Digest::SHA is the most notable missing package at runtime
for a minimal system.
Tests don't run at all without Test::Simple (or Test::More).
Plack::Test is also a separate package, too...
Also, the package for IO::Compress::Gzip should be IO::Compress;
as perl-PerlIO-gzip is a different thing entirely which is not
relevant to our needs.
Test::HTTP::Server::Simple doesn't seem required at all for Plack
tests.
ExtUtils::MakeMaker needs to be documented as a install dependency
for people installing this, too; since AFAIK public-inbox is not
yet in any distros.