After actually reading the `trace` documentation I got a callback to work via that mechanism, but it's clearly not the way to go. There are of course way too many return statements between the entry of a given port phase and its potential bailing.
It looks like the best way to achieve what I'm looking for is to roll a custom
`build {}` block that `catch`es errors in the actual build execution and might
then even try to take the suggested corrective action and re-launch the build
command.
