Mercury Editor dialogs won't open after upgrading to Drupal core 10.3

We are experiencing the same issue with ME and upgrading to 10.3

Same here! I go into the node editing form (existing basic page with mercury editor enabled, and layout paragraphs functionality), and I get this in browser console (Firefox on Windows 11):

Uncaught TypeError: event is undefined
    handle https://my-site.pantheonsite.io/core/misc/dialog/dialog-deprecation.js?v=10.3.0:12
    jQuery 7
    openDialog https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/dialog.drupal.js?sfp58z:194
    show https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/dialog.drupal.js?sfp58z:217
    attach https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/edit-screen.js?sfp58z:168
    attachBehaviors https://my-site.pantheonsite.io/core/misc/drupal.js?v=10.3.0:166
    attachBehaviors https://my-site.pantheonsite.io/core/misc/drupal.js?v=10.3.0:162
    <anonymous> https://my-site.pantheonsite.io/core/modules/big_pipe/js/big_pipe.js?v=10.3.0:153
    <anonymous> https://my-site.pantheonsite.io/core/modules/big_pipe/js/big_pipe.js?v=10.3.0:184
dialog-deprecation.js:12:24

When I click the "plus" icon, it loads the paragraph picker dialog, but there's this in console:

An error occurred during the execution of the Ajax response: TypeError: event is undefined ajax.js:1147:19
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1147
    (Async: promise callback)
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1145
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:588
    jQuery 6
    execute https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:711
    lpbUiClick https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/post-messages-listener.js?sfp58z:14
    attach https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/post-messages-listener.js?sfp58z:59

Then I pick a paragraph type (button, in my case, because it's simple, just a plain text field and a link URL field), and the next dialog loads, but I get this in console:

An error occurred during the execution of the Ajax response: TypeError: event is undefined ajax.js:1147:19
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1147
    (Async: promise callback)
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1145
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:588
    jQuery 6
    eventResponse https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:803
    Ajax https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:650
    jQuery 8
    Ajax https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:639
    ajax https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:267
    bindAjaxLinks https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:335
    bindAjaxLinks https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:307
    attach https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:54
    attachBehaviors https://my-site.pantheonsite.io/core/misc/drupal.js?v=10.3.0:166
    attachBehaviors https://my-site.pantheonsite.io/core/misc/drupal.js?v=10.3.0:162
    insert https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1393
    jQuery 2
    insert https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1385
    openMercuryDialog https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/dialog.ajax.js?sfp58z:43
    commandExecutionQueue https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1050
    (Async: promise callback)
    commandExecutionQueue https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1043
    commandExecutionQueue https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1040
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1099
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:588
    jQuery 6
    execute https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:711
    lpbUiClick https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/post-messages-listener.js?sfp58z:14
    attach https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/post-messages-listener.js?sfp58z:59

Then, I fill in the two simple fields, and hit "Save" -- nothing happens, dialog stays up, no button is added to my layout -- and I get this in console:

An error occurred during the execution of the Ajax response: TypeError: event is undefined ajax.js:1147:19
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1147
    (Async: promise callback)
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1145
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:588
    jQuery 9
    eventResponse https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:800
    Ajax https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:650
    jQuery 8
    Ajax https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:639
    ajax https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:267
    loadAjaxBehavior https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:47
    loadAjaxBehavior https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:44
    attach https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:52
    attachBehaviors https://my-site.pantheonsite.io/core/misc/drupal.js?v=10.3.0:166
    attachBehaviors https://my-site.pantheonsite.io/core/misc/drupal.js?v=10.3.0:162
    insert https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1393
    jQuery 2
    insert https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1385
    openMercuryDialog https://my-site.pantheonsite.io/modules/contrib/mercury_editor/build/js/dialog.ajax.js?sfp58z:43
    commandExecutionQueue https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1050
    (Async: promise callback)
    commandExecutionQueue https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1043
    commandExecutionQueue https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1040
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:1099
    success https://my-site.pantheonsite.io/core/misc/ajax.js?v=10.3.0:588
    jQuery 3

"Cancel" also doesn't work, but the "X" at the top-right of the dialog does work, so that's how I make my escape.

Hopefully MR55 is the ticket - this change dispatches the custom DrupalDialogEvent instead of using jQuery's trigger. This needs testing for backwards compatibility.

Patched with MR55 in Drupal 10.3 without an issue and confirmed previous failing Cypress tests on our end our now passing. Thank you @just2pin for such a quick update.

I installed this patch into a D10.2 site to test, and get this error:

Uncaught ReferenceError: DrupalDialogEvent is not defined

So this MR requires 10.3 as it stands at this moment.

MR55 works for me on 10.3, too (was going to test on 10.2.6 buuuut thank you @sethhill for already doing that!)

Tested on 10.2 and 10.3, and the latest changes seem to work well.

Has this patch already been deployed or does it need to be applied manually? I wanted to test Mercury Editor but I'm on Drupal 10.3.0 and I'm getting the AJAX error shown above.

Yes, I'm testing the 2.1.0+9-dev version