From 56726638ec1fc8c61994bf89fa42529e64130568 Mon Sep 17 00:00:00 2001
From: Scott Latz <scottla@zillowgroup.com>
Date: Mon, 8 Jun 2026 08:31:52 -0500
Subject: [PATCH 1/2] Fix preview pane scrolling to bottom on checkbox click

When clicking a task-list checkbox in preview mode, dispatching the
source edit could trigger scroll-sync via the editor's scrollDOM and
jump the preview to the editor's cursor position (often the bottom of
the document). Save and restore the preview pane's scroll position
around the dispatch to prevent this.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/view.ts | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/view.ts b/src/view.ts
index cf5cb16..4e9f9f0 100644
--- a/src/view.ts
+++ b/src/view.ts
@@ -377,10 +377,17 @@ function handleTaskItemToggle(event: MouseEvent) {
 
   // Let the native toggle stand for instant feedback; just sync the source
   const from = lineRange.from + toggle.offset;
+
+  // Dispatch can trigger scroll-sync via the editor's scrollDOM; preserve preview position.
+  const savedScrollTop = previewPane.scrollTop;
+
   MarkEdit.editorView.dispatch({
     changes: { from, to: from + 1, insert: toggle.replacement },
     annotations: silentChange.of(true),
   });
+
+  previewPane.scrollTop = savedScrollTop;
+  requestAnimationFrame(() => { previewPane.scrollTop = savedScrollTop; });
 }
 
 const states: {

From 9e7212fc79d8469975fb9fae7fe37b817b3339b9 Mon Sep 17 00:00:00 2001
From: Scott Latz <scottla@zillowgroup.com>
Date: Mon, 8 Jun 2026 08:43:43 -0500
Subject: [PATCH 2/2] Fix preview pane scrolling to bottom on checkbox click

When clicking a task-list checkbox in preview mode, the editor's
scrollDOM could emit a scrollend event that triggered syncScrollProgress
and jumped the preview to the editor's cursor position (often the bottom
of the document).

Instead of saving/restoring scrollTop (which risks overriding user
momentum scrolling from a delayed rAF callback), suppress the scroll-sync
listener for the duration of the dispatch and re-enable it on the next
animation frame. The preview position is never touched, so user scroll
state is fully preserved.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/scroll.ts | 20 ++++++++++++++++++--
 src/view.ts   | 12 +++++-------
 2 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/src/scroll.ts b/src/scroll.ts
index 1a56bb7..62fa8eb 100644
--- a/src/scroll.ts
+++ b/src/scroll.ts
@@ -8,7 +8,11 @@ export function startObserving(sourcePane: HTMLElement, targetPane: HTMLElement)
   }
 
   if ('onscrollend' in window) {
-    sourcePane.addEventListener('scrollend', () => syncScrollProgress(sourcePane, targetPane));
+    sourcePane.addEventListener('scrollend', () => {
+      if (!states.syncSuppressed) {
+        syncScrollProgress(sourcePane, targetPane);
+      }
+    });
   } else {
     sourcePane.addEventListener('scroll', () => {
       if (states.scrollUpdater !== undefined) {
@@ -16,12 +20,22 @@ export function startObserving(sourcePane: HTMLElement, targetPane: HTMLElement)
       }
 
       states.scrollUpdater = setTimeout(() => {
-        syncScrollProgress(sourcePane, targetPane);
+        if (!states.syncSuppressed) {
+          syncScrollProgress(sourcePane, targetPane);
+        }
       }, 100);
     });
   }
 }
 
+export function suppressScrollSync() {
+  states.syncSuppressed = true;
+}
+
+export function resumeScrollSync() {
+  states.syncSuppressed = false;
+}
+
 export function syncScrollProgress(sourcePane: HTMLElement, targetPane: HTMLElement, animated = true) {
   const { line, progress } = getScrollProgress(sourcePane);
   scrollToProgress(targetPane, line, progress, animated);
@@ -136,6 +150,8 @@ function clampProgressValue(value: number) {
 
 const states: {
   scrollUpdater: ReturnType<typeof setTimeout> | undefined;
+  syncSuppressed: boolean;
 } = {
   scrollUpdater: undefined,
+  syncSuppressed: false,
 };
diff --git a/src/view.ts b/src/view.ts
index 4e9f9f0..8dfe5e6 100644
--- a/src/view.ts
+++ b/src/view.ts
@@ -5,7 +5,7 @@ import { renderMarkdown, renderMermaid, renderKatex, handlePostRender, applyStyl
 import { replaceImageURLs } from './features/image';
 import { hidePreviewButtons, previewModes } from './support/settings';
 import { localized } from './shared/strings';
-import { syncScrollProgress } from './scroll';
+import { syncScrollProgress, suppressScrollSync, resumeScrollSync } from './scroll';
 import { resolveTaskToggle } from './features/task';
 import { ClassNames, CacheKeys } from './shared/const';
 
@@ -378,16 +378,14 @@ function handleTaskItemToggle(event: MouseEvent) {
   // Let the native toggle stand for instant feedback; just sync the source
   const from = lineRange.from + toggle.offset;
 
-  // Dispatch can trigger scroll-sync via the editor's scrollDOM; preserve preview position.
-  const savedScrollTop = previewPane.scrollTop;
-
+  // Suppress scroll-sync for this dispatch: the editor's scrollDOM can emit a
+  // scrollend event that would jump the preview to the editor's cursor line.
+  suppressScrollSync();
   MarkEdit.editorView.dispatch({
     changes: { from, to: from + 1, insert: toggle.replacement },
     annotations: silentChange.of(true),
   });
-
-  previewPane.scrollTop = savedScrollTop;
-  requestAnimationFrame(() => { previewPane.scrollTop = savedScrollTop; });
+  requestAnimationFrame(resumeScrollSync);
 }
 
 const states: {