Day 21/90: Practice - Library management system

90 Day C++ Challenge: Zero to Production

Today I wanted library management system to feel like a real engineering decision, not a syntax demo. The useful shift was using practice - library management system to keep a larger C++ system understandable under change.

The checks that mattered were domain boundaries, dependencies that point the right way, and failure paths designed as early as the happy path.

The failure mode I was actively trying to avoid was spreading workflow rules across components without a clear ownership model. Practice days are where library management system stops being theory. I wanted a version that could survive one more requirement without collapsing into copy-paste fixes.

That is the bar I want from this track: code that stays readable when requirements move, not just code that compiles today. I also want to keep tracing one concrete path through the code because that exposes weak assumptions faster than a larger demo.