`status` hung. It composes a declaration for every node to answer *is
this machine running what I would send it*, and composing one assigns
each module a machine port — so the question wrote to the database, and
wrote to the same rows as the machine it was asking about.
`port_assignment` is unique on (node, machine). Two transactions
inserting the same port do not race, they queue: the second waits on the
index until the first commits. A status polled every two seconds while a
node applies is two writers on those rows, and the poll stopped
returning rather than returning something wrong — which is the better
failure of the two, and still a failure.
The latent version of this was there before anything polled: two
compositions running at once could both allocate.
So allocation belongs to the send path alone. The mesh chooses a port
when it commits to sending one; every other caller reads what was
chosen. A module with nothing assigned has never been sent, which is
precisely what "waiting" means — the read needs no number to be right
about that, and inventing one would make the answer worse.
Named rather than passed as a bare bool: at three call sites, `true` and
`false` say nothing about which of these two things is meant.
Checked by the lab, which now polls status throughout an apply.
jschoubben
0d975a051d