cachey: Instructions file for Codex

cachey is a read-through cache for S3-compatible object storage

• NO TRIVIAL COMMENTS
• Follow Rust idioms and best practices
• Latest Rust features can be used
• Descriptive variable and function names
• No wildcard imports
• Explicit error handling with Result<T, E> over panics
• Use eyre::Report when the specific error is not as important
• Use custom error types using thiserror for domain-specific errors
• Format: cargo +nightly fmt
• Lint: cargo clippy --locked --all-features --all-targets -- -D warnings --allow deprecated
• Dependency policy: cargo deny check
• Place unit tests in the same file using #[cfg(test)] modules
• Integration tests go in the tests/ directory
• Run tests with: cargo nextest run --locked
• Use --locked for Cargo commands that build, check, test, run, document, fetch, or read metadata
• Use cargo +nightly add, cargo +nightly update, cargo +nightly remove, or cargo +nightly generate-lockfile for dependency changes
• Do not use the stable forms of these dependency commands
• Do not edit dependency declarations or Cargo.lock directly
• Do not run cargo install as part of a coding task
• Prefer well-maintained crates from crates.io
• Be mindful of allocations in hot paths
• Prefer structured logging
• Provide helpful error messages
• Use conventional commit format for commit messages and PR titles
• PR descriptions should include Closes #<issue> when applicable