The forum list says what you may do in it
GET /api/v1/forums and GET /api/v1/board now return canPost, canReply and locked on every forum, resolved for the calling token by the same resolvePermissions the write routes use.
Before this, a client could not tell a feed-only forum from an ordinary one until it tried to post and got a 403. A board whose news forum is fed by a crawler and takes replies only looked exactly like one anybody may start a topic in, so a posting client found out in public.
A category is never postable: it holds forums, not topics.
Nothing about who may post has changed. This publishes a decision the board was already making, and the test asserts the claim against the write route in the same run so the two cannot drift.
Boards following releases pick this up within about five minutes.