[Bug]: WebSocket clients ignore Node's global WebSocket in ESM builds

Is there an existing issue for the same bug?

• I have searched existing issues and this is not a duplicate.

Bug Description

The package is emitted as ESM, and Node 22 provides a standards-compatible globalThis.WebSocket.

The conversation and bash event clients only check window.WebSocket, then attempt require("ws"). Since require is unavailable in ESM, starting either client reports that no WebSocket implementation is available.

Expected Behavior

The TypeScript WebSocket callback clients use Node's global WebSocket constructor when globalThis.WebSocket is available.

Actual Behavior

The error callback receives "WebSocket implementation not available", even though globalThis.WebSocket exists. This is reproducible after running uv sync --dev and building the TypeScript package.

Steps to Reproduce

1. Install dependencies with uv sync --dev.
2. Build the TypeScript package on Node 22.
3. Import WebSocketCallbackClient from dist/events/websocket-client.js in an ESM process.
4. Create a client and call start().

Example:

node --input-type=module -e "const {WebSocketCallbackClient}=await import('./dist/events/websocket-client.js'); const client=new WebSocketCallbackClient({host:'http://127.0.0.1:9',conversationId:'test',callback:()=>{},onError:console.error}); client.start(); client.stop()"

Acceptance Criteria

• The TypeScript WebSocket callback clients use globalThis.WebSocket in Node ESM when available.
• The fallback path still supports injected WebSocket implementations and browser window.WebSocket.
• A TypeScript client test covers Node's global WebSocket constructor path.

Installation Method

uv sync --dev; npm ci in clients/typescript

If you selected "Other", please specify

No response

SDK Version

Current main branch

Version Confirmation

• I have confirmed this bug exists on the LATEST version of OpenHands SDK

Python Version

No response

Model Name (if applicable)

No response

Operating System

Linux

Logs and Error Messages

WebSocket implementation not available

Minimal Code Sample

node --input-type=module -e "const {WebSocketCallbackClient}=await import('./dist/events/websocket-client.js'); const client=new WebSocketCallbackClient({host:'http://127.0.0.1:9',conversationId:'test',callback:()=>{},onError:console.error}); client.start(); client.stop()"

Screenshots and Additional Context

this is the issue backing https://github.com/OpenHands/software-agent-sdk/pull/4799

Start with the TypeScript source that builds to dist/events/websocket-client.js and inspect the conversation and bash WebSocket callback clients. Reproduce the failure with the Node 22 ESM command after uv sync --dev and the TypeScript build, then run the existing client tests. Done means globalThis.WebSocket is covered while injected implementations and browser window.WebSocket still work.