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) # Why When installing an app onto a physical iOS device, Apple's xcrun devicectl tool frequently drops the connection immediately after the initial handshake, throwing com.apple.dt.CoreDeviceError error 4000 (0xFA0). Because @expo/cli currently reads stderr synchronously on the process close event (childProcess.stderr.read()), this error is often swallowed if the stream is already flushed. This results in an unhelpful Error: null crash that leaves developers confused and without any actionable debugging information. Furthermore, the lack of a retry mechanism means these transient network/USB disconnects strictly fail the build every time. # How 1. Fixed `Error: null` masking: Replaced the synchronous stderr.read() call with an asynchronous stderr.on('data', ...) buffer accumulator to reliably capture and surface the true error output from the Apple toolchain. 2. Added Exponential Backoff: Wrapped the devicectl spawn logic in an exponential backoff retry loop (up to 3 attempts). 3. Targeted Retries: The retry loop strictly checks the error message and only intercepts transient disconnect errors (CoreDeviceError / 0xFA0). All other deterministic errors fail immediately. 4. Preserved Cancellation: Explicitly catches error.code === 'detached' to ensure that user cancellations (e.g., pressing Ctrl+C) immediately abort the process instead of trapping the developer in the retry loop. 5. Preserved UX: Maintained the asynchronous spawn approach and standard IO parsing so the CLI ora spinner and 34%... progress updates remain fully functional. # Test Plan - Ran npx expo run:ios --device <uuid> targeting a physical iPhone via USB. - Before: Observed an immediate CLI crash outputting Error: null. - After (Error surfacing): Verified that the CLI successfully captures and prints the underlying CoreDeviceError error 4000 (0xFA0). - After (Retry Logic): Verified that the CLI catches the transient error, waits 2 seconds, updates the ora spinner to Installing (attempt 2), and successfully installs the app on the second attempt without breaking the event loop. - Cancellation: Verified that pressing Ctrl+C during an installation attempt successfully and immediately aborts the process. # Checklist - [X] I added a `changelog.md` entry and rebuilt the package sources according to [this short guide](https://github.com/expo/expo/blob/main/CONTRIBUTING.md#-before-submitting) - [X] This diff will work correctly for `npx expo prebuild` & EAS Build (eg: updated a module plugin). - [ ] Conforms with the [Documentation Writing Style Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md) --------- Co-authored-by: Phil Pluckthun <phil@kitten.sh>
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