fix: cursor jumps to end of text when editing a comment (#1924)

* fix: cursor jumps to end of text when editing a comment

When editing a comment mid-text, the cursor would jump to the end after
every keystroke, making it impossible to insert text at any position
other than the end.

Root cause: on each keystroke, the comment editor's onUpdate callback
updated parent state (setContent), which changed the defaultContent prop
passed back to CommentEditor. A useEffect watching defaultContent then
called commentEditor.commands.setContent(), which reset the entire
editor content and moved the cursor to the end.

Fix:
- Store in-progress edits in a ref instead of state to avoid triggering
  React re-renders and the prop->effect->setContent cascade
- Read from the ref when saving the comment
- Sync the ref back into state after a successful save so the read-only
  view updates immediately
- Guard the setContent useEffect to only run for read-only editors, so
  websocket-driven updates from other browsers still work

Fixes #1791

Functionally tested on Firefox and Chrome: mid-text editing, saving,
cross-browser live updates via websocket.

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

* fix stale content on edit cancel

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Philipinho <16838612+Philipinho@users.noreply.github.com>

apps/client/src/features/comment/components/comment-editor.tsx

@@ -84,9 +84,14 @@ const CommentEditor = forwardRef(
       autofocus: (autofocus && "end") || false,
     });
 
+    // Sync content from props for read-only editors (e.g. when updated via
+    // websocket on another browser). Skip for editable editors to avoid
+    // resetting the cursor position on every keystroke.
     useEffect(() => {
+      if (!editable && commentEditor && defaultContent) {
         commentEditor.commands.setContent(defaultContent);
-    }, [defaultContent]);
+      }
+    }, [defaultContent, editable, commentEditor]);
 
     useEffect(() => {
       setTimeout(() => {

apps/client/src/features/comment/components/comment-list-item.tsx

@@ -1,5 +1,5 @@
 import { Group, Text, Box, Badge } from "@mantine/core";
-import React, { useEffect, useState } from "react";
+import React, { useEffect, useRef, useState } from "react";
 import classes from "./comment.module.css";
 import { useAtom, useAtomValue } from "jotai";
 import { timeAgo } from "@/lib/time";
@@ -40,6 +40,7 @@ function CommentListItem({
   const [isLoading, setIsLoading] = useState(false);
   const editor = useAtomValue(pageEditorAtom);
   const [content, setContent] = useState<string>(comment.content);
+  const editContentRef = useRef<any>(null);
   const updateCommentMutation = useUpdateCommentMutation();
   const deleteCommentMutation = useDeleteCommentMutation(comment.pageId);
   const resolveCommentMutation = useResolveCommentMutation();
@@ -56,9 +57,13 @@ function CommentListItem({
       setIsLoading(true);
       const commentToUpdate = {
         commentId: comment.id,
-        content: JSON.stringify(content),
+        content: JSON.stringify(editContentRef.current ?? content),
       };
       await updateCommentMutation.mutateAsync(commentToUpdate);
+      if (editContentRef.current) {
+        setContent(editContentRef.current);
+        editContentRef.current = null;
+      }
       setIsEditing(false);
 
       emit({
@@ -128,6 +133,7 @@ function CommentListItem({
     setIsEditing(true);
   }
   function cancelEdit() {
+    editContentRef.current = null;
     setIsEditing(false);
   }
 
@@ -194,7 +200,7 @@ function CommentListItem({
             <CommentEditor
               defaultContent={content}
               editable={true}
-              onUpdate={(newContent: any) => setContent(newContent)}
+              onUpdate={(newContent: any) => { editContentRef.current = newContent; }}
               onSave={handleUpdateComment}
               autofocus={true}
             />