buscompose: the assigner may read the controller's lease, to choose where grants are read from (issue 774)

go/buscompose/buscompose_test.go

@@ -439,7 +439,7 @@ func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 			}
 		}
 		announced := map[string]announce.States{ControllerSeat: ControllerAnnouncement("novox")}
-		for reader, want := range map[string]bool{VaultSeat: true, GrantsModule: true, "mesh-delivery-view": false} {
+		for reader, want := range map[string]bool{VaultSeat: true, GrantsModule: true, AssignerModule: true, "mesh-delivery-view": false} {
 			granted, _ := ReadsAnnouncedBy(reader, []string{ControllerLease}, announced)
 			if (len(granted) == 1) != want {
 				t.Errorf("%s reads the lease: %v, want %v", reader, granted, want)

go/buscompose/userlist_switch.go

@@ -79,9 +79,13 @@ const VaultBusAccounts = "mesh-vault.bus-accounts"
 
 // NamedReaders are the states only the modules named may read, by `<owner>.<name>`: the grants part's wanted accounts
 // are read by the vault alone (novox/hq ADR 0561 §2).
-// The controller's lease is read by the two parts that turn on at its write (ADR 0561 §3, §6).
+// The controller's lease is read by the two parts that turn on at its write (ADR 0561 §3, §6) and by the assigner, which
+// reads the grants from the grants part from then on (ADR 0547 §4, §5; delivery.GrantSource).
 var NamedReaders = map[string][]string{VaultBusAccounts: {GrantsModule}, GrantsAccounts: {VaultSeat},
-	ControllerLease: {VaultSeat, GrantsModule}}
+	ControllerLease: {VaultSeat, GrantsModule, AssignerModule}}
+
+// AssignerModule is the assigner, which reads the lease to choose the source of the grants.
+const AssignerModule = "mesh-delivery-assigner"
 
 // ReaderMay says whether module may read the state read (`<owner>.<name>`) by the named readers: always, for a state
 // that names none.