AI in the flow

One rule puts a model in the flow:

WHEN @src == "lmtp"
WITH prompt  = "Classify this support mail: {{@lmtp.msg.text}}",
     system  = "You answer with one word: billing, technical, or other.",
     model   = "openai/gpt-4o-mini",
     intent  = "classify_support_ticket"
EXEC "ai://chat"

The model’s reply merges into the document as .text — and whatever resonates with that at the next step, fires. The classifier doesn’t route; it just answers, like every other op.

Prompts read the document

{{@path}} markers in prompt and system are filled from the envelope — {{@web.req.body}}, {{@lmtp.msg.subject}} — JSON-escaped automatically so values splice into the prompt without breaking it. Missing paths render empty rather than failing. For a computed scratch value, use SET PRE (sets a field on this op’s input only, without propagating downstream):

SET PRE @summary_input = .order.notes
WITH prompt = "Summarize: {{@summary_input}}"
EXEC "ai://chat"

For full control, skip prompt/system and author the conversation directly: WITH messages = [...] (OpenAI-style role/content turns).

Structured output

WITH schema = {...} (a JSON Schema) switches to structured-output mode: the chassis validates the model’s reply against the schema and merges the validated object as .schema_validated_payload. On failure — or any provider error — the op contributes .chat.error instead, and your next step’s rules can resonate on that.

Keys, costs, and accounting

• Secrets come from the secret store. The backend declares what it needs (the OpenRouter backend: OPENROUTER_KEY); the chassis materializes it per tenant. On a dev machine, an environment variable works as fallback (--ai-chat-env-fallback, default on). Cleartext is contained by construction — it can’t reach traces, logs, or continuations.
• Telemetry rides the envelope. Every call stamps _txc.chat.{provider, model, tokens.in, tokens.out, latency_ms, retries} — visible in the trace, aggregatable for cost reporting. Token counts are not charged to fuel: provider compute is its own dimension.
• Limits per call. WITH limits.timeout_ms and limits.max_cost_usd cap one call; the chassis-wide default timeout for AI ops is --ai-default-timeout (60s — deliberately longer than the 5s op default).