A repeat assignment says nothing changed (ADR 0115)

One assignment of a module per node is now the rule, not a limitation —
the operator dropped the multi-assignment requirement, and the schema's
(node, module) key has been the decision since migration 0005. What
changed: Assign reports whether the assignment was new, and the command
says 'already runs — one node runs one of each (ADR 0115); nothing
changed' instead of printing 'is assigned' for a no-op, which read as
an action that happened. Idempotence stays: a repeat is exit 0, because
a script stating what is already true is not wrong.

cmd/mesh-controller/acts.go

@@ -46,9 +46,16 @@ func assign(ctx context.Context, open *stores, node, module string) (string, err
 		return "", err
 	}
 	defer release()
-	if err := open.inventory.Assign(ctx, node, module); err != nil {
+	fresh, err := open.inventory.Assign(ctx, node, module)
+	if err != nil {
 		return "", err
 	}
+	if !fresh {
+		// Nothing changed, and saying "is assigned" would read as an action. One node runs one
+		// of each — the module's name is the assignment's identity (novox/hq ADR 0115).
+		return fmt.Sprintf("%s already runs %s — one node runs one of each (ADR 0115); nothing changed",
+			node, module), nil
+	}
 	said := fmt.Sprintf("%s is assigned %s", node, module)
 	plan, _, err := planFor(ctx, open, node)
 	if err != nil {

cmd/mesh-controller/adoption.go

@@ -355,7 +355,7 @@ func converge(ctx context.Context, open *stores, node string, yes bool, digest s
 			strings.Join(assigned, ", "))
 	}
 	if !slices.Contains(assigned, filter) {
-		if err := inv.Assign(ctx, node, filter); err != nil {
+		if _, err := inv.Assign(ctx, node, filter); err != nil {
 			return "", err
 		}
 		if _, _, err := planFor(ctx, open, node); err != nil {

cmd/mesh-controller/mesh_for_test.go

@@ -73,7 +73,7 @@ func aMesh(t *testing.T) *stores {
 		if err := open.inventory.RecordOverlayKey(t.Context(), record.ID, aPublicKey(t)); err != nil {
 			t.Fatal(err)
 		}
-		if err := open.inventory.Assign(t.Context(), name, overlay.Name); err != nil {
+		if _, err := open.inventory.Assign(t.Context(), name, overlay.Name); err != nil {
 			t.Fatal(err)
 		}
 	}