chore(multiplexer): drop Event/CloseEvent/MessageEvent polyfills, keep ErrorEvent

Node 24 (repo engines floor) has Event, CloseEvent, and MessageEvent as
globals — the typeof checks in Event.ts / CloseEventClass.ts /
MessageEventClass.ts always picked native on any supported runtime.
Inlining native constructors at the 5 Multiplexer/Message call sites and
deleting the three dead polyfill files.

ErrorEvent is NOT yet a Node global — verified on Node 24.14.1 via
'typeof ErrorEvent === "undefined"' (tracked upstream at
nodejs/node#49986; internal-only ErrorEvent lives in undici). Kept
ErrorEventClass.ts and rewrote it to extend native Event (it previously
extended the now-deleted Event2). Runtime smoke test confirms the
polyfill dispatches and listeners see error/message/filename/lineno/colno
fields correctly.

Net: -137/+18 across 6 files, 0 tsc errors, 89/89 tests pass, webpack
clean, generated .d.ts byte-identical (920 bytes).

Author: bilbospocketses

src/packages/multiplexer/CloseEventClass.ts

@@ -1,20 +1,24 @@
-import { Event2 } from './Event';
+// Polyfill for ErrorEvent on server runtimes. Node 24 still has not
+// promoted ErrorEvent to a global (tracked at nodejs/node#49986) though
+// Event, CloseEvent, and MessageEvent are all present. In browsers it's
+// always available, so the export below picks native when defined.
 
-export class ErrorEvent2 extends Event2 implements ErrorEvent {
+class ErrorEventPolyfill extends Event {
     readonly colno: number;
-    readonly error: any;
+    readonly error: unknown;
     readonly filename: string;
     readonly lineno: number;
     readonly message: string;
 
     constructor(type: string, { colno, error, filename, lineno, message }: ErrorEventInit = {}) {
         super(type);
         this.error = error;
-        this.colno = colno || 0;
-        this.filename = filename || '';
-        this.lineno = lineno || 0;
-        this.message = message || '';
+        this.colno = colno ?? 0;
+        this.filename = filename ?? '';
+        this.lineno = lineno ?? 0;
+        this.message = message ?? '';
     }
 }
 
-export const ErrorEventClass = typeof ErrorEvent !== 'undefined' ? ErrorEvent : ErrorEvent2;
+export const ErrorEventClass: typeof ErrorEvent =
+    typeof ErrorEvent !== 'undefined' ? ErrorEvent : (ErrorEventPolyfill as unknown as typeof ErrorEvent);

src/packages/multiplexer/ErrorEventClass.ts

@@ -1,4 +1,3 @@
-import { CloseEventClass } from './CloseEventClass';
 import { MessageType } from './MessageType';
 
 export class Message {
@@ -56,7 +55,7 @@ export class Message {
                 reason = new TextDecoder().decode(new Uint8Array(this.data, 6, length));
             }
         }
-        return new CloseEventClass('close', {
+        return new CloseEvent('close', {
             code,
             reason,
             wasClean: code === 1000,

src/packages/multiplexer/Event.ts

@@ -1,10 +1,7 @@
 import Util from '../../app/Util';
 import { TypedEmitter } from '../../common/TypedEmitter';
-import { CloseEventClass } from './CloseEventClass';
 import { ErrorEventClass } from './ErrorEventClass';
-import { EventClass } from './Event';
 import { Message } from './Message';
-import { MessageEventClass } from './MessageEventClass';
 import { MessageType } from './MessageType';
 
 interface MultiplexerEvents extends WebSocketEventMap {
@@ -100,7 +97,7 @@ export class Multiplexer extends TypedEmitter<MultiplexerEvents> implements WebS
                     const data = this.channels.get(message.channelId);
                     if (data) {
                         const { channel } = data;
-                        const msg = new MessageEventClass('message', {
+                        const msg = new MessageEvent('message', {
                             data: new TextDecoder().decode(new Uint8Array(message.data)),
                             lastEventId: event.lastEventId,
                             origin: event.origin,
@@ -116,7 +113,7 @@ export class Multiplexer extends TypedEmitter<MultiplexerEvents> implements WebS
                     const data = this.channels.get(message.channelId);
                     if (data) {
                         const { channel } = data;
-                        const msg = new MessageEventClass('message', {
+                        const msg = new MessageEvent('message', {
                             data: message.data,
                             lastEventId: event.lastEventId,
                             origin: event.origin,
@@ -132,7 +129,7 @@ export class Multiplexer extends TypedEmitter<MultiplexerEvents> implements WebS
                     const data = this.channels.get(message.channelId);
                     if (data) {
                         const { emitter } = data;
-                        const msg = new MessageEventClass('message', {
+                        const msg = new MessageEvent('message', {
                             data: message.data,
                             lastEventId: event.lastEventId,
                             origin: event.origin,
@@ -247,7 +244,7 @@ export class Multiplexer extends TypedEmitter<MultiplexerEvents> implements WebS
                 } else {
                     this.ws.send(message);
                 }
-                this.emit('close', new CloseEventClass('close', { code, reason }));
+                this.emit('close', new CloseEvent('close', { code, reason }));
             } finally {
                 this.readyState = this.CLOSED;
             }
@@ -301,7 +298,7 @@ export class Multiplexer extends TypedEmitter<MultiplexerEvents> implements WebS
             if (this.readyState === this.OPEN) {
                 Util.setImmediate(() => {
                     channel.readyState = this.OPEN;
-                    channel.dispatchEvent(new EventClass('open'));
+                    channel.dispatchEvent(new Event('open'));
                 });
             }
         } else {