As far as I remember, this has always been so, long before DiscussionTools became a thing.

Yeah, unrelated to DiscussionTools, which just piggybacks off of mediawiki's existing behavior around the "new topic" link.

I think this is because __NONEWSECTIONLINK__ is extracted by the parser, so it's only available when you've actually parsed the wikitext for the page... and so we only know about it when we're on the read-view for the page. To fix this we'd need to either:

1. Reparse the page wikitext whenever non-read actions are visited, even though we're not going to display the output
2. Cache the magic-word directives like this somewhere that can be independently checked

The former has potential performance implications (lots more mostly-unnecessary wikitext parsing would be happening), but would avoid us needing to keep a cache in sync as revisions change. I'd be inclined to say that doing either is pretty low-priority, given the trade-offs involved.

Cache the magic-word directives like this somewhere that can be independently checked

They are sort of cached in the page_props database table. One more read query in these views shouldn't, in my opinion, make things worse.

@matej_suchanek huh, you're right, it's in there as newsectionlink -- I could have sworn it wasn't available. 😂