[reece00]

Fixes clickable chat names covering the scroll-to-bottom button and intercepting clicks.

Overrides OutputPanel.ChildAdded to move the button to the end of the child list, keeping it above newly added rich-text controls for both rendering and mouse input.

Fixes space-wizards/space-station-14#46641.
Test:

[Aeshus]

This look good, as it does much the same as ScrollContainer does (which has similar layering issues). There may be a performance impact, but we already deal with it for ScrollContainer.

The only issue with your PR is that you also need to do the same for the _scrollBar, as that will also get potentially buried under richtext-generated controls.

This bug was only exposed because Content is using the richtext-generated controls a bunch more for the text links in chat.

For future work (out of scope of this bug fix), I think a better design would involve RichTextEntry putting the Controls it creates into a child container of OutputContainer, so it wouldn't have to change the ordering of its siblings constantly. Similar work could be done to ScrollContainer to fix this as well.

[reece00]

A content container changes the parent-child hierarchy to handle stacking and would require checking code that relies on direct children.
A sibling ZIndex preserves the tree, but needs consistent ordering for rendering and hit-testing, with either repeated sorting or cache invalidation to manage.
I'm not familiar with the codebase. I haven't taken this any further.

[Aeshus]

Should be good