Support for internal signaling federation

How to use GitHub

• Please use the 👍 reaction to show that you are affected by the same issue.
• Please don't comment if you have no relevant information to add. It's just extra noise for everyone subscribed to this issue.
• Subscribe to receive notifications on status change and new comments.

From #12604

Joining/leaving with the federated session IDs seems to work with internal signaling too (and the participant status is eventually updated in the sidebar), but is something else needed? For example, relaying the ping from the federated server to the host or something like that.

It should be verified if cleaning participants works as intended (it seems that only secondary sessions are cleaned when inactive, but if a single session is kept in the room without a ping it is not cleaned), as it could be relevant for internal signaling if the behaviour is changed

• Related: https://github.com/nextcloud/spreed/pull/12741

Start with the participant-cleaning logic in lib/Controller/RoomController.php around lines 944-952 and review related pull request #12741. Verify internal signaling for federated session joins, leaves, pings, and inactive participant cleanup; done means the required behavior is established and covered by the relevant checks.