Rust learning: lessons, notes, and exercise crates

MISSION.md

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+# Mission: Rust
+
+## Why
+Land a backend/CLI job that uses Rust. Two months on the book already happened, but the knowledge did not stick — the goal now is real fluency (can write and reason about Rust under pressure), not a second pass at "having read the book."
+
+## Success looks like
+- Explain ownership/borrowing rules without hesitating, and predict compile errors before running `cargo build`.
+- Write a small CLI or backend service (e.g. a JSON API) from scratch, handling errors with `Result`/`?`, not `panic!`.
+- Use structs, enums, traits, generics, and modules idiomatically in own code, not just recognize them in a book example.
+- Pass a Rust-focused technical interview or take-home without needing to relearn fundamentals first.
+
+## Constraints
+- ~2 months already spent on [The Rust Book](https://doc.rust-lang.org/stable/book/), chapters 1–9 covered (variables through error handling), but retention is weak — treat as "seen before, not owned" until proven otherwise.
+- Sessions are crash-course paced: prioritize fast, high-yield retrieval practice over slow first-pass reading.
+
+## Out of scope
+- Embedded / `no_std` Rust.
+- Deep async internals — only as much async as a backend job needs (revisit if the job requires more).