feat(diagnostics): split error and shutdown messages

tools/sitl/src/config/tests.rs

@@ -345,11 +345,12 @@ fn rejected_config_result_enqueues_a_separate_high_level_error_payload() {
     let Some(DiagnosticPayload::Error(payload)) = service.pending_diagnostic_payload() else {
         panic!("rejected configuration result must enqueue KAPTAN_ERROR");
     };
-    let message = std::str::from_utf8(&payload.message[..usize::from(payload.message_length)])
-        .expect("derived error identity remains UTF-8");
+    let error_path = std::str::from_utf8(&payload.path[..usize::from(payload.path_length)])
+        .expect("derived error path remains UTF-8");
     assert_eq!(
-        message,
+        error_path,
         "kaptan_config_mavlink::protocol::ProtocolError::GenerationConflict"
     );
+    assert_eq!(payload.additional_information_length, 0);
     let _ = fs::remove_file(&path);
 }