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It looks like Emacs rather than Unix.

Ah this is a really nice feature, really adds to the experience and feel that you are looking for. In your place I would add some simple bar on top, just a bunch of horizontal lines or whatever, so that the UI "affords" to be dragged.

Hover states are no longer viable for interaction affordance because they do not exist on mobile.

I still include, however I always try and make interaction immediately apparent.

you could add little window decoration / border / title bar which would better indicate that it's actually a draggable "window" of sorts? :)

Well done mate :)