Distinguish reported and rendered preview scroll offsets

crates/oa-desktop/src/app/source_rename/preview_scroll_tests.rs

@@ -435,11 +435,15 @@ async fn details_remount_restores_wheel_offset_before_any_rescroll() {
         let mut mounted = Mounted::new(&app);
         let reports = mounted.wheel(&app);
         assert_eq!(reports.len(), 1, "one actual preview scroll report");
-        assert!(matches!(
-            reports[0],
-            Message::SourceRename(Event::PreviewScrolled(..))
-        ));
+        let reported_offset = match &reports[0] {
+            Message::SourceRename(Event::PreviewScrolled(_, _, _, offset)) => *offset,
+            _ => panic!("expected an actual preview scroll report"),
+        };
+        assert!(reported_offset.is_finite() && reported_offset > 0.);
         let offset = mounted.offset(&app);
+        // Iced reports fractional absolute offsets but exposes rounded display
+        // translation to widget operations. Preserve both representations exactly.
+        assert_eq!(reported_offset.round(), offset);
         assert!(
             offset > 10.,
             "real wheel input must move the overflowing fixture"
@@ -457,7 +461,7 @@ async fn details_remount_restores_wheel_offset_before_any_rescroll() {
         assert_eq!(evidence(&app), before);
         assert_eq!(
             app.source_rename.form.as_ref().unwrap().preview_offset,
-            offset
+            reported_offset
         );
 
         let details = app.update(Message::SourceRename(Event::Details(invocation, true)));
@@ -493,7 +497,7 @@ async fn details_remount_restores_wheel_offset_before_any_rescroll() {
         let form = app.source_rename.form.as_ref().unwrap();
         assert_eq!((form.file, form.hunk, form.line, form.segment), page);
         assert_eq!(form.approval.as_ref().unwrap().id, approval);
-        assert_eq!(form.preview_offset, offset);
+        assert_eq!(form.preview_offset, reported_offset);
         assert!(!app.source_rename_envelope(&stale));
         let task = app.update(Message::SourceRename(stale));
         assert_eq!(mounted.execute(&app, task).await, 0);