How Tapflow Solved Async Clipboard Sync Between Browser and Mobile Simulators

Tapflow, a browser-based device viewer, faced a two-part clipboard challenge: device clipboards operate asynchronously, and browsers enforce permission checks before a response from the device arrives. For paste, the browser captures the paste event and relays the text to a device agent, which writes it to the simulator's clipboard and triggers a platform-specific paste input — Cmd+V on iOS and KEYCODE_PASTE on Android. For copy, a fixed delay proved unreliable, so Tapflow instead writes a random sentinel value to the device clipboard, waits until it is confirmed visible, then polls for a changed value to confirm the app's copy command actually landed. If the copy fails, the original clipboard content is restored and verified before the device is unblocked for further clipboard operations. An additional browser constraint — Safari rejecting clipboard writes after the original user gesture expires — further shaped the final implementation approach.