On second glance, the way that we determined a media tile to be 'waiting for media' was too implicit for my taste. It would appear on a surface reading to depend on whether a participant was currently publishing any video. But in reality, the 'video' object was always defined as long as a LiveKit participant existed, so in reality it depended on just the participant. We should show this relationship more explicitly by moving the computation into the view model, where it can depend on the participant directly.
We would show 'waiting for media' on participants that were connected but had no published tracks, because we were filtering them out of the remote participants list on connections. I believe this was done in an attempt to limit our view to only the participants that have a matching MatrixRTC membership. But that's fully redundant to the "Matrix-LiveKit members" module, which actually has the right information to do this (the MatrixRTC memberships).
Semantically, behaviors are only meaningful for as long as their scope is running. Setting a behavior's value to an empty array once its scope ends is not guaranteed to work (as it depends on execution order of how the scope is ended), and subscribers should be robust enough to handle clean-up of all connections at the end of the scope either way.
While looking into what had regressed https://github.com/element-hq/element-call/issues/3588, I found that 28047217b8 had filled in a couple of behaviors with non-reactive default values, the "natural window mode" behavior being among them. This meant that the app would no longer determine the correct window mode upon joining a call, instead always guessing "normal" as the value. This change restores its reactivity.