Exercise 2: What Happens to grub.cfg When a New Kernel Is Installed — Possible Solution
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Explanation:

Installing a new kernel via the package manager triggers a
regeneration of grub.cfg (typically as part of the kernel package's
own post-install steps, running update-grub / grub-mkconfig
automatically) -- the chapter's own point that grub.cfg gets silently
rewritten, often triggered by exactly this kind of routine package
update. The regenerated grub.cfg now includes a new menu entry for
the newly installed kernel, alongside the entries for whichever
kernels were already present.

The specific script responsible: 10_linux, one of the numbered
scripts in /etc/grub.d/. Per the chapter's own description, 10_linux
is the script that scans /boot for every installed kernel and
generates one menu entry per kernel found there -- when a new kernel
package adds new kernel files to /boot, the next time grub-mkconfig
runs, 10_linux discovers that new kernel during its scan and
generates a corresponding new entry for it in the regenerated
grub.cfg, without anyone needing to write that entry by hand.

WHY THIS WORKS AS AN ANSWER
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This connects a kernel package installation to grub.cfg regeneration
(rather than treating them as unrelated events), and names the exact
numbered script (10_linux) responsible, along with what specifically
it scans for, rather than a vague "some script handles it."