OK, so this sequence of commands seems to work fine:

(set -euxo pipefail; mkdir -p tmp; python3 -m venv venv; source venv/bin/activate; python3 -m pip install volare; which volare)

. So my python install is fine, as are the binary/file permissions, but something else during setup is going amiss...

Alright, I got it to work. Looking inside the caravel makefile, it looks like the setup flow was trying to install volare at the system level (i.e. not in a virtual environment or otherwise sandboxed area); since I did not run the flow as root, volare wasn't actually being installed. Creating a caravel python virtual environment first and then running

make setup

solves the issue

I think this really ought to be fixed; it is unreasonable to expect users to install any python packages at the system level, since that's widely regarded as a bad practice.