idna-stub

Local stub for the idna crate (v1.1.0) that replaces ICU-based IDNA processing with a WIT host import, eliminating ~275 KB of ICU/Unicode lookup tables from the WASM binary.

Domain-to-ASCII conversion is delegated to the JS host via the vercel:python-analysis/host-utils WIT interface, which uses the Node.js URL API internally. This means the runtime behavior follows IDNA2008 (via Node.js/ICU) rather than UTS #46 (as in the upstream crate).

API surface

Only the subset of idna used by the url crate is implemented:

domain_to_ascii_from_cow(domain, deny_list) -> Result<Cow<str>, Errors>
domain_to_unicode(domain) -> (String, Result<(), Errors>) -- passthrough, no round-trip decoding
AsciiDenyList -- URL, STD3, EMPTY variants

Fast paths avoid host calls for all-ASCII lowercase domains.

Upstream

Based on idna v1.1.0 from servo/rust-url.