nit

frontend/src/components/editor/CodeEditor.tsx

@@ -4,7 +4,7 @@
  * Wherever this editor is used, it provides the same features (syntax highlighting + Nunjucks).
  * The parent (node) provides the expected base language for highlighting.
  */
-import React, { useCallback, useRef } from 'react'
+import React, { useCallback, useLayoutEffect, useRef } from 'react'
 import Editor from 'react-simple-code-editor'
 import { highlight, type HighlightLanguage } from '@/lib/syntaxHighlight'
 
@@ -53,6 +53,7 @@ export function CodeEditor({
   minHeight = 120,
 }: CodeEditorProps) {
   const containerRef = useRef<HTMLDivElement | null>(null)
+  const selectionRestoreRef = useRef<{ start: number; end: number } | null>(null)
 
   const highlightCode = useCallback(
     (code: string) => highlight(code, language),
@@ -69,17 +70,27 @@ export function CodeEditor({
         (textareaId ? document.getElementById(textareaId) : containerRef.current?.querySelector('textarea')) as HTMLTextAreaElement | null
       const start = ta?.selectionStart ?? newValue.length
       const end = ta?.selectionEnd ?? newValue.length
+      selectionRestoreRef.current = { start, end }
       onValueChange(newValue)
-      requestAnimationFrame(() => {
-        const el = (textareaId
-          ? document.getElementById(textareaId)
-          : containerRef.current?.querySelector('textarea')) as HTMLTextAreaElement | null
-        if (el) el.setSelectionRange(start, end)
-      })
     },
     [onValueChange, readOnly, textareaId]
   )
 
+  useLayoutEffect(() => {
+    const pending = selectionRestoreRef.current
+    if (pending == null) return
+    selectionRestoreRef.current = null
+    const el = (textareaId
+      ? document.getElementById(textareaId)
+      : containerRef.current?.querySelector('textarea')) as HTMLTextAreaElement | null
+    if (el) {
+      const { start, end } = pending
+      const safeEnd = Math.min(end, el.value.length)
+      const safeStart = Math.min(start, safeEnd)
+      el.setSelectionRange(safeStart, safeEnd)
+    }
+  }, [value, textareaId])
+
   return (
     <div ref={containerRef} className="code-editor" style={{ minHeight: 0 }}>
       <Editor