A file whose top-level symbol spans almost all of it — createFoo() returning
an object of closures — is how Svelte 5 rune stores, React custom-hook modules,
IIFE module-pattern JS and Zustand's create((set,get)=>({…})) are all written.
probe-factory-closure.mjs measures what such a file DELIVERS from within: which
inner symbols' definitions reach the agent, not how many bytes did.