fix: Correct syntax error when shutdown called before BG service is running (#1940)

Author: jsantell

packages/background-charm-service/src/main.ts

@@ -39,15 +39,16 @@ const service = new BackgroundCharmService({
   workerTimeoutMs,
 });
 
-const shutdown = () => {
-  // @ts-ignore: Object is possibly 'undefined'
-  service.stop().then(() => {
-    Deno.exit(0);
-  });
-};
+function shutdown(service: BackgroundCharmService) {
+  return () => {
+    service.stop().then(() => {
+      Deno.exit(0);
+    });
+  };
+}
 
-Deno.addSignalListener("SIGINT", shutdown);
-Deno.addSignalListener("SIGTERM", shutdown);
+Deno.addSignalListener("SIGINT", shutdown(service));
+Deno.addSignalListener("SIGTERM", shutdown(service));
 
 service.initialize().then(() => {
   console.log("Background Charm Service started successfully");

packages/background-charm-service/src/service.ts

@@ -57,11 +57,11 @@ export class BackgroundCharmService {
     this.charmsCell.sink((cs) => this.ensureCharms(cs));
   }
 
-  stop() {
+  stop(): Promise<PromiseSettledResult<void>[]> {
     // FIXME(ja): stop listening to the charms cell ?
     if (!this.isRunning) {
       console.log("Service is not running");
-      return;
+      return Promise.resolve([]);
     }
 
     const promises = Array.from(this.charmSchedulers.values()).map(