Challenge 2: Should /account/ Be Added to the Cache Zone? — Solution
Walkthrough

The answer: No, /account/ should not be added to the CacheEnable disk
zone the way /static/ was.

Why not:

Per Chapter 9's own material, mod_cache_disk is safe to use for
content that's genuinely shared across visitors -- the same response
for anyone requesting that URL. /account/ is the opposite: it shows
each logged-in user their own personalized order history, meaning the
correct response is different for every single user, and there is no
single "the" response for that URL to cache and reuse. Adding it to
the same disk cache zone as /static/ risks exactly the cross-user
leak Web Servers Fundamentals originally warned about -- one user's
order history being served from cache to a completely different
user who happens to request the same URL.

What should happen instead:

The PHP application's own response for /account/ should be marked
Cache-Control: private (or no-store), which mod_cache_disk respects
by default -- this keeps that response out of the cache entirely
rather than trying to key it safely. Per Chapter 9's own point, even
a correctly-configured Vary-based approach would likely yield close
to zero real cache hit rate on a page this personalized anyway, so
simply not caching it is both the safer and the more honest choice.

WHY THIS WORKS AS AN ANSWER
------------------------------
This exercise checks that the reader can apply Chapter 9's own
caching-safety material to a new, concrete scenario rather than just
reciting the rule -- correctly identifying /account/ as personalized
content that doesn't belong in the same cache zone as genuinely
shared static content.