I decided to add a pinentry backend to #fuzzel.
Turns out it's not that difficult. The protocol is line based (on STDIN). That means we can re-use a lot of code from the dmenu mode.
Then all we need to do is force a couple of options, like --prompt-only, and we're good to go.
We ignore most of the pinentry options and commands, since they're not applicable in fuzzel.
Biggest downside I've found so far: since fuzzel is a layer shell application, you can't switch window focus while fuzzel is running.