Exercise 1: Redirecting Three Distinct Codes a Mixed Number of Times — Possible Solution
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THE SEQUENCE
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    code_a = shortener.create_short_url('https://example.com/article-a')
    code_b = shortener.create_short_url('https://example.com/article-b')
    code_c = shortener.create_short_url('https://example.com/article-c')

    # 5 redirects of code_a, 3 of code_b, 10 of code_c = 18 total redirects

RESULT
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    total redirects performed: 18
    store_lookups (should be 3 - one genuine miss per distinct code): 3

Across 18 total redirect calls spanning three distinct short codes,
store_lookups landed at exactly 3 - not 1 (this chapter's own single-
code result) and not 18 (no caching at all).

WHY EXACTLY 3, NOT 1 AND NOT 18
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CacheAsideRedirectService.cache is keyed by short_code - each DISTINCT
code genuinely needs its own first real store lookup before it becomes
cached, exactly like Chapter 3's own two-key PROD-1/PROD-2 exercise
confirmed. code_a's first redirect is a genuine miss (lookup #1); its
remaining 4 redirects are cache hits. code_b's first redirect is a
second genuine miss (lookup #2); its remaining 2 are cache hits. code_c's
first redirect is a third genuine miss (lookup #3); its remaining 9 are
cache hits. Three distinct codes, three genuine misses, regardless of
how many times each one is subsequently redirected.

WHY THIS CONFIRMS THE CAPSTONE'S CACHING SCALES TO A REALISTIC WORKLOAD
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This chapter's own original demonstration only tested one short code.
A real URL shortener serves many distinct codes simultaneously, each
with its own independent popularity - this exercise confirms the
cache-aside layer correctly gives every distinct code its own
independent caching lifecycle, with no cross-contamination between
codes and no unnecessary re-fetching for codes that are already
popular and cached.

WHY THIS WORKS AS AN ANSWER
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Three genuinely distinct codes are created and redirected different
numbers of times using this chapter's own unmodified UrlShortener, and
the resulting store_lookups count is verified directly against the
specific expected value (3) with the reasoning for why it's neither of
the two obvious wrong answers (1 or 18) explained precisely.