tree 0cdefe7960f6dfe3efd2efb365405755bcac9d84
parent 723f095496be9e6d80536fb07b3a54a66832e256
author Hong Shin <hongshin@google.com> 1731424895 -0800
committer Copybara-Service <copybara-worker@google.com> 1731425067 -0800

hpb: Establish plumbing for returning a default msg for extensions

Not invoked just yet, as extant users may expect the old `GetOrPromote` pathway.

An incremental Δ for getting message extensions up to parity with proto2.

PiperOrigin-RevId: 695723050