The CI runner image starts with empty package lists, so installing Go
with apt-get failed with "Unable to locate package golang". The apt
branch of pkg_install now runs apt-get update once per run, before the
first apt-get install, with the same code as the shared copy in
sneak/prompts PR 116.
Deviation from the vendored copy, replaced by the next re-vendor once
that PR lands.
Model: opus-5-5