Chromium's touch selection takeover swallows pointerup in the fx iframe,
so the PDF popover's only trigger never fired on real phones — it only
appeared when timing happened to deliver the event. Mirror the EPUB
path: a selectionchange debounce (400ms settle) opens the popover, with
the pointerup path kept for desktop plus the quick-tap word-select guard.
Also place the popover BELOW the selection on coarse pointers (+90px
clearing the native selection menu and drag handles), matching the
reflowable path; desktop keeps above-placement.
John O'Keefe
960305dfa9