A deleting head's answer compares the controller's compositions with what runs, and is refused only without returning; fold the shadow's tests into TestInput (issue 1126, review of the shadow, round 1)

go/compose/frombus/answer_rows_test.go

@@ -17,7 +17,7 @@ import (
 // Issue 1126 (the seed's shadow, round 2): a node's answer names every module it cannot compose, not the first only;
 // and a module folded into its own composition that names a build of the old form (de-spiegel on novox, nats, photos,
 // systemd-resolved: their haves name a build-... id and no fingerprint) is left to the node, carried as it runs.
-func TestTheAnswerNamesEveryRefusalAndLeavesAnOldBuildToTheNode(t *testing.T) {
+func answerNamesEveryRefusalAndLeavesAnOldBuildToTheNode(t *testing.T) {
 	ctx := context.Background()
 	image := "alpine@sha256:" + strings.Repeat("a", 64)
 	manifest := func(module string) []byte {
@@ -138,7 +138,7 @@ func TestTheAnswerNamesEveryRefusalAndLeavesAnOldBuildToTheNode(t *testing.T) {
 
 // A node that reaches no artifact store says what its composition holds of one (issue 1126: ace and g14 answered
 // "reaches no artifact store", and nothing said why).
-func TestNoStoreReachedSaysWhy(t *testing.T) {
+func noStoreReachedSaysWhy(t *testing.T) {
 	in := compose.Input{Catalogue: map[string]catalogue.Manifest{
 		"distribution": {Module: "distribution", Serves: map[string]map[string]any{catalogue.ArtifactStoreProvision: {"port": 5000}}}},
 		Nodes: []compose.Node{{Name: "g14", Assigned: []string{"adwaita"}}, {Name: "novox", Assigned: []string{"distribution"}}}}

go/compose/frombus/frombus_test.go

@@ -119,6 +119,10 @@ func publicKey(t *testing.T) string {
 // controller's store fills for compose's own two-machine mesh (compose's aMesh: anchor the hub, laptop), and that Input
 // composes; a node reads only its own config values; what cannot be composed is refused, naming it.
 func TestInput(t *testing.T) {
+	// Issue 1126, the seed's shadow: every refusal named, an old-form module left to the node, and no store reached
+	// saying why (answer_rows_test.go).
+	t.Run("every refusal, and an old build left to the node", answerNamesEveryRefusalAndLeavesAnOldBuildToTheNode)
+	t.Run("no store reached says why", noStoreReachedSaysWhy)
 	ctx := context.Background()
 	xterm, err := os.ReadFile("../../catalogue/testdata/catalogue-835bf22b-xterm.module.json")
 	if err != nil {

go/delivery/placement_candidate.go

@@ -134,8 +134,9 @@ type CandidateAnswer struct {
 	Refused string `json:"refused,omitempty"`
 	// Returns is, for a head that deletes the node's placement file, what the node does then: it returns to the
 	// controller's compositions (ReturnsToController), as a node the catalogue does not place composes none of its own
-	// (issue 1126: the seed's revert). The verdict is then same, and nothing else is named: the node composes nothing
+	// (issue 1126: the seed's revert). Same, Differs, Added and Removed then compare the controller's compositions at
-	// with the candidate, and judges nothing of what the controller composes.
+	// the node's wants with what it runs, and the verdict is theirs; a want the controller holds no composition for is
+	// refused (Refused, without Returns).
 	Returns string `json:"returns,omitempty"`
 }
 
@@ -195,8 +196,9 @@ func (a CandidateAnswer) check() error {
 	if a.Refused != "" && len(a.Same)+len(a.Differs)+len(a.Added)+len(a.Removed)+len(a.Refusals) > 0 {
 		return fmt.Errorf("delivery: a candidate the node could not compose names modules")
 	}
-	if a.Returns != "" && (a.Refused != "" || len(a.Same)+len(a.Differs)+len(a.Added)+len(a.Removed)+len(a.Refusals) > 0) {
+	if a.Returns != "" && (a.Refused != "" || len(a.Refusals) > 0) {
-		return fmt.Errorf("delivery: a candidate the node returns to the controller's compositions on names what it composed")
+		return fmt.Errorf("delivery: a candidate the node returns to the controller's compositions on is compared, never refused: " +
+			"a composition the controller holds none of is refused without returning")
 	}
 	for _, d := range a.Differs {
 		if d.Module == "" || d.Why == "" {

go/delivery/placement_test.go

@@ -231,7 +231,9 @@ func TestPlacement(t *testing.T) {
 			"a value": {Head: "h1", Verdict: CandidateRefused, Same: []string{"node"}, Refusals: []ModuleRefused{{Module: "db", Why: "stands in for db/password"}}},
 			// A head that deletes the node's placement file: the node returns to the controller's compositions (issue 1126,
 			// the seed's revert, mesh-catalog #526).
-			"returns": {Head: "h1", Verdict: CandidateSame, Returns: ReturnsToController},
+			"returns": {Head: "h1", Verdict: CandidateSame, Returns: ReturnsToController, Same: []string{"app", "node"}},
+			"returns, the controller's differs": {Head: "h1", Verdict: CandidateDiffers, Returns: ReturnsToController, Same: []string{"node"},
+				Differs: []ModuleDiffers{{Module: "app", Resource: "file:/etc/app", Why: "the resource differs"}}, Removed: []string{"old"}},
 		}
 		n := HaveNode{Composed: "sha256:" + strings.Repeat("a", 64), Sealed: []string{"box"}, Candidates: answers,
 			Composes: ComposesOwn, ComposesWhy: "the catalogue places it (placement.n1)"}
@@ -297,7 +299,7 @@ func TestPlacement(t *testing.T) {
 			"same with an added":  {Head: "h", Verdict: CandidateSame, Added: []ModuleAdded{{Module: "a"}}},
 			"differs refusing":    {Head: "h", Verdict: CandidateDiffers, Removed: []string{"a"}, Refusals: []ModuleRefused{{Module: "b", Why: "x"}}},
 			"refused and modules": {Head: "h", Verdict: CandidateRefused, Refused: "x", Same: []string{"a"}},
-			"returns and removes": {Head: "h", Verdict: CandidateDiffers, Returns: ReturnsToController, Removed: []string{"a"}},
+			"returns refusing":    {Head: "h", Verdict: CandidateRefused, Returns: ReturnsToController, Refusals: []ModuleRefused{{Module: "b", Why: "x"}}},
 			"returns refused":     {Head: "h", Verdict: CandidateRefused, Returns: ReturnsToController, Refused: "x"},
 		} {
 			if _, err := EncodeHaveNode(HaveNode{Candidates: map[string]CandidateAnswer{"g": a}}); err == nil {