1. Phorge at 0873b36569bfcf502a092870d7d5f4d088ed9003
2. Create some custom action class in the Herald codebase
3. Set up a Herald Rule in Maniphest applying this new custom action
4. Remove your custom class again so your Herald rule will have problems

Expected results:

Some way for a Phorge admin to notice that there is an issue to be fixed with a Herald rule, e.g. via an entry in the server log or in DarkConsole.

Actual results:

Issue can only be realized by having the idea to go through Herald transcripts from time to time:

Other comments:

• This is a corner case but I'd say an additional phlog() won't hurt anyone.
• See also T15869: Herald rule referring to a disabled rule silently fails, T15885: Herald rule referring to an invalid key silently fails.