLike): TouchPoint {
+  const touch = event.touches[0] ?? event.changedTouches[0];
+  return {
+    clientX: touch?.clientX ?? 0,
+    clientY: touch?.clientY ?? 0,
+  };
+}
+
+export function resolveTouchDragDecision(
+  state: TouchDecisionState,
+  point: TouchPoint,
+  thresholdPx = 8,
+): { nextState: TouchDecisionState; shouldHandleDrag: boolean } {
+  if (state.decided) {
+    return { nextState: state, shouldHandleDrag: true };
+  }
+
+  const dx = Math.abs(point.clientX - state.x);
+  const dy = Math.abs(point.clientY - state.y);
+  if (dx <= thresholdPx && dy <= thresholdPx) {
+    return { nextState: state, shouldHandleDrag: false };
+  }
+
+  const nextState = { ...state, decided: true };
+  return {
+    nextState,
+    shouldHandleDrag: dx >= dy,
+  };
+}