J4 (J3 item 7): merge A3's wip/registry-a3-sdk (c974a11): a holder's receiving side of a file in parts joins its sender

Brings A3's parts receiver and bus adapters, the shared caller lists and builder versions question, a transfer read
back from bus state (0424e87) and catalogue.SeatReference (c10ef07). c974a11 adds nothing: its version_numbered.go
and BuildAnswer.OutOfStep are the join's own. publish stays out (ADR 0627, 1a149d4): packages_list_test keeps the
join's form. TestAHolderTakesAFileInParts is a subtest of TestAFileTravelsInTheParts, so unit tests stay at 476.

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

go/delivery/builder_test.go

@@ -1,7 +1,9 @@
 package delivery
 
 import (
+	"encoding/json"
 	"errors"
+	"fmt"
 	"reflect"
 	"strings"
 	"testing"
@@ -174,6 +176,21 @@ func TestBuilderBuildVersion(t *testing.T) {
 			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

go/delivery/builder_versions.go

@@ -0,0 +1,38 @@
+package delivery
+
+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
+}