[Xcode 27] Newly paired and/or upgraded devices hang on white screen after launch #189284

When using Xcode 27, DeviceSupport symbols are download into an arm64e subdirectory:

- $HOME/Library/Developer/Xcode/iOS DeviceSupport/iPad14,3 27.0 (24A5370h)/Symbols
+ $HOME/Library/Developer/Xcode/iOS DeviceSupport/iPad14,3 27.0 (24A5370h)/arm64e/Symbols

This causes LLDB to not be able to find them, which then causes LLDB to be extremely slow. It does start eventually, but only after ~5 minutes of hanging on the white screen.

Steps to repro:

Do the following steps to start with a clean slate:

1. Connect a physical iOS device via USB
2. Open Device Hub
3. Right click on device and select "Unpair..." and disconnect the device via USB
4. Device Hub > Quit Device Hub
5. Navigate in Finder to "/Users/username/Library/Developer/Xcode/iOS DeviceSupport" and delete the subdirectory for the device

Then do these steps as if connecting the device for the first tim:

1. Connect the device via USB
2. Click "Trust" on the device
3. Open Device Hub
4. Right click on device and select "Pair"
5. Open Xcode 27 (this is the only way I could figure out to trigger Xcode to start downloading the symbols)
6. If you look in the iOS DeviceSupport directory, you'll see the symbols have started to download:

And you can tell it's done when there's a .finalized

7. Do flutter run
8. The app will launch with a white screen and then hang.
   After about ~10 seconds, you should see message warning: libobjc.A.dylib is being read from process memory. This indicates that LLDB could not find the on-disk shared cache for this device. This will likely reduce debugging performance.

If you wait ~5 minutes, it will eventually start