Decomposing fused items

Synthesis reading. When an item visibly fuses mechanisms, decompose in this order:

1. Name the data journey: input type → transformation(s) → output type. Write the arrow chain; every arrow is one code segment.
2. Locate the interaction: the difficulty lives where the segments meet (a parsed value feeds a list index; a static counter outlives the loop). Write that sentence explicitly.
3. Implement segment-by-segment, testing each against a one-element example before composing. Fused code written all-at-once fails in fused ways that are miserable to trace.

The FRQ here (the studio below) is a three-mechanism class: numeric state, a list, and a text lookup. Do the three independently bankable parts FIRST — synthesis FRQs are where partial-credit discipline pays the most.