The sandbox fails a node whose change refuses a module the node-engine did not hold, in that module's words, instead of passing it with the rest composed (issue 774, review of the sandbox input)

internal/compose/frombus/frombus.go

@@ -604,7 +604,21 @@ func ComposeSent(in compose.Input, node string) (map[string]delivery.Composed, b
 		held = map[string]string{}
 	}
 	out, _, _, err := composeEach(in, node, c.Builds, false, c.Running, held, nil)
-	return out, true, err
+	if err != nil {
+		return nil, true, err
+	}
+	// A module the sandbox held that the node-engine did not is the change refusing it: the node does not compose, said
+	// in that module's words, never passed with the rest composed (issue 774, review of the sandbox input).
+	var refused []string
+	for _, m := range sortedKeys(held) {
+		if _, was := c.Held[m]; !was {
+			refused = append(refused, m+": "+held[m])
+		}
+	}
+	if len(refused) > 0 {
+		return nil, true, fmt.Errorf("on %s the change refuses %s", node, strings.Join(refused, "; "))
+	}
+	return out, true, nil
 }
 
 // Plans is the provisioning plan of each module handed to the provisioner on the scope's node, composed from the bus

internal/composer/composer_test.go

@@ -143,6 +143,30 @@ func TestARequestItCannotRunIsRefused(t *testing.T) {
 		if m := sent.Cases[0].Machines["a"]; !m.Composes || m.Reason != "" {
 			t.Errorf("the input that says how the node composes, its bus folded: %+v", m)
 		}
+		// A module the change refuses beside the folded one fails the node in its words, never passed with the rest
+		// composed (review of the sandbox input); held already where the node-engine composed, it stays held as there.
+		app, err := catalogue.Decode([]byte(`{"module": "app", "version": "1", ` +
+			`"resources": [{"id": "env", "type": "file", "path": "/var/lib/app/env", "mode": "0600", "content": "N=${secret:repository}\n"}]}`))
+		if err != nil {
+			t.Fatal(err)
+		}
+		in.Catalogue["app"] = app
+		in.Nodes[0].Assigned = []string{"bus", "app"}
+		refused, err := Run(request(in))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if m := refused.Cases[0].Machines["a"]; m.Composes || !strings.Contains(m.Reason, "app: ") || !strings.Contains(m.Reason, "repository") {
+			t.Errorf("a module the change refuses on a node composed as its node-engine does: %+v", m)
+		}
+		in.ComposedHow.Held = map[string]string{"app": "held on the node"}
+		held, err := Run(request(in))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if m := held.Cases[0].Machines["a"]; !m.Composes {
+			t.Errorf("a module the node-engine holds too: %+v", m)
+		}
 	})
 	v, err := Run(Request{V: Version, Cases: []Case{{Name: "only-read", Manifests: map[string]Manifest{"demo": {Raw: json.RawMessage(demo)}}}}})
 	if err != nil || len(v.Cases) != 1 || !v.Cases[0].Manifests["demo"].Accepted || v.Cases[0].Machines != nil || v.SDK == "" {