Exercise 3: Which Component Needs a Level 3 Diagram to Show Chapter 8's Bug — Possible Solution
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THE COMPONENT IN QUESTION
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Chapter 8's verified bug (mobile client returning 103.0, web client
returning 103.5 for the identical $120 loyalty-member order) lived
entirely INSIDE the client-side pricing logic, before either client
called the shared Pricing API. The relevant component isn't shown as
its own box anywhere on this chapter's own Level 1/2 diagram at all -
"Mobile client" and "Web client" appear only as single boxes, with no
detail about what happens inside either one.

WHY A LEVEL 3 (COMPONENT) DIAGRAM ON THE CLIENTS WOULD BE NEEDED
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A Level 3 diagram zoomed into "Mobile client" would need to show its
own internal calculate_total() logic as a distinct component - and,
critically, so would a separate Level 3 diagram zoomed into "Web
client," showing ITS OWN independently-written calculate_total()
logic. Only by drawing both clients' own internal components
separately, side by side, would the diagram reveal that two DIFFERENT
implementations of "apply loyalty discount, then $5-off" exist at all -
information the Level 2 diagram's single "Mobile client" / "Web
client" boxes actively hide by treating each client as one opaque
unit.

WHY THE LEVEL 2 DIAGRAM COULDN'T HAVE SHOWN THIS BUG
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Level 2 (Container) diagrams, by design, only show WHICH major pieces
exist and how they connect - they deliberately don't show what happens
INSIDE any one container. This chapter's own diagram correctly shows
that both "Mobile client" and "Web client" eventually connect to
"Pricing API" - but a diagram drawn at this level has no way to
represent that, before Chapter 8's own fix, neither client was
actually calling that API for pricing at all; each was computing its
own answer internally. The container-level view is accurate about
WHAT EXISTS in the post-fix architecture, but it was never the right
tool for surfacing a bug that lived entirely inside two containers'
own private internals.

WHY THIS WORKS AS AN ANSWER
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The answer identifies the specific missing detail (each client's own
internal pricing logic) rather than vaguely gesturing at "more detail
would help," and it explains precisely why Level 2's own defining
scope (containers and their connections, not what's inside them)
structurally excludes the kind of bug Chapter 8 found, rather than
treating the diagram as simply "not detailed enough."