Guardrail

withGuardrails enforces an XML output contract and sets an assistant prefill so the model's output format can't drift — auto-degraded on providers without native prefill support.

chef.withGuardrails(options): this

Applies output format guardrails and optional prefill.

chef.withGuardrails({
  enforceXML: { outputTag: "final_code" }, // wraps output rules in EPHEMERAL_MESSAGE
  prefill: "<thinking>\n1.", // trailing assistant message (auto-degraded for OpenAI/Gemini)
});

v4 semantics

Options are now stored and applied at compile(), so call order relative to setDynamicState no longer matters (pre-4.0, calling setDynamicState after withGuardrails silently discarded the guardrail).

• Order-independent — withGuardrails before or after setDynamicState gives the same output.
• Replace semantics — each call replaces the previous options (no accumulation).
• withGuardrails(null) clears the stored options.
• Own tail message — the guardrail message lands at the very end of the sandwich as its own message — closest to generation, no longer merged into the dynamic-state message.
• Persisted — the stored options are persisted in ChefSnapshot (guardrailOptions); snapshot/restore round-trips them.

// v3 — order mattered, this silently dropped the guardrail:
chef.withGuardrails({ enforceXML: { outputTag: 'answer' } });
chef.setDynamicState(state); // guardrail gone

// v4 — same code works in any order; to remove a guardrail, be explicit:
chef.withGuardrails(null);

Provider degradation

Prefill is a trailing assistant message. The Anthropic target supports it natively; OpenAI and Gemini cannot end on an assistant message, so the adapter degrades the prefill to a [System Note] instruction folded into the prompt instead. See Adapters for the full per-provider feature matrix.