`#target in this` inside a JavaScript method reads the actual call-site
receiver, a checked value, so the brand check fenced at run time
(undici's FastIterableIterator, and the corpus program that pins it,
which coverage counted as one deferred site). The brand is present
exactly when the value is a class instance at or below the declarer:
a typed reference boxed under the declarer or a descendant answers true,
and one boxed under an ancestor answers with an instanceof test.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
