Pinned rooms will be used for special events such as spotlights or other ongoing featured contests and tournaments. They will be indicated by a yellow pin marker in the upper right corner of the room panel:

and shown at the top of the room listing.

• Closes Add "pinned" category for playlist rooms #34537
• Depends on Add pinned flag & description field to multiplayer rooms osu-web#12362

As mentioned in the web-side pull, I expect that all spotlights & featured artist rooms will also be implicitly pinned. They were not until now, which meant that in a worst-case scenario that probably never happened, the client-side hack for pinning those that was used in RoomListing up until now could fail if the rooms were not returned in the first page by osu-web (which was not guaranteed until now).

Notably there's also the part wherein the game does deficient polling because it never attempts to retrieve more than the first page of active rooms, but that probably requires a significant restructuring of how the lounge screens work that I am not doing without getting explicit buy-in first.

I've already seen someone report last week that they're not able to see their friends' multiplayer rooms that could possibly be caused by that. As far as I can tell the problem is currently masked unless there are more than 250 active rooms / playlists at any point in time.

Visual adjustments to the private room marker made at @peppy's behest.