Avoid redundant decoded graph clones

internal/framework/evidencecontext/build.go

@@ -84,11 +84,11 @@ func Build(request BuildRequest) (Document, error) {
 		}
 		document.Contexts = append(document.Contexts, context)
 	}
-	canonical, err := canonicalize(document)
+	canonical, err := canonicalizeOwned(document)
 	if err != nil {
 		return Document{}, fmt.Errorf("validate evidence context: %w", err)
 	}
-	return clone(canonical)
+	return canonical, nil
 }
 
 type evidenceKey struct {