feat(desktop): hover X close button on zone tabs

[austinpickett]

What

Adds a hover-to-close X button to PaneTab — the shared tab shell used by the fancy-zones layout, the file-preview rail, and collapsed vertical rails.

Why

Closing a tab required middle-click or ⌘-click — discoverable only by reading the code. A hover X is the standard IDE affordance and makes the feature self-evident.

How

• The close button slot is always reserved inline (shrink-0 size-4 mr-1.5) when onClose is set on a horizontal tab. The X is opacity-0 by default and opacity-100 on group-hover/tab. Because the slot is always present, the tab width never shifts when the X appears.
• The dirty dot yields to the X: when both onClose and dirty are present, the X renders (visible on hover) and the dirty dot is suppressed. Without onClose, the dirty dot still renders as before.
• Vertical tabs skip the X — writing-mode: vertical-rl makes an inline button awkward. The absolute-positioned dirty dot still works there.
• onPointerDown on the button is stopped so the tab's drag/activate pointerdown handlers never fire — the X is a leaf close action, not a drag start.

Files

• apps/desktop/src/components/ui/pane-tab.tsx — the close button + dirty-dot coordination
• apps/desktop/src/components/ui/pane-tab.test.tsx — tests for the new button (render, click, vertical skip, no-onClose skip)

Verification

cd apps/desktop
npx vitest run src/components/ui/pane-tab.test.tsx   # 10 passed
npx tsc --noEmit                                        # clean
npx eslint src/components/ui/pane-tab.tsx src/components/ui/pane-tab.test.tsx  # clean

[github-actions]

૮ >ﻌ< ა ci review

_{running on b281134}

CI timings

CI timings · View job

Wall time 7m21s vs 8m32s (-13.9%). 3 job(s) slower, 4 faster,

• Build&Test Docker image / build (amd64, ubuntu-latest, linux/amd64, type=gha,scope=docker-amd64, type=gha,mode=max,scope=do...: -39.0s
• Build&Test Docker image / build (arm64, ubuntu-24.04-arm, linux/arm64, type=gha,scope=docker-arm64, type=gha,mode=max,scope...: +32.0s
• OSV scan / Emit review status: +7.0s
• Detect affected areas: -3.0s
• Check uv.lock / uv lock --check: +3.0s

[rwxyx518-prog]

Real-world user here: I hit this today on v0.20.0 — the preview rail opens and there's no visible way to close it. I literally had to read the source to find the middle-click/Ctrl-click gestures. A hover X (or any visible close affordance) on preview tabs would save a lot of confusion. This PR would have fixed my exact complaint — hoping it gets merged soon. 🙏

[spfcraze]

This was generated by AI during triage.

Summary:
The new close button has no focus-visible state: it sits at opacity-0 until group-hover/tab, and since apps/desktop/src/styles.css removes focus outlines globally (outline: none on *:focus-visible), keyboard focus lands on an invisible button.

Problems:

• The button's className in apps/desktop/src/components/ui/pane-tab.tsx is opacity-0 group-hover/tab:opacity-100 — the only reveal path is pointer hover, with no focus-visible:opacity-100.
• apps/desktop/src/styles.css:993 sets outline: none for *:focus, *:focus-visible, so there is no native focus ring to fall back on either.
• The minimize button in the same strip (apps/desktop/src/components/pane-shell/tree/renderer/tree-group.tsx:435) carries focus-visible:opacity-100 — the established pattern for hover-reveal buttons in the desktop app.

Solution:
Add focus-visible:opacity-100 to the button's className, matching the minimize-button pattern.

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Checked against b281134 — the tip of feat/pane-tab-hover-close when this was written — and 83a1ca6, main at the same moment.

[angel12]

Confirmed this exact UX failure on Hermes v0.20.3 for a macOS artifact preview: the visible toolbar offered Copy and Download but no discoverable close action. Because this branch is now unmergeable against main and maintainer_can_modify is false, I opened #89243 as a current-main replacement by cherry-picking b281134 to preserve Austin’s authorship. The follow-up commit also adds the requested focus-visible path and keeps the dirty marker visible until hover/focus. This PR remains the source credited in the replacement body.