So, that got poked in the face... Happy bug-hunting!

One last item to fix: the link behind the download button.

I don't remember where to do this in a way that fixes it permanently, so I've hot-fixed it.

plugins/calendar/calendar.php:

function load_settings()
{
[…]
    $settings['itip_notify'] = (int)$this->rc->config->get('calendar_itip_send_option', $this->defaults['calendar_itip_send_option']);
    $settings['week_numbers'] = 1;  // FIXME, needs to be similar like the line above
[…]
}

Not sure what is meant by "real estate", but my resolution is 1366x768, just to have it mentioned here.

Okay, I spent now some time with the code: My whole suggestion is already implemented, there are both, "weekNumbers" and "weekNumberTitle" variables in "plugins/calendar/lib/js/fullcalendar.js" which are later used by "plugins/calendar/calendar_ui.js".

Ok, I see now. libkolab.css is not added to the page. I don't know why yet, maybe something related to assets_dir.

@machniak; since we can reproduce this on webmail.kolabsys.com, I can verify there's no discernible error in the console.

In T4241#62348, @rsc wrote:

Closing this as invalid is not nice.

Disabled registration through third part providers, disabled trusting email addresses associated with those providers.

Closing this as invalid is not nice. It would be really helpful to have at least the second proposal done, given it adds no new screen space requirements. Aside of that, just having calendar weeks in mini-calendar is not really helpful when really actively working with the calendar a lot. Please consider reopening.

We currently have a problem with the OTP-20 compatibility of most of the erlang packages. Who would have guessed?

The week number is already included in the miniature calendar on the left-hand side, for both month and week views.

I have no idea. @rsc check browser console for errors.

There was an upstream ticket that has been closed. https://github.com/roundcube/roundcubemail/issues/6376

@rsc; what is the size of the real estate so we can attempt to reproduce?

This can be reproduced reliably.

Confirmed.

This should now be resolved, please verify.

The channel mode has been set to +C +r +s, which should put an end to the spamming.

I don't know what to do about it, to be honest. There doesn't seem to be any modules or settings that protect against this type of thing, as far as I could find.