Challenges raised by removed FIXMEs can never happen: there is no ordering of events that prevents modified peered from getting back to partner.
If the root receives an unsuccessful first phase commit message, instantly try to reschedule event.
Deadlock detection requires knowing which host a resource is on.  That
means I needed to push host_uuid through a lot of places in the code.
Added code to detect potential deadlocks during first phase commit variable locking.  It will be untested until finish writing code for endpoint calls.
For commit #abaf46d, forgot to update benchmark scripts.