chore(api): update SSE contracts and legacy checkpoint verification

[jbeckwith-oai]

Summary

Updates streaming contracts and authenticates legacy ownership checkpoints.

Changes

• Add SSE response declarations while preserving command-line behavior.
• Recognize authenticated legacy checkpoints without relaxing ownership checks.

[github-actions]

Castiron custom code

Evaluated main: efda4149c76e1093c656d10feb69b4959fbf7a78.

Trusted main policy: efda4149c76e1093c656d10feb69b4959fbf7a78.

✅ No new custom-code files detected.

0 mixed files remain; 0 existing customizations changed.

Compared efda4149c76e → 2bfbb0928b39. Generated baselines verified.

A changed generated baseline means this report cannot reliably identify which handwritten lines changed.

Inspect the custom-code diff

Download the exact patch produced by this run (requires repository access):

gh run download 38925903333 --repo openai/openai-cli \
  --name castiron-custom-code-38925903333-1 --dir /tmp/castiron-custom-code-38925903333-1
git apply --stat /tmp/castiron-custom-code-38925903333-1/custom-code.patch
cat /tmp/castiron-custom-code-38925903333-1/custom-code.patch

Or reproduce it from an SDK checkout containing the vendored reporter:

git fetch --no-tags origin efda4149c76e1093c656d10feb69b4959fbf7a78 2bfbb0928b392370f4c845753cff39d4344135af
python3 scripts/castiron/custom_code_report.py report \
  --base efda4149c76e1093c656d10feb69b4959fbf7a78 \
  --head 2bfbb0928b392370f4c845753cff39d4344135af --fetch --require-head-hash --public \
  --out /tmp/castiron-custom-code-2bfbb0928b39
cat /tmp/castiron-custom-code-2bfbb0928b39/custom-code.patch

This is the current full custom patch for mixed files, not an attribution of only the handwritten lines changed by this PR.

Full report and patch

[saioai]

[saibot]

review pending. draft PR needs the author to mark it ready. no approval yet.

[jbeckwith-oai]

Closing this scope expansion. The Java-only handwritten test extraction is already merged in openai/openai-java#1190.