diff --git a/cmd/mesh-controller/bus_runs_test.go b/cmd/mesh-controller/bus_runs_test.go
new file mode 100644
index 00000000..7c77c6ba
--- /dev/null
+++ b/cmd/mesh-controller/bus_runs_test.go
@@ -0,0 +1,29 @@
+package main
+
+import (
+	"context"
+	"testing"
+)
+
+// 1945 (dev-r6-controller's B8 follows it): what a bus machine runs is read from its have, not from a send kept, so a
+// machine whose have names the build the mesh holds is not moved by a bus upgrade, and one whose have names an older
+// build is.
+func TestABusMachineRunsWhatItsHaveNames(t *testing.T) {
+	was := busRuns
+	t.Cleanup(func() { busRuns = was })
+	busRuns = func(_ context.Context, node, _ string) (string, bool, error) {
+		return map[string]string{"novox": "src2:new", "ace": "src2:old"}[node], node != "g14", nil
+	}
+	b := busPending{module: "nats", to: "c-new", from: map[string]string{}, same: map[string]bool{}}
+	commitOf := map[string]string{"src2:new": "c-new", "src2:old": "c-old"}
+	for _, n := range []string{"novox", "ace", "g14"} {
+		fp, known, _ := busRuns(context.Background(), n, "nats")
+		if c, ok := commitOf[fp]; known && ok {
+			b.from[n] = c
+		}
+	}
+	if b.moves("novox") || !b.moves("ace") || !b.moves("g14") {
+		t.Errorf("novox moves %v (runs the new build), ace %v (an older one), g14 %v (says none)", b.moves("novox"),
+			b.moves("ace"), b.moves("g14"))
+	}
+}
diff --git a/cmd/mesh-controller/bus_step.go b/cmd/mesh-controller/bus_step.go
index d8026078..fa594e6c 100644
--- a/cmd/mesh-controller/bus_step.go
+++ b/cmd/mesh-controller/bus_step.go
@@ -113,20 +113,44 @@ func pendingBus(ctx context.Context, inv *inventory.Inventory) (busPending, erro
 			b.same[commit] = true
 		}
 	}
+	// What each machine runs is its have's fingerprint (novox/hq ADR 0539 clause 9), the commit of the build of it.
+	commitOf := map[string]string{}
+	for commit, src := range sources {
+		if src != "" {
+			commitOf[src] = commit
+		}
+	}
 	for _, n := range b.machines {
-		sent, known, err := inv.SentBuilds(ctx, n)
+		fp, known, err := busRuns(ctx, n, b.module)
 		if err != nil {
 			return b, err
 		}
-		if known {
-			if c, carried := sent[b.module]; carried {
-				b.from[n] = c
-			}
+		if c, ok := commitOf[fp]; known && ok {
+			b.from[n] = c
 		}
 	}
 	return b, nil
 }
 
+// busRuns is the fingerprint a machine's node-engine says it runs of a module, from its have; known is false when it
+// says none. A variable so a test reads it without a bus.
+var busRuns = func(ctx context.Context, node, module string) (string, bool, error) {
+	bus, err := aBus()
+	if err != nil {
+		return "", false, err
+	}
+	defer bus.Close()
+	js, err := jetstream.New(bus.Conn())
+	if err != nil {
+		return "", false, err
+	}
+	h, found, err := haveOn(ctx, js, node, module)
+	if err != nil || !found || h.FP == "" {
+		return "", false, err
+	}
+	return h.FP, true, nil
+}
+
 // busHeld names the machines a push may not send because sending them would replace the bus: the
 // planned step's, not a push's (ADR 0236). Said with the remedy.
 func busHeld(ctx context.Context, inv *inventory.Inventory, machines []string) (map[string]string, error) {