finalize api for plugin events in backend

just need frontend impl now

backend/decky_loader/wsrouter.py

@@ -1,3 +1,4 @@
+from _typeshed import DataclassInstance
 from logging import getLogger
 
 from asyncio import AbstractEventLoop, create_task
@@ -8,7 +9,8 @@ from aiohttp.web import Application, WebSocketResponse, Request, Response, get
 from enum import IntEnum
 
 from typing import Callable, Coroutine, Dict, Any, cast, TypeVar, Type
-from dataclasses import dataclass
+
+from dataclasses import asdict, is_dataclass
 
 from traceback import format_exc
 
@@ -24,15 +26,9 @@ class MessageType(IntEnum):
 
 # WSMessage with slightly better typings
 class WSMessageExtra(WSMessage):
+    # TODO message typings here too
     data: Any
     type: WSMsgType
-@dataclass
-class Message:
-    data: Any
-    type: MessageType
-
-# @dataclass
-# class CallMessage
 
 # see wsrouter.ts for typings
 
@@ -133,7 +129,11 @@ class WSRouter:
         return ws
 
     # DataType defaults to None so that if a plugin opts in to strict pyright checking and attempts to pass data witbout specifying the type (or any), the type check fails
-    async def emit(self, event: str, data: DataType | None = None, data_type: Type[DataType]|None = None):
+    async def emit(self, event: str, data: DataType | None = None, data_type: Type[DataType] | None = None):
         self.logger.debug('Firing frontend event %s with args %s', data)
+        sent_data: Dict[Any, Any] | None = cast(Dict[Any, Any], data)
+        if is_dataclass(data):
+            data_as_dataclass = cast(DataclassInstance, data)
+            sent_data = asdict(data_as_dataclass)
 
-        await self.write({ "type": MessageType.EVENT.value, "event": event, "data": data })
+        await self.write({ "type": MessageType.EVENT.value, "event": event, "data": sent_data })