Reconcile the reasoning-passthrough change (#2520) with the Responses API
work: dedupe the shared reasoning_effort capability, keep upstream's
upstream_model_id YAML plumbing and the _apply_reasoning_effort chat path,
and run the Responses branch ahead of it so responses-flavor models skip
the chat-only top-level reasoning_effort injection.
Route opted-in models to /v1/responses while keeping Chat Completions as
the default. The flavor is selected per-model in the catalog YAML and
threaded through ModelCapabilities (with a new reasoning_effort field).
- Translate chat-shaped messages/tools/structured-output into the
Responses input / text.format / flattened-tool shapes at the provider
boundary; stored history and intra-turn tool round-trips need no
migration.
- Normalize the typed SSE event stream back into the existing handler
contract (content / thought / tool-call chunks) so the streaming
accumulator and OpenAI handler stay unchanged.
- Carry encrypted reasoning items across the in-turn tool loop
(provider-local, keyed by call_id) for stateless reasoning continuity.
- OPENAI_RESPONSES_STORE opt-in enables server-side state and
previous_response_id chaining across turns, persisted in message
metadata.
- Set gpt-5.5 to api_flavor: responses, reasoning_effort: medium.
- Remove AzureOpenAILLM and the azure_openai provider/catalog.
Alex