Accept an async listener in the types and normalise any rejection reason

test/error-from.test.ts

@@ -0,0 +1,17 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { errorFrom } from '../src/error-from.ts';
+
+test('carries an Error through and describes anything else, including what String() refuses', () => {
+	const original = new Error('the original');
+	const undescribable: unknown = Object.create(null);
+
+	assert.equal(errorFrom(original), original);
+	assert.equal(errorFrom('a string').message, 'a string');
+	assert.equal(errorFrom(null).message, 'null');
+	assert.equal(errorFrom(undefined).message, 'undefined');
+	assert.equal(
+		errorFrom(undescribable).message,
+		'A thrown value that cannot be converted to a string',
+	);
+});