diff --git a/go/clients/nodeengineclient/composed.go b/go/clients/nodeengineclient/composed.go
index b8f5356..aded503 100644
--- a/go/clients/nodeengineclient/composed.go
+++ b/go/clients/nodeengineclient/composed.go
@@ -20,16 +20,18 @@ import (
 // alone, so the encoding keeps the field order its first writer used, which the contract's generated type (fields sorted)
 // does not: the wire structs below hold it.
 
-// SourcePrefix is the start of a fingerprint of the new form, `src2:` and 64 lowercase hex digits.
-const SourcePrefix = "src2:"
+// sourcePrefix opens a source fingerprint of the form mesh-catalog's client defines (meshcatalogclient.SourcePrefix2,
+// KeyPart); a client imports no other seat's client (ADR 0625 §4), so a composition's field is checked here for that form
+// only, and a caller makes the key part with meshcatalogclient.KeyPart.
+const sourcePrefix = "src2:"
 
-// FingerprintKeyPart is a new-form fingerprint as the key part of ComposedKey: its 64 hex digits without the prefix.
-func FingerprintKeyPart(fp string) (string, error) {
-	part, ok := strings.CutPrefix(fp, SourcePrefix)
+// checkFingerprintForm refuses a fingerprint that is not `src2:` and 64 lowercase hex digits, naming it.
+func checkFingerprintForm(fp string) error {
+	part, ok := strings.CutPrefix(fp, sourcePrefix)
 	if !ok || !keys.IsHex64(part) {
-		return "", fmt.Errorf("node-engine: %q is not a fingerprint of the new form, %s and 64 lowercase hex digits", fp, SourcePrefix)
+		return fmt.Errorf("node-engine: %q is not a fingerprint of the new form, %s and 64 lowercase hex digits", fp, sourcePrefix)
 	}
-	return part, nil
+	return nil
 }
 
 // Composition is one module's resources composed for one node at one fingerprint, or, with Module and FP empty, the node's
@@ -171,11 +173,10 @@ func (c Composition) check() error {
 			return fmt.Errorf("node-engine: the node's own composition carries no plan and no refusal: only a module's does")
 		}
 	} else {
-		part, err := FingerprintKeyPart(c.FP)
-		if err != nil {
+		if err := checkFingerprintForm(c.FP); err != nil {
 			return err
 		}
-		if _, err := ComposedKey(c.Node, c.Module, part); err != nil {
+		if _, err := ComposedKey(c.Node, c.Module, strings.TrimPrefix(c.FP, sourcePrefix)); err != nil {
 			return err
 		}
 		if !ownIsEmpty(c.Own) {
diff --git a/go/clients/nodeengineclient/composed_test.go b/go/clients/nodeengineclient/composed_test.go
index 725b824..0fe22fa 100644
--- a/go/clients/nodeengineclient/composed_test.go
+++ b/go/clients/nodeengineclient/composed_test.go
@@ -36,7 +36,7 @@ func captured(t *testing.T) (account string, byModule map[string][]json.RawMessa
 	return c.Account, byModule
 }
 
-func fp(n int) string { return SourcePrefix + fmt.Sprintf("%064x", n) }
+func fp(n int) string { return sourcePrefix + fmt.Sprintf("%064x", n) }
 
 // TestCompositionDigests: a composition's digest is the one the first writer computed (the values are the digests
 // mesh-sdk's delivery package gave for the same compositions when it moved here), whatever order the contract's generated