We're using this package in the web engine unit tests for Flutter. I am attempting to add some unit tests that run with Safari and dart2wasm (Safari now has WasmGC support) but I am running into a bug where the bootstrapping handshake between the host page and the iframe stalls out and fails. The reason for this is this check

For whatever reason, message.source.location?.href returns the URL of the host page rather than the URL loaded in the iframe. This only happens in Safari, and only happens when running a test compiled via dart2wasm. This seems like a Safari bug, but we might need a workaround for this if we want Safari+dart2wasm to work with this package.

FWIW, just commenting out that check does seem to allow my tests to run, but the web engine unit tests don't need to disambiguate between different test suites because we only run one at a time on the page (only one iframe).