SGLang's Mistral tool-call parser rejects logprobs/top_logprobs with 422,
while vLLM accepts them. Clients like OpenClaw send these by default.
New architecture: haproxy (port N) → middleware (port N+2) → SGLang (port N+1)
The middleware is a thin FastAPI app that strips incompatible params from
chat completion request bodies and passes everything else through unchanged.
SGLang now runs on port+1, haproxy binds the original vLLM port.
haproxy serves a stub /metrics endpoint (200, empty body) and
passes all other traffic through to SGLang via raw TCP proxy.
