[isaacroldan]

WHY are these changes introduced?

shopify app dev exits when a client of the /extensions WebSocket breaks the WebSocket protocol, for example with a frame larger than maxPayload. The local proxy stops with it.

getConnectionDoneHandler registers a message listener on each socket, but no error listener. On a protocol error, ws emits error on the socket. With no listener, Node throws it as an unhandled error (RangeError: Max payload size exceeded) and the process exits.

WHAT is this pull request doing?

• Adds an error listener to each /extensions socket. It logs the error with outputDebug. ws already closes the failing connection (code 1009 for an oversized frame), so the server and the other clients keep working.
• Adds regression tests in handlers.test.ts:
  • An error event on a connected socket does not throw and is logged.
  • With a real server, a client that sends an oversized frame is closed with 1009. A new client can then connect and send a dispatch, and an existing client receives it.
• Adds a patch changeset for @shopify/app.

How to manually test your changes?

1. Run shopify app dev --verbose in an app with a UI extension.
2. Find the local server port in the output, then connect to ws://localhost:<port>/extensions with a WebSocket client and send a frame larger than 100 MiB. With ws in Node:

   const ws = new (require('ws'))('ws://localhost:<port>/extensions')
   ws.on('open', () => ws.send(Buffer.alloc(101 * 1024 * 1024)))
   ws.on('close', (code) => console.log('closed', code))

3. Before this change, app dev exits with RangeError: Max payload size exceeded. After this change, the client prints closed 1009, app dev keeps running, and the verbose output shows Websocket connection error: Max payload size exceeded.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add