The Codex Responses backend (ChatGPT-subscription `/backend-api/codex/responses`)
returns 400 `{"detail":"Unsupported parameter: temperature"}` for every sampling
control, but `buildTransformedCodexRequestBody` forwarded `temperature`, `top_p`,
`top_k`, `min_p`, `presence_penalty`, and `repetition_penalty` straight through
whenever the caller's `StreamOptions` carried them — so any non-default sampling
setting failed every turn.
- Provider drops the full sampling set (matching codex-rs, which sends none).
- `RequestBody` no longer types fields it never populates for codex.
- Auth-gateway defensive strip in `buildStreamOptions` and the pi-native handler
widened from `{temperature, topP}` to the same set plus
`stopSequences`/`frequencyPenalty`.
- Regression test pins the captured body to omit every key even when the caller
sets all of them.
Fixes#3117
roboomp
f6c4d6fb62