Engine-agnostic core of proef, the declarative multi-engine e2e test runner.

This crate owns the full front-end pipeline (gherkin parse → bind → lower → emit), the engine seam ([engine::EngineFactory] / [engine::EngineSession], ADR-0002), the [world::World] variable scope (ADR-0005), the serde [event::Event] spine (ADR-0008), and the fault taxonomy with stable exit codes (ADR-0009).

Core purity (sans-IO lite)

The pipeline stages in this crate do no IO, read no clocks or environment, and generate no randomness — run_id, timestamps, and env snapshots are injected values. The single sanctioned persistence component is [world::GlobalStore], whose load/save functions are invoked only from the orchestrating edge (the CLI), never from pipeline code. This is what makes snapshot and property tests bit-deterministic; do not break it for convenience.