Fix model fallback across main/background/sync agents

src/plugin-interface.ts

@@ -5,6 +5,7 @@ import { createChatParamsHandler } from "./plugin/chat-params"
 import { createChatHeadersHandler } from "./plugin/chat-headers"
 import { createChatMessageHandler } from "./plugin/chat-message"
 import { createMessagesTransformHandler } from "./plugin/messages-transform"
+import { createSystemTransformHandler } from "./plugin/system-transform"
 import { createEventHandler } from "./plugin/event"
 import { createToolExecuteAfterHandler } from "./plugin/tool-execute-after"
 import { createToolExecuteBeforeHandler } from "./plugin/tool-execute-before"
@@ -49,6 +50,10 @@ export function createPluginInterface(args: {
       hooks,
     }),
 
+    "experimental.chat.system.transform": createSystemTransformHandler({
+      hooks,
+    }),
+
     config: managers.configHandler,
 
     event: createEventHandler({