libpkgobject is the durable local provider for exact reusable package archive
bytes in the native Zeppe-Lin package-management ecosystem.
The provider is deliberately content-addressed. A package object is requested by
its pkgimage::complete_archive_digest; package names, versions, installed
state, transaction history, and archive path history are not lookup authority.
Every reopen verifies the present bytes before returning them.
libpkgobject stores archive bytes only. Normalized package-image authority
remains in libpkgimage, tree realization remains in libpkgimage-exec, and
concrete pkgexec::resource_identity remains the execution composer's job.