Properly merge envelopes with parent flows and the like.
Properly merge envelopes with parent flows and the like.

Child envelopes should just not conflict with parent envelopes.  This
should be checked automatically later.

Also add an assert in case we ever find a False invariant.  I don't
think it's necessarily wrong but for these tests it certainly is wrong.

JoeOsborn/hyped,JoeOsborn/hyped