chore: add agent skills

.agents/skills/rust-best-practices/SKILL.md

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+---
+name: rust-best-practices
+description: >
+  Guide for writing idiomatic Rust code based on Apollo GraphQL's best practices handbook. Use this skill when:
+  (1) writing new Rust code or functions,
+  (2) reviewing or refactoring existing Rust code,
+  (3) deciding between borrowing vs cloning or ownership patterns,
+  (4) implementing error handling with Result types,
+  (5) optimizing Rust code for performance,
+  (6) writing tests or documentation for Rust projects.
+license: MIT
+compatibility: Rust 1.70+, Cargo
+metadata:
+  author: apollographql
+  version: "1.1.0"
+allowed-tools: Bash(cargo:*) Bash(rustc:*) Bash(rustfmt:*) Bash(clippy:*) Read Write Edit Glob Grep
+---
+
+# Rust Best Practices
+
+Apply these guidelines when writing or reviewing Rust code. Based on Apollo GraphQL's [Rust Best Practices Handbook](https://github.com/apollographql/rust-best-practices).
+
+## Best Practices Reference
+
+Before reviewing, familiarize yourself with Apollo's Rust best practices. Read ALL relevant chapters in the same turn in parallel. Reference these files when providing feedback:
+
+- [Chapter 1 - Coding Styles and Idioms](references/chapter_01.md): Borrowing vs cloning, Copy trait, Option/Result handling, iterators, comments
+- [Chapter 2 - Clippy and Linting](references/chapter_02.md): Clippy configuration, important lints, workspace lint setup
+- [Chapter 3 - Performance Mindset](references/chapter_03.md): Profiling, avoiding redundant clones, stack vs heap, zero-cost abstractions
+- [Chapter 4 - Error Handling](references/chapter_04.md): Result vs panic, thiserror vs anyhow, error hierarchies
+- [Chapter 5 - Automated Testing](references/chapter_05.md): Test naming, one assertion per test, snapshot testing
+- [Chapter 6 - Generics and Dispatch](references/chapter_06.md): Static vs dynamic dispatch, trait objects
+- [Chapter 7 - Type State Pattern](references/chapter_07.md): Compile-time state safety, when to use it
+- [Chapter 8 - Comments vs Documentation](references/chapter_08.md): When to comment, doc comments, rustdoc
+- [Chapter 9 - Understanding Pointers](references/chapter_09.md): Thread safety, Send/Sync, pointer types
+
+## Quick Reference
+
+### Borrowing & Ownership
+- Prefer `&T` over `.clone()` unless ownership transfer is required
+- Use `&str` over `String`, `&[T]` over `Vec<T>` in function parameters
+- Small `Copy` types (≤24 bytes) can be passed by value
+- Use `Cow<'_, T>` when ownership is ambiguous
+
+### Error Handling
+- Return `Result<T, E>` for fallible operations; avoid `panic!` in production
+- Never use `unwrap()`/`expect()` outside tests
+- Use `thiserror` for library errors, `anyhow` for binaries only
+- Prefer `?` operator over match chains for error propagation
+
+### Performance
+- Always benchmark with `--release` flag
+- Run `cargo clippy -- -D clippy::perf` for performance hints
+- Avoid cloning in loops; use `.iter()` instead of `.into_iter()` for Copy types
+- Prefer iterators over manual loops; avoid intermediate `.collect()` calls
+
+### Linting
+Run regularly: `cargo clippy --all-targets --all-features --locked -- -D warnings`
+
+Key lints to watch:
+- `redundant_clone` - unnecessary cloning
+- `large_enum_variant` - oversized variants (consider boxing)
+- `needless_collect` - premature collection
+
+Use `#[expect(clippy::lint)]` over `#[allow(...)]` with justification comment.
+
+### Testing
+- Name tests descriptively: `process_should_return_error_when_input_empty()`
+- One assertion per test when possible
+- Use doc tests (`///`) for public API examples
+- Consider `cargo insta` for snapshot testing generated output
+
+### Generics & Dispatch
+- Prefer generics (static dispatch) for performance-critical code
+- Use `dyn Trait` only when heterogeneous collections are needed
+- Box at API boundaries, not internally
+
+### Type State Pattern
+Encode valid states in the type system to catch invalid operations at compile time:
+```rust
+struct Connection<State> { /* ... */ _state: PhantomData<State> }
+struct Disconnected;
+struct Connected;
+
+impl Connection<Connected> {
+    fn send(&self, data: &[u8]) { /* only connected can send */ }
+}
+```
+
+### Documentation
+- `//` comments explain *why* (safety, workarounds, design rationale)
+- `///` doc comments explain *what* and *how* for public APIs
+- Every `TODO` needs a linked issue: `// TODO(#42): ...`
+- Enable `#![deny(missing_docs)]` for libraries