annotations.proto source of truth: copied from commit 326c6be009be4018defde9a147536ee31c7ac515; current commit
To regenerate:
$ cd chromite/lib/protos $ wget https://github.com/luci/luci-go/raw/master/common/proto/milo/annotations.proto $ protoc --python_out=. *.proto # Update current commit hash in README. $ vi README.md