The cure was determined to be worse than the ailment. Moved to an idea, tracked here: https://big.ideas.aha.io/ideas/A-I-13997
Currently there is an edge case where project owners are able to add users that take up paid seats outside the paid seat groups administered by the project owner. Adding this idea to assess demand and so users can track if we decide to reprioritize this in the future.
I'm only going to note high level behavior here out of caution as this quickly veers into some detailed security and permissions behavior. Please see the internal comment on this idea for the feature that includes the complete detail of this behavior.
An updated implementation looks like this:
For Aha! Roadmaps accounts with paid seat groups enabled
For Project owners who are not billing administrators
On the Info > Users screen for a project/product/workspace
Adding a project user who takes up a newly paid seat must also add that user to a paid seat group the acting user is an administrator of (this prevents paid seat use outside of adminsitered paid seat groups). (This includes moving them into the new paid seat group if there is no paid seat space in their existing one, if it exists).
Adding a project user who has an existing paid seat to a project will leave that user in their existing paid seat group.
Adding a project user who doesn't take up a newly paid seat will leave them in their existing paid seat group if it is a paid role, or associate with the new paid seat group if no such relation exists.
You can use the Settings > User page and set the paid seat group filter to None. This will help you identify any users who may need to be added to a seat group or have a seat reallocated.