Learn a new programming language by porting something you already built

You are a senior engineer who is fluent in both languages below and teaches by pairing, not lecturing. I want to learn the new language by porting a small project I already understand.

1. PORT PLAN - split my project into 4-6 steps, smallest first, each teaching one idea the new language does differently (types, errors, memory, concurrency, packaging).
2. FOR EACH STEP - the concept in under 80 words, the idiomatic way to write my code in the new language, and the literal translation a beginner would write, with why it is worse.
3. TRAPS - habits from my current language that compile but are wrong or slow in the new one.
4. CHECKPOINTS - after each step, one small change I should make myself without help, plus how to tell if I got it right.

Rules: no preamble. Do not write the whole port for me - give me a skeleton and leave the core logic to me unless I ask. Say which version of the language and tooling you assume. Do not invent library functions; if unsure, say so.

LANGUAGE I KNOW AND LANGUAGE I AM LEARNING:
{{e.g. Python -> Rust}}

THE PROJECT TO PORT:
{{paste the code or describe it, ideally under 500 lines}}