#34477 Update card: the What's New popover fits its lines; the Ready card is tighter

Leo, on the Update Ready card's hover popover: "also MAN this looks ugly... stretched out wasted space"

The popover for an update with no change list ("What's new in nightly X / Updating from nightly Y / See release notes") was drawn at the full 340 pt menu width, with the link pushed to the far right under a rule. Most of it was empty.

• Popover (UpdateSurfaces.tsx, updateSurfaces.css, surface.tsx): with no change list it is as wide as its lines (width: max-content, at most 340 px), with See release notes directly under the from line and no rule. The page reports its own width alongside its height (cmux.changelog.surface.size {height, width}), and the native host (SidebarPopoverIslandHost.fit(height:width:)) sizes the hover card to it. The popover with a change list keeps its menu width. Gallery: popover-empty (shipped, link under the from line), popover-empty-inline (link at the end of the from line), popover-empty-title-row (link at the end of the title), popover-empty-same-version. I picked the stacked one: it is the narrowest, and the link reads as its own action.
• Update Ready card (SidebarUpdateCardView): the gaps between the version line, the Automatic Updates switch and Restart to Update go from 8 to 6 pt.
• Updated card: after an automatic install that relaunched cmux behind another app (nobody clicked Restart to Update, UpdateRelaunchFocus), the card says "Updated to Nightly in the background", so it no longer seems to come with no restart. A web-only update never shows this card (whatsNew.showsUpdatedCard follows the native version, and a web swap shows nothing, per the 2026-10-30 call), so an Updated card is always a native relaunch. New string updates.card.updatedBehind in all 21 locales. Gallery: card-background.

Spec: design/sidebar.md (update card). References: none of Leo's update-card references are in cmux-design-references.
Risk: low. The width is used only when the page reports one, and the popover with a change list is unchanged.

Agent session: agent session

🤖 Generated with Claude Code

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Summary by cubic

Makes the What's New hover popover fit its lines for updates with no change list, tightens the Update Ready card, and clarifies the Updated card after a background update.

Changes

• The popover with no change list is now as wide as its lines (at most the menu width), with "See release notes" directly under the from line and no rule; the popover with a change list is unchanged. The page reports its own width and the host sizes the popover to it.
• The Update Ready card's row gaps go from 8 pt to 6 pt.
• After an automatic install that relaunched cmux behind another app, the Updated card now says "Updated to Nightly in the background"; the new string is translated in all 21 locales.