Function node_id 

pub fn node_id(hash_input: &Value) -> String

Compute the Vasari node ID: sha256 of the RFC 8785 JCS canonical form of the hash-input value.

Full RFC 8785 compliance requires specific number serialization and unicode escape handling beyond key-sorting. This implementation covers the critical invariant (key-sorted JSON, no whitespace) which is sufficient for hash stability within a single implementation. Full JCS compliance is tracked in INTENT-SPEC.md §3 (Canonicalization).