Apply Herald subscription effects immediately
Fixes T8464. We could incorrectly use a cached value when computing CC's.
Just load a fresh value. There are no other callers that would benefit from this cache, so it's more complicated to reload it correctly prior to publishing than to just skip it.
Also make the PHID headers unique.
- Verified that users received mail about the transactions which caused them to be added to an object.
- Veirfied that headers no longer have redundant values.
Reviewed By: btrahan
Maniphest Tasks: T8464
Differential Revision: https://secure.phabricator.com/D13206