fix: normalize HTTP/2 headers for legacy dispatch handlers

[Knowzzz]

This relates to...

Fixes #5865. Supersedes #5866 after renaming the source branch.

Rebased onto main at 8145595. Main has since reverted #5811 in #5860; this PR preserves that revert, including the HTTP/1.1 restriction for legacy dispatcher consumers and the native-fetch redirect regression test.

Rationale

HTTP/2 controllers expose rawHeaders / rawTrailers as objects, whereas legacy dispatch callbacks require raw arrays. LegacyHandlerWrapper currently forwards non-null object values unchanged.

The normalization remains necessary when Dispatcher1Wrapper.wrapHandler() is used directly with an HTTP/2-capable dispatcher. This PR does not re-enable HTTP/2 for legacy global fetch.

Changes

• Preserve existing HTTP/1.1 raw arrays without copying them.
• Convert HTTP/2 header/trailer objects with the existing toRawHeaders helper before calling legacy onHeaders, onComplete, or onUpgrade.
• Preserve main's allowH2: false dispatch guard and native-fetch redirect/WebSocket behavior.
• Keep the upstream deletion of the HTTP/2-only native-fetch fixture.
• Exercise the handler bridge directly against real TLS servers: HTTP/1.1 and HTTP/2 headers/trailers, Latin-1 values, repeated Set-Cookie, and HTTP/2 CONNECT headers.

No public API or type changes.

Validation

Node.js 22.23.2 and 24.20.0, Linux x86_64:

npm ci --ignore-scripts --no-audit --no-fund
npm run generate-pem
node --test --test-timeout=15000 \
  test/dispatcher1-http2-headers.js \
  test/node-test/global-dispatcher-version.js \
  test/dispatcher.js \
  test/websocket/issue-4989.js
# Each Node version: 11 passed, 1 skipped (existing Node-26-only test)

npx eslint lib/dispatcher/dispatcher1-wrapper.js \
  test/dispatcher1-http2-headers.js \
  test/node-test/global-dispatcher-version.js
# passed (Node 24)
git diff --check upstream/main
# passed

The first run before generating the PEM fixtures failed TLS handshakes; after the repository's certificate-generation step, both Node versions passed. The full test suite has not been run. No typechecks.

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested (targeted coverage above)
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[mcollina]

There are conflicts now, unfortunatelyt.

[Knowzzz]

Thanks for the heads-up @mcollina! Rebased on latest main and resolved the conflicts. The revert from #5860 is preserved, and the targeted tests pass on Node 22 and 24.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.89%. Comparing base (8145595) to head (40736a3).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5867      +/-   ##
==========================================
- Coverage   93.90%   93.89%   -0.01%     
==========================================
  Files         110      110              
  Lines       39901    39907       +6     
==========================================
+ Hits        37470    37472       +2     
- Misses       2431     2435       +4     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[mcollina]

lgtm