[Windows Desktop] Preserve viewport position when reasoning/progress blocks collapse

Environment

• Application: Codex Desktop for Windows
• Powered by: Codex & OWL
• Version: 26.803.41515
• Release date: August 7, 2026
• Platform: Windows

Problem

While using the Codex Desktop app on Windows, the viewport unexpectedly shifts while I am reading a newly generated response.

A typical interaction is:

1. Codex answers a question.
2. I scroll down to read the complete response, ending up at the bottom of the conversation.
3. I ask another question.
4. The new response starts appearing roughly around the middle of the screen, which is a comfortable position for reading.
5. I start reading the response while Codex continues generating it.
6. Temporary reasoning/progress content above the answer is then hidden or collapsed.
7. When that content disappears, the layout height changes and the viewport/scroll position is adjusted.
8. As a result, the text I was reading suddenly moves vertically, usually leaving the current response much lower on the screen.

This makes it difficult to read Codex responses while they are being generated because the content can move unexpectedly.

Expected behavior

Collapsing or hiding reasoning/progress content above the current viewport should not change the visual position of the text the user is currently reading.

If content above the viewport changes height, Codex should compensate for that height difference and preserve the current reading position.

For example, the UI could preserve an anchor element and its viewport offset, or adjust scrollTop by the height removed when the reasoning/progress block collapses.

The important UX behavior is:

If I am reading a specific line of the response, that line should remain at approximately the same position on my screen when reasoning/progress content above it is collapsed.

Steps to reproduce

1. Open Codex Desktop for Windows.
2. Use a conversation long enough to require scrolling.
3. Ask Codex a question.
4. Scroll down and read the complete response until reaching the bottom.
5. Send another question.
6. Start reading the new response while it is still being generated.
7. Wait for the temporary reasoning/progress content above the answer to be hidden or collapsed.
8. Observe that the viewport shifts and the text currently being read changes position.

Actual behavior

The viewport moves when temporary reasoning/progress content collapses, interrupting the user's reading position.

Expected behavior

The viewport should compensate for layout changes above the visible area so that the content currently being read remains stationary.

Related

Possibly related to issue #32030, involving scroll-anchor recalculation when content changes height.