set an interface for evaluated widgets?

[thePrivacyFanatic]

Hello, i am having trouble understanding how the runtimeWidget works (mostly due to my current lack of experience in flutter).
i am trying to make a modular app that can load custom widgets from bytecode files and use them, but it would require the widgets to expose some interface or inherit from some class, I.E.

interface class EvWidget {
  void init(String stateJson, Function(String messageJson) sendCallback) {}
  void update(String transactionJson) {}
}

how can i verify the interface's implementation across these widgets (if i can) so that i can show the user an error if incompatible widgets are loaded?
alternatively is there a way to make the evaluated widgets inherit from a class? (it would allow a more elegant and maybe efficient way to define the widgets but the file has no access to the apps classes before evaluation)
an answer would be appreciated