xAI's /v1/responses endpoint rejects service_tier with HTTP 400
"Argument not supported: service_tier" when users activate /fast mode.
Also add a safety-net strip_slash_enum call in _preflight_codex_api_kwargs
to catch any tool schemas that might slip through the caller-level
sanitization. xAI's Responses API grammar compiler rejects enum values
containing forward slashes (e.g. HuggingFace model IDs like
"Qwen/Qwen3.5-0.8B") with the opaque "Invalid arguments passed to the
model" error.
Fixes the root cause of "Invalid arguments passed to the model" errors
reported by xAI OAuth (SuperGrok) users.
Nami4D
a699de83ec