Entering picture-in-picture read as the lightbox being dismissed, and the
session died with it: both Teleport and KeepAlive move their subtree on
deactivation, which the PiP spec treats as removal.
MediaLightbox now listens for the video's own enterpictureinpicture event —
so PiP entered by the browser's native control behaves identically to the
toolbar button — and follows a fixed order: adopt, animate, then emit close.
Adopting first is what makes the element survive the unmount the emit
triggers; the invariant is documented in place so a refactor cannot reorder
it innocently.
The backdrop animates a handoff on the PiP path only, closing on transitionend
with a bounded 350ms fallback for browsers that skip the transition and for
the reduced-motion path where the duration is zero and the event never fires.
Verified: 5 new tests plus the full frontend suite green.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
