Sometimes it is confusing that you cannot add a tag to a topic. It is not obvious that it is part of a tag group, which requires you to add a different tag first.
When you create a new topic by using the new topic button while you have filtered the topic list for that tag, the tag is added to the tag field of the composer, but does not add the parent tag. However, when you submit the topic, Discourse is so smart that it adds the required parent tag automatically.
The tag is also re-added when you remove it. So, when a topic is tagged with “ai” and “ai-helper” and you remove the “ai” tag, it is added back on save.
Is it possible to add something similar when you try to add a tag? So, when you try to add “ai-helper” to a topic, you don’t have to wonder why it is impossible, but Discourse just adds both ai and ai-helper to the tag field?