I thought I was going mad, but I've reproduced this twice now.

When pushing, the Herald rule is working fine (the transcript all looks good), but a Buildable is never created.

When re-running Herald via reparse.php, a Buildable is created just fine and everything works as expected - the Herald transcript is identical.

Looking at the code, I have no clue what is going wonky here.

It seems ./bin/phd restart solves the problem for me.