--runtime auto?

TuxMake supports --runtimes docker and podman. The problem is that to provide a 'build reproducer', one needs to be picked. And then if a user uses the other, they have to know that they can specify the other and how, or, we need to produce several reproducers, or, we need the reproducer to be a script which then starts to defeat the purpose.

What if --runtime auto did a if $(podman); elif $(docker); else exit to set --runtime dynamically at uh, runtime? So that our reproducers were portable between both supported container runtimes.

I looked but couldn't find any standard way to determine a user's preferred docker runtime.