Exercise 3: Do Existing Public Grants Need Manual Deletion First? — Possible Solution
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Public Access Prevention works by overriding existing public
permissions, not by requiring them to be deleted first. Once
enforced, any request relying on the allUsers or allAuthenticatedUsers
principals fails outright with an HTTP 401 or 403 error - regardless
of whether the underlying IAM grant establishing that public access is
still technically present in the bucket's own policy.

This means enforcement genuinely takes effect immediately once
applied, without needing an administrator to first go through and
manually identify and remove every individual public grant on the
bucket - a real, meaningfully faster and less error-prone path to
actually shutting off public exposure than requiring cleanup first.

ANSWER: No, the existing public grants do not need to be manually
deleted first - Public Access Prevention overrides them in place, so
enforcement blocks public access immediately, with the old grants
simply becoming inert rather than needing to be found and removed one
by one before the protection takes effect.

WHY THIS WORKS AS AN ANSWER
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This correctly identifies the real mechanism (override, not deletion)
described in the chapter, and explains the genuine practical benefit
this design choice provides - avoiding a slow, error-prone manual
cleanup step as a prerequisite for real, immediate protection.