The link had a custom hover tooltip that took the hidden events with
dayEvents.slice(3) - correct while dayMaxEvents was a fixed 3, wrong the moment
that cap started varying with the row height. On a short row showing one chip,
'+4 more' sliced from index 3 and listed the wrong events; on a day with three
events it sliced to nothing, hit the empty-list guard and rendered no tooltip at
all. A link with nothing behind it.
FullCalendar's own popover replaces it rather than the arithmetic being fixed:
no index to drift out of step with the cap, a header and a close button, every
event for that day listed, and it works on a touch screen - which a hover
tooltip never did on a kiosk. Clicking an event in the popover still opens the
detail modal.
That takes the hover handlers, the container mouseenter/mouseleave delegation,
the tooltip markup and styles, and the by-date index that existed only to feed
them: 108 lines out, 25 in. The popover is themed through the CSS variables,
since FullCalendar ships it light.
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