Add simple messenger to check it Tridactyl is running in a tab

src/content.ts

@@ -48,6 +48,9 @@ messaging.addListener(
     messaging.attributeCaller(controller),
 )
 
+// eslint-disable-next-line @typescript-eslint/require-await
+messaging.addListener("alive", async () => true)
+
 // Hook the keyboard up to the controller
 import * as ContentController from "@src/content/controller_content"
 import { getAllDocumentFrames } from "@src/lib/dom"

src/lib/messaging.ts

@@ -13,6 +13,7 @@ export type TabMessageType =
     | "commandline_frame"
     | "state"
     | "lock"
+    | "alive"
 
 export type NonTabMessageType =
     | "owntab_background"
@@ -140,7 +141,7 @@ export async function messageActiveTab(
 export async function messageTab(
     tabId,
     type: TabMessageType,
-    command,
+    command?,
     args?,
 ): Promise<any> {
     const message: Message = {