fix(responses): send stable beta header

[zemaj]

Summary

• switch our Responses requests to OpenAI-Beta: responses=v1 and share the value across both Rust clients
• add a regression test that checks the header value on the responses request builder
• align the local proxy comment with the new default

Fixes #331

Testing

• ./build-fast.sh

Risks

• minimal: requests now match the documented v1 header; verified by unit test

[zemaj]

Updated the header logic so public api.openai.com requests use , backend/azure/default hosts stay on , and provider-specific headers win. If there are additional backend host patterns we should encode (beyond ), please let me know so we can pin them explicitly.

[zemaj]

Recap of the amended logic:

• Public OpenAI hosts () get by default.
• Backend / Azure endpoints (name or URLs containing / existing Azure pattern) stay on .
• Provider-defined headers always win—we only add the beta header if one isn’t already set.

Unit coverage exists for each branch in both and . Please let me know if there are any additional backend host patterns we should codify explicitly.

[zemaj]

CI note: the preview build is still hitting on the musl/darwin legs. This matches the toolchain-target gap addressed in #356, so we’ll rerun once that merges.

[zemaj]

Preview Build rerun triggered after #364 merged; watching for green checks.

[zemaj]

Fresh Preview Build queued with updated toolchain after #364 merged; watching for green checks.

[zemaj]

Preview Build rerun queued with Rust 1.90.0 plus MUSL targets after #370 merged. Tracking run: https://github.com/just-every/code/actions/runs/18870460099

[zemaj]

Heads-up: the changes from this PR have already landed on main via commit 245617c (Merge pr362). Closing remains accurate.