Function steps_to_yaml 

pub fn steps_to_yaml(steps: &[Step]) -> String

Serialize steps to the canonical on-disk dayscript form — a flow: document of - <op>: { <params> } entries (§14.1), byte-compatible with the file day-cli’s parse_flow reads. Each Step serializes to its internal-op-tag map ({op: tap, id: inc, …}); this lifts the op out to become the entry key and drops null-valued optional params, then serde_norway renders the whole {flow: […]} document as YAML.