Module engine 

The workflow engine v3 (RFC 0027): the dialect-3 model + validation (model), templates (template), and the durable run record + pure scheduler (run). Step execution (turn workers, MCP calls, internal tools, timers) is the runtime’s job (crate::runtime): the engine says what is ready and records what happened. P3 ships the model, validation and the scheduler with the core step kinds; P4 completes the catalogue (iteration, waits, child runs, start nodes beyond once/manual).

Re-exports

pub use model::Workflow;

pub use model::parse_workflow;

pub use model::workflow_schema;

pub use run::Next;

pub use run::RunState;

pub use run::RunStatus;

pub use run::StepStatus;

Modules

data

The data steps (RFC 0027 §5 “Data”): array and text operations without a model — map, filter, reduce, sort, dedupe, chunk, parse — as pure functions over JSON values. Element expressions are CEL (item, index, acc, plus the run data) or {{template}} strings; by keys are dotted paths.

model

The dialect-3 workflow model (RFC 0027 §2–§5, §8): a named DAG of steps beginning at start nodes, parsed from a JSON/YAML document with a strict per-kind field check (unknown fields are refused — the RFC 0021 §4.1 typo shield carried over), validated for acyclicity, reachability, finish reachability, dependency existence, schema well-formedness, CEL compilation and the caps. The node catalogue is one table (KINDS) — the validator, the executor and --workflow-schema all read it.

run

The run record and the scheduler (RFC 0027 §6, §7, §9): a run is a durable transition log over a workflow’s DAG — per-step {status, attempt, started, finished, output, error}, vars, the start payload, budgets and the terminal outcome. The scheduler is pure: given a workflow and a run it names the steps that are ready (all depends_on terminal, when true), applies step outcomes (on_error routing, goto recovery edges), and decides the run’s terminal state (finish reached, failed, cancelled, or stalled — no ready step and no finish).

template

Workflow templates (RFC 0027 §3): {{path}} interpolation with dotted / JSON-pointer paths and {{path | default}} over the run data (inputs, run, steps.<id>.output, vars, memory.<key>, item, index, batch, env), plus CEL: expressions over the same names (feature cel; a non-CEL build refuses them at validation). Dependency-free.