A site added two slides to the lobby display and it never changed between them.
onMounted awaited fetchSlides, which starts the slideshow itself once it has
more than one slide, and then started it AGAIN unconditionally. Two timer chains
ran, and the second assignment to slideTimer lost the handle to the first, so
nothing could ever cancel it. Both fired about ten seconds later, milliseconds
apart, and each advanced one slide.
With exactly two slides that is 0 -> 1 -> 0 every cycle: the display looked
frozen. With three or more it advanced by two and merely skipped one, which is
why this survived so long - and why adding a third slide would have appeared to
"fix" it.
onMounted no longer starts it; fetchSlides owns that. scheduleNextSlide also
cancels any pending timer before setting a new one, so a future double-call
replaces the chain rather than leaking an untracked one.
While here: the feed has always sent a per-slide duration and the display
ignored it, hardcoding ten seconds, so a slide set to hold for a minute changed
after ten. It now uses the slide's own value, and the progress bar animates over
that same duration instead of finishing early and sitting full.
b44108f70c