The globalThis.FaustWorkletProcessor attachment on the base class isn't
enough in practice: Chrome's AudioWorkletGlobalScope isolates top-level
class declarations between separate addModule() calls, so a subclass
script loaded via a second addModule() still throws ReferenceError on
its 'extends FaustWorkletProcessor' clause.
Workaround: fetch both files, concatenate, and addModule() a single
blob URL. The base class and subclass end up in the same script
evaluation context and the extends clause resolves. Processor names
are memoised on a static Set so repeated sub-engine swaps don't try
to re-register (which would throw).
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