Maintainability Code Review

Principles

KISS: treat simplicity as a design goal. Flag solutions that are harder to read, test, reason about, operate, or repair than the changed behavior requires.
DRY: every piece of changing knowledge should have one clear, authoritative representation. Flag repeated business rules, mappings, constants, schemas, validations, queries, test setup, build logic, or documentation that are likely to drift.
Balance the two principles. Do not recommend abstraction only because code is textually similar; prefer duplication over the wrong abstraction when the repeated code has different reasons to change.
Boolean design: treat a Boolean as the answer to one clear yes-or-no question. Prefer names and APIs that make the question and the meaning of each value evident at the use site.