Found via real-browser verification: with useState the prior commit's
handleTouchEnd captures swipeStart from its render closure, so when
touchstart and touchend fire inside the same React batch (fast swipe,
synthetic events, or a tight render cycle) the end handler reads the
stale null and skips navigation. useRef sidesteps the closure entirely
and is the right primitive for cross-event scratchpad state anyway.
Verified in a 4-photo gallery on mobile-emulation (390x844 touch):
- left swipe (-200px) advances 1/4 → 2/4
- right swipe (+200px) returns 2/4 → 1/4
- 20px swipe (under threshold) does not navigate
- vertical swipe (dy 300, dx 20) does not navigate
Paul Nothaft
fcddfe094b