fix: do not mask runtime errors with require() fallback

lib/worker.js

@@ -136,10 +136,19 @@ async function start () {
       // When bundled with pkg, an undefined error is thrown when called with realImport
       // When bundled with pkg and using node v20, an ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING error is thrown when called with realImport
       // More info at: https://github.com/pinojs/thread-stream/issues/143
+
       try {
         worker = realRequire(decodeURIComponent(filename.replace(process.platform === 'win32' ? 'file:///' : 'file://', '')))
-      } catch {
-        throw error
+      } catch (requireError) {
+        // MODULE_NOT_FOUND and ERR_REQUIRE_ESM mean the file couldn't be loaded
+        // via require — fall back to the original import error.
+        // All other errors (SyntaxError, ReferenceError, TypeError, etc.) are real
+        // runtime errors from the loaded module and should bubble up to the user.
+        // More info at: https://github.com/pinojs/thread-stream/issues/156
+        if (requireError.code === 'MODULE_NOT_FOUND' || requireError.code === 'ERR_REQUIRE_ESM') {
+          throw error
+        }
+        throw requireError
       }
     } else if (filename.endsWith('.ts') || filename.endsWith('.cts')) {
       // Native TypeScript import failed (type stripping not enabled).

test/base.test.js

@@ -133,7 +133,7 @@
   stream.on('finish', () => {
     readFile(dest, 'utf8', (err, data) => {
       assert.ifError(err)
       assert.strictEqual(data, 'hello world\nsomething else\n')
     })
   })
 
@@ -253,7 +253,18 @@
   })
 
   stream.on('error', (err) => {
     assert.strictEqual(err.message, 'Unexpected end of input')
     done()
   })
 })
+
+test('runtime error in worker module is not hidden by require retry', function (t, done) {
+  const stream = new ThreadStream({
+    filename: join(__dirname, 'reference-error.js')
+  })
+
+  stream.on('error', (err) => {
+    assert.ok(err.message.includes('undeclaredVariable'))
+    done()
+  })
+})

test/reference-error.js

@@ -0,0 +1,19 @@
+'use strict'
+
+// This module intentionally has a ReferenceError to test
+// that runtime errors are not masked by the require() fallback.
+// See https://github.com/pinojs/thread-stream/issues/156
+
+undeclaredVariable.foo() // eslint-disable-line no-undef
+
+const { Writable } = require('stream')
+
+async function run (opts) {
+  return new Writable({
+    write (chunk, enc, cb) {
+      cb()
+    }
+  })
+}
+
+module.exports = run