Rotate a credential and move both ends together

The invariant novox/hq ADR 0001 records as unowned, and it was measurably
false in HAL: a provision documented as never rotating minted a new password on
every adoption and updated only the provider's row. Consumers on three nodes
held dead credentials for two days while the mesh reported success. Nothing
enumerated who held the old one.

Three things make that impossible here. The holders are a set the mesh can name
— each pair has its own credential, so rotating one consumer touches one role
and the affected list is a query rather than an assumption. Both ends are
pushed by this command rather than a later one, because leaving the sending to
whoever remembered is the fault exactly. And it is all-or-nothing: if any
affected machine cannot be resolved, nothing is sent and the old credential
keeps working, which is a mesh that has not rotated rather than one that has
half-rotated.

The window is stated rather than hidden: a role's password changes on the
provider and the file changes on the consumer, and they cannot be simultaneous.

The provisioner now takes its superuser password from the file the mesh wrote,
which is how the mesh delivers one. Passing it through the environment needed a
person in the middle of the one path that exists so there is not one — and put
a superuser password where `docker inspect` prints it.

Makefile

@@ -42,6 +42,17 @@ builder-image:
 	@echo
 	@docker image inspect $(BUILDER_IMAGE) --format 'built {{.RepoTags}}  {{.Size}} bytes'
 
+# The provisioner ships as an image too, because it is the thing that makes a sealed credential
+# true on a machine -- and the mesh cannot, having discarded the plaintext.
+PROVISIONER_IMAGE ?= mesh-provision-postgres:$(VERSION)
+PROVISIONER_DEV_TAG ?= mesh-provision-postgres:development
+
+provisioner-image:
+	docker build -f examples/postgres-provisioner/Dockerfile \
+		-t $(PROVISIONER_IMAGE) -t $(PROVISIONER_DEV_TAG) .
+	@echo
+	@docker image inspect $(PROVISIONER_IMAGE) --format 'built {{.RepoTags}}  {{.Size}} bytes'
+
 # The whole gate. Raises a database, runs everything against it, and takes it down again --
 # including when the tests fail, which is why the teardown is not conditional.
 check: fmt vet postgres