Detach prepared execution ownership from runners

internal/domain/session.go

@@ -18,5 +18,5 @@ func NormalizeSessionID(raw string) (string, error) {
 	if length := utf8.RuneCountInString(normalized); length > SessionIDMaxLength {
 		return "", fmt.Errorf("session_id length %d exceeds maximum %d", length, SessionIDMaxLength)
 	}
-	return normalized, nil
+	return strings.Clone(normalized), nil
 }