Documentation for client-side validation API?

Where are you trying to add your custom JavaScript?

As I said, "I used the Joomla headTags module to inject my script into the head." This injects my scripts before CB's jQuery scripts (but so does CB Auto Actions - see the end of this posting).
I've tried temporarily removing my headTags config for my user profile and register menus.

Instead, I've now removed polling from my script, installed CB Auto Actions and configured as you specified, except for Method I used javaScript, not jQuery, and loaded two css / js dependencies first:

• Method: CSS (URL) [library]
• Method JavaScript (URL) [library script; 311kB]
• Method JavaScript (URL) [my script; 11kB]

In my script, I've still wrapped my jQuery in this condition:
    if (window.cbjQuery && window.cbjQuery.validator) { ...}
Execution now fails to reach my validator. Using console log messages, I've found it's failing the above if() condition.
If I reinstate the polling, the above condition succeeds, and it all works again.

Or for CB Auto Actions, did you advise to use the jQuery Method specifically, knowing that JavaScript (URL) wouldn't work, for some reason?

________________
FYI, inspecting the HTML served in each case, here's a few of the salient scripts in their order in the head:...
With headTags:
    ...
    intlTelInput.css
    ...
    jquery.min.js?3.7.1
    jquery-noconflict.min.js
    ...
    intlTelInputWithUtils.min.js
    intlTelInput_cb_validation_practical.js
    ...
    jquery-3.5.1.min.js
    ...
    jquery.validate.min.js
    jquery.cbvalidate.min.js

With CB Auto Actions
    ...
    intlTelInput.css
    ...
    intlTelInputWithUtils.min.js
    intlTelInput_cb_validation_practical.js
    ...
    jquery-3.5.1.min.js
    ...
    jquery.validate.min.js
    ...
    jquery.cbvalidate.min.js



 

Your jQuery needs to use the jQuery method. You can't put it in JavaScript as that won't be properly wrapped by the jQuery NoConflict logic and document load process. You won't even need your IF check in it. Your Code action can have 2 rows. First one being your JavaScript and the second one being your jQuery. That should then work as expected.