For anyone who encounters a missing package as a result of untimely interruption to an upgrade, a hint.
Either:
- activate the boot environment that preceded the upgrade; or
- take relevant information from the environment.
In the screenshot below, I mounted the environment at /tmp/down
then ran:
pkg -r /tmp/down prime-origins | sort -u > ~/pkg\ prime-origins.txt

The list in the pkg prime-origins.txt file will help to identify which missing packages, if any, should be installed.
After installations:
pkg check -d