# Passthru


`create` builds a typed `PassthruSpec` from `{ langName; baseName;
baseDeps; extensions ? {} }`. The spec is the canonical structured
representation of language-tagged package metadata.

Hash stability invariant: a `PassthruSpec` depends only on its
constructor arguments. Two `create` calls with equal inputs produce
equal specs; no ambient state, no derivation references at the
spec level.