Rust essentials

Canonical: docs/fcis-rust.md

Goal

Every .rs change follows FCIS and the ponytail ladder.

Inputs / outputs

• In: current crate + the behaviour to change
• Out: Rust that compiles, no extra crates, illegal states unrepresentable

Reads / writes

• Read: Cargo.toml, files the task already opened, docs/fcis-rust.md in this pack
• Write: none unless a playbook opened the task

Approval