fix(transpile): preserve Unicode core export names in asm.js

packages/jco-transpile/src/asm.ts

@@ -226,6 +226,9 @@ ${autoInstantiate}`;
  * See https://github.com/WebAssembly/binaryen/blob/main/src/asmjs/asmangle.cpp
  */
 function asmMangle(name: string) {
+    // Binaryen mangles the UTF-8 bytes of a name, rather than UTF-16 code units.
+    name = Buffer.from(name, 'utf8').toString('latin1');
+
     if (name === '') {
         return '$';
     }

packages/jco-transpile/test/asm.ts

@@ -0,0 +1,46 @@
+import { rm, writeFile } from 'node:fs/promises';
+import { join } from 'node:path';
+import { pathToFileURL } from 'node:url';
+
+import { assert, describe, test } from 'vitest';
+
+import { transpileBytes, writeFiles } from '../src/index.js';
+import { parse } from '../src/wasm-tools.js';
+import { getTmpDir } from './helpers.js';
+
+describe.each([false, true])('asm.js core exports (minify: %s)', (minify) => {
+    test.concurrent.each([
+        '$value',
+        '0',
+        'return',
+        'quoted"slash\\line\n',
+        '\u00e9',
+        'caf\u00e9',
+        '\u6f22\u5b57',
+        '\ud83d\ude00run',
+        'run\ud83d\ude00',
+        'line\u2028\u2029',
+    ])('preserves the core export name %j', async (name) => {
+        const outDir = await getTmpDir();
+        try {
+            // WAT byte escapes preserve the exact UTF-8 name, including quotes and controls.
+            const quoted = `"${Array.from(Buffer.from(name), (byte) => `\\${byte.toString(16).padStart(2, '0')}`).join('')}"`;
+            const component = await parse(`(component
+                (core module $m (func (export ${quoted}) (result i32) i32.const 42))
+                (core instance $i (instantiate $m))
+                (func (export "run") (result u32) (canon lift (core func $i ${quoted}))))`);
+            const { files } = await transpileBytes(component, {
+                name: 'asm-export-name',
+                js: true,
+                instantiation: 'sync',
+                minify,
+            });
+            await writeFiles(files, { baseDir: outDir });
+            await writeFile(join(outDir, 'package.json'), JSON.stringify({ type: 'module' }));
+            const { instantiate } = await import(pathToFileURL(join(outDir, 'asm-export-name.js')).href);
+            assert.strictEqual(instantiate({}).run(), 42);
+        } finally {
+            await rm(outDir, { recursive: true, force: true });
+        }
+    });
+});