diff --git a/modules/mesh-delivery-builder/internal/versions/names.go b/modules/mesh-delivery-builder/internal/versions/names.go
index 65b57eff..17eea4d4 100644
--- a/modules/mesh-delivery-builder/internal/versions/names.go
+++ b/modules/mesh-delivery-builder/internal/versions/names.go
@@ -2,18 +2,10 @@ package versions
 
 import (
 	"context"
-	"encoding/json"
 	"sort"
-	"strings"
-)
 
-// seriesName is what the builder reads of a series key of the indexer's packages state (delivery.PackagesState): the
-// package's name in its ecosystem and the `<module>/<artifact>` it is built from. The value's type is the indexer's own
-// (its SeriesPackage, fields `name` and `package`); the fields are read here by their names, not by its type.
-type seriesName struct {
-	Name    string `json:"name"`
-	Package string `json:"package"`
-}
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
 
 // PackagesState is the indexer's packages state as the builder reads it (its manifest's reads grant): its keys, and one
 // key's value (found false when it holds none).
@@ -34,15 +26,18 @@ func NamesIn(s PackagesState) PackageNames {
 		sort.Strings(keys)
 		built := NameOf(module, artifact)
 		for _, key := range keys {
-			if !strings.Contains(key, ".") {
+			if !delivery.IsSeriesPackageKey(key) {
 				continue
 			}
 			value, found, err := s.Get(ctx, key)
 			if err != nil {
 				return "", false, err
 			}
-			var v seriesName
-			if !found || json.Unmarshal(value, &v) != nil || v.Package != built || v.Name == "" {
+			if !found {
+				continue
+			}
+			v, err := delivery.DecodeSeriesPackage(value) // the indexer's value of a series key (mesh-sdk's contract, J4)
+			if err != nil || v.Package != built {
 				continue
 			}
 			return v.Name, true, nil
diff --git a/modules/mesh-delivery-indexer/internal/index/package_users.go b/modules/mesh-delivery-indexer/internal/index/package_users.go
index 04adff0c..5f2d2faf 100644
--- a/modules/mesh-delivery-indexer/internal/index/package_users.go
+++ b/modules/mesh-delivery-indexer/internal/index/package_users.go
@@ -1,7 +1,6 @@
 package index
 
 import (
-	"encoding/json"
 	"fmt"
 	"maps"
 	"slices"
@@ -63,8 +62,8 @@ func PackageUsersOf(modules, manifests, packages views.Source, only string) ([]P
 		if !ok {
 			continue
 		}
-		var s SeriesPackage
-		if err := json.Unmarshal(e.Value, &s); err != nil {
+		s, err := delivery.DecodeSeriesPackage(e.Value)
+		if err != nil {
 			return nil, fmt.Errorf("packages.%s holds what is not a series: %w", key, err)
 		}
 		p := get(s.Name)
diff --git a/modules/mesh-delivery-indexer/internal/index/series.go b/modules/mesh-delivery-indexer/internal/index/series.go
index 4daaf744..b18dca58 100644
--- a/modules/mesh-delivery-indexer/internal/index/series.go
+++ b/modules/mesh-delivery-indexer/internal/index/series.go
@@ -9,7 +9,6 @@ import (
 	"path"
 	"slices"
 	"strings"
-	"time"
 
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
 	"git.novox.be/novox/mesh-sdk/go/delivery"
@@ -24,44 +23,19 @@ import (
 // A series key always holds a dot (`mesh-sdk/go.0.1`), which EscapeName never leaves in a per-module key: a reader tells the
 // two forms apart by IsSeriesKey.
 
-// SeriesPackage is the value of a series key.
-type SeriesPackage struct {
-	V int `json:"v"`
-	// Name is the package's name in its own ecosystem (design 32, the lead's design limit of 2026-11-04): a Go package's
-	// module path in its go.mod at the commit, an npm package's package.json name. The series key is named by it, and a
-	// user's `packages` names it. Package is the module and artifact it is built from, `<module>/<artifact>`, by which
-	// the builder finds the name to number under; Series its `<major>.<minor>`.
-	Name    string `json:"name"`
-	Package string `json:"package,omitempty"`
-	Series  string `json:"series"`
-	// Seat is the registry seat it is published through; GoModule the Go module path a Go package is fetched under (from
-	// go-package-registry's published), empty for any other.
-	Seat     string `json:"seat,omitempty"`
-	GoModule string `json:"go-module,omitempty"`
-	// Newest is the newest version of the series a seat published: what a user accepting the series builds against.
-	Newest *SeriesVersion `json:"newest,omitempty"`
-	// Numbered is the newest version of the series the builder numbered, published or not yet.
-	Numbered *SeriesVersion `json:"numbered,omitempty"`
-	At       time.Time      `json:"at"`
-}
+// SeriesPackage is the value of a series key, and SeriesVersion one version of a series: mesh-sdk's
+// delivery.SeriesPackage and SeriesVersion (J4), the contract every reader of the state decodes with
+// delivery.DecodeSeriesPackage.
+type (
+	SeriesPackage = delivery.SeriesPackage
+	SeriesVersion = delivery.SeriesVersion
+)
 
-// SeriesVersion is one version of a series: its number, the source commit it was built from, the digest and fingerprint.
-type SeriesVersion struct {
-	Version     string `json:"version"`
-	Commit      string `json:"commit,omitempty"`
-	Digest      string `json:"digest,omitempty"`
-	Fingerprint string `json:"fingerprint,omitempty"`
-	// Contents are, for a series' newest of a Go package, its Go module's requirements' and packages' digests read from the
-	// forge's listing at Commit (DLV-I6): what a user accepting the series is fingerprinted against. Nil when the forge
-	// could not list it (said), and on a numbered version.
-	Contents *delivery.PublishedPackages `json:"contents,omitempty"`
-}
+// SeriesKey is the key of a package's series in the packages state (delivery.SeriesPackageKey).
+func SeriesKey(pkg, series string) string { return delivery.SeriesPackageKey(pkg, series) }
 
-// SeriesKey is the key of a package's series in the packages state.
-func SeriesKey(pkg, series string) string { return delivery.EscapeName(pkg) + "." + series }
-
-// IsSeriesKey says whether a key of the packages state is a series key, not a per-module one.
-func IsSeriesKey(key string) bool { return strings.Contains(key, ".") }
+// IsSeriesKey says whether a key of the packages state is a series key, not a per-module one (delivery.IsSeriesPackageKey).
+func IsSeriesKey(key string) bool { return delivery.IsSeriesPackageKey(key) }
 
 // SeriesOf is the series of a trunk version (`0.1.15` is of `0.1`); false for a version that is no `<major>.<minor>.<patch>`
 // or that carries a tag (a pre-release).
@@ -102,6 +76,9 @@ func (ix *Indexer) HearVersion(ctx context.Context, h HeardVersion) (bool, error
 		case !ok:
 			ix.logf("%s %s: the forge's listing at %s holds no Go module %s, so its users keep the commit form", h.Package, h.Version, h.Commit, h.GoModule)
 		default:
+			// When the contents were read: delivery.SeriesVersion.Contents is a PublishedPackages, which names its time
+			// (DecodeSeriesPackage refuses one with none).
+			p.At = ix.now().UTC()
 			v.Contents = &p
 		}
 	}
@@ -162,8 +139,8 @@ func (ix *Indexer) SeriesAll(ctx context.Context) map[string]SeriesPackage {
 		if err != nil || !found {
 			continue
 		}
-		var s SeriesPackage
-		if err := json.Unmarshal(value, &s); err != nil {
+		s, err := delivery.DecodeSeriesPackage(value)
+		if err != nil {
 			ix.logf("packages.%s holds what is not a series, left out: %v", key, err)
 			continue
 		}