diff --git a/modules/mesh-delivery-builder/builds/builds.go b/modules/mesh-delivery-builder/builds/builds.go
new file mode 100644
index 00000000..04bd7751
--- /dev/null
+++ b/modules/mesh-delivery-builder/builds/builds.go
@@ -0,0 +1,372 @@
+// Package builds holds what the builder module owns and no seat carries (novox/hq ADR 0634 §1): the layout of its state
+// `builds` (a build per module and fingerprint) and the rules its writer keeps, the question a registry seat's holder asks
+// it before it stores a publish, its event version.numbered and the entries of its build log. Other modules import it from
+// the builder by its published version (ADR 0573 §1); the builder's manifest declares it as a package artifact.
+package builds
+
+import (
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"slices"
+	"strings"
+
+	"git.novox.be/novox/mesh-delivery/contracts/go/seats/containerimageregistry"
+	"git.novox.be/novox/mesh-delivery/contracts/go/seats/ociartifactregistry"
+	"git.novox.be/novox/mesh-delivery/sdk/buildstep"
+	"git.novox.be/novox/mesh-delivery/sdk/fingerprint"
+	"git.novox.be/novox/mesh-delivery/sdk/kept"
+	"git.novox.be/novox/mesh-delivery/sdk/reference"
+	"git.novox.be/novox/mesh-delivery/sdk/trunk"
+	"git.novox.be/novox/mesh-sdk/go/keys"
+)
+
+// seats are the names of the registry seats a reference names first, from their contracts.
+var seats = reference.Seats{Image: containerimageregistry.Seat, Object: ociartifactregistry.Seat}
+
+// askLanguages are the languages a build seat is named after (node-build-<language>), which a building key's Asks are keyed by.
+var askLanguages = []string{"go", "node", "image"}
+
+func checkAskLanguage(language string) error {
+	if !slices.Contains(askLanguages, language) {
+		return fmt.Errorf("builds: the ask language %q is not go, node or image", language)
+	}
+	return nil
+}
+
+// The builder's keys (novox/hq ADR 0429 clauses 5 and 16, ADR 0437 clause 5, ADR 0405 clauses 2 and 7, ADR 0453
+// clause 4): a build is `<module>.<fingerprint key part>` in the builder's bucket, one key per fingerprint, since equal
+// fingerprints are equal content and the same source is never built twice. They are written only by the builder part
+// from R4c and read by the checker, the assigner and the view. They are not the ended controller's build records
+// (buildrecord.go: BuildKey).
+//
+// **The rules its writer keeps.** A builder claims a fingerprint that has no build key by creating it queued or
+// building, a create that fails when the key exists, and moves it by compare-and-set; a builder reclaims only a build
+// whose `by` is offline in presence. A failed key is built again as a new revision of the same key (ADR 0429 clause
+// 18). Only the builder's credential writes the bucket (clause 5); every other part reads it.
+const (
+	// BuilderModule is the module of the builder part.
+	BuilderModule = "mesh-delivery-builder"
+	// BuilderBuildsBucket is the builder's bucket of builds: `<owner module>_<name>`.
+	BuilderBuildsBucket = BuilderModule + "_builds"
+	// BuilderBuildsHistory is the revisions the bucket keeps per key.
+	BuilderBuildsHistory = 5
+)
+
+// The states of a build.
+const (
+	BuildQueued   = "queued"
+	BuildBuilding = "building"
+	BuildDone     = "done"
+	BuildFailed   = "failed"
+)
+
+// BuilderBuildKey is the key, in BuilderBuildsBucket, of a module's build at a fingerprint: `<module>.<hex>`, the hex
+// being the fingerprint's key part (fingerprint.KeyPart), since a bus key may not hold ':'. A module holding a dot or a
+// character a key refuses, and a fingerprint not of the new form, are refused, naming them.
+func BuilderBuildKey(module, fp string) (string, error) {
+	if err := kept.CheckName("module", module); err != nil {
+		return "", err
+	}
+	part, err := fingerprint.KeyPart(fp)
+	if err != nil {
+		return "", err
+	}
+	return module + "." + part, nil
+}
+
+// ParseBuilderBuildKey is the inverse of BuilderBuildKey: the module and the fingerprint (`src2:` and the hex).
+func ParseBuilderBuildKey(key string) (module, fp string, err error) {
+	module, part, ok := strings.Cut(key, ".")
+	if !ok {
+		return "", "", fmt.Errorf("builds: %q is not a builder build key, <module>.<fingerprint hex>", key)
+	}
+	if err := kept.CheckName("module", module); err != nil {
+		return "", "", fmt.Errorf("builds: %q is not a builder build key: %w", key, err)
+	}
+	if fp, err = fingerprint.ParseKeyPart(part); err != nil {
+		return "", "", fmt.Errorf("builds: %q is not a builder build key: %w", key, err)
+	}
+	return module, fp, nil
+}
+
+// BuiltArtifact is one artifact of a done build: its name in the manifest, its kind, its content digest (`sha256:` and
+// 64 hex digits) and the reference that names where it is (novox/hq ADR 0498 clauses 1, 5 and 6; the lead's decision
+// L1 of R4e), by kind:
+//
+//	bundle, archive     artifact-store://<module>/<artifact>/blobs/<digest>  the blob pushed to the artifact store
+//	image, upstream     <registry>/<module>/<artifact>@<digest>              the image registry's reference, which
+//	                    artifact-store://<module>/<artifact>@<digest>        catalogue.Recorded keeps without its address
+//	package             <name>@<version>                                     the version published from the trunk
+//
+// From the registry milestone a done key names the reference its seat answered (novox/hq ADR 0605 §9, design 51 *The
+// done key names the reference the seat answered*): `<seat>/<module>/<artifact>@<digest>`, <seat> the registry seat it
+// came through (oci-artifact-registry for a bundle or an archive, container-image-registry for an image or an upstream
+// copy), and `<name>@<version>` for a package as before. A key written in the older form keeps it; this reads both, and
+// no build is built again for its form (seats.InArtifactStore reads both the same way).
+//
+// <artifact> is Name and <digest> is Digest. A reference is empty for a candidate's image or package, which is never
+// pushed or published (ADR 0498 clause 6), and in a key done before R4e; the controller delivers only from a key whose
+// every artifact names one (Referenced, clause 8). A kind left empty (a key written before kinds) is not checked.
+type BuiltArtifact struct {
+	Name      string `json:"name"`
+	Kind      string `json:"kind,omitempty"`
+	Digest    string `json:"digest"`
+	Reference string `json:"reference,omitempty"`
+	// References are every form this artifact is named in, Reference among them (novox/hq ADR 0618, ADR 0624): a build
+	// keeps each form that a counted node-engine states, away nodes included, and Reference stays the form every one
+	// of them reads. A reader that does not know the field reads Reference alone.
+	References []string `json:"references,omitempty"`
+}
+
+const artifactStore = "artifact-store://"
+
+// referenceProblem says what is wrong with a's reference for its kind, or "".
+func (a BuiltArtifact) referenceProblem() string {
+	r := a.Reference
+	if r == "" || a.Kind == "" {
+		return ""
+	}
+	// An upstream copy may be named by the holder's own naming, upstream/<host>/<path>@<digest>, in either form: the
+	// holder names it, not the module that asked for it (reference.InUpstream).
+	if path, kept := seats.InArtifactStore(r); kept && a.Kind == "upstream" {
+		if _, image, ok := reference.InUpstream(path); ok {
+			if _, digest, _ := strings.Cut(image, "@"); digest != a.Digest {
+				return "does not name its digest " + a.Digest
+			}
+			return ""
+		}
+	}
+	if seat, path, ok := seats.InRegistrySeat(r); ok {
+		want := "container-image-registry"
+		if a.Kind == "bundle" || a.Kind == "archive" {
+			want = "oci-artifact-registry"
+		}
+		module, rest, _ := strings.Cut(path, "/")
+		if a.Kind == "package" || seat != want || module == "" || rest != a.Name+"@"+a.Digest {
+			return "is not " + want + "/<module>/" + a.Name + "@" + a.Digest
+		}
+		return ""
+	}
+	switch a.Kind {
+	case "bundle", "archive":
+		path, ok := strings.CutPrefix(r, artifactStore)
+		module, rest, _ := strings.Cut(path, "/")
+		if !ok || module == "" || rest != a.Name+"/blobs/"+a.Digest {
+			return "is not artifact-store://<module>/" + a.Name + "/blobs/" + a.Digest
+		}
+	case "image", "upstream":
+		path, digest, ok := strings.Cut(r, "@")
+		if !ok || digest != a.Digest {
+			return "does not name its digest " + a.Digest
+		}
+		var host, module, name string
+		if rest, kept := strings.CutPrefix(path, artifactStore); kept {
+			module, name, _ = strings.Cut(rest, "/")
+			host = "kept"
+		} else {
+			parts := strings.Split(path, "/")
+			if len(parts) == 3 {
+				host, module, name = parts[0], parts[1], parts[2]
+			}
+		}
+		if host == "" || !(host == "kept" || host == "localhost" || strings.ContainsAny(host, ".:")) || module == "" || name != a.Name {
+			return "is not <registry>/<module>/" + a.Name + "@" + a.Digest
+		}
+	case "package":
+		at := strings.LastIndex(r, "@")
+		if at <= 0 || at == len(r)-1 || r[:at] == "@" {
+			return "is not <name>@<version>"
+		}
+	}
+	return ""
+}
+
+// Referenced says whether b is done and every artifact names where it is, which the controller delivers from (novox/hq
+// ADR 0498 clause 8), and names the artifacts that name no reference. A done key with no artifact (a module that builds
+// none, issue 1613) is referenced.
+func (b BuilderBuild) Referenced() (ok bool, missing []string) {
+	for _, a := range b.Artifacts {
+		if a.Reference == "" {
+			missing = append(missing, a.Name)
+		}
+	}
+	return b.State == BuildDone && len(missing) == 0, missing
+}
+
+// The prefixes of a failed key's error that a build module answers (novox/hq ADR 0498 clauses 2, 4 and 5; ADR 0478
+// clause 2), each followed by the artifact and the words of what refused it.
+const (
+	// NotStored: the push of a bundle, an archive or an upstream copy to the artifact store failed; built again.
+	NotStored = "not stored: "
+	// NotPinned: an upstream artifact names no digest.
+	NotPinned = "not pinned: "
+	// VersionTaken: the package registry holds the package's version with another packed file.
+	VersionTaken = "version taken: "
+	// RefusedKind: no build module builds this kind of artifact in its language.
+	RefusedKind = "refused kind: "
+	// WaitsFor: a fetch found the module's lock naming a package version the registry does not hold yet; the builder
+	// writes the key queued with Waits (novox/hq ADR 0500 clause 6), and it is built once the package is published.
+	WaitsFor = "waits for: "
+)
+
+// FailedUntilChanged says whether a failed key's error is one that is not built again until the module's fingerprint
+// changes (not pinned, version taken, refused kind: the same source fails the same way); every other failed key, a
+// push that was not stored included, is built again as a new revision (ADR 0429 clause 18).
+func FailedUntilChanged(err string) bool {
+	return strings.HasPrefix(err, NotPinned) || strings.HasPrefix(err, VersionTaken) || strings.HasPrefix(err, RefusedKind)
+}
+
+// ToolchainUsed is what a build used for one language (ADR 0405 clauses 2 and 7): the installed toolchain's version and
+// the build module's recipe version.
+type ToolchainUsed struct {
+	Version string `json:"version"`
+	Recipe  string `json:"recipe"`
+}
+
+// BuilderBuild is the value of a builder build key: its State (queued, building, done or failed), By the builder
+// instance that holds it, Step what it is doing or did last, Manifest the digest of the module's manifest (the key of
+// the indexer's manifests bucket), Artifacts when done, Toolchains by language when it built or is building (a done
+// build names them, so two builders that differ are seen: ADR 0405 clause 2), Error when failed, and Waits when queued for a
+// package version.
+type BuilderBuild struct {
+	V          int                      `json:"v"`
+	State      string                   `json:"state"`
+	By         string                   `json:"by,omitempty"`
+	Step       string                   `json:"step,omitempty"`
+	Manifest   string                   `json:"manifest,omitempty"`
+	Artifacts  []BuiltArtifact          `json:"artifacts,omitempty"`
+	Toolchains map[string]ToolchainUsed `json:"toolchains,omitempty"`
+	Error      string                   `json:"error,omitempty"`
+	// Waits is, on a queued key only, the package version `<name>@<version>` the module's lock names and the registry
+	// does not yet hold: the key is not claimed until that package's trunk key is done and published (novox/hq ADR 0500
+	// clause 6). A reader that does not know the field reads the key as queued.
+	Waits string `json:"waits,omitempty"`
+	// Asks are, on a building key, the asks the builder put for it by build seat language (AskGo, AskNode, AskImage), each
+	// its id (novox/hq ADR 0525 §1; issue 1887 A4b): a builder that takes the key over at its start waits for those asks'
+	// steps and never puts them again. A reader that does not know the field reads the key as before.
+	Asks map[string]string `json:"asks,omitempty"`
+	// Imports are, on a done key, the mesh packages the built programs import, as the build module answered them
+	// (BuildAnswer.Imports; novox/hq ADR 0593 §2): the builder carries them onto the build's end (BuildLogEntry.Imports).
+	Imports []string `json:"imports,omitempty"`
+	// Needs are, on a done key only, the reader capabilities (`form:<name>`) the build's reference forms need of a
+	// node-engine, beside the ones its manifest needs (novox/hq ADR 0618 §1). A reader that does not know the field
+	// reads the build as needing none.
+	Needs []string `json:"needs,omitempty"`
+}
+
+func (b BuilderBuild) check() error {
+	if err := trunk.CheckImports(b.Imports); err != nil {
+		return err
+	}
+	switch b.State {
+	case BuildQueued, BuildBuilding, BuildDone, BuildFailed:
+	default:
+		return fmt.Errorf("builds: the build state %q is not queued, building, done or failed", b.State)
+	}
+	if b.Manifest != "" {
+		if !kept.IsHex64(b.Manifest) {
+			return fmt.Errorf("builds: %q is not a manifest digest, 64 lowercase hex digits", b.Manifest)
+		}
+	}
+	for language, t := range b.Toolchains {
+		if t.Version == "" {
+			return fmt.Errorf("builds: the toolchain of %q has no version", language)
+		}
+		if t.Recipe == "" {
+			return fmt.Errorf("builds: the toolchain of %q has no recipe version", language)
+		}
+	}
+	for i, a := range b.Artifacts {
+		if a.Name == "" {
+			return fmt.Errorf("builds: artifact %d of the build has no name", i)
+		}
+		if a.Digest == "" {
+			return fmt.Errorf("builds: the artifact %q of the build has no digest", a.Name)
+		}
+		if p := a.referenceProblem(); p != "" {
+			return fmt.Errorf("builds: the reference %q of the %s %q %s", a.Reference, a.Kind, a.Name, p)
+		}
+		if len(a.References) > 0 && !slices.Contains(a.References, a.Reference) {
+			return fmt.Errorf("builds: the references of the %s %q do not name its reference %q", a.Kind, a.Name, a.Reference)
+		}
+		for _, r := range a.References {
+			if p := (BuiltArtifact{Name: a.Name, Kind: a.Kind, Digest: a.Digest, Reference: r}).referenceProblem(); p != "" {
+				return fmt.Errorf("builds: the reference %q of the %s %q %s", r, a.Kind, a.Name, p)
+			}
+		}
+	}
+	for _, n := range b.Needs {
+		if !strings.HasPrefix(n, "form:") || len(n) == len("form:") {
+			return fmt.Errorf("builds: the need %q of the build is not form:<name>", n)
+		}
+	}
+	if len(b.Needs) > 0 && b.State != BuildDone {
+		return fmt.Errorf("builds: a %s build names needs; only a done key does", b.State)
+	}
+	for language, id := range b.Asks {
+		if b.State != BuildBuilding {
+			return fmt.Errorf("builds: a %s build names the ask %s; only a building key does", b.State, id)
+		}
+		if err := checkAskLanguage(language); err != nil {
+			return err
+		}
+		if err := buildstep.CheckAskID(id); err != nil {
+			return err
+		}
+	}
+	if b.Waits != "" {
+		if b.State != BuildQueued {
+			return fmt.Errorf("builds: a %s build waits for %q; only a queued key waits for a package", b.State, b.Waits)
+		}
+		if p := (BuiltArtifact{Kind: "package", Reference: b.Waits}).referenceProblem(); p != "" {
+			return fmt.Errorf("builds: the package a key waits for, %q, %s", b.Waits, p)
+		}
+	}
+	switch b.State {
+	case BuildQueued, BuildBuilding:
+		if len(b.Artifacts) > 0 || b.Error != "" {
+			return fmt.Errorf("builds: a %s build carries no artifact and no error", b.State)
+		}
+	case BuildDone:
+		// A module that builds no artifact gets a done key too, and is delivered from it (issue 1613).
+		if b.Manifest == "" {
+			return fmt.Errorf("builds: a done build names no manifest digest")
+		}
+		if b.Error != "" {
+			return fmt.Errorf("builds: a done build carries an error")
+		}
+	case BuildFailed:
+		if b.Error == "" {
+			return fmt.Errorf("builds: a failed build says no error")
+		}
+	}
+	return nil
+}
+
+// EncodeBuilderBuild is b as JSON at Version; it refuses a build its state does not allow (done without a manifest
+// digest, failed without an error, an artifact without a name or digest, a toolchain without a version or a
+// recipe version).
+func EncodeBuilderBuild(b BuilderBuild) ([]byte, error) {
+	if err := b.check(); err != nil {
+		return nil, err
+	}
+	b.V = keys.Version
+	return json.Marshal(b)
+}
+
+// DecodeBuilderBuild reads a builder build value; it refuses an unknown version (kept.ErrUnknownVersion) and what
+// EncodeBuilderBuild refuses.
+func DecodeBuilderBuild(data []byte) (BuilderBuild, error) {
+	var b BuilderBuild
+	if err := kept.Decode(data, &b); err != nil {
+		return BuilderBuild{}, err
+	}
+	if err := b.check(); err != nil {
+		return BuilderBuild{}, err
+	}
+	return b, nil
+}
+
+// SameBuilderBuild says whether two builds are the same value, so the builder writes only when they differ.
+func SameBuilderBuild(a, b BuilderBuild) bool { return reflect.DeepEqual(a, b) }
diff --git a/modules/mesh-delivery-builder/builds/builds_test.go b/modules/mesh-delivery-builder/builds/builds_test.go
new file mode 100644
index 00000000..e49c966e
--- /dev/null
+++ b/modules/mesh-delivery-builder/builds/builds_test.go
@@ -0,0 +1,224 @@
+package builds
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-delivery/sdk/buildrecord"
+	"git.novox.be/novox/mesh-delivery/sdk/kept"
+	"git.novox.be/novox/mesh-sdk/go/keys"
+)
+
+func digestOf(c byte) string { return strings.Repeat(string(c), 64) }
+
+func fp2of(c byte) string { return "src2:" + digestOf(c) }
+
+func doneBuild() BuilderBuild {
+	return BuilderBuild{
+		State:    BuildDone,
+		By:       "builder.novox.1",
+		Step:     "pushed",
+		Manifest: digestOf('4'),
+		Artifacts: []BuiltArtifact{
+			{Name: "code", Kind: "bundle", Digest: "sha256:" + digestOf('5')},
+			{Name: "server", Kind: "image", Digest: "sha256:" + digestOf('6'), Reference: "registry.example/mail/server@sha256:" + digestOf('6')},
+		},
+		Toolchains: map[string]ToolchainUsed{
+			"go":         {Version: "1.26.0", Recipe: "3"},
+			"typescript": {Version: "5.9.2", Recipe: "1"},
+		},
+	}
+}
+
+func builderSamples() map[string]BuilderBuild {
+	failed := BuilderBuild{State: BuildFailed, By: "builder.novox.1", Step: "test", Error: "go test: 2 failed"}
+	both := doneBuild()
+	both.Needs = []string{"form:artifact-registry"}
+	both.Artifacts[1].References = []string{both.Artifacts[1].Reference, "artifact-store://mail/server@" + both.Artifacts[1].Digest}
+	return map[string]BuilderBuild{
+		"done with needs and both forms": both,
+		"queued":                         {State: BuildQueued, Manifest: digestOf('4')},
+		"building":                       {State: BuildBuilding, By: "builder.novox.1", Step: "fetch", Manifest: digestOf('4')},
+		"done":                           doneBuild(),
+		"failed":                         failed,
+	}
+}
+
+// 1358/AC1: the key is <module>.<hex>, parsing gives both back; a module with a dot, an empty one, and a fingerprint not
+// of the new form are refused, naming it.
+func TestBuilderBuildKey(t *testing.T) {
+	fp := fp2of('a')
+	key, err := BuilderBuildKey("mesh-mail", fp)
+	if err != nil || key != "mesh-mail."+strings.Repeat("a", 64) {
+		t.Fatalf("key = %q, %v", key, err)
+	}
+	module, back, err := ParseBuilderBuildKey(key)
+	if err != nil || module != "mesh-mail" || back != fp {
+		t.Errorf("parse = %q, %q, %v", module, back, err)
+	}
+	src1 := "src1:" + strings.Repeat("1", 64)
+	for module, fp := range map[string]string{"a.b": fp, "": fp, "mesh-mail": src1, "mail ": fp} {
+		if _, err := BuilderBuildKey(module, fp); err == nil {
+			t.Errorf("BuilderBuildKey(%q, %q) accepted", module, fp)
+		}
+	}
+	if _, err := BuilderBuildKey("a.b", fp); err == nil || !strings.Contains(err.Error(), "a.b") {
+		t.Errorf("a dotted module is not named: %v", err)
+	}
+	if _, err := BuilderBuildKey("mesh-mail", src1); err == nil || !strings.Contains(err.Error(), src1) {
+		t.Errorf("a src1 fingerprint is not named: %v", err)
+	}
+	for _, bad := range []string{"", "mesh-mail", "mesh-mail.", "mesh-mail.abc", "mesh-mail." + strings.Repeat("A", 64), ".x", "mesh-mail.build.7", "a.b." + strings.Repeat("a", 64)} {
+		if _, _, err := ParseBuilderBuildKey(bad); err == nil || !strings.Contains(err.Error(), "\""+bad+"\"") {
+			t.Errorf("ParseBuilderBuildKey(%q) = %v, want a refusal naming it", bad, err)
+		}
+	}
+}
+
+// 1358/AC2: a build value in each state encodes and decodes unchanged.
+func TestBuilderBuildRoundTrip(t *testing.T) {
+	for name, b := range builderSamples() {
+		data, err := EncodeBuilderBuild(b)
+		if err != nil {
+			t.Fatalf("%s: %v", name, err)
+		}
+		if !strings.HasPrefix(string(data), `{"v":1,`) {
+			t.Errorf("%s at %s", name, data)
+		}
+		got, err := DecodeBuilderBuild(data)
+		b.V = keys.Version
+		if err != nil || !SameBuilderBuild(got, b) {
+			t.Errorf("%s: %+v %v", name, got, err)
+		}
+	}
+}
+
+// 1358/AC3: done without a manifest digest, failed without an error, an artifact without a digest
+// and an unknown state are refused.
+func TestBuilderBuildChecked(t *testing.T) {
+	cases := map[string]struct {
+		edit  func(*BuilderBuild)
+		words []string
+	}{
+		"done without a manifest":      {func(b *BuilderBuild) { b.Manifest = "" }, []string{"manifest"}},
+		"a malformed manifest":         {func(b *BuilderBuild) { b.Manifest = "abc" }, []string{"abc"}},
+		"an artifact without a digest": {func(b *BuilderBuild) { b.Artifacts[1].Digest = "" }, []string{"digest", "server"}},
+		"an artifact without a name":   {func(b *BuilderBuild) { b.Artifacts[0].Name = "" }, []string{"name"}},
+		"a need that is not a form":    {func(b *BuilderBuild) { b.Needs = []string{"word:x"} }, []string{"word:x", "form:"}},
+		"a reference not among the references": {func(b *BuilderBuild) {
+			b.Artifacts[1].References = []string{"artifact-store://mail/server@" + b.Artifacts[1].Digest}
+		}, []string{"server", "references"}},
+		"a reference of another artifact": {func(b *BuilderBuild) {
+			b.Artifacts[1].References = []string{b.Artifacts[1].Reference, "registry.example/mail/other@" + b.Artifacts[1].Digest}
+		}, []string{"server", "other"}},
+		"an unknown state":              {func(b *BuilderBuild) { b.State = "paused" }, []string{"paused"}},
+		"a toolchain without a version": {func(b *BuilderBuild) { b.Toolchains["go"] = ToolchainUsed{Recipe: "3"} }, []string{"go", "version"}},
+		"a toolchain without a recipe":  {func(b *BuilderBuild) { b.Toolchains["go"] = ToolchainUsed{Version: "1.26.0"} }, []string{"go", "recipe"}},
+	}
+	for name, c := range cases {
+		b := doneBuild()
+		c.edit(&b)
+		_, err := EncodeBuilderBuild(b)
+		if err == nil {
+			t.Errorf("%s accepted", name)
+			continue
+		}
+		for _, w := range c.words {
+			if !strings.Contains(err.Error(), w) {
+				t.Errorf("%s: error %q does not name %q", name, err, w)
+			}
+		}
+	}
+	f := builderSamples()["failed"]
+	f.Error = ""
+	if _, err := EncodeBuilderBuild(f); err == nil || !strings.Contains(err.Error(), "error") {
+		t.Errorf("failed without an error: %v", err)
+	}
+	// a queued or building value may not already carry an outcome
+	q := builderSamples()["queued"]
+	q.Needs = []string{"form:x"}
+	if _, err := EncodeBuilderBuild(q); err == nil {
+		t.Error("a queued build with needs accepted")
+	}
+	q.Needs = nil
+	q.Artifacts = doneBuild().Artifacts
+	if _, err := EncodeBuilderBuild(q); err == nil {
+		t.Error("a queued build with artifacts accepted")
+	}
+	// decode refuses what encode refuses
+	if _, err := DecodeBuilderBuild([]byte(`{"v":1,"state":"done"}`)); err == nil {
+		t.Error("decoded a done build without a manifest digest")
+	}
+}
+
+// 1358/AC4: a done value names the toolchain version per language and the recipe version; two values that differ only
+// there are not the same.
+func TestBuilderBuildNamesItsToolchains(t *testing.T) {
+	a, b, c := doneBuild(), doneBuild(), doneBuild()
+	b.Toolchains["go"] = ToolchainUsed{Version: "1.26.1", Recipe: "3"}
+	c.Toolchains["go"] = ToolchainUsed{Version: "1.26.0", Recipe: "4"}
+	if SameBuilderBuild(a, b) || SameBuilderBuild(a, c) || SameBuilderBuild(b, c) {
+		t.Error("values differing only in a toolchain's version or recipe are the same")
+	}
+	if !SameBuilderBuild(a, doneBuild()) {
+		t.Error("equal values differ")
+	}
+	data, err := EncodeBuilderBuild(a)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := DecodeBuilderBuild(data)
+	if err != nil || !reflect.DeepEqual(got.Toolchains, a.Toolchains) {
+		t.Errorf("toolchains = %+v, %v", got.Toolchains, err)
+	}
+}
+
+// 1358/AC5: a value of another version, or none, is refused with kept.ErrUnknownVersion.
+func TestBuilderBuildVersion(t *testing.T) {
+	for _, in := range []string{`{"v":2,"state":"queued"}`, `{"state":"queued"}`} {
+		if _, err := DecodeBuilderBuild([]byte(in)); !errors.Is(err, kept.ErrUnknownVersion) {
+			t.Errorf("DecodeBuilderBuild(%s) = %v", in, err)
+		}
+	}
+	// A holder's question before it stores (ADR 0605 §4): asked at the builder's address with name, version and digest;
+	// an answer without recorded is an error, never a yes.
+	for answer, want := range map[string]string{`{"recorded":true}`: "true ", `{"recorded":false,"why":"other digest"}`: "false other digest",
+		`{"name":"x"}`: "error", `not json`: "error"} {
+		b := BuilderVersions{Ask: func(addr string, body any) (json.RawMessage, error) {
+			if a := body.(map[string]any); addr != BuilderVersionsAddress || a["name"] != "n" || a["version"] != "0.1.2" || a["digest"] != "sha256:d" {
+				t.Errorf("asked %s %v", addr, body)
+			}
+			return json.RawMessage(answer), nil
+		}}
+		ok, why, err := b.Recorded("n", "0.1.2", "sha256:d")
+		if got := fmt.Sprintf("%v %s", ok, why); err != nil && want != "error" || err == nil && got != want {
+			t.Errorf("answer %s: %s, %v; want %s", answer, got, err, want)
+		}
+	}
+}
+
+// 1358/AC6: the builder's bucket and module do not collide with the controller's build layout (buildrecord.go), which
+// this change leaves as it was.
+func TestBuilderLayoutDoesNotCollideWithTheControllers(t *testing.T) {
+	if BuilderBuildsBucket != "mesh-delivery-builder_builds" || BuilderBuildsHistory != 5 || BuilderModule != "mesh-delivery-builder" {
+		t.Errorf("bucket %s history %d module %s", BuilderBuildsBucket, BuilderBuildsHistory, BuilderModule)
+	}
+	if buildrecord.BuildKey("m", "7") != "m.build.7" || buildrecord.NewestKey("m") != "m.newest" {
+		t.Error("the controller's layout changed")
+	}
+	// the two key forms are never read as each other
+	key, _ := BuilderBuildKey("m", fp2of('a'))
+	if key == buildrecord.BuildKey("m", "a") || key == buildrecord.NewestKey("m") {
+		t.Errorf("builder key %q equals a controller key", key)
+	}
+	if _, _, err := ParseBuilderBuildKey(buildrecord.BuildKey("m", digestOf('a'))); err == nil {
+		t.Error("a controller build key parsed as the builder's")
+	}
+	if _, _, err := ParseBuilderBuildKey(buildrecord.NewestKey("m")); err == nil {
+		t.Error("a controller newest key parsed as the builder's")
+	}
+}
diff --git a/modules/mesh-delivery-builder/builds/go.mod b/modules/mesh-delivery-builder/builds/go.mod
new file mode 100644
index 00000000..8fc38072
--- /dev/null
+++ b/modules/mesh-delivery-builder/builds/go.mod
@@ -0,0 +1,10 @@
+module git.novox.be/novox/mesh-delivery/modules/mesh-delivery-builder/builds
+
+go 1.26.0
+
+require (
+	git.novox.be/novox/mesh-delivery/contracts/go/seats/containerimageregistry v0.0.0
+	git.novox.be/novox/mesh-delivery/contracts/go/seats/ociartifactregistry v0.0.0
+	git.novox.be/novox/mesh-delivery/sdk v0.0.0
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261104174359-05b3e2e1b94f
+)
diff --git a/modules/mesh-delivery-builder/builds/log.go b/modules/mesh-delivery-builder/builds/log.go
new file mode 100644
index 00000000..d7344eee
--- /dev/null
+++ b/modules/mesh-delivery-builder/builds/log.go
@@ -0,0 +1,177 @@
+package builds
+
+import (
+	"encoding/json"
+	"fmt"
+	"sort"
+	"time"
+
+	"git.novox.be/novox/mesh-delivery/sdk/kept"
+	"git.novox.be/novox/mesh-delivery/sdk/trunk"
+	"git.novox.be/novox/mesh-sdk/go/keys"
+)
+
+// The builder's log (clause 1; the lead and the operator, 2026-10-29): the builder's own module log (ADR 0297) `build-log`,
+// kept 30 days (max-age-days), one entry under the key `<module>` when a build of a fingerprint starts and one when it
+// ends, so the newest entry of a key is the module's newest start or end. The builder's tools read it through the
+// runtime's log verbs; another module reads it by naming BuildLogRead in its manifest's `reads`: a bundle through the
+// runtime (stdio.Log(BuildLogRead)), a process on its own credential (process.Conn.ReadLog), each by newest per key,
+// from a time, or following new entries. The catalogue module asks the builder's tool BuildsSinceTool instead.
+const (
+	BuilderLog        = "build-log"
+	BuildLogRead      = BuilderModule + "." + BuilderLog
+	BuildStartedEvent = "build.started"
+	BuildEndedEvent   = "build.ended"
+	// BuildSaidEvent is a build's narration between its start and its end (design 51: a build narrates its publish,
+	// asked, waiting on a seat, stored, refused, at least every five minutes while it waits): its module, fingerprint,
+	// line and why.
+	BuildSaidEvent = "build.said"
+	// BuilderLogDays is how long the log keeps its entries.
+	BuilderLogDays = 30
+	// BuildsSinceTool is the builder's tool answering every ended build since a time, in order (clause 9): its
+	// argument `since` (RFC 3339), its answer BuildsSince.
+	BuildsSinceTool = "builder_builds_since"
+)
+
+// BuildLogKey is the key of a module's entries in the builder's log: the module's name, refused when a log key could not
+// hold it.
+func BuildLogKey(module string) (string, error) {
+	if err := kept.CheckName("module", module); err != nil {
+		return "", err
+	}
+	return module, nil
+}
+
+// BuildLogEntry is one entry of the builder's log: the module, the fingerprint, the source revision, where the module is
+// built from (its repository, its directory there, the commit and the ref), the build node and the time; at the end,
+// the outcome, the manifest built (its digest, read from the indexer's state `manifests` under ManifestsKey), what it was
+// built against (the bases' references, as the controller's built-before said them) and each artifact made
+// (BuiltArtifact, the done key's: its name, kind, digest and reference). The repository, directory and commit are what
+// the indexer's PathOf, the outside-built registrations and the assigner's running commits read; the manifest, against
+// and made what the catalogue module registers a build from (the lead, 2026-10-29).
+type BuildLogEntry struct {
+	V          int             `json:"v"`
+	Event      string          `json:"event"`
+	Module     string          `json:"module"`
+	FP         string          `json:"fp"`
+	Source     string          `json:"source"`
+	Repository string          `json:"repository"`
+	Directory  string          `json:"directory"`
+	Commit     string          `json:"commit"`
+	Ref        string          `json:"ref,omitempty"`
+	Node       string          `json:"node"`
+	At         time.Time       `json:"at"`
+	Outcome    string          `json:"outcome,omitempty"`
+	Manifest   string          `json:"manifest,omitempty"`
+	Against    []string        `json:"against,omitempty"`
+	Made       []BuiltArtifact `json:"made,omitempty"`
+	// Imports are, at a build's end, the mesh packages (import paths) the built programs import, their tests left out,
+	// sorted and each once, as the build module answered them (BuildAnswer.Imports; novox/hq ADR 0593 §2): the indexer
+	// keeps them on the module (KeptInputs2.Imports) when the build's fingerprint is the module's.
+	Imports []string `json:"imports,omitempty"`
+	// OutOfStep are, at a build's end, the generated files its test step found out of step with what their generator
+	// writes, as the build module answered them (its test step's `out-of-step`): the indexer raises a finding naming them
+	// for a trunk build, and only a clean build of the same module clears it. A start or a narration names none.
+	OutOfStep []string `json:"out-of-step,omitempty"`
+	// Line is a narration's words, Why what it narrates (asked, waiting, stored, refused): a build.said entry's alone.
+	Line string `json:"line,omitempty"`
+	Why  string `json:"why,omitempty"`
+}
+
+// BuildsSince is the answer of BuildsSinceTool: every ended build since a time, oldest first, and whether the log held
+// more than one answer carries (then ask again from the last one's time).
+type BuildsSince struct {
+	Since  time.Time       `json:"since"`
+	Builds []BuildLogEntry `json:"builds"`
+	More   bool            `json:"more,omitempty"`
+}
+
+// NewestPerModule is each module's newest entry of entries (one kind, read from the last per subject or whole), by
+// module: the reader's helper for the five newest and the running commits.
+func NewestPerModule(entries []BuildLogEntry) map[string]BuildLogEntry {
+	out := map[string]BuildLogEntry{}
+	for _, e := range entries {
+		if have, ok := out[e.Module]; !ok || e.At.After(have.At) {
+			out[e.Module] = e
+		}
+	}
+	return out
+}
+
+// EndedSince is, of entries, the ended builds at or after since, oldest first: the reader's helper for history and for
+// BuildsSinceTool's answer.
+func EndedSince(entries []BuildLogEntry, since time.Time) []BuildLogEntry {
+	var out []BuildLogEntry
+	for _, e := range entries {
+		if e.Event == BuildEndedEvent && !e.At.Before(since) {
+			out = append(out, e)
+		}
+	}
+	sort.SliceStable(out, func(i, j int) bool { return out[i].At.Before(out[j].At) })
+	return out
+}
+
+// EncodeBuildLogEntry is e as JSON at Version; it refuses an entry a reader could not place.
+func EncodeBuildLogEntry(e BuildLogEntry) ([]byte, error) {
+	e.V = keys.Version
+	switch {
+	case e.Event == BuildSaidEvent:
+		switch {
+		case e.Module == "" || e.FP == "" || e.At.IsZero() || e.Line == "":
+			return nil, fmt.Errorf("builds: a build's narration names its module, fingerprint, line and time")
+		case e.Outcome != "" || len(e.Made) > 0 || e.Manifest != "" || len(e.Against) > 0 || len(e.Imports) > 0 || len(e.OutOfStep) > 0:
+			return nil, fmt.Errorf("builds: a build's narration names no outcome, manifest, base, artifact, import or file out of step")
+		}
+		return json.Marshal(e)
+	case e.Event != BuildStartedEvent && e.Event != BuildEndedEvent:
+		return nil, fmt.Errorf("builds: a build log entry is %s, %s or %s, not %q", BuildStartedEvent, BuildSaidEvent, BuildEndedEvent, e.Event)
+	case e.Line != "" || e.Why != "":
+		return nil, fmt.Errorf("builds: a build's start or end carries no narration's line")
+	case e.Module == "" || e.FP == "" || e.Node == "" || e.At.IsZero() || e.Repository == "" || e.Commit == "":
+		return nil, fmt.Errorf("builds: a build log entry names its module, fingerprint, repository, commit, node and time")
+	case e.Event == BuildEndedEvent && e.Outcome == "":
+		return nil, fmt.Errorf("builds: a build's end names its outcome")
+	case e.Event == BuildStartedEvent && (e.Outcome != "" || len(e.Made) > 0 || e.Manifest != "" || len(e.Against) > 0 || len(e.Imports) > 0 ||
+		len(e.OutOfStep) > 0):
+		return nil, fmt.Errorf("builds: a build's start names no outcome, manifest, base, artifact, import or file out of step")
+	}
+	if err := trunk.CheckImports(e.Imports); err != nil {
+		return nil, err
+	}
+	return json.Marshal(e)
+}
+
+// DecodeBuildLogEntry reads one entry.
+func DecodeBuildLogEntry(data []byte) (BuildLogEntry, error) {
+	var e BuildLogEntry
+	if err := json.Unmarshal(data, &e); err != nil {
+		return BuildLogEntry{}, fmt.Errorf("builds: a build log entry is not readable: %w", err)
+	}
+	if e.V != keys.Version {
+		return BuildLogEntry{}, fmt.Errorf("builds: a build log entry of version %d, and this reads %d", e.V, keys.Version)
+	}
+	return e, nil
+}
+
+// BuildDuration is a build's duration, its end less its start (clause 1): false unless both are the same module's
+// build of the same fingerprint, the start first.
+func BuildDuration(start, end BuildLogEntry) (time.Duration, bool) {
+	if start.Event != BuildStartedEvent || end.Event != BuildEndedEvent || start.Module != end.Module || start.FP != end.FP ||
+		end.At.Before(start.At) {
+		return 0, false
+	}
+	return end.At.Sub(start.At), true
+}
+
+// IsBuildEntry says whether an entry of the builder's log is a build's start or end, read from its event alone, so an entry of
+// another kind (a build's narration, build.said) is passed over before its form is read. One whose event cannot be read is
+// taken as a build's, so its decoding says what is wrong with it.
+func IsBuildEntry(value []byte) bool {
+	var e struct {
+		Event *string `json:"event"`
+	}
+	if json.Unmarshal(value, &e) != nil || e.Event == nil {
+		return true
+	}
+	return *e.Event == BuildStartedEvent || *e.Event == BuildEndedEvent
+}
diff --git a/modules/mesh-delivery-builder/builds/log_test.go b/modules/mesh-delivery-builder/builds/log_test.go
new file mode 100644
index 00000000..4f62c5e0
--- /dev/null
+++ b/modules/mesh-delivery-builder/builds/log_test.go
@@ -0,0 +1,60 @@
+package builds
+
+import (
+	"testing"
+	"time"
+)
+
+func TestTheBuildersLogKeepsAStartAndAnEndAndTheirDuration(t *testing.T) {
+	// ADR 0571 clause 1: the builder's log, a start and an end, and the duration between them.
+	at := time.Date(2026, 10, 29, 22, 0, 0, 0, time.UTC)
+	start := BuildLogEntry{Event: BuildStartedEvent, Module: "letta", FP: "src2:a", Source: "abc", Repository: "novox/mesh-catalog",
+		Directory: "modules/letta", Commit: "abc123", Node: "ace", At: at}
+	end := start
+	end.Event, end.At, end.Outcome, end.Manifest, end.Against = BuildEndedEvent, at.Add(3*time.Minute), "done", "sha256:m", []string{"artifact-store://base/image@sha256:b"}
+	end.Made = []BuiltArtifact{{Name: "image", Kind: "image", Digest: "sha256:1", Reference: "artifact-store://letta/image@sha256:1"}}
+	for _, e := range []BuildLogEntry{start, end} {
+		raw, err := EncodeBuildLogEntry(e)
+		back, derr := DecodeBuildLogEntry(raw)
+		if err != nil || derr != nil || back.Event != e.Event || back.Outcome != e.Outcome || back.Directory != "modules/letta" ||
+			back.Repository != "novox/mesh-catalog" || back.Commit != "abc123" {
+			t.Errorf("%s read back as %+v, %v %v", e.Event, back, err, derr)
+		}
+	}
+	if d, ok := BuildDuration(start, end); !ok || d != 3*time.Minute {
+		t.Errorf("the build took %s, %v", d, ok)
+	}
+	older := end
+	older.At, older.FP = at.Add(-time.Hour), "src2:b"
+	other := end
+	other.Module = "mesh-catalog"
+	if n := NewestPerModule([]BuildLogEntry{older, end, other}); n["letta"].FP != "src2:a" || len(n) != 2 {
+		t.Errorf("each module's newest is %v", n)
+	}
+	if e := EndedSince([]BuildLogEntry{end, start, older}, at.Add(-2*time.Hour)); len(e) != 2 || e[0].FP != "src2:b" {
+		t.Errorf("the ended builds since are %v", e)
+	}
+	if k, err := BuildLogKey("letta"); k != "letta" || err != nil || BuildLogRead != "mesh-delivery-builder.build-log" {
+		t.Errorf("the key is %q, %v", k, err)
+	}
+	if _, err := BuildLogKey("a.b"); err == nil {
+		t.Error("a module with a dot was taken as a key")
+	}
+	for _, edit := range []func(*BuildLogEntry){func(e *BuildLogEntry) { e.Outcome = "" }, func(e *BuildLogEntry) { e.Commit = "" },
+		func(e *BuildLogEntry) { e.Event, e.Outcome, e.Against = BuildStartedEvent, "", nil }} {
+		bad := end
+		edit(&bad)
+		if _, err := EncodeBuildLogEntry(bad); err == nil {
+			t.Errorf("%+v was encoded", bad)
+		}
+	}
+}
+
+func TestOnlyABuildsStartOrEndIsABuildEntry(t *testing.T) {
+	for entry, want := range map[string]bool{`{"event":"build.started"}`: true, `{"event":"build.ended"}`: true, `{"event":"build.said"}`: false,
+		`not json`: true, `{}`: true} {
+		if got := IsBuildEntry([]byte(entry)); got != want {
+			t.Errorf("IsBuildEntry(%s) = %v", entry, got)
+		}
+	}
+}
diff --git a/modules/mesh-delivery-builder/builds/numbered.go b/modules/mesh-delivery-builder/builds/numbered.go
new file mode 100644
index 00000000..0eca558a
--- /dev/null
+++ b/modules/mesh-delivery-builder/builds/numbered.go
@@ -0,0 +1,57 @@
+package builds
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// The builder's event version.numbered (design 51 *Events of the builder*, *The floor*): said once per version the builder
+// numbers, on its own family `version` (seven days), apart from its builds' ends, so a waiter on a build's end does not
+// wake on it. A build module consumes it to publish a build's version with the held digest, which stores nothing.
+const (
+	// VersionNumberedEvent is the event's local name.
+	VersionNumberedEvent = "version.numbered"
+	// VersionNumberedSubject is its subject, as a consumer's filter names it.
+	VersionNumberedSubject = "mesh.mod." + BuilderModule + ".event." + VersionNumberedEvent
+)
+
+// VersionNumbered is the body of VersionNumberedEvent: a numbered version of a name, the build it was numbered for, and
+// what the build module needs to publish it.
+type VersionNumbered struct {
+	// Name is the numbered name, as builder_versions lists it; Kind its artifact's kind.
+	Name    string `json:"name"`
+	Kind    string `json:"kind"`
+	Version string `json:"version"`
+	Tag     string `json:"tag,omitempty"`
+	// Module and Fingerprint are the build the version was numbered for; Commit its source commit.
+	Module      string `json:"module"`
+	Fingerprint string `json:"fingerprint"`
+	Commit      string `json:"commit,omitempty"`
+	// Digest is the built artifact's, when the build held one; Seat the registry seat it is published through.
+	Digest string `json:"digest,omitempty"`
+	Seat   string `json:"seat,omitempty"`
+	// Head is the head the version answers, when it answers a tag ask.
+	Head string `json:"head,omitempty"`
+	// Again is when builder_publish_again said it once more, so the bus's dedup does not drop it.
+	Again string `json:"again,omitempty"`
+}
+
+// EncodeVersionNumbered writes the body, refusing one that names no name, version, module or fingerprint.
+func EncodeVersionNumbered(n VersionNumbered) ([]byte, error) {
+	if n.Name == "" || n.Version == "" || n.Module == "" || n.Fingerprint == "" {
+		return nil, fmt.Errorf("builds: %s names its name, version, module and fingerprint", VersionNumberedEvent)
+	}
+	return json.Marshal(n)
+}
+
+// DecodeVersionNumbered reads the body, with the same refusal.
+func DecodeVersionNumbered(data []byte) (VersionNumbered, error) {
+	var n VersionNumbered
+	if err := json.Unmarshal(data, &n); err != nil {
+		return VersionNumbered{}, fmt.Errorf("builds: %s is not readable: %w", VersionNumberedEvent, err)
+	}
+	if _, err := EncodeVersionNumbered(n); err != nil {
+		return VersionNumbered{}, err
+	}
+	return n, nil
+}
diff --git a/modules/mesh-delivery-builder/builds/reference_test.go b/modules/mesh-delivery-builder/builds/reference_test.go
new file mode 100644
index 00000000..8032e036
--- /dev/null
+++ b/modules/mesh-delivery-builder/builds/reference_test.go
@@ -0,0 +1,157 @@
+package builds
+
+import (
+	"strings"
+	"testing"
+)
+
+func artifactOf(name, kind, digest, reference string) BuiltArtifact {
+	return BuiltArtifact{Name: name, Kind: kind, Digest: digest, Reference: reference}
+}
+
+// A done key names where each artifact is (novox/hq ADR 0498 clauses 1, 5 and 6; the lead's decision L1 of R4e): a
+// bundle or an archive by its artifact-store blob, an image or an upstream copy by the registry's reference to its
+// digest (or the kept artifact-store form), a package by name and version. A reference of the wrong form for its kind,
+// or naming another digest or artifact, is refused, naming the artifact.
+func TestADoneKeyNamesEachArtifactsReferenceInTheFormOfItsKind(t *testing.T) {
+	d := "sha256:" + digestOf('6')
+	good := []BuiltArtifact{
+		artifactOf("code", "bundle", d, "artifact-store://mail/code/blobs/"+d),
+		artifactOf("files", "archive", d, "artifact-store://mail/files/blobs/"+d),
+		artifactOf("server", "image", d, "10.0.0.1:5000/mail/server@"+d),
+		artifactOf("server", "image", d, "artifact-store://mail/server@"+d),
+		artifactOf("nats", "upstream", d, "registry.example/nats/nats@"+d),
+		artifactOf("lib", "package", d, "@novox/mesh-sdk@0.1.15"),
+		artifactOf("lib", "package", d, "left-pad@1.3.0"),
+		artifactOf("old", "", d, "anything at all"),
+		// The form a registry seat answers (ADR 0605 §9), beside the older one.
+		artifactOf("code", "bundle", d, "oci-artifact-registry/mail/code@"+d),
+		artifactOf("files", "archive", d, "oci-artifact-registry/mail/files@"+d),
+		artifactOf("server", "image", d, "container-image-registry/mail/server@"+d),
+		artifactOf("nats", "upstream", d, "container-image-registry/nats/nats@"+d),
+		// An upstream copy under the holder's own naming, upstream/<host>/<path>, in either form (ADR 0624 §1).
+		artifactOf("app", "upstream", d, "container-image-registry/upstream/quay.io:443/org/app@"+d),
+		artifactOf("app", "upstream", d, "artifact-store://upstream/quay.io:443/org/app@"+d),
+	}
+	for _, a := range good {
+		b := doneBuild()
+		b.Artifacts = []BuiltArtifact{a}
+		if _, err := EncodeBuilderBuild(b); err != nil {
+			t.Errorf("%+v was refused: %v", a, err)
+		}
+	}
+	other := "sha256:" + digestOf('7')
+	bad := []BuiltArtifact{
+		artifactOf("code", "bundle", d, "artifact-store://mail/code/blobs/"+other),
+		artifactOf("code", "bundle", d, "artifact-store://mail/other/blobs/"+d),
+		artifactOf("code", "bundle", d, "10.0.0.1:5000/mail/code@"+d),
+		artifactOf("server", "image", d, "10.0.0.1:5000/mail@"+d),
+		artifactOf("server", "image", d, "10.0.0.1:5000/mail/server@"+other),
+		artifactOf("server", "image", d, "mail/server@"+d),
+		artifactOf("server", "image", d, "artifact-store://mail/server/blobs/"+d),
+		artifactOf("lib", "package", d, "@novox/mesh-sdk"),
+		artifactOf("lib", "package", d, "0.1.15"),
+		artifactOf("code", "bundle", d, "container-image-registry/mail/code@"+d),
+		artifactOf("server", "image", d, "oci-artifact-registry/mail/server@"+d),
+		artifactOf("server", "image", d, "container-image-registry/mail/server@"+other),
+		artifactOf("server", "image", d, "container-image-registry/mail/other@"+d),
+		artifactOf("lib", "package", d, "container-image-registry/mail/lib@"+d),
+		artifactOf("app", "upstream", d, "container-image-registry/upstream/quay.io:443/org/app@"+other),
+		artifactOf("app", "upstream", d, "artifact-store://upstream/quay.io:443/org/app@"+other),
+		artifactOf("app", "upstream", d, "oci-artifact-registry/upstream/quay.io:443/org/app@"+d),
+		artifactOf("server", "image", d, "container-image-registry/upstream/quay.io:443/org/server@"+d),
+	}
+	for _, a := range bad {
+		b := doneBuild()
+		b.Artifacts = []BuiltArtifact{a}
+		if _, err := EncodeBuilderBuild(b); err == nil || !strings.Contains(err.Error(), `"`+a.Name+`"`) {
+			t.Errorf("%+v: %v, wanted a refusal naming the artifact", a, err)
+		}
+	}
+}
+
+// The controller delivers only from a done key whose every artifact names a reference (ADR 0498 clause 8): Referenced
+// says so and names the artifacts without one.
+func TestReferencedNamesTheArtifactsWithoutAReference(t *testing.T) {
+	d := "sha256:" + digestOf('6')
+	b := doneBuild()
+	b.Artifacts = []BuiltArtifact{
+		artifactOf("code", "bundle", d, "artifact-store://mail/code/blobs/"+d),
+		artifactOf("server", "image", d, ""),
+	}
+	if ok, missing := b.Referenced(); ok || len(missing) != 1 || missing[0] != "server" {
+		t.Fatalf("Referenced = %v, %v; want false, [server]", ok, missing)
+	}
+	b.Artifacts[1].Reference = "10.0.0.1:5000/mail/server@" + d
+	if ok, missing := b.Referenced(); !ok || len(missing) != 0 {
+		t.Fatalf("Referenced = %v, %v; want true", ok, missing)
+	}
+	if ok, _ := (BuilderBuild{State: BuildQueued}).Referenced(); ok {
+		t.Fatal("a queued key is referenced")
+	}
+}
+
+// The errors a build module answers open with a fixed prefix (ADR 0498 clauses 2, 4 and 5; ADR 0478 clause 2), and three
+// of them are not built again until the module's fingerprint changes; a failed push is.
+func TestOnlyAPushFailureIsBuiltAgainBeforeTheFingerprintChanges(t *testing.T) {
+	for _, c := range []struct {
+		err   string
+		again bool
+	}{
+		{NotStored + "code: the store said 500", true},
+		{NotPinned + "nats: upstream names no digest", false},
+		{VersionTaken + "@novox/mesh-sdk@0.1.15 holds another file", false},
+		{RefusedKind + "a package in go", false},
+		{"go test: 2 failed", true},
+	} {
+		if got := FailedUntilChanged(c.err); got == c.again {
+			t.Errorf("FailedUntilChanged(%q) = %v", c.err, got)
+		}
+	}
+	if NotStored != "not stored: " || NotPinned != "not pinned: " || VersionTaken != "version taken: " || RefusedKind != "refused kind: " {
+		t.Fatal("a prefix changed its words")
+	}
+	// A Node fetch that finds the lock naming a package version the registry does not hold fails with WaitsFor; the
+	// builder then writes the key queued with Waits, and the error is not one that waits for the fingerprint to change.
+	if WaitsFor != "waits for: " || FailedUntilChanged(WaitsFor+"@novox/mesh-sdk@0.1.15") {
+		t.Fatalf("WaitsFor = %q", WaitsFor)
+	}
+}
+
+// A key whose module's lock names a version of the group's package not yet published waits, queued, saying which
+// (ADR 0500 clause 6): an older reader reads it as queued, and only a queued key waits.
+func TestAKeyWaitsQueuedForAPackageVersion(t *testing.T) {
+	b := BuilderBuild{State: BuildQueued, Manifest: digestOf('4'), Waits: "@novox/mesh-sdk@0.1.15"}
+	data, err := EncodeBuilderBuild(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+	back, err := DecodeBuilderBuild(data)
+	if err != nil || back.Waits != b.Waits || back.State != BuildQueued {
+		t.Fatalf("decoded %+v, %v", back, err)
+	}
+	building := BuilderBuild{State: BuildBuilding, By: "x", Waits: "@novox/mesh-sdk@0.1.15"}
+	if _, err := EncodeBuilderBuild(building); err == nil {
+		t.Fatal("a building key that waits was accepted")
+	}
+	if _, err := EncodeBuilderBuild(BuilderBuild{State: BuildQueued, Waits: "mesh-sdk"}); err == nil {
+		t.Fatal("a wait naming no version was accepted")
+	}
+}
+
+// A module that builds no artifact gets a done key too (issue 1613), and it is delivered: Referenced is ok for a done
+// key with no artifact, since no artifact lacks a reference; a queued one with none still is not.
+func TestADoneKeyWithNoArtifactIsReferenced(t *testing.T) {
+	b := BuilderBuild{State: BuildDone, Manifest: digestOf('4')}
+	data, err := EncodeBuilderBuild(b)
+	if err != nil {
+		t.Fatalf("a done key with no artifact was refused: %v", err)
+	}
+	back, err := DecodeBuilderBuild(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ok, missing := back.Referenced(); !ok || len(missing) != 0 {
+		t.Fatalf("Referenced = %v, %v; want true", ok, missing)
+	}
+}
diff --git a/modules/mesh-delivery-builder/builds/versions.go b/modules/mesh-delivery-builder/builds/versions.go
new file mode 100644
index 00000000..a8abcf45
--- /dev/null
+++ b/modules/mesh-delivery-builder/builds/versions.go
@@ -0,0 +1,38 @@
+package builds
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// The holder's question before it stores a publish (novox/hq ADR 0605 §4, design 51 *Publishing*): did the builder
+// number this version with this digest? Every registry seat's holder asks it the same way, so the asking lives here
+// once (ADR 0627 §2), beside the builder's layouts; no holder writes it again.
+//
+// The builder answers it today only as its module's tool builder_versions: no seat in the seat set names the builder's
+// role yet. Once one does, BuilderVersionsAddress becomes that seat's verb and nothing else changes for a holder.
+const BuilderVersionsAddress = BuilderModule + ".builder_versions"
+
+// AskFunc is the runtime's request and reply over the bus (mesh-sdk stdio.Ask), given by the holder so this package does
+// not depend on the runtime.
+type AskFunc func(address string, body any) (json.RawMessage, error)
+
+// BuilderVersions asks the builder whether it numbered a version with a digest. It answers the holder's Check:
+// recorded, and why not when it is not.
+type BuilderVersions struct{ Ask AskFunc }
+
+// Recorded asks the builder about name@version with digest. An answer without `recorded` is an error, never a yes.
+func (b BuilderVersions) Recorded(name, version, digest string) (bool, string, error) {
+	raw, err := b.Ask(BuilderVersionsAddress, map[string]any{"name": name, "version": version, "digest": digest})
+	if err != nil {
+		return false, "", err
+	}
+	var a struct {
+		Recorded *bool  `json:"recorded"`
+		Why      string `json:"why"`
+	}
+	if err := json.Unmarshal(raw, &a); err != nil || a.Recorded == nil {
+		return false, "", fmt.Errorf("builder_versions answered no recorded: %s", raw)
+	}
+	return *a.Recorded, a.Why, nil
+}
diff --git a/modules/mesh-delivery-builder/module.json b/modules/mesh-delivery-builder/module.json
index 3bf21661..504beb60 100644
--- a/modules/mesh-delivery-builder/module.json
+++ b/modules/mesh-delivery-builder/module.json
@@ -167,6 +167,15 @@
         "loads": [
           "mesh-delivery-builder-tools"
         ]
+      },
+      {
+        "name": "builds",
+        "kind": "package",
+        "language": "go",
+        "paths": [
+          "builds"
+        ],
+        "series": "0.1"
       }
     ]
   }
diff --git a/sdk/buildstep/steps.go b/sdk/buildstep/steps.go
index 6a6a306a..e39bb9f9 100644
--- a/sdk/buildstep/steps.go
+++ b/sdk/buildstep/steps.go
@@ -187,3 +187,12 @@ type Ask struct {
 		Fetch map[string]any `json:"fetch"`
 	} `json:"compose"`
 }
+
+// CheckAskID refuses an id that is no ask's: base-36 milliseconds and six hex digits, as NewID gives. Its form keeps it apart from
+// a module's or a node's name in a key.
+func CheckAskID(id string) error {
+	if !askIDOK.MatchString(id) {
+		return fmt.Errorf("buildstep: %q is not an ask id (base-36 milliseconds and six hex digits)", id)
+	}
+	return nil
+}
diff --git a/sdk/kept/kept.go b/sdk/kept/kept.go
new file mode 100644
index 00000000..1d907361
--- /dev/null
+++ b/sdk/kept/kept.go
@@ -0,0 +1,73 @@
+// Package kept holds what the layouts of the Delivery domain's kept values share: the version check on reading one, the
+// rule a name must keep to be a key part, and the form of a digest. It names no seat and no module (ADR 0634 §2). The
+// version itself (keys.Version) and the escaping of a name (keys.EscapeName) are mesh-sdk's, since more than one domain uses
+// them.
+package kept
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"regexp"
+
+	"git.novox.be/novox/mesh-sdk/go/keys"
+)
+
+// ErrUnknownVersion is what Decode returns for a value whose version is missing or not keys.Version. Test it with errors.Is.
+var ErrUnknownVersion = errors.New("kept: unknown value version")
+
+var nameOK = regexp.MustCompile(`^[-/_=a-zA-Z0-9]+$`)
+
+// CheckName refuses a name that is empty or holds a dot, a wildcard, whitespace or a character a bus key refuses.
+func CheckName(kind, name string) error {
+	if name == "" {
+		return fmt.Errorf("kept: the %s name is empty", kind)
+	}
+	if !nameOK.MatchString(name) {
+		return fmt.Errorf("kept: the %s name %q holds a dot, a wildcard, whitespace or a character a key refuses", kind, name)
+	}
+	return nil
+}
+
+var hex64 = regexp.MustCompile(`^[0-9a-f]{64}$`)
+
+// IsHex64 says whether s is 64 lowercase hex digits.
+func IsHex64(s string) bool { return hex64.MatchString(s) }
+
+// CheckVersion refuses a value with no version or one this reader does not read.
+func CheckVersion(data []byte) error {
+	var probe struct {
+		V *int `json:"v"`
+	}
+	if err := json.Unmarshal(data, &probe); err != nil {
+		return fmt.Errorf("kept: value is not JSON: %w", err)
+	}
+	if probe.V == nil {
+		return fmt.Errorf("%w: no version in the value, this reader reads %d", ErrUnknownVersion, keys.Version)
+	}
+	if *probe.V != keys.Version {
+		return fmt.Errorf("%w: the value is version %d, this reader reads %d", ErrUnknownVersion, *probe.V, keys.Version)
+	}
+	return nil
+}
+
+// Decode reads data into into after CheckVersion.
+func Decode(data []byte, into any) error {
+	if err := CheckVersion(data); err != nil {
+		return err
+	}
+	if err := json.Unmarshal(data, into); err != nil {
+		return fmt.Errorf("kept: value does not fit its shape: %w", err)
+	}
+	return nil
+}
+
+var digestForm = regexp.MustCompile(`^sha256:[0-9a-f]{64}$`)
+
+// CheckDigest refuses a digest that is not sha256:<64 lowercase hex digits>, saying what it is of.
+func CheckDigest(digest, of string) error {
+	if !digestForm.MatchString(digest) {
+		return fmt.Errorf("kept: %s %q is not sha256:<64 lowercase hex digits>", of, digest)
+	}
+	return nil
+}
diff --git a/sdk/kept/kept_test.go b/sdk/kept/kept_test.go
new file mode 100644
index 00000000..aeff9ec0
--- /dev/null
+++ b/sdk/kept/kept_test.go
@@ -0,0 +1,31 @@
+package kept
+
+import (
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestAKeptValueIsReadOnlyAtItsVersionAndAKeyPartOnlyOfKeyCharacters(t *testing.T) {
+	var v struct{ V int }
+	for data, ok := range map[string]bool{`{"v":1}`: true, `{"v":2}`: false, `{}`: false} {
+		err := Decode([]byte(data), &v)
+		if (err == nil) != ok || (!ok && !errors.Is(err, ErrUnknownVersion)) {
+			t.Errorf("Decode(%s) = %v", data, err)
+		}
+	}
+	if Decode([]byte(`nope`), &v) == nil {
+		t.Error("a value that is no JSON is read")
+	}
+	for name, ok := range map[string]bool{"a-b_c/d=": true, "": false, "a.b": false, "a b": false, "a*": false} {
+		if (CheckName("module", name) == nil) != ok {
+			t.Errorf("CheckName(%q) = %v", name, CheckName("module", name))
+		}
+	}
+	if !IsHex64(strings.Repeat("a", 64)) || IsHex64(strings.Repeat("A", 64)) || IsHex64("a") {
+		t.Error("IsHex64 reads a wrong form")
+	}
+	if CheckDigest("sha256:"+strings.Repeat("0", 64), "x") != nil || CheckDigest("sha256:0", "x") == nil {
+		t.Error("CheckDigest reads a wrong form")
+	}
+}
diff --git a/sdk/trunk/packages.go b/sdk/trunk/packages.go
index 442767e0..4d5f653b 100644
--- a/sdk/trunk/packages.go
+++ b/sdk/trunk/packages.go
@@ -1,6 +1,7 @@
 package trunk
 
 import (
+	"fmt"
 	"strings"
 )
 
@@ -26,3 +27,17 @@ func PackageRepository(pkg string) (repository, dir string, ok bool) {
 	}
 	return "novox/" + name, dir, true
 }
+
+// CheckImports refuses an import set (the imports of a module's kept inputs, of a build's answer and of a build log entry)
+// that holds a path that is no mesh package's, or is not sorted and each once.
+func CheckImports(imports []string) error {
+	for i, pkg := range imports {
+		if _, _, ok := PackageRepository(pkg); !ok || strings.ContainsAny(pkg, " \t\n@") {
+			return fmt.Errorf("trunk: the import %q is no mesh package's path (it starts with %s)", pkg, ForgeModulePrefix)
+		}
+		if i > 0 && imports[i-1] >= pkg {
+			return fmt.Errorf("trunk: the imports are not sorted and each once (%s after %s)", pkg, imports[i-1])
+		}
+	}
+	return nil
+}
diff --git a/sdk/trunk/trunk_test.go b/sdk/trunk/trunk_test.go
index 7ea841e8..c0c6b53f 100644
--- a/sdk/trunk/trunk_test.go
+++ b/sdk/trunk/trunk_test.go
@@ -33,3 +33,15 @@ func TestSameRepository(t *testing.T) { // 1281/AC1
 		t.Errorf("RepositoryName = %q", got)
 	}
 }
+
+func TestAnImportSetHoldsMeshPackagesSortedAndEachOnce(t *testing.T) {
+	a, b := ForgeModulePrefix+"mesh-sdk/go", ForgeModulePrefix+"mesh-delivery/sdk"
+	if err := CheckImports([]string{b, a}); err != nil {
+		t.Errorf("a sorted set is refused: %v", err)
+	}
+	for name, bad := range map[string][]string{"unsorted": {a, b}, "twice": {a, a}, "not a mesh package": {"github.com/x/y"}, "a version": {a + "@v1"}} {
+		if CheckImports(bad) == nil {
+			t.Errorf("%s: %v is taken", name, bad)
+		}
+	}
+}