The OpenAI gateway previously 400'd every response_format; the mux engine path
ran with speculation disabled entirely. Now:
- openai_server.py: response_format {"type":"json_object"} (generic ws-tolerant
JSON grammar), {"type":"json_schema"} (schema forwarded as-is, compiled
engine-side by schema_gbnf.h), and a raw-GBNF {"type":"gbnf"} extension.
Draft-source semantics throughout: a schema the engine cannot compile costs
the speedup, never the request and never the output.
- SUBMIT protocol: optional 7th field gbytes; grammar text appended to the
payload after the prompt. 6-field headers unchanged (back-compatible).
- Engine: per-slot GrDraft (grammar_setup_text/grammar_teardown split out of
the env-driven setup); walkers fed on every emitted token. Grammar-forced
drafting in run_serve_mux for greedy requests: a drafting slot leaves the
shared batch for one forward and runs the proven single-sequence verify path
(kv_bind + step_all) — the same primitives prefill already uses per
submission — then rejoins; rejected drafts' KV entries are overwritten by the
next forward exactly like the existing prefix-truncation path. Sampling
requests never draft (verification under sampling needs rejection resampling;
out of scope).
Tests: 7-field SUBMIT parse cases; response_format->grammar plumbing incl.
fail cases; test doubles updated; generic JSON grammar parse+walk validated
against grammar.h. make test-c green; python suite green except the known
environmental memory_available failure (#150 fixes it).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
FABIOTESS
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