Keep the builds of the grants step's machine alone, not of every machine its composition resolves (repo-check of #230)

Composing the bus's machine resolves the others on the same context, and
a machine never recorded as sent refused the whole composition.

cmd/mesh-controller/grants_step_store_test.go

@@ -105,7 +105,10 @@ func TestTheGrantsStepSendsTheUserListAndNothingElse(t *testing.T) {
 			t.Fatal(err)
 		}
 	}
-	kept := keepingEveryBuild(keepingRecorded(ctx))
+	// Kept for anchor alone. laptop is never recorded as sent, on purpose: composing anchor resolves laptop
+	// too (who is on the private network), and a step that kept every machine's builds refused anchor's
+	// composition for want of laptop's last send (repo-check of #230 at 0f853e93).
+	kept := keepingEveryBuild(keepingRecorded(ctx), "anchor")
 
 	// What anchor was last sent: everything at the builds of before the merge, as an ordinary send sends it.
 	_, before := compose(keepingRecorded(ctx))