Reference

Public API

item	what it is
TransformEngine	the trait a pass engine implements
TransformMode	how a pass applies: rewrite vs overlay
install_transform_overlay	install a rewritten arena as the new AST
node_ref, child_ref, descendant_ref, child_is_kind, contains	arena navigation without holding borrows
declined, out, ast, lang	result and context accessors

Crate

crate	role
hnl-engine-transform	abstraction — contract only

Build and test

cargo build     # sibling [patch] tables resolve deps from ../<repo>
cargo test      # no test suite here — covered by consumers

Dependencies are git deps on branch = "main"; locally the [patch] tables point at sibling checkouts (regenerated by host/scripts/dev-link.sh).