Documentation mentions sanitization:

If you need to log these errors or report then to a third-party service such as BugSnag or Sentry, then you can do this through a handleError export in your app/entry.server.js. This method receives the un-sanitized versions of the error since it is also running on the server.

https://remix.run/docs/en/main/guides/errors#error-sanitization

Where is this logic implemented and how do I override it?

My use case is that I need to attach an additional property to the error.

Namely, when an error occurs, I want to generate Sentry error ID and display that to the user.

import { captureException } from '@sentry/node';

// ...

const sentryErrorId = captureException(error);

I would imagine that I can do this in the error sanitization stage, e.g.

const sanitizeError = (error) => {
  const sentryErrorId = captureException(error);

  const sanitizedError = originalSanitizeError(error);

  sanitizedError.sentryErrorId = sentryErrorId;

  return sanitizedError;
};

I just realized that if I do this, then I will get errors reported twice, because @sentry/remix already wraps error handler. I can always remove it, but just flagging that there is this issue.