cc-code-quality-principles

Use the six-principle checklist covering module size, call depth, fan-in/fan-out, interface boundaries, scope cohesion, and predictability. Each principle has measurable thresholds, such as call depth at or below 3 layers and fan-out at or below 5 dependencies.

A call depth of 1-3 layers is healthy, 4-5 layers is acceptable but worth watching, and 6 or more layers is a design smell. Fix deep chains with guard clauses, merging pass-through adapter layers, event-driven decoupling, and dependency inversion.

Extract a core service that depends only on repositories and domain logic, move notifications, auditing, caching, and metrics to event listeners, and use a facade to collapse multiple related services into one entry point for callers.

Require an idempotency key on every write operation and back it with a database unique constraint or INSERT ON CONFLICT semantics. Pass the same key to downstream payment gateways so duplicate requests return the original result instead of executing twice.

This skill is a decision framework and checklist, not an executor. For concrete enforcement of file size limits, refactoring safety, time zone handling, or API contract rules, it delegates to specialized skills like cc-size-check and cc-refactor-safety.