Exercise 2: Why the Cleanup Function's Track-Stopping Line Matters — Possible Solution
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WHAT HAPPENS IF THAT LINE IS OMITTED
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Without stream?.getTracks().forEach(track => track.stop()) in the
cleanup function, the camera stream keeps running even after the
component that started it unmounts. A getUserMedia stream isn't
automatically released just because the React component that requested
it is gone — something has to explicitly call stop() on each track, and
the cleanup function returned from useEffect is the only place that
happens.

WHY THIS MATTERS SPECIFICALLY FOR A SCAN SCREEN
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A scan screen is exactly the kind of component a user navigates to and
away from repeatedly — scan an item, go back, scan another one later.
Each mount without a matching cleanup leaves one more orphaned camera
stream running in the background. Beyond draining battery and leaving
the camera's "in use" indicator lit when it shouldn't be, repeated
visits can eventually hit the browser's own limit on simultaneous open
camera streams, causing a later getUserMedia call to fail for reasons
that would look confusing without knowing about the leaked streams
underneath.

WHY THIS WORKS AS AN ANSWER
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It correctly explains that a camera stream isn't automatically released
on unmount and requires an explicit stop() call, and it correctly ties
that specifically to a scan screen's own repeated mount/unmount
pattern, naming concrete consequences rather than a vague "it's bad
practice" statement.