refactor: unify monitor abort lifecycle handling

src/discord/monitor/gateway-error-guard.ts

@@ -0,0 +1,36 @@
+import type { Client } from "@buape/carbon";
+import { getDiscordGatewayEmitter } from "../monitor.gateway.js";
+
+export type EarlyGatewayErrorGuard = {
+  pendingErrors: unknown[];
+  release: () => void;
+};
+
+export function attachEarlyGatewayErrorGuard(client: Client): EarlyGatewayErrorGuard {
+  const pendingErrors: unknown[] = [];
+  const gateway = client.getPlugin("gateway");
+  const emitter = getDiscordGatewayEmitter(gateway);
+  if (!emitter) {
+    return {
+      pendingErrors,
+      release: () => {},
+    };
+  }
+
+  let released = false;
+  const onGatewayError = (err: unknown) => {
+    pendingErrors.push(err);
+  };
+  emitter.on("error", onGatewayError);
+
+  return {
+    pendingErrors,
+    release: () => {
+      if (released) {
+        return;
+      }
+      released = true;
+      emitter.removeListener("error", onGatewayError);
+    },
+  };
+}