For this:

		cmdq_error(item, "can't show a pane while window is zoomed");

Why not just unzoom? Isn't that what we normally do?

Is having this (hidden panes) going to make layout changes harder? I don't think we have a pressing need for hidden panes if they are going to cause any problems and could be done later.

Right, yes. I don't recall why that is in there. I'll adjust that.

Adding hidden panes will make layouts a little more complicated and will necessarily make adding features take more consideration. I'm not sure as to the magnitude of the effect, but there is something I should probably audit in this PR, and that is window_count_panes. It was given a parameter to interact with floating panes, and will need one for hidden as well. It feels like the function should be broken up into how it is used, instead of making a flag soup. It looks like it cares about counting visible, tiled, and all panes. I couldn't see any other immediate effects.

This feature can certainly wait as its impact on complexity is non-zero!