Чото поменял

src/textObserverPlugin.ts

@@ -0,0 +1,10 @@
+import { ViewPlugin, ViewUpdate } from '@codemirror/view'
+
+export const textObserverPlugin = (callback: (text: string) => void) =>
+    ViewPlugin.define(() => ({
+        update(update: ViewUpdate) {
+            if (update.docChanged) {
+                callback(update.state.doc.toString())
+            }
+        },
+    }))