diff --git a/frontend/src/lib/components/PersonMentionEditor.svelte b/frontend/src/lib/components/PersonMentionEditor.svelte
index 592fdd7d..1347f545 100644
--- a/frontend/src/lib/components/PersonMentionEditor.svelte
+++ b/frontend/src/lib/components/PersonMentionEditor.svelte
@@ -241,8 +241,15 @@ onDestroy(() => {
 // Keep editor in sync with the reactive `disabled` prop. Tiptap's setEditable
 // flips contenteditable on the inner DOM and stops accepting input — matches
 // the textarea's old `disabled` semantics for keyboard users (WCAG 2.1.1).
+//
+// Guard: setEditable triggers a ProseMirror transaction which fires onUpdate;
+// onUpdate writes through bind:value / bind:mentionedPersons. Without this
+// idempotence check, the effect would loop on every prop pass-through.
 $effect(() => {
-	editor?.setEditable(!disabled);
+	const shouldBeEditable = !disabled;
+	if (editor && editor.isEditable !== shouldBeEditable) {
+		editor.setEditable(shouldBeEditable);
+	}
 });
 </script>