A Flutter-command that attaches to applications that have been launched without
flutter run and provides a HotRunner (enabling hot reload/restart).
There are three ways for the attach command to discover a running app:
$ flutter attach --module=mod_name. This can be called either before or after the application is started, attach will poll the device if it cannot immediately discover the port
flutter attachsuffices. Flutter tools will search for an already running Flutter app or module if available. Otherwise, the tool will wait for the next Flutter app or module to launch before attaching.
$ flutter attach --debug-port 12345
See the source for the attach command.