PythonBridge class

An in-process Dart ↔ Python byte channel, backed by the dart_bridge native library.

Each PythonBridge owns a ReceivePort whose native port doubles as the channel key in both directions:

• Python → Dart: when Python calls dart_bridge.send_bytes(port, payload), the payload arrives on this bridge's messages stream.
• Dart → Python: send hands bytes to the Python handler registered for this port via dart_bridge.set_enqueue_handler_func(port, handler).

Multiple bridges (UI channel, logging channel, future camera-stream channel, ...) can coexist in a single app — each bridge has its own port and its own Python-side handler.

Typical use:

final ui   = PythonBridge();
final logs = PythonBridge();

ui.messages.listen((Uint8List bytes) { /* UI events */ });
logs.messages.listen((Uint8List bytes) { /* log lines */ });

await SeriousPython.run('app/main.py', environmentVariables: {
  'MY_APP_UI_PORT':   '${ui.port}',
  'MY_APP_LOGS_PORT': '${logs.port}',
});

ui.send(Uint8List.fromList([1, 2, 3]));

The Python side reads the chosen env-var names to discover its port numbers — no convention is baked in here.