[bug] React: cap-widget throws `null is not an object (evaluating 'this.#s._ensureSize')` when unmounting

[seratonik]

bug description:
When cap-widget is used within a react component, and later gets unmounted from the page on navigate or otherwise, the following error can happen (but seems to have a race condition preventing it from always triggering, but it is frequent enough that a manual test case shows it, particularly on a fresh page load with caches cleared):

Unhandled Promise Rejection: TypeError: null is not an object (evaluating 'this.#s._ensureSize')

affects:

• widget (ui) ("cap-widget": "0.1.56")

to reproduce:

1. Create a react component to hold cap-widget like this:

import 'cap-widget';
import { useEffect, useRef } from 'react';

export default function CaptchaInput({
  api,
  onChange,
}: {
  api: any;
  onChange: (token: string) => void;
}) {
  if (!api) return console.error('CaptchaInput requires an API instance', api);

  const widgetRef = useRef<any | null>(null);

  const handleSolve = (e: CustomEvent) => {
    onChange(e.detail.token);
  };

  const handleError = (e: CustomEvent) => {
    console.error('Captcha error:', e.detail.message);
  };

  const handleProgress = (e: CustomEvent) => {
    console.log('Captcha progress:', e.detail.progress);
  };

  const handleReset = () => {
    console.log('Captcha reset');
    onChange('');
  };

  useEffect(() => {
    widgetRef.current?.addEventListener('solve', handleSolve);
    widgetRef.current?.addEventListener('error', handleError);
    widgetRef.current?.addEventListener('progress', handleProgress);
    widgetRef.current?.addEventListener('reset', handleReset);
    return () => {
      widgetRef.current?.removeEventListener('solve', handleSolve);
      widgetRef.current?.removeEventListener('error', handleError);
      widgetRef.current?.removeEventListener('progress', handleProgress);
      widgetRef.current?.removeEventListener('reset', handleReset);
    };
  }, [handleReset, handleProgress, handleError, handleSolve]);

  return <cap-widget ref={widgetRef} data-cap-api-endpoint={`${api.host()}/captcha`} />;
}

2. Put that component on a page with a toggle button to conditionally render it
3. Toggle it a bunch and observe errors in console

expected behavior:
Should unmount cleanly without errors

screenshots:
Not applicable

versions and environment:
Observed in:

• Safari 26.5.2 on MacOS
• Microsoft Edge 151 on Windows 11,
• Chrome 151 on MacOS and Windows 11,
• Mobile Safari 26.5.2 on iOS

additional context:
Doesn't seem to hold up subsequent Javascript execution, but creates a lot of noise when tracking errors via Sentry.

[seratonik]

Thank you so much for the quick turn-around time fixing this!