http2-dual-stack

Standalone dual-stack HTTP/2 origin verifying that browser traffic negotiates real h2 through Cypress when the MITM proxy is disabled, while the Cypress commands that run server-side (cy.visit's resolve:url pre-flight, cy.request) keep working over HTTP/1.1 against the same origin.

This replaces the h2-only fixtures from #34165, which could not pass as written: with allowHTTP1: false the resolve:url pre-flight was ALPN-rejected before the browser ever navigated, and flipping allowHTTP1: true crashed the in-process system-tests harness (Node's h1.1 compat path dies under Express-over-http2.createSecureServer in the mocha process). Real h2 servers are dual-stack, so this origin is too — and it runs out-of-band as a plain node script instead of inside the harness. See #34308.

Running locally

bash

# terminal 1 — the origin (self-signed certs are generated on first run)
node system-tests/projects/http2-dual-stack/server.mjs

# terminal 2 — h2 (proxy disabled): expect in-page fetches at HTTP/2.0
CYPRESS_INTERNAL_DISABLE_PROXY=1 yarn cypress:run \
  --project system-tests/projects/http2-dual-stack --browser chrome

# contrast — proxy enabled: the MITM terminates browser connections, so all
# browser traffic downgrades to HTTP/1.1
yarn cypress:run --project system-tests/projects/http2-dual-stack \
  --browser chrome --expose expectedBrowserProtocol=1.1

The server log shows the split directly: resolve:url and cy.request arrive as HTTP/1.1 lines while the browser's in-page fetches arrive as HTTP/2.0 (proxy disabled) or HTTP/1.1 (proxy enabled). The visited document itself never reaches the origin from the browser — cy.visit buffers the resolve:url response and fulfills the navigation with it, so the page always embeds 1.1 regardless of proxy mode.