/diff is hiding some lines seemingly at random

### Describe the bug

I noticed _sometimes_ the diff is not showing all lines:

The line 193 is not showing! The line "appears" (it's still looks like it's _under_ the "original" line) when I move my cursor to the missing line:

Git diff shows this code section just fine, I also can't see any weird characters in hexedit:
```c#
internal static JniRuntime.JniValueManager CreateValueManager ()
{
if (RuntimeFeature.IsMonoRuntime) {
return new AndroidValueManager ();
}

if (RuntimeFeature.IsCoreClrRuntime || RuntimeFeature.IsNativeAotRuntime) {
return new JavaMarshalValueManager ();
}

throw new NotSupportedException ("Internal error: unknown runtime not supported");
}
```

I noticed that different lines disappear as I scroll. As I scroll, the line 193 appears, but now line 196 is hidden:

### Affected version

GitHub Copilot CLI 1.0.42-0.

### Steps to reproduce the behavior

The bug appears seemingly at random, I don't know how to reliably reproduce it.

### Expected behavior

All lines are shown in the diff.

### Additional context

- macOS
- ghostty

Beginne am Einstiegspunkt /diff und reproduziere das Verhalten fehlender Zeilen unter macOS in Ghostty beim Scrollen. Vergleiche den gerenderten Diff mit der Ausgabe von git diff; abgeschlossen ist die Aufgabe, wenn jede Diff-Zeile während des Scrollens sichtbar und stabil bleibt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.