From 25cd44ecb34bc007ee59452aef9eacd71153f4a7 Mon Sep 17 00:00:00 2001
From: "haixin.yang" <haixin.yang@weimob.com>
Date: Wed, 22 Jul 2026 13:46:44 +0800
Subject: [PATCH] Prevent mobile trim release rollback

---
 src/lib/timelineEdgeAutoScroll.js      |  3 ++-
 src/lib/timelineEdgeAutoScroll.test.js | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/lib/timelineEdgeAutoScroll.js b/src/lib/timelineEdgeAutoScroll.js
index 1757eb5..21c829d 100644
--- a/src/lib/timelineEdgeAutoScroll.js
+++ b/src/lib/timelineEdgeAutoScroll.js
@@ -51,6 +51,7 @@ export function createTimelineEdgeAutoScroller({ trackElement, pointerType, time
     (pointerType === "touch" && isMobile)
     || (["mouse", "pen"].includes(pointerType) && !isMobile)
   );
+  const usesDesktopTrailingSpacer = enabled && !isMobile;
   const rulerElement = enabled ? trackElement.closest?.(".timeline-board")?.querySelector?.(".timeline-ruler-canvas") : null;
   if (enabled) {
     trackElement.classList?.add("is-trimming");
@@ -79,7 +80,7 @@ export function createTimelineEdgeAutoScroller({ trackElement, pointerType, time
     spacerElement.style.width = `${geometry.width}px`;
   };
 
-  if (enabled && scrollElement?.ownerDocument?.createElement) {
+  if (usesDesktopTrailingSpacer && scrollElement?.ownerDocument?.createElement) {
     const previousSpacer = scrollElement.querySelector?.("[data-timeline-trim-scroll-spacer]");
     previousSpacer?.__timelineTrimCleanup?.();
     previousSpacer?.remove?.();
diff --git a/src/lib/timelineEdgeAutoScroll.test.js b/src/lib/timelineEdgeAutoScroll.test.js
index b58e762..08da88a 100644
--- a/src/lib/timelineEdgeAutoScroll.test.js
+++ b/src/lib/timelineEdgeAutoScroll.test.js
@@ -66,6 +66,29 @@ describe("mobile timeline edge auto-scroll", () => {
     expect(rulerClasses.has("is-trimming")).toBe(false);
   });
 
+  it("never creates or settles a desktop trailing spacer on mobile", () => {
+    let appended = 0;
+    const scrollElement = {
+      clientWidth: 400,
+      scrollLeft: 120,
+      ownerDocument: { createElement: () => ({}) },
+      appendChild: () => { appended += 1; },
+    };
+    const track = {
+      classList: { add() {}, remove() {} },
+      closest: () => null,
+      parentElement: scrollElement,
+    };
+    const scroller = createTimelineEdgeAutoScroller({
+      trackElement: track,
+      pointerType: "touch",
+      win: { matchMedia: () => ({ matches: true }), requestAnimationFrame: () => 1, cancelAnimationFrame() {} },
+    });
+    scroller.stop();
+    expect(appended).toBe(0);
+    expect(scrollElement.scrollLeft).toBe(120);
+  });
+
   it("enables the same edge-scroll lifecycle for desktop mouse trimming", () => {
     const values = new Set();
     const track = {