rust

Rust (language skill)

This is a knowledge skill, not an agent: it loads from context whenever Rust is written or reviewed, and the role agents (/be, /rev, /arch) route into it for the language-level rules. It carries the standards inline; the deep material lives in references/ and is loaded on demand.

Trigger

Use this skill when:

• Writing, editing, or reviewing .rs files
• Changing Cargo.toml or Cargo.lock — dependencies, features, lints, workspace layout
• Diagnosing a cargo or clippy failure
• Designing a Rust component — crate boundaries, error surface, async topology
• Planning tests for Rust code
• Adding a dependency to a Rust workspace

Do NOT load it for merely running or installing a compiled Rust tool — that is an operations task, not a Rust task.

Context

This skill exists to make Rust reviews boring. Invariants live in types, so the compiler argues about them instead of the reviewer. Failure paths are enumerated before code is written, so error handling is a table being filled in, not an improvisation. Policy — toolchain, lints, formatting, dependency rules, coverage — lives in checked-in files, not in anyone's head, so "what does this repo require?" has exactly one answer. The two goals behind every rule here: predictable consequences and cheap extension.

Documentation Lookup (MANDATORY)

Before implementing any feature, check current documentation. Rust ships a new stable release every six weeks and several load-bearing crates are pre-1.0; recall is not a source.

Context7 MCP

Use Context7 MCP to retrieve up-to-date documentation for any crate or tool:

1. Resolve library: Call mcp__context7__resolve-library-id with the crate name
2. Query docs: Call mcp__context7__query-docs with the resolved library ID and your question

When to use: tokio primitives, axum extractors/routing/middleware, rusqlite API, serde attributes, clap derive, proptest strategies.

Example queries:

• "tokio JoinSet and graceful shutdown"
• "axum 0.8 State extractor and middleware ordering"
• "rusqlite transactions and prepared statement caching"
• "thiserror 2 derive attributes and #[from]"
• "clap 4 derive subcommands and value parsing"
• "proptest strategies for recursive data"