m03▌

Layer 1: Language Mechanics

Rust mutability design: choosing between &mut , interior mutability, and thread-safe patterns. \n \n Guides decision-making for E0596, E0499, E0502 errors by asking whether mutation is necessary and who controls it, rather than reflexively adding mut \n Covers single-thread patterns (Cell, RefCell) and multi-thread patterns (Mutex, RwLock, Atomic types) with clear selection criteria \n Includes borrow rule reference, anti-patterns (RefCell overuse, Mutex in hot loops), and decision tables f