Module engine 

The flow interpreter — doc 48’s “the daemon runs the flow”.

The loop is deliberately tiny: run the current node, get either the next node id or a terminal, append a trace step, repeat. All the side effects a component needs (speak, collect a DTMF digit, ring the human, record, transfer, hang up) sit behind the FlowEffects trait — the “component-implementation seam” doc 48 keeps the engine generic over. The daemon supplies the real impl (wiring wavekat-tts for prompts, RFC 4733 receive for DTMF, the normal incoming-call path for ring, the recording pipeline for message, REFER for transfer); tests supply a scripted mock. Nothing here touches SQLite, the renderer, sync, or cpal — the whole module stays extractable.

Control-flow logic (menu retry counting, hours branching) lives here and is pure; only the actual audio/telephony effects cross the trait. That is what makes a full call testable with no call.

This crate owns the FlowEffects trait definition; the daemon keeps its live CallFlowEffects impl in its own codebase.

Structs

Slot

One offerable appointment, as absolute instants (RFC 3339). The engine never invents these and never adjusts them — it offers what it was given and hands the chosen one straight back.

SlotOffer

The answer to FlowEffects::fetch_slots.

SlotQuery

What a book node needs to know to ask “when is this business free?” — its own config, nothing about the caller and nothing about which calendar answers. Borrowed from the node, so the engine copies no schedules around.

Enums

BookOutcome

What came of trying to book one slot.

Digit

A DTMF key a caller can press.

RingOutcome

Result of a ring node.

Traits

FlowEffects

The side effects the components need. The engine calls these; the impl performs the telephony/audio. &mut self because a real impl holds the live call. Methods return anyhow::Result so the daemon impl can surface call-dropped / device errors uniformly; the engine treats any Err as “the call is gone” and aborts with a trace.

Functions

run

Run a validated flow to completion against fx, filling trace.