Sentry reports many cases of the xhr object being missing in the
error handler.
Ensure the error handling code doesn't crash because of the missing xhr.
There are two cases where the draft auto-save might fail because the
user is no longer authenticated:
- The user signed-out in another tab,
- The brower quit and re-opened, so the Session cookie expired.
In both cases, the auto-save will never succeed until the user
authenticates again, so displaying a "Retry" button is cruel.
Moreover, in plus of all auto-save requests failing with a small error,
the actual hard failure only occurs after filling all the form and
trying to submit it. Then the user is redirected to the sign-in page –
but all their changes are lost.
Instead, we now redirect to the sign-in page on the first 401 error
during the auto-save, let the user sign-in, and then redirect back to
the form.