[Bug]: Middle-click closing a right panel tab also pastes the primary selection into the composer on Linux

[kevinmarrec]

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. On Linux, select some text anywhere so it goes into the primary selection.
2. Open two or more right panel tabs, such as PR, browser, or Files.
3. Click into the composer so it has focus.
4. Without clicking anywhere else, middle-click one of the right panel tabs to close it.

Expected behavior

The tab closes and nothing is pasted into the composer.

Actual behavior

The tab closes, and the primary selection is also pasted into the composer.

This only happens when the composer has focus right before the middle-click. If I first click on an empty area so the composer loses focus, the middle-click only closes the tab. Middle-clicking a tab doesn't move focus, so the paste lands in whatever editable still has it.

This comes up all the time in my daily workflow: I switch back and forth between the composer and the right panel tabs (PR, browser, Files), so the composer almost always has focus when I go to close a tab.

Likely cause: RightPanelTabs.tsx handles middle-click close (added in #3161). It calls preventDefault() on the middle mousedown and in onAuxClick, but never on the middle mouseup. Chromium pastes the primary selection on Linux at mouseup time, before auxclick fires, so the preventDefault() in handleTabAuxClick runs too late to stop it.

The terminal already handles this: surface.ts cancels the middle mouseup on platforms where isMiddleClickPastePlatform() is true (#11018). The tab handler could add a matching onMouseUp that calls preventDefault() when event.button === 1.

Related: #15531 has the same root cause in the chat timeline. A shared fix, such as a document-level capture mouseup guard for middle-clicks that don't land in an editable, would cover both.

Impact

Minor bug or occasional failure

Version or commit

v0.0.46-nightly.20261005.2667

Environment

Linux (Omarchy / Hyprland, Wayland), T3 Code desktop v0.0.46-nightly.20261005.2667

Workaround

Click on an empty area first so the composer loses focus, or close tabs with the × button instead of a middle-click.

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Note

This issue was generated by Claude Opus 5.5 (high effort).