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/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 {