Background

OpenAI is moving to the responses API. Mostly they support the older chat completions API still, but in some cases they don't and we throw an error.

https://platform.openai.com/docs/guides/migrate-to-responses
https://platform.openai.com/docs/api-reference/responses

Job to do

Add the new API to the OpenAI provider (goose/crates/goose/src/providers/openai.rs). Make this the default for actual OpenAI calls but allow for a switch in custom providers to choose between the old and the new, either by adding a protocol field to the DeclarativeProviderConfig or by having a different OpenAI provider type.

Acceptance

We can declare that this works if OpenAI works well (./scripts/test_providers.sh runs), you can create custom providers with the old and the new and that the current declarative providers still work and that we can upgrade them to the new protocol