Concept-Check: Foundations

These questions target the three ideas Part I installed: the four seams of the pipeline, the transient-vs-permanent error split that drives retries, and newtype id-safety. The Tracing questions are compiled and run by the real Rust compiler when this book builds — predict the output (or the refusal to compile) before you reveal. Answer honestly; a wrong answer with a good explanation teaches more than a lucky guess.