The P1 from the enterprise data-residency report: with
model.base_url=https://us.api.openai.com/v1, every tool-calling turn 400'd
('Function tools with reasoning_effort are not supported ... use
/v1/responses') because the runtime resolvers hardcoded
api_mode=chat_completions and consulted URL detection only. openai-api
declares codex_responses in its overlay; the declaration was never
consulted, so any OpenAI host that wasn't literally api.openai.com landed
on the wrong wire protocol.
New _fallback_api_mode(provider, base_url, model): URL detection first
(host-mandated wire shapes keep priority), then
providers.determine_api_mode() (the provider's declared transport), then
chat_completions only for genuinely unknown providers. All three runtime
fallback sites route through it: the pool-entry path, the explicit-runtime
path, and the API-key-provider path, so the lanes cannot drift apart.
Blast radius beyond openai-api: minimax, minimax-cn, and copilot-acp were
the other overlays whose declared non-chat transport fell through to
chat_completions on the same paths (same latent bug class). openrouter is
unaffected (declares openai_chat). _detect_api_mode_for_url also now uses
the shared official-host predicate, so regional hosts detect as
codex_responses on the direct-URL lane too.
Victor Kyriazakos