[Windows] PPTX preview should advance slides when mouse wheel reaches the page boundary

What version of the Codex App are you using (From “About Codex” dialog)?

26.818.8289.0 (Windows Store package version)

What subscription do you have?

ChatGPT subscription (exact tier not disclosed; this appears unrelated to the issue)

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

When a multi-slide .pptx file is opened in the Codex Desktop right-side preview, the mouse wheel only scrolls the viewport for the currently selected slide. Once the current slide has no remaining content in the wheel direction, continued scrolling does not advance to the next or previous slide.

This is especially noticeable when the whole slide already fits inside the preview. The wheel event appears to remain captured by the slide viewport even though there is nothing left to scroll. To continue reading, the user must move to the thumbnail list and select another slide manually.

This differs from the navigation behavior users commonly expect from PowerPoint and Windows document previews.

What steps can reproduce the bug?

1. Open Codex Desktop on Windows.
2. Open a conversation containing a .pptx file with multiple slides.
3. Click the file to open it in the right-side preview.
4. Place the pointer over the large selected-slide area, not over the thumbnail list.
5. Scroll downward until the selected slide has no remaining vertical content.
6. Continue scrolling downward with the mouse wheel.

Actual result: the preview stays on the same slide. The large preview may move only within its own viewport, but the selected slide does not change.

The same occurs in reverse at the top boundary when scrolling upward.

What is the expected behavior?

The wheel should continue scrolling inside the current slide while that slide has content remaining in the requested direction. At the scroll boundary:

• scrolling down should select the next slide;
• scrolling up should select the previous slide;
• the active thumbnail and large preview should stay synchronized;
• the first and last slides should remain bounded;
• Ctrl+wheel zoom behavior should be preserved;
• trackpad momentum should be debounced or accumulated so one gesture does not skip several slides unintentionally.

In short, the viewer should hand off a wheel gesture from viewport scrolling to slide navigation only when the current viewport cannot scroll farther in that direction.

Additional information

• Reproduced with a multi-slide teaching presentation at approximately 46% zoom, where the current slide fit entirely inside the visible preview area.
• The issue concerns the Codex Desktop PPTX preview UI, not the PPTX file itself. The same file navigates normally in Microsoft PowerPoint.
• A screenshot is available but was not attached because it contains project-specific filenames and institution branding. A sanitized reproduction can be provided if needed.