Cherry-picked from #39840 by @flyinhigh and rebased cleanly on main.
- Defer config fetch in createGatewayEventHandler until gateway.ready to
avoid render-phase RPC that can mutate transcript state and trigger
React error 301 in embedded dashboard PTYs.
- Use undici WebSocket fallback when globalThis.WebSocket is unavailable
(Node attach mode and sidecar mirror sockets).
- Add regression tests for both fixes.
Co-authored-by: flyinhigh <flyinhigh@users.noreply.github.com>
e2145a5c9c