Solo Popover

The two pieces a surface needs when its floating cards are built one Popover per trigger — which is what a calendar, a board or a seating chart wants, because Headless then measures the button the card was opened from and nothing has to compute a coordinate.

OnlyOne keeps a single card open across all of them. Headless cannot: a Popover only knows about clicks outside itself, and PopoverButton stops that event while it takes focus, so the first card never hears the second opening. PopoverGroup manages focus, not siblings.

PopoverTrigger forwards every prop, including the ref Headless anchors against. A local button that names only the props it uses drops that ref, and the panel lands in the top-left corner of the page.