Function required_schema_version 

pub fn required_schema_version(flow: &Flow) -> i64

The lowest schema_version that can carry this document’s components — the version it needs, as against the one it declares.

The engine has no use for this; it is here for authoring tools, which set the declared version from it so the number tracks the steps the author placed rather than being one more thing they must know about. A document needing nothing newer stays at 1, which is also the widest: every engine in the field can run it.

Twin: model.ts requiredSchemaVersion.