When the primary provider's auth fails (expired token / 429 quota cap),
_resolve_runtime_agent_kwargs() falls through to the fallback provider
chain, whose runtime dict carries its own 'model' key. api_server's
_create_agent then did AIAgent(model=model, **runtime_kwargs), colliding
on 'model' and 500ing every /v1/chat/completions request while a fallback
was active. Pop the runtime model and let it override the config model,
mirroring the native gateway path (_resolve_session_agent_runtime).
Salvaged from #35716 by @ryo-solo (earliest submitter); the PR's second
half (Mistral reasoning_content strip) is already handled on main and
dropped.
Co-authored-by: Hermes Agent <noreply@nousresearch.com>
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