fix: CJS/ESM p-limit import race

lib/asyncbox.ts

@@ -1,4 +1,4 @@
-import {limitFunction} from 'p-limit';
+import type {limitFunction} from 'p-limit';
 
 import type {
   CancellablePromise,
@@ -11,6 +11,17 @@ import type {
 
 const LONG_SLEEP_THRESHOLD = 5000; // anything over 5000ms will turn into a spin
 
+type PLimitModule = {limitFunction: typeof limitFunction};
+
+// p-limit is ESM-only. tsc downlevels a plain `import()` in CommonJS output into a
+// require()-in-a-microtask, which still hits Node's require(esm) interop and can race with a
+// concurrent dynamic import() of the same module elsewhere in the process
+// (ERR_REQUIRE_ESM_RACE_CONDITION). Route through `new Function` so tsc can't see or rewrite the
+// import() call, keeping it a genuine native dynamic import in both the ESM and CJS builds.
+const dynamicImport = new Function('specifier', 'return import(specifier)') as (
+  specifier: string,
+) => Promise<PLimitModule>;
+
 /** Error thrown by {@link withTimeout} when the deadline is exceeded. */
 export class TimeoutError extends Error {
   constructor(message?: string) {
@@ -241,7 +252,7 @@ export async function asyncmap<T, R>(
     );
   }
   const adjustedMapper =
-    options === true ? mapperAsync : limitFunction(mapperAsync, {concurrency: options.concurrency});
+    options === true ? mapperAsync : (await getLimitFunction())(mapperAsync, {concurrency: options.concurrency});
   return Promise.all(coll.map(adjustedMapper));
 }
 
@@ -271,7 +282,7 @@ export async function asyncfilter<T>(
     }, Promise.resolve([]));
   }
   const adjustedFilter =
-    options === true ? filterAsync : limitFunction(filterAsync, {concurrency: options.concurrency});
+    options === true ? filterAsync : (await getLimitFunction())(filterAsync, {concurrency: options.concurrency});
   const bools = await Promise.all(coll.map(adjustedFilter));
   return coll.reduce<T[]>((acc, item, i) => {
     if (bools[i]) {
@@ -363,3 +374,9 @@ function parseSleepArg(arg: SleepArg): {ms: number; cancelError?: string | Error
   }
   throw new TypeError('sleep: expected a finite number or an object with ms');
 }
+
+let limitFunctionPromise: Promise<PLimitModule> | undefined;
+async function getLimitFunction() {
+  limitFunctionPromise ??= dynamicImport('p-limit');
+  return (await limitFunctionPromise).limitFunction;
+}