fix(eio): report oversized polling payloads

[wangxpych]

Summary

• emit a transport error when an HTTP polling payload exceeds maxHttpBufferSize
• preserve the existing HTTP 413 response
• assert that server-side close handlers receive an actionable TransportError

Context

The polling transport returned HTTP 413 when the incoming body crossed the configured limit, but it did not notify the Engine.IO socket about the cause. As a result, server-side Socket.IO handlers only received transport close without a description.

The uWebSockets polling implementation already reports payload too large, and the WebSocket implementation reports the corresponding ws range error. This change brings the Node.js polling transport in line with those paths by using the existing transport error pipeline after the request has been cleaned up.

Fixes socketio/engine.io#706

Verification

• npm run compile --workspace=engine.io
• npm run format:check --workspace=engine.io
• Engine.IO Node test suite: 175 passing, 2 pending
• Engine.IO v3 compatibility suite: 175 passing, 2 pending
• regression test fails before the fix with transport close and passes after the fix with transport error / payload too large

The aggregate npm test --workspace=engine.io command reaches 175 passing tests but the local WebTransport test times out because the optional @fails-components/webtransport-transport-http3-quiche native module is not built in this environment.

AI assistance disclosure: OpenAI Codex assisted with reproduction, implementation, and verification. The change was reviewed and tested against the repository's current main branch.

[wangxpych]

Withdrawing this contribution after re-evaluating the repository's recent human review and merge activity. No action is needed from maintainers. Thank you.