An assignment issues its bus credential, a push refuses one nobody issued, and what reads a secret restarts on it (hq issue 203)

`assign` recorded a module and `push` sealed a random own secret where its bus credential belongs;
the process crash-looped until a person ran `module issue` and pushed again, and the only warning was
one line in a list printed on every push. Now assigning a module that declares a broker secret issues
the credential in the same act — kept when one exists, so re-assigning rotates nothing — and when the
bus cannot be reached from here the assignment says which verb to run. A push never seals a
placeholder in a credential's place: a module whose bus user is unminted is refused by name, with the
verb. The control plane's own user is the installer's, seeded at genesis, which the test now says.

And what reads one of a module's own secrets is restarted when it changes — composed for a container
or daemon that names the secret's path in its volumes, environment or env-files, so a manifest need
not say it: the build machine ran on an hour-old credential because its manifest restarted it on its
environment file alone (issue 206). A scheduled or run-once process is left alone; it reads afresh.

cmd/mesh-controller/plan.go

@@ -533,6 +533,23 @@ func renderingFor(ctx context.Context, open *stores, node string,
 			var sealed string
 			var err error
 			if choosing == Allocating {
+				// **The broker credential is never invented here** (novox/hq issue 203). Every other
+				// own secret is the mesh's to make — a password nobody else knows — but this one
+				// is an account on the bus, minted by `module issue` and sealed by it; a push that
+				// made a random one would deliver a file the process cannot read and report the
+				// machine applied. Refused by name, with the verb.
+				if name == "broker" {
+					user := broker.Principal{Kind: broker.KindModule, Node: node, Module: m.Module}.Username()
+					if _, minted, err := inv.BusUserHash(ctx, user); err != nil {
+						return catalogue.Rendering{}, inventory.Node{}, err
+					} else if !minted {
+						return catalogue.Rendering{}, inventory.Node{}, fmt.Errorf(
+							"%s on %s has no bus credential: nothing was issued for %s, and a push "+
+								"would seal a placeholder its process cannot read (novox/hq issue 203). "+
+								"`module issue %s --node %s`, then push again",
+							m.Module, node, user, m.Module, node)
+					}
+				}
 				sealed, err = inv.SecretForModule(ctx, node, m.Module, name)
 			} else {
 				var held bool