diff --git a/go/delivery/buildrecord.go b/go/delivery/buildrecord.go
new file mode 100644
index 0000000..ef8b874
--- /dev/null
+++ b/go/delivery/buildrecord.go
@@ -0,0 +1,36 @@
+package delivery
+
+import "time"
+
+// BuildRecord is the layout mesh-controller internal/chain/records.go Build writes (line 91), the fields a reader outside
+// the controller reads (novox/hq ADR 0437 §4 §5, issue 1223). The controller's record carries more; a decode ignores
+// what is not here. SourceInputs has no json keys of its own: it is written under its Go field names, as the controller
+// writes it.
+type BuildRecord struct {
+	ID                string        `json:"id"`
+	State             string        `json:"state,omitempty"`
+	Repository        string        `json:"repository"`
+	Ref               string        `json:"ref,omitempty"`
+	Module            string        `json:"module,omitempty"`
+	Commit            string        `json:"commit,omitempty"`
+	At                time.Time     `json:"at,omitzero"`
+	SourceFingerprint string        `json:"source-fingerprint,omitempty"`
+	SourceInputs      *SourceInputs `json:"source-inputs,omitempty"`
+}
+
+// BuildsBucket is the bucket the builds are kept in: mesh-controller internal/broker/controller_buckets.go:101,
+// BucketName(ControllerSeat, ChainBuilds), with ControllerSeat "mesh-controller" (internal/broker/streams.go:359) and
+// ChainBuilds "builds" (controller_buckets.go:113).
+const BuildsBucket = "mesh-controller_builds"
+
+// BuildKey is a build's record under its module, a build that knew none under the request's key: copied from
+// mesh-controller internal/chain/keys.go:35-41 (BuildKey, with RequestKey at line 43).
+func BuildKey(module, id string) string {
+	if module == "" {
+		return "req." + id
+	}
+	return module + ".build." + id
+}
+
+// NewestKey is the key of a module's newest build, of any state: copied from mesh-controller internal/chain/keys.go:46.
+func NewestKey(module string) string { return module + ".newest" }
diff --git a/go/delivery/buildrecord_test.go b/go/delivery/buildrecord_test.go
new file mode 100644
index 0000000..fccddc2
--- /dev/null
+++ b/go/delivery/buildrecord_test.go
@@ -0,0 +1,86 @@
+package delivery
+
+import (
+	"encoding/json"
+	"os"
+	"testing"
+	"time"
+)
+
+// The fixture is a record the controller's own encoder wrote (json.Marshal of a chain.Build, mesh-controller
+// internal/chain, a throwaway test run once and deleted) with build-agent's build-1792395447088936520 values, plus a
+// manifest-digest and one made artifact, which a BuildRecord does not carry.
+func loadBuildFixture(t *testing.T) []byte {
+	t.Helper()
+	raw, err := os.ReadFile("testdata/build-record-build-agent.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	return raw
+}
+
+func TestBuildRecordDecodes(t *testing.T) { // 1223/AC1
+	var r BuildRecord
+	if err := json.Unmarshal(loadBuildFixture(t), &r); err != nil {
+		t.Fatal(err)
+	}
+	for _, c := range []struct{ name, got, want string }{
+		{"id", r.ID, "build-1792395447088936520"},
+		{"module", r.Module, "build-agent"},
+		{"repository", r.Repository, "novox/mesh-controller"},
+		{"ref", r.Ref, "main"},
+		{"commit", r.Commit, "7a74cee83f88e6585a5511c3cc53bdf0f5303d20"},
+		{"state", r.State, "built"},
+		{"source-fingerprint", r.SourceFingerprint, "src1:e846efe73716b78e80860baaac96153de2cb76551325753838ca245d2160a3d7"},
+	} {
+		if c.got != c.want {
+			t.Errorf("%s = %q, want %q", c.name, c.got, c.want)
+		}
+	}
+	if want := time.Date(2026, 10, 19, 9, 38, 0, 0, time.UTC); !r.At.Equal(want) {
+		t.Errorf("at = %v, want %v", r.At, want)
+	}
+	if r.SourceInputs == nil {
+		t.Fatal("source-inputs missing")
+	}
+	fp, none := SourceFingerprint(*r.SourceInputs)
+	if none != "" || fp != r.SourceFingerprint {
+		t.Errorf("SourceFingerprint of the decoded inputs = %q (none %q), the record says %q", fp, none, r.SourceFingerprint)
+	}
+}
+
+func TestBuildRecordWithoutInputs(t *testing.T) { // 1223/AC2
+	var m map[string]json.RawMessage
+	if err := json.Unmarshal(loadBuildFixture(t), &m); err != nil {
+		t.Fatal(err)
+	}
+	delete(m, "source-inputs")
+	raw, _ := json.Marshal(m)
+	var r BuildRecord
+	if err := json.Unmarshal(raw, &r); err != nil {
+		t.Fatal(err)
+	}
+	if r.SourceInputs != nil {
+		t.Errorf("source-inputs = %+v, want nil", r.SourceInputs)
+	}
+	if r.Module != "build-agent" {
+		t.Errorf("module = %q, want build-agent", r.Module)
+	}
+}
+
+func TestBuildKeys(t *testing.T) { // 1223/AC3
+	// Literal values of mesh-controller internal/broker/controller_buckets.go:101 (BucketName(ControllerSeat, ChainBuilds)
+	// is "mesh-controller_builds") and internal/chain/keys.go:35-46.
+	if BuildsBucket != "mesh-controller_builds" {
+		t.Errorf("BuildsBucket = %q", BuildsBucket)
+	}
+	if got := BuildKey("build-agent", "build-1"); got != "build-agent.build.build-1" {
+		t.Errorf("BuildKey = %q", got)
+	}
+	if got := BuildKey("", "build-1"); got != "req.build-1" {
+		t.Errorf("BuildKey without a module = %q", got)
+	}
+	if got := NewestKey("build-agent"); got != "build-agent.newest" {
+		t.Errorf("NewestKey = %q", got)
+	}
+}
diff --git a/go/delivery/testdata/build-record-build-agent.json b/go/delivery/testdata/build-record-build-agent.json
new file mode 100644
index 0000000..028ad4b
--- /dev/null
+++ b/go/delivery/testdata/build-record-build-agent.json
@@ -0,0 +1 @@
+{"id":"build-1792395447088936520","state":"built","repository":"novox/mesh-controller","ref":"main","module":"build-agent","commit":"7a74cee83f88e6585a5511c3cc53bdf0f5303d20","manifest-digest":"sha256:0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef","source-fingerprint":"src1:e846efe73716b78e80860baaac96153de2cb76551325753838ca245d2160a3d7","source-inputs":{"Module":"build-agent","Tree":"11c0b4f90cae0d6e4ef9cc48cbfdf9f6dbe52bca","Bases":["sha256:d9e853e87e55526f6b2917df91a2115c36dd7c696a35be12163d44e6e2a4b6bc","sha256:8ac98ca534ac3f51e1f420a1dd2c15e74c75cfa0f23f3ad27eb5d7236c349a0c"],"Contexts":{"server":"narrow:d51ca744fd11af59d616c858f76c27b3e58e16e11fbdc0c720eb9d7d19d55fac"},"Toolchains":null,"Unpinned":""},"made":[{"name":"server","kind":"image","reference":"registry.example/build-agent@sha256:d9e853e87e55526f6b2917df91a2115c36dd7c696a35be12163d44e6e2a4b6bc"}],"at":"2026-10-19T09:38:00Z"}