Why are supposedly ActivityPub-federated Discourse threads inaccessible via external AP clients?

Bug
10

github.com/mastodon/mastodon/discussions/34600#discussioncomment-13031935 states:

The Discourse AP plugin makes ActivityPub objects available when you click the green ActivityPub logo and click the “Note” button to copy the URL: Why are supposedly ActivityPub-federated Discourse threads inaccessible via external AP clients? - #9 by rokejulianlockhart - Support - Discourse Meta

Discourse AP needs to make the url link back to the id in some way, preferably via a redirect on requests with the correct Accept content negotiation header.

Consequently, I’ll tentatively set this as a Bug. (I can’t. Too old.)