iOS Scroll freezes entire Rust event loop #5091
Description
iOS Scroll freezes entire Rust event loop
Problem
On iOS, all events are blocked while the user is scrolling. Events queue up and deliver only after scrolling stops.
This breaks every Tao-based iOS app that needs real-time updates during scroll.
Affected
- Signal/state updates
- Async task completions
- Cross-thread UI communication
Screen Recording of Issue
https://github.com/rapporian/ios-scroll-blocks-rust/raw/refs/heads/main/ScreenRecording.mp4
(Red dot = Rust, Green dot = JavaScript. Watch the red dot freeze during scroll while green continues.)
Reproduction
Repo: https://github.com/rapporian/ios-scroll-blocks-rust
Scroll the page. Watch the Rust-driven animation freeze while JavaScript requestAnimationFrame continues.
Root Cause
During scroll, iOS switches to UITrackingRunLoopMode — observers don't fire, events don't get processed.