Caldera headless: graceful handling when USB DAC is fully unplugged (powered off or source-switched)

Thanks for the detailed reply, and sorry for the noise. My original clean-exit-at-startup report turned out to be a red herring on my end: I had never actually completed –login on that install, so there was no saved session. Once I logged in properly, that exit went away entirely — nothing to do with the audio backend.