fix(ext/webidl): follow GetIterator semantics in async iterable converter

ext/webidl/00_webidl.js

@@ -998,7 +998,7 @@ function createAsyncIterableConverter(converter) {
     context = undefined,
     opts = EMPTY_OPTS,
   ) {
-    if (type(V) !== "Object") {
+    if (V === undefined || V === null) {
       throw makeException(
         TypeError,
         "can not be converted to async iterable.",
@@ -1007,12 +1007,16 @@ function createAsyncIterableConverter(converter) {
       );
     }
 
+    // Follows the GetIterator(obj, async) abstract operation: the @@asyncIterator
+    // and @@iterator methods are looked up with GetMethod semantics, which treats
+    // both `undefined` and `null` as an absent method, and which performs ToObject
+    // on `V` (so primitives such as strings are accepted).
     let isAsync = true;
     let method = V[SymbolAsyncIterator];
-    if (method === undefined) {
+    if (method === undefined || method === null) {
       method = V[SymbolIterator];
 
-      if (method === undefined) {
+      if (method === undefined || method === null) {
         throw makeException(
           TypeError,
           "is not iterable.",

tests/unit/streams_test.ts

@@ -1,10 +1,5 @@
 // Copyright 2018-2026 the Deno authors. MIT license.
-import {
-  assertEquals,
-  assertRejects,
-  assertThrows,
-  fail,
-} from "./test_util.ts";
+import { assertEquals, assertRejects, fail } from "./test_util.ts";
 
 // `resourceForReadableStream` is registered on the internals object only when
 // `ext:deno_web/06_streams.js` first evaluates, which is now lazy. Touch the
@@ -578,13 +573,16 @@ Deno.test(async function decompressionStreamInvalidGzipStillReported() {
   );
 });
 
-Deno.test(function readableStreamFromWithStringThrows() {
-  assertThrows(
-    // @ts-expect-error: primitives are not acceptable
-    () => ReadableStream.from("string"),
-    TypeError,
-    "Failed to execute 'ReadableStream.from': Argument 1 can not be converted to async iterable.",
-  );
+Deno.test(async function readableStreamFromString() {
+  // Per the Streams spec, ReadableStream.from() accepts any iterable, including
+  // strings, which are iterated by code point. The TS type requires an object,
+  // so a string primitive is rejected statically even though it works at runtime.
+  // @ts-expect-error: string is iterable at runtime but the type requires an object
+  const stream = ReadableStream.from("ab");
+  const reader = stream.getReader();
+  assertEquals(await reader.read(), { value: "a", done: false });
+  assertEquals(await reader.read(), { value: "b", done: false });
+  assertEquals((await reader.read()).done, true);
 });
 
 Deno.test(async function readableStreamFromWithStringThrows() {

tests/wpt/runner/expectations/streams.json

@@ -115,18 +115,8 @@
     "templated.any.worker.html": true,
     "async-iterator.any.worker.html": true,
     "cross-realm-crash.window.html": false,
-    "from.any.html": {
-      "expectedFailures": [
-        "ReadableStream.from ignores a null @@asyncIterator",
-        "ReadableStream.from accepts a string"
-      ]
-    },
-    "from.any.worker.html": {
-      "expectedFailures": [
-        "ReadableStream.from ignores a null @@asyncIterator",
-        "ReadableStream.from accepts a string"
-      ]
-    },
+    "from.any.html": true,
+    "from.any.worker.html": true,
     "crashtests": {
       "garbage-collection.any.html": true,
       "garbage-collection.any.worker.html": true