video_generate advertised an optional `model` argument (and the xAI edit/extend
tools a model override) so the LLM could route a single call to a different
model family — a different endpoint and billing tier — than the one the user
selected in `hermes tools`. image_generate never exposed this, and #83080 asked
to extend it there; the ruling is the opposite: models do not choose models.
The `model` property is gone from the static and dynamic video_generate schema
and from xai_video_edit / xai_video_extend; a `model` smuggled into the call is
ignored and the configured `video_gen.model` (then the provider default) is what
reaches the request. Config-side selection (`video_gen.model`,
`video_gen.<provider>.model`, `<PROVIDER>_VIDEO_MODEL`) is unchanged, and the
xAI plugin's explicit-model branch is no longer reachable from the tool layer.
Refs #83080
19b29df13b