Consider a Dart usage of a C api through ffi. A common pattern is the usage of context objects that must be explicitly setup and torn down for a given thread. ( This is simplified from an example program I wrote using https://sol.gfxile.net/soloud/ )

final lib = ffi.DynamicLibrary.open('some.dll');

class SoundSystem {
  ffi.Pointer _audioContext = lib.createContext();

  SoundSystem() {
    lib.setupContext(_audioContext);
   }
   
   void playSound() {
     lib.playSound(_audioContext);
   }
   
   void dispose() {
     lib.destroyContext(_audioContext);
   }
}

While this works well enough when performing a hot reload, but a hot restart may cause a native crash as recreating the SoundSystem with cause another audio context to be created without destroying the previous one.

During normal program execution this isn't a problem, since the dispose can be connected to the correct part of the application teardown logic ( or the handled by the OS as the program exits).

Trying to do something like teardown the entire widget tree may solve this problem, but would be expensive as well as a large behavior change with unintended consequences. Instead, I would propose adding a binding hook that allows developers/library authors to run callbacks before the hot restart is performed. The risk should be lower since the feature is opt-in, and failures could be ignored since the isolate would be destroyed anyway (though detecting these failures without using something like a timeout will be tricky).

For example, the above code could be modified like:

final lib = ffi.DynamicLibrary.open('some.dll');

class SoundSystem {
  ffi.Pointer _audioContext = lib.createContext();

  SoundSystem() {
    if (kDebugMode) {
      SomeBinding.instance!.addHotRestartTeardown(dispose);
    }
    lib.setupContext(_audioContext);
   }
   
   void playSound() {
     lib.playSound(_audioContext);
   }
   
   void dispose() {
     lib.destroyContext(_audioContext);
   }
}

This won't work if the library is trying to be platform agnostic though - which means we might need to consider either dart level support or a convention around using a dart:developer API. For example, something like

import 'dart:developer';

final lib = ffi.DynamicLibrary.open('some.dll');

class SoundSystem {
  ffi.Pointer _audioContext = lib.createContext();

  SoundSystem() {
    if (kDebugMode) {
      registerExtension('dart.ext.hotRestartTeardown', dispose);
    }
    lib.setupContext(_audioContext);
   }
   
   void playSound() {
     lib.playSound(_audioContext);
   }
   
   void dispose() {
     lib.destroyContext(_audioContext);
   }
}

Unfortunately I don't think that will work out of the box, since the various different libraries would stomp on eachother with different callbacks