code-architecture-best-practiceslisted

# Architecture Best Practices Apply these principles when designing systems, reviewing structure, or making architectural decisions. ## Reuse Check (Do This First) Before writing new logic, search the codebase (`grep`/`ast-grep`) for an existing function or pattern that already does something similar — reuse it or extract a shared abstraction rather than reimplementing it per call site. This is the single highest-value check in this skill: the canonical failure mode it catches is the same bug-prone logic (e.g. a check-then-mutate ordering rule) getting copy-pasted across sibling functions, each with its own chance to get it wrong, instead of being centralized once. Do this check *before* design-pattern selection below, not after — a pattern applied to duplicated logic just formalizes the duplication. If the file you're about to edit is a known churn/complexity hotspot, run `code-hotspot-analysis`'s inline spot-check first — a file that already changes often and is already complex is exactly where uncaught duplication compounds fastest. ## Core Principles (Language-Agnostic) ### SOLID - **S**ingle Responsibility: One reason to change per class/module - **O**pen/Closed: Open for extension, closed for modification (use interfaces/protocols) - **L**iskov Substitution: Subtypes must be substitutable for base types - **I**nterface Segregation: Many focused interfaces > one fat interface - **D**ependency Inversion: Depend on abstractions, not concretions ### Clean Architectur