BL6 (key codec): the catalog key's codec is meshcatalogkey, so the builder's builds package reaches no bus

meshcatalogclient imports the new package and keeps two one-line wrappers for the callers of the other parts until
they move to it.

Builds: design 47 G §670, §614 (wiring unchanged)

Claude-Session: https://claude.ai/code/session_01JG73KEq4zoDfM9WtYpcQgZ

contracts/go/clients/meshcatalogclient/fingerprint.go

@@ -5,14 +5,11 @@
 package meshcatalogclient
 
 import (
-	"fmt"
-	"strings"
-
-	"git.novox.be/novox/mesh-sdk/go/keys"
+	"git.novox.be/novox/mesh-delivery/contracts/go/clients/meshcatalogkey"
 )
 
 // SourcePrefix2 opens every source fingerprint of the form.
-const SourcePrefix2 = "src2:"
+const SourcePrefix2 = meshcatalogkey.SourcePrefix2
 
 // Toolchain2 is what an artifact's toolchain enters the fingerprint as (novox/hq ADR 0405 clause 7): the artifact's
 // language, the installed toolchain's version and the build module's recipe version.
@@ -22,20 +19,8 @@ type Toolchain2 struct {
 	Recipe   string
 }
 
-// KeyPart is a fingerprint as a key part: its 64 hex digits without the prefix, since a bus key may not hold ':'. It
-// refuses a value that is not `src2:` and 64 lowercase hex digits, a src1 fingerprint included, naming it.
-func KeyPart(fp string) (string, error) {
-	part, ok := strings.CutPrefix(fp, SourcePrefix2)
-	if !ok || !keys.IsHex64(part) {
-		return "", fmt.Errorf("fingerprint: %q is not a fingerprint of the form, %s and 64 lowercase hex digits", fp, SourcePrefix2)
-	}
-	return part, nil
-}
+// KeyPart is meshcatalogkey.KeyPart, the codec of a catalog key's parts (design 47 G §670).
+func KeyPart(fp string) (string, error) { return meshcatalogkey.KeyPart(fp) }
 
-// ParseKeyPart is the inverse of KeyPart. It refuses a part that is not 64 lowercase hex digits, naming it.
-func ParseKeyPart(part string) (string, error) {
-	if !keys.IsHex64(part) {
-		return "", fmt.Errorf("fingerprint: %q is not the key part of a fingerprint, 64 lowercase hex digits", part)
-	}
-	return SourcePrefix2 + part, nil
-}
+// ParseKeyPart is meshcatalogkey.ParseKeyPart.
+func ParseKeyPart(part string) (string, error) { return meshcatalogkey.ParseKeyPart(part) }

contracts/go/clients/meshcatalogclient/go.mod

@@ -3,6 +3,7 @@ module git.novox.be/novox/mesh-delivery/contracts/go/clients/meshcatalogclient
 go 1.26.0
 
 require (
+	git.novox.be/novox/mesh-delivery/contracts/go/clients/meshcatalogkey v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/contracts/go/seats/meshcatalog v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-sdk/go v0.0.0-00010101000000-000000000000
 )

contracts/go/clients/meshcatalogkey/go.mod

@@ -0,0 +1,5 @@
+module git.novox.be/novox/mesh-delivery/contracts/go/clients/meshcatalogkey
+
+go 1.26.0
+
+require git.novox.be/novox/mesh-sdk/go v0.0.0-00010101000000-000000000000

contracts/go/clients/meshcatalogkey/key.go

@@ -0,0 +1,32 @@
+// Package meshcatalogkey is the codec of a catalog key's parts (design 47 G §670): a fingerprint as the part of a bus
+// key, and back. It imports neither mesh-sdk's views nor the bus client, so a package that only reads and writes keys
+// (the builder's builds package) reaches no bus; meshcatalogclient imports it.
+package meshcatalogkey
+
+import (
+	"fmt"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/keys"
+)
+
+// SourcePrefix2 is the prefix of a fingerprint of the current form.
+const SourcePrefix2 = "src2:"
+
+// KeyPart is a fingerprint as a key part: its 64 hex digits without the prefix, since a bus key may not hold ':'. It
+// refuses a value that is not `src2:` and 64 lowercase hex digits, a src1 fingerprint included, naming it.
+func KeyPart(fp string) (string, error) {
+	part, ok := strings.CutPrefix(fp, SourcePrefix2)
+	if !ok || !keys.IsHex64(part) {
+		return "", fmt.Errorf("fingerprint: %q is not a fingerprint of the form, %s and 64 lowercase hex digits", fp, SourcePrefix2)
+	}
+	return part, nil
+}
+
+// ParseKeyPart is the inverse of KeyPart. It refuses a part that is not 64 lowercase hex digits, naming it.
+func ParseKeyPart(part string) (string, error) {
+	if !keys.IsHex64(part) {
+		return "", fmt.Errorf("fingerprint: %q is not the key part of a fingerprint, 64 lowercase hex digits", part)
+	}
+	return SourcePrefix2 + part, nil
+}

contracts/go/clients/meshcatalogkey/key_test.go

@@ -0,0 +1,39 @@
+package meshcatalogkey
+
+import (
+	"go/build"
+	"strings"
+	"testing"
+)
+
+func TestKeyPartRoundTripsAndRefusesOthers(t *testing.T) {
+	fp := "src2:" + strings.Repeat("a", 64)
+	part, err := KeyPart(fp)
+	if err != nil || part != strings.Repeat("a", 64) {
+		t.Fatalf("KeyPart = %q, %v", part, err)
+	}
+	if back, err := ParseKeyPart(part); err != nil || back != fp {
+		t.Fatalf("ParseKeyPart = %q, %v", back, err)
+	}
+	for _, bad := range []string{"src1:" + strings.Repeat("a", 64), "src2:abc", strings.Repeat("a", 64)} {
+		if _, err := KeyPart(bad); err == nil {
+			t.Errorf("KeyPart(%q) accepted", bad)
+		}
+	}
+	if _, err := ParseKeyPart("abc"); err == nil {
+		t.Error("ParseKeyPart(abc) accepted")
+	}
+}
+
+// Design 47 G §670: the package imports no bus.
+func TestThePackageImportsNoBus(t *testing.T) {
+	p, err := build.ImportDir(".", 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, i := range p.Imports {
+		if strings.Contains(i, "nats") || strings.Contains(i, "/views") {
+			t.Errorf("meshcatalogkey imports %s", i)
+		}
+	}
+}

modules/mesh-delivery-builder/builds/go.mod

@@ -4,7 +4,7 @@ go 1.26.0
 
 require (
 	git.novox.be/novox/mesh-delivery/contracts/go/clients/containerimageregistryclient v0.0.0-00010101000000-000000000000
-	git.novox.be/novox/mesh-delivery/contracts/go/clients/meshcatalogclient v0.0.0-00010101000000-000000000000
+	git.novox.be/novox/mesh-delivery/contracts/go/clients/meshcatalogkey v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/contracts/go/seats/containerimageregistry v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/contracts/go/seats/ociartifactregistry v0.0.0-00010101000000-000000000000
 	git.novox.be/novox/mesh-delivery/sdk v0.0.0-00010101000000-000000000000