Exercise 3: Where LDA $FF,X Actually Reads From — Possible Solution
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GIVEN
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X = $02
Instruction: LDA $FF,X

THE NAIVE (WRONG) EXPECTATION
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A programmer thinking of this like ordinary absolute,X addressing
might expect the base address $FF plus X ($02) to simply carry over
into the next page, landing at $0101 — treating the addition as
normal, full 16-bit arithmetic the way absolute,X genuinely does.

WHAT ACTUALLY HAPPENS
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Per this chapter's own warn-box, zero page,X addressing wraps WITHIN
zero page itself — the high byte of the resulting address stays
permanently zero no matter how far the addition would otherwise
carry. The addition $FF + $02 is performed as 8-bit arithmetic
confined to the single zero-page byte, not as a full 16-bit address
computation:

  $FF + $02 = $101 in ordinary arithmetic, but confined to 8 bits,
  the carry is simply dropped, leaving $01.

So LDA $FF,X actually reads from address $0001 — a location near the
very START of zero page, not $0101 in page 1 as the naive expectation
would predict.

WHY THE NAIVE EXPECTATION IS WRONG
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The mistake is applying absolute,X's behavior (ordinary 16-bit
addition, no wraparound, able to spill into any later page) to
zero page,X, which is a genuinely different mode with its own
wraparound rule. Per the chapter's own distinction, "absolute,X has
no such limit; only the zero-page indexed modes wrap this way" — the
two modes look similar (both add an index register to a base
address) but behave differently specifically at page boundaries,
which is exactly the kind of quirk this chapter flags as a real,
documented source of bugs.

WHY THIS WORKS AS AN ANSWER
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It computes the actual wrapped result ($0001, not $0101) using 8-bit
arithmetic as the chapter describes, states clearly what the
(incorrect) naive expectation would have predicted instead, and
explains the root cause of the mistake — conflating zero page,X's
wrapping behavior with absolute,X's non-wrapping behavior.