diff --git a/crates/oa-desktop/src/app/scenario_reorder/tests.rs b/crates/oa-desktop/src/app/scenario_reorder/tests.rs
index 67fe3ed7..a5bc5308 100644
--- a/crates/oa-desktop/src/app/scenario_reorder/tests.rs
+++ b/crates/oa-desktop/src/app/scenario_reorder/tests.rs
@@ -78,6 +78,8 @@ fn setup(saved: bool) -> (App, Id, [Id; 4]) {
             id: diagram,
             label: "Saved".into(),
         }));
+    } else {
+        let _ = app.update(Message::Page(Page::Behavior));
     }
     for (id, choice) in [
         (f.reply, multiselect::Choice::Replace),
@@ -335,11 +337,11 @@ fn temporal_refusal_is_terminal_without_model_or_history_change() {
 }
 
 #[test]
-fn source_write_refusal_is_atomic_and_dirty_properties_block_begin() {
-    let (mut app, owner, _) = setup(true);
+fn exact_source_budget_permutation_preserves_trivia_and_dirty_properties_block_begin() {
+    let (mut app, owner, [a, b, x, y]) = setup(true);
     let mut bundle = app.document.bundle().clone();
-    // A legal compact authored list is smaller than the source writer's new
-    // canonical list. The exact source budget forces a real write failure.
+    // Reordering existing list chunks preserves their authored trivia and byte
+    // count; an exact budget is not a source-write failure injection.
     for text in bundle.files.values_mut() {
         *text = text
             .split_inclusive('\n')
@@ -369,20 +371,38 @@ fn source_write_refusal_is_atomic_and_dirty_properties_block_begin() {
     let epoch = app.canvas_epoch;
     finish(&mut app, slot);
     assert!(
-        app.status.starts_with("Reorder was not applied:"),
+        app.status.starts_with("Semantic order updated."),
         "{}",
         app.status
     );
     assert_ne!(app.canvas_epoch, epoch);
-    assert_eq!(app.project(), &baseline.decoded.project);
-    assert_eq!(app.document.bundle(), &baseline.bundle);
+    let mut expected = baseline.decoded.project.clone();
+    *expected
+        .elements
+        .get_mut(&owner)
+        .unwrap()
+        .steps_mut()
+        .unwrap() = vec![x, y, a, b];
+    assert_eq!(app.project(), &expected);
+    assert_eq!(
+        app.document
+            .bundle()
+            .files
+            .values()
+            .map(String::len)
+            .sum::<usize>(),
+        limits.model.max_source_bytes
+    );
     assert_eq!(
         app.multiselect_snapshot().unwrap().targets(),
         selection.targets()
     );
     assert_eq!(app.selected, primary);
     assert!(camera == app.behavior.scenario.camera_boundary());
-    assert!(!app.document.can_undo());
+    assert!(app.document.can_undo());
+    let _ = app.update(Message::Undo);
+    assert_eq!(app.project(), &baseline.decoded.project);
+    assert_eq!(app.document.bundle(), &baseline.bundle);
     let _ = app.update(Message::Field("/name".into(), "Unapplied name".into()));
     assert!(app.draft_dirty());
     let event = packet(&app, Intent::Begin);