OpenRouter's /v1/models entries advertise reasoning capability
(supported_parameters + reasoning.mandatory/supported_efforts). Use that
metadata as the primary gate in _supports_reasoning_extra_body instead of
the hand-maintained vendor-prefix allowlist, which went stale one vendor at
a time (nvidia/ missing -> #75386). Also clamp the requested effort to the
nearest LOWER catalog-supported level in the OpenRouter profile so ultra/max
against a high-capped route no longer 4xxes.
Cache-only on the hot path: capabilities parse for free out of the existing
fetch_openrouter_models() payload, a background warmer covers cold starts,
and unknown models/offline catalogs fall back to the static prefix list
unchanged.
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