useBackToClose closes an overlay programmatically (X button or ESC) by
setting the module-global suppressPop=true and calling history.back(), so
the remaining overlays' popstate handlers ignore that synthetic pop. But
the flag was only ever reset by one of those handlers — when the closed
overlay had no overlay underneath it (the common single-player case),
nothing consumed it and suppressPop leaked true.
The next overlay's first real Back then hit the stale true, reset it and
returned early without closing — the Back was silently swallowed. Symptom
in the YouTube-search flow: close the player with the X button, open
another, press Back once -> nothing happens; a second Back closes it AND
discards the search results, dumping you on the normal feed.
Fix: register a one-shot popstate listener alongside suppressPop=true so
the flag is cleared on that very pop even when no overlay remains to
consume it. Nesting is unaffected (an underlying overlay still short-
circuits first and the one-shot is a redundant no-op).
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