#24022 check-overlay-glass: hover card bodies draw only on the one glass window (stacked on #23801)

Native hover cards can't turn solid again. The new lint rules apply to every hover card body.

Leo-ask: ask-d547ac77f0

Stacked on #23801, which adds scripts/cmux-next/check-overlay-glass.py. This branch starts from #23801's head (433dfb01), so review only the top commit (2df1ca09). After #23801 squash-merges, a base merge reduces the diff to that commit.

Audit (native). Every native hover card already shows in the app's one hover card window, HoverCardPanel, which is plain themed glass (#23740; #23801 made the card fill opt-in). None needed a fix:

• tab and tab group cards (TabHoverCardView, GroupHoverCardView)
• link chip preview in Home (HomeLinkPreviewCardView)
• sidebar workspace and group cards (WorkspaceHoverCard)
• sidebar pull request card (SidebarPullRequestCard)
• What's New highlights (SidebarUpdateCardView+Popover)

The only fills inside them are Palette.hoverFill (thumbnail placeholder, row hover), clear, and a pill tint at 14%.

Change. check-overlay-glass.py now treats any file that hands a body to that window (HoverCardBody() or reports a card's lines (HoverCardTextReporting) as a hover card body, and flags:

• hover-own-window: the body builds its own window or material (NSPanel, NSPopover, NSWindow, NSVisualEffectView, OverlaySurfaceView, makeOverlayPanel).
• hover-body-fill: a backgroundColor, fillColor or .background(...) that isn't Palette.hoverFill, clear, nil, or a color under 0.6 alpha. Each branch of a ternary is checked.

The panel and its definitions are exempt (HoverCardPanel.swift, HoverCardSource.swift, HoverCardRow.swift). The glass-opaque-allow: escape and the ALLOWED table work as before. check-overlay-glass.test.sh adds fixtures that should fail (popover, own glass, solid fill, solid ternary branch) and ones that should pass (hover fill, clear, 14% pill, escaped dot, the same fill outside a body).

The web hover cards are covered by #23997.

Verification (huge-blue):

• python3 -I scripts/cmux-next/check-overlay-glass.py . → ok.
• bash scripts/cmux-next/tests/check-overlay-glass.test.sh → ok.
• Mutation check: adding layer?.backgroundColor = Palette.background.cgColor to TabHoverCardView.swift gives [hover-body-fill] at that line. Reverted afterwards.

This commit changes no Swift; the only Swift in the diff comes from #23801.

No capture: lint only, nothing on screen changes.

Agent session: cosmic-gray

🤖 Generated with Claude Code

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Summary by cubic

Adds hover card body rules to check-overlay-glass.py so native hover cards can't turn solid again. With #23801 merged into base, this branch carries only the lint and its tests. Hover card bodies must draw only on the app's one glass hover card window (HoverCardPanel).

• hover-own-window flags a body that builds its own window or material (NSPanel, NSPopover, NSWindow, NSVisualEffectView, OverlaySurfaceView, makeOverlayPanel).
• hover-body-fill flags a backgroundColor / fillColor / .background(...) that isn't Palette.hoverFill, clear, nil, or under 0.6 alpha; each ternary branch is checked.
• Existing glass-opaque-allow: comments and the ALLOWED table still apply, and stale allowances fail.
• check-overlay-glass.test.sh adds failing and passing fixtures for each rule form.