Exercise 2: Why the Registry Needs "use client" and the Catalog Doesn't — Possible Solution
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The registry needs "use client" because it holds live references to
real, interactive React components (Card, Badge, and so on) that get
handed to the renderer at the moment a spec is actually drawn to
screen - that's inherently a client-side concern in Next.js's App
Router, since Server Components can't carry that kind of live
component reference the way client components can.

The catalog doesn't need the same directive because it isn't doing
that job at all - it's just a plain data structure describing what
component types are allowed to exist and what shape their definitions
take, with no live component references inside it. Since the catalog
never touches actual renderable React components, there's nothing in
it that requires the client boundary the registry specifically needs.

ANSWER: registry.tsx needs "use client" because it holds live
references to real, interactive React components that must be
available at render time, a client-side requirement in Next.js's App
Router. catalog.ts doesn't need it because it only describes allowed
component types as plain data - it never touches an actual component
reference, so there's nothing in it that requires the client boundary.

WHY THIS WORKS AS AN ANSWER
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This correctly explains the real distinction (live component
references vs. plain data) that determines which file needs the
client-component boundary, rather than treating "use client" as an
arbitrary requirement.