Read this node's placement from its node and module keys, or its placement.<node> before the holder converts it, so a write of the holder's is composed only once its node key lands (issue 774, research 072 row 37)

internal/selfcompose/selfcompose_test.go

@@ -550,7 +550,50 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 	// secrets. A key written again with what it held, or a want whose words moved and not its build, makes none.
 	worded, _ := delivery.EncodeWant(delivery.Want{FP: fp, Self: true, Words: "lemurs is held at aaaaaaaaaaaa"})
 	elsewhere, _ := delivery.EncodeWant(delivery.Want{FP: delivery.SourcePrefix2 + strings.Repeat("e", 64), Self: true})
-	for _, row := range []struct {
+	// Research 072 row 37: the placement converted to one key per module and node moves nothing composed; a write in
+	// keys makes its pass at its node key, the commit, and not at a module key written before it nor at the mirror.
+	placeBase := delivery.Placement{Node: "n1", Decided: delivery.NodeDecided{Hub: true, Address: "10.77.0.1"},
+		Modules: []delivery.PlacedModule{{Module: "lemurs"}, {Module: "oldie"}}}
+	placeKeys := delivery.NewPlacementKeys()
+	keyRows := func(after delivery.Placement, what string) []struct {
+		name, bucket, key string
+		value             []byte
+		pass              bool
+	} {
+		writes, err := placeKeys.Writes("n1", &after)
+		if err != nil {
+			t.Fatal(err)
+		}
+		var rows []struct {
+			name, bucket, key string
+			value             []byte
+			pass              bool
+		}
+		for i, w := range writes {
+			_, _ = placeKeys.Put(w.Key, w.Value, uint64(i+1), w.Value == nil)
+			rows = append(rows, struct {
+				name, bucket, key string
+				value             []byte
+				pass              bool
+			}{what + ": " + w.Key, delivery.PlacementBucket, w.Key, w.Value, w.Commit && what != "converted"})
+		}
+		return rows
+	}
+	_, _ = placeKeys.Put("placement.n1", place, 1, false)
+	lemursMoved := placeBase
+	lemursMoved.Modules = []delivery.PlacedModule{{Module: "lemurs", Values: map[string]any{"greeting": "hoi"}}, {Module: "oldie"}}
+	var placementRows []struct {
+		name, bucket, key string
+		value             []byte
+		pass              bool
+	}
+	for _, step := range []struct {
+		what string
+		p    delivery.Placement
+	}{{"converted", placeBase}, {"lemurs moved", lemursMoved}, {"lemurs back", placeBase}} {
+		placementRows = append(placementRows, keyRows(step.p, step.what)...)
+	}
+	for _, row := range append([]struct {
 		name, bucket, key string
 		value             []byte
 		pass              bool
@@ -562,7 +605,7 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 		{"lemurs's module again", delivery.ModulesBucket, "lemurs", mod, false},
 		{"lemurs's want at another build", delivery.AssignerWantsBucket, "want.n1.lemurs", elsewhere, true},
 		{"lemurs's want back at its build", delivery.AssignerWantsBucket, "want.n1.lemurs", want, true},
-	} {
+	}, placementRows...) {
 		before := passes()
 		b.put(t, row.bucket, row.key, row.value)
 		if !row.pass {
@@ -690,7 +733,17 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 	both, _ := delivery.EncodePlacement(delivery.Placement{Node: "n1", Decided: delivery.NodeDecided{Hub: true, Address: "10.77.0.1"},
 		Modules: []delivery.PlacedModule{{Module: "lemurs"}, {Module: "oldie"}, {Module: "keeper"}}})
 	b.put(t, delivery.ModulesBucket, "keeper", kmod)
-	b.put(t, delivery.PlacementBucket, "placement.n1", both)
+	// n1 is held in keys per module and node since the rows above, which a legacy key no longer moves.
+	bothPlaced, _ := delivery.DecodePlacement(both)
+	bothWrites, err := placeKeys.Writes("n1", &bothPlaced)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, w := range bothWrites {
+		if w.Value != nil {
+			b.put(t, delivery.PlacementBucket, w.Key, w.Value)
+		}
+	}
 	b.put(t, delivery.AssignerWantsBucket, "want.n1.keeper", want)
 	keeperKey, _ := delivery.ComposedKey("n1", "keeper", fp)
 	var handed string
@@ -1227,7 +1280,7 @@ func TestTheNodeComposesItsWantsFromTheBus(t *testing.T) {
 	}{
 		"switched: placed after two failures":                {answers: []error{fmt.Errorf("nats: timeout"), fmt.Errorf("nats: timeout")}, value: []byte(`{}`), placed: true, tries: 3, switched: true},
 		"never switched: a timeout is not placed, said once": {answers: []error{fmt.Errorf("nats: timeout")}, placed: false, tries: 1},
-		"no key":                 {placed: false, tries: 1},
+		"no key":                 {placed: false, tries: 2}, // its node key, then its legacy key (research 072 row 37)
 		"no placement state yet": {answers: []error{fmt.Errorf("the bucket %s: %w", delivery.PlacementBucket, nats.ErrBucketNotFound)}, placed: false, tries: 1, quiet: true},
 		"switched: failing until the link ends": {answers: []error{fmt.Errorf("jetstream not ready"), fmt.Errorf("jetstream not ready"),
 			fmt.Errorf("jetstream not ready")}, end: true, tries: 3, switched: true},