Summary: Depends on D19064. Ref T13054. See that task for additional discussion. When buildables are created by `arc` and have lint/unit messages, they can currently pass or fail before Herald triggers actual builds. This puts them in a pre-build state where they can't complete until Herald says it's okay. On its own, this change intentionally strands `arc diff --only` diffs in the "PREPARING" stage forever. Test Plan: - Ran a build with `bin/harbormaster`, saw it build normally. - Ran a build with web UI, saw it build normally. - Ran a build with `arc diff`, saw it build normally. - Ran a build with `arc diff --only`, saw it hang in "PREPARING" forever. Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam Maniphest Tasks: T13054 Differential Revision: https://secure.phabricator.com/D19065