See swaywm/sway#5299 (comment)

Would it be possible to have Peek automatically start the render after capture, saving it using the default filepath it already uses?

Scale has a few options which are not documented, scale-title-filter isn't documented on the wiki either.

Waybar keeps crashing when clicking the idle inhibitor module. On sway it seems to work so that leads me to believe it is a problem with river not implementing the idle inhibit protocol.

I'm fine if you decide to not support the protocol, but could there be a little note about

When wl-copy is sent a signal to terminate it, it should clean up the temp buffer files instead of leaving them around.

This is a very simple shell protocol only allowing for fullscreen surfaces. You can find a very basic implementation here: https://github.com/swaywm/wlroots/blob/master/examples/fullscreen-shell.c