Got the morning ERRORLOG email courtesy of EN. And I got several hundred messages from ERRORLOG. During a patch, the Agent XPs were disabled but not reenabled. So the Agent service was up, but didn't do anything.
Ironically enough, it wasn't just the ERRORLOGs that saved me - it was SQL Sentry, which hit (and failed) the XPs once a minute. Which, yay, caused an ERRORLOG message, but didn't actually TELL me it wasn't working. (I've submitted a bug fix for that).
Just another of those "my god, how do I live without this" posts.
ALL my EN code is in this share:
Additionally, my Gists (source code of the code I use in production) are at: