Plots: Horizontal thumbnail gallery cannot be scrolled

[jmcphers]

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System details:

Positron and OS details:

Positron Version: 2025.06.0 (Universal) build 107
Code - OSS Version: 1.99.0
Commit: 74fd52a2bde0b2d9fe1f9cd38e6f41687a62bced
Date: 2025-05-20T03:33:38.969Z
Electron: 34.3.2
Chromium: 132.0.6834.210
Node.js: 20.18.3
V8: 13.2.152.41-electron.0
OS: Darwin arm64 24.4.0

Interpreter details:

N/A

Describe the issue:

Using a mouse, it is not possible to scroll the thumbnail gallery when it is at the bottom of the plots area (horizontal).

Steps to reproduce the issue:

1. Make a bunch of plots. In R, demo(graphics) will give you a bunch.
2. Resize the Plots panel so that it is taller than it is wide.
3. Attempt to scroll the plot thumbnail gallery on the bottom of the pane.

The gallery has no scrollbar. Focusing on it and using the mouse scroll wheel doesn't scroll it, either.

Expected or desired behavior:

Scrollable thumbnail gallery. When oriented vertically, the gallery has a scrollbar and can be scrolled correctly with the mouse wheel.

[jthomasmock]

I can scroll via Shift + Mouse Wheel or with my laptop's touchpad (without Shift)

[testlabauto]

Problem seems to primarily the absence of the scrollbar.

[timtmok]

Is scrolling attempted with a vertical scroll? It works for me when scrolling horizontally with a trackpad. Scrolling vertically with a mouse does not work and shift+scroll is normal for scrolling horizontally. A horizontal scrollbar would make sense to show the user it's not a vertical scroll.

[rodrigosf672]

Verified Fixed

Positron Version(s) : 2025.07.0 (Universal) build 88
OS Version          : Sequoia 15.5

Test scenario(s)

Scrolling horizontally across multiple plots in the Plots pane works.