Exercise 3: Explaining One Attribution-Table Row in Depth — Possible Solution
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CHOSEN ROW: STEP 6 — SAFE EDIT (CHAPTER 8, CHAPTER 9)
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This solution picks Step 6, "A safe edit," attributed to Chapter 8 (the
mutation, updateTag) and Chapter 9 (the fix that protects it).

WHY CHAPTER 8 ALONE WASN'T ENOUGH
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Chapter 8 built updatePageTitle as a genuinely working Server Action -
it could already update a page's title and immediately reflect that
change via updateTag. But it was deliberately left with no auth check
at all. Without Chapter 9, Step 6 in this capstone would still "work"
technically, but it would prove nothing about safety - literally anyone
who discovered the endpoint could rename any page, session or no
session. The capstone's own framing - Sam performing a safe, authorized
edit - would be false if only Chapter 8 existed.

WHY CHAPTER 9 ALONE WASN'T ENOUGH EITHER
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Chapter 9 built real authentication - a working login, a real session -
but by itself, authentication without an actual protected action to
guard is just infrastructure with nothing to demonstrate. Chapter 9's
own auth() check only becomes meaningful because Chapter 8 already gave
it a real, working, previously-exploitable mutation to gate.

WHY THE STEP GENUINELY NEEDS BOTH
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Step 6 depends on Chapter 8 for the mutation to exist and actually
work, and on Chapter 9 for that mutation to only be reachable by an
authenticated Sam. Removing either chapter breaks the step in a
different way - remove Chapter 8 and there's no mutation to protect;
remove Chapter 9 and the "safe" in "safe edit" becomes false. Both are
genuinely necessary, not just conveniently paired.

WHY THIS WORKS AS AN ANSWER
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It explains the specific contribution of each attributed chapter
separately, rather than treating the pairing as self-evident, and shows
concretely what would break if either one were removed - directly
demonstrating the capstone's own claim that "nothing here is arbitrary."