fix(web): restore horizontal scrolling in right panel tabs

[Radu028]

Problem

The right panel tab strip doesn't scroll horizontally in the desktop app. Once the tabs overflow, the ones past the right edge can't be reached unless you widen the panel or close tabs. Trackpad and wheel do nothing over the strip.

Before

t3code-horizontal-scroll-before.mp4

After

t3code-horizontal-scroll-after.mp4

Cause

c2d44a3 ("Unify compact subheaders and diff file navigation") moved drag-region off the topbar container in RightPanelTabs.tsx and onto the tab strip's ScrollArea:

-  ownsDesktopTitleBar && "drag-region wco:pr-[...]",     // topbar container
+  ownsDesktopTitleBar && "wco:pr-[...]",
...
-  className="min-w-0 flex-1 rounded-none"
+  className={cn("min-w-0 flex-1 rounded-none", ownsDesktopTitleBar && "drag-region")}

-webkit-app-region: drag hands the area to the window manager, so the element stops getting pointer and wheel events. Putting it on the scroll container is what kills the scroll. Browser builds were never affected, since ownsDesktopTitleBar is isElectron && mode === "inline".

Fix

Drag region goes back on the topbar container, the ScrollArea gets [-webkit-app-region:no-drag]. Same split DiffPanelShell and the chat header already use: the container drags, the interactive children opt out.

The tradeoff is that you can no longer drag the window by the empty space inside the tab strip. The container padding on both sides becomes draggable instead, which it wasn't before, and that empty space only exists when the tabs fit, which is exactly when nobody needs to scroll.

RightPanelTabs was the only drag region in the app wrapping a scroll container. The others (SidebarChrome, NoActiveThreadState, settings, ChatView, DiffPanelShell) wrap buttons and labels, which the .drag-region button rule in index.css already excludes.

Test

RightPanelTabs.test.tsx renders the component with isElectron mocked true and checks that the drag region sits on the topbar and not on the scroll container. It fails on the pre-fix component.

Also ran vp test run src/components/RightPanelTabs.test.tsx and tsgo --noEmit in apps/web, vp lint, and the desktop app on macOS for the videos above.

8 changed lines in the component, plus the test.

---

Note

Low Risk
Small Electron-only CSS/class change for titlebar drag vs scroll, with a focused unit test and no auth or data-path impact.

Overview
Fixes horizontal tab scrolling in the Electron desktop app when the right panel owns the title bar.

RightPanelTabs moves drag-region back onto the topbar (data-right-panel-tabbar) and applies [-webkit-app-region:no-drag] on the tab strip ScrollArea instead of putting drag on the scroll container—matching DiffPanelShell / chat header so wheel and pointer events reach the scroller.

Adds RightPanelTabs.test.tsx (SSR markup with isElectron mocked) to assert drag stays on the tabbar and the tab list opts out of drag.

^{Reviewed by Cursor Bugbot for commit 3e7fb5a. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix horizontal scrolling in RightPanelTabs scroll area when Electron title bar is active

In Electron inline mode, the tab bar container was applying drag-region to the scroll area, which blocked pointer and wheel events needed for horizontal scrolling. The fix moves drag-region to the outer container and applies [-webkit-app-region:no-drag] to the ScrollArea instead, allowing the tab list to receive scroll events while the surrounding bar remains draggable. A new test in RightPanelTabs.test.tsx verifies both classes are applied to the correct elements.

^{Macroscope summarized 3e7fb5a.}

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[macroscopeapp]

Approvability

Verdict: Approved 3e7fb5a

Straightforward CSS fix for Electron titlebar drag behavior. Moves the drag-region to the parent container while opting the scroll container out with -webkit-app-region:no-drag, allowing horizontal tab scrolling. Includes a unit test verifying the expected behavior.

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