Keep the files of every composition a want still names, not only each key's newest (issue 1945; the review's C1)

A node applies exactly the composition its want names (ADR 0539 clause 1), which may be a revision a newer one
replaced: its files over 64 KiB stay until no want names it.

cmd/mesh-controller/declaration_sweep.go

@@ -116,8 +116,10 @@ func namedByCompositions(node string, values [][]byte) (map[string]bool, error)
 	return named, nil
 }
 
-// keptCompositionsOf are the values of every composition in a node's bucket `composed-<node>`: what the controller keeps there
-// are each module's five newest fingerprints and the node's own (ADR 0539 §4). A node with no bucket has none.
+// keptCompositionsOf are the values of every composition in a node's bucket `composed-<node>` a node may still apply:
+// each key's newest revision (each module's five newest fingerprints and the node's own, ADR 0539 §4), and any older
+// revision of it whose digest a want of the node names, since the node applies exactly the composition its want names
+// (clause 1) and a want may still name a revision a newer one replaced (the review's C1). A node with no bucket has none.
 func keptCompositionsOf(ctx context.Context, js jetstream.JetStream, node string) ([][]byte, error) {
 	bucket, err := sdkdelivery.ComposedBucketFor(node)
 	if err != nil {
@@ -137,16 +139,76 @@ func keptCompositionsOf(ctx context.Context, js jetstream.JetStream, node string
 	if err != nil {
 		return nil, fmt.Errorf("the compositions of %s: %w", node, err)
 	}
+	wanted, err := digestsWantedOn(ctx, js, node)
+	if err != nil {
+		return nil, err
+	}
 	var out [][]byte
 	for _, key := range keys {
-		e, err := kv.Get(ctx, key)
+		history, err := kv.History(ctx, key)
 		if errors.Is(err, jetstream.ErrKeyNotFound) {
 			continue
 		}
 		if err != nil {
 			return nil, fmt.Errorf("the composition %s: %w", key, err)
 		}
-		out = append(out, e.Value())
+		out = append(out, keptRevisions(history, wanted)...)
+	}
+	return out, nil
+}
+
+// keptRevisions are, of one key's history oldest first, the newest value when the key is not deleted, and every older
+// value whose composition's digest is wanted.
+func keptRevisions(history []jetstream.KeyValueEntry, wanted map[string]bool) [][]byte {
+	var out [][]byte
+	for i, e := range history {
+		if e.Operation() != jetstream.KeyValuePut {
+			continue
+		}
+		if i == len(history)-1 {
+			out = append(out, e.Value())
+			continue
+		}
+		c, err := sdkdelivery.DecodeComposed(e.Value())
+		if err != nil {
+			continue
+		}
+		if d, err := sdkdelivery.ComposedDigestOf(c); err == nil && wanted[d] {
+			out = append(out, e.Value())
+		}
+	}
+	return out
+}
+
+// digestsWantedOn is the digest of every composition a want of the node names, its own want's among them; none when
+// the assigner's bucket is not there yet.
+func digestsWantedOn(ctx context.Context, js jetstream.JetStream, node string) (map[string]bool, error) {
+	kv, err := js.KeyValue(ctx, sdkdelivery.AssignerWantsBucket)
+	if errors.Is(err, jetstream.ErrBucketNotFound) {
+		return map[string]bool{}, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("the wants of %s: %w", node, err)
+	}
+	lister, err := kv.ListKeys(ctx, jetstream.MetaOnly())
+	if err != nil {
+		return nil, fmt.Errorf("the wants of %s: %w", node, err)
+	}
+	out := map[string]bool{}
+	for key := range lister.Keys() {
+		e, err := kv.Get(ctx, key)
+		if err != nil {
+			continue
+		}
+		if n, _, err := sdkdelivery.ParseWantKey(key); err == nil && n == node {
+			if w, err := sdkdelivery.DecodeWant(e.Value()); err == nil && w.Composed != "" {
+				out[w.Composed] = true
+			}
+		} else if n, err := sdkdelivery.ParseWantNodeKey(key); err == nil && n == node {
+			if w, err := sdkdelivery.DecodeNodeWant(e.Value()); err == nil {
+				out[w.Composed] = true
+			}
+		}
 	}
 	return out, nil
 }