The threaded runtime is required at least for hledger's pager output,
and probably for other things. It's controlled by the "threaded" build
flag for some historical reason. Now, that flag is marked as manual,
so that it can no longer be toggled by cabal. (Probably the build flag
should be dropped, that can be tried later.)
Related: Debian bug #1120833, causing an unusable hledger-1.50.2 package.
A simple web-based user interface for the hledger accounting system,
providing a more modern UI than the command-line or terminal interfaces.
It can be used as a local single-user UI, or as a multi-user UI for
viewing/adding/editing on the web.