# Internal Engineering Guidelines

## Rust file sizing and layout
- Soft cap: keep Rust source files at or below ~400 lines; if a change would exceed that, split into modules first.
- Hard cap: avoid exceeding 650 lines in any Rust file; refactor before merging (main.rs should stay <350 lines).
- Single-responsibility: group code by concern (config, TLS/setup, auth/session, storage adapters, RPC handlers, CLI parsing) instead of piling into one file.
- Structure new features as small modules wired from the entrypoint rather than expanding existing large files.
- Co-locate unit tests with their module; keep integration tests in `crates/*/tests` with focused scopes.
- Prefer descriptive module names and re-exports over deep `mod` trees that hide logic in `main.rs`.