[design-doctor effort high] replacement clone of sourcebot#2: [design-doctor test] sourcebot-1154: Commit diff viewer

[rohanneilkapoor]

Replacement Design Doctor reasoning-effort A/B clone for #2.

Variant: high.

This branch adds a no-op commit on top of the original PR head so the file contents are equivalent while GitHub checks stay isolated to this test PR.

Replaces contaminated setup PR: #26.

[softlight]

Header controls render with an extra nested button box

The action and close controls in the commit diff and file-preview headers are wired with an extra interactive layer around each button, which can surface a stray outline, doubled focus stops, and uneven hover feedback. They should feel like the single, clean controls used elsewhere in the commit views.

Prompt to fix with AI

This is a comment left during a design review.

Comment:
**Header controls render with an extra nested button box**
The action and close controls in the commit diff and file-preview headers are wired with an extra interactive layer around each button, which can surface a stray outline, doubled focus stops, and uneven hover feedback. They should feel like the single, clean controls used elsewhere in the commit views.

Issue:
All three new headers render `<TooltipTrigger>` (no asChild) directly wrapping `<Button asChild ...>` which itself Slots into a `<Link>`. Because Radix `TooltipTrigger` defaults to rendering its own `<button>`, the result is a `<button>` wrapping the Button's `<a>` — a nested interactive element with a redundant default button box, two focus targets, and hover/focus styling applied to the inner anchor only. fullCommitDiffPanel.tsx L79, focusedCommitDiffPanel.tsx L156, codePreviewPanel.tsx L105.

Suggested fix:
Add `asChild` to each `<TooltipTrigger>` in fullCommitDiffPanel.tsx (L79, Browse files), focusedCommitDiffPanel.tsx (L156, Exit diff view), and codePreviewPanel.tsx (L105, Close preview), matching commitParts.tsx CommitActionLink.

How can I resolve this? Keep the fix scoped to the PR-touched UI and preserve existing design-system patterns.

[softlight]

Close and exit controls don't match the shared icon action

The close and exit controls in the focused diff and file-preview headers are built by hand instead of matching the shared icon action used on the file rows, so their sizing, tooltip, and hover behavior can drift from the rest of the commit views. Reusing the standard control keeps these affordances consistent and predictable.

Prompt to fix with AI

This is a comment left during a design review.

Comment:
**Close and exit controls don't match the shared icon action**
The close and exit controls in the focused diff and file-preview headers are built by hand instead of matching the shared icon action used on the file rows, so their sizing, tooltip, and hover behavior can drift from the rest of the commit views. Reusing the standard control keeps these affordances consistent and predictable.

Issue:
focusedCommitDiffPanel.tsx (L156) and codePreviewPanel.tsx (L105) inline-build an icon-only ghost action: `<Tooltip><TooltipTrigger><Button asChild variant="ghost" size="icon" className="h-6 w-6 text-muted-foreground"><Link aria-label=...><X/></Link></Button></TooltipTrigger><TooltipContent>...`.

Suggested fix:
Replace the inline Tooltip+Button+Link X controls in focusedCommitDiffPanel.tsx and codePreviewPanel.tsx with `<CommitActionLink href=... label="Exit diff view"|"Close preview" icon={<X className="h-4 w-4"/>} />`, which also resolves the asChild issue for these two controls.

How can I resolve this? Keep the fix scoped to the PR-touched UI and preserve existing design-system patterns.