`JSON.stringify(new Url(...))` was refused (SC1090) for every program
class, although JSON.stringify of a class with a toJSON hook serializes
whatever toJSON(key) returns. A class whose chain declares toJSON now
crosses into the runtime JSON walker through its checked-dynamic class
view, which calls the hook with the root key "" and handles nested hooks;
an undefined hook result keeps the dyn-root undefined rule.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
