Adopt genesis's bus through the bus's planned step, its streams snapshotted first (hq issue 590, ADR 0333 §3)

The broker step sent the nats module with a plain push, and the controller refuses a push that would
replace the bus: that is a planned step, bus upgrade, which snapshots the streams first and checks
them after (ADR 0236). Genesis stopped at step 18.

The step now snapshots every stream with the module's own snapshot program (no backup holder exists
yet to be asked), asks bus upgrade with that snapshot and why, says the one restart, and waits until
the bus runs the module's image, answers, and the controller ends the step done. The bundle's bus runs
the release the module's image is built on (2.11.17, by the same digest, where it ran 2.10.29), so the
step changes no server release and is said reversible.

internal/bootstrap/phase3_test.go

@@ -69,6 +69,7 @@ func aBusThatAdopts() (*asked, func(context.Context, string) (int, string, error
 func busStepWith(t *testing.T, o Options, runtime *asked,
 	fetch func(context.Context, string) (int, string, error)) ([]string, error) {
 	t.Helper()
+	aGenesisBusOnDisk(t)
 	rewritten, err := Rewrite(theRealBundle(t), held)
 	if err != nil {
 		t.Fatal(err)
@@ -222,7 +223,7 @@ func TestTheBrokerStepSaysTheRestartAndWaitsForTheBusToAnswer(t *testing.T) {
 	runtime.answer = func(name string, args []string) (string, error) {
 		joined := strings.Join(args, " ")
 		switch {
-		case strings.Contains(joined, "push anchor"):
+		case strings.Contains(joined, "bus upgrade --why"):
 			pushed = true
 		case strings.Contains(joined, "inspect --format {{.Config.Image}} mesh-broker-nats"):
 			if !pushed {
@@ -304,7 +305,7 @@ func TestARerunAfterTheAdoptionSaysTheBusIsTheModulesAlready(t *testing.T) {
 		t.Fatal(err)
 	}
 	text := strings.Join(said, "\n")
-	if strings.Contains(text, "restarting") || !strings.Contains(text, "already restarted mesh-broker-nats") {
+	if strings.Contains(text, "restarting") || !strings.Contains(text, "already adopted   mesh-broker-nats") {
 		t.Errorf("a re-run announced a restart, or did not say the bus is the module's already:\n%s", text)
 	}
 }
@@ -417,3 +418,30 @@ func TestTheBundlesBusFilesAreSeeds(t *testing.T) {
 		}
 	}
 }
+
+// aGenesisBusOnDisk puts what the adoption reads on the machine in a test's own directory: the bus's
+// certificate, the controller's bus credential, and where the snapshot goes. The step's wait is short.
+func aGenesisBusOnDisk(t *testing.T) {
+	t.Helper()
+	dir := t.TempDir()
+	cert := filepath.Join(dir, "tls.crt")
+	if err := os.WriteFile(cert, []byte(aCertificatePEM), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	secret := filepath.Join(dir, "bus-controller.secret")
+	if err := os.WriteFile(secret, []byte("BUS-PW"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	was := []string{busSnapshotFile, busSnapshotCredential, busCertificateFile, busControllerSecret}
+	wasWithin := busStepWithin
+	busSnapshotFile, busSnapshotCredential = filepath.Join(dir, "bus.tar"), filepath.Join(dir, "bus.credential")
+	busCertificateFile, busControllerSecret = cert, secret
+	busStepWithin = 50 * time.Millisecond
+	t.Cleanup(func() {
+		busSnapshotFile, busSnapshotCredential, busCertificateFile, busControllerSecret = was[0], was[1], was[2], was[3]
+		busStepWithin = wasWithin
+	})
+}
+
+// aCertificatePEM is a PEM block standing for the bus's certificate; its pin is the sha256 of these bytes.
+const aCertificatePEM = "-----BEGIN CERTIFICATE-----\nAAECAwQFBgcICQ==\n-----END CERTIFICATE-----\n"