The 0.4.75 iid tagging made the bootstrap's __tag helper reference __IID
unconditionally, but the web worker script never declared it — every
widget message threw 'ReferenceError: __IID is not defined' and JS
widgets on the web client hung on the loading spinner (engine loaded,
renderer built, first render never arrived).

Fix: inject  at the top of the
generated worker script (before sendMessage definition and the shared
bootstrap). Contract test asserts the declaration order and the __tag
reference.