CLQMS backend is a PHP 8.1+ CodeIgniter 4 API-only project that follows PSR-12 spacing/brace rules and prefers short arrays. New PHP files should enable `declare(strict_types=1)` and use typed arguments/returns (nullable unions over doc-only hints). Controllers use `ResponseTrait` to emit `{ status, message, data }` JSON responses; shared logic lives in `app/Libraries`/`app/Traits`. Guard clauses and single-purpose helpers keep methods ~40 lines; repeated flows are extracted. Database work uses Query Builder/Model methods, `helper('utc')`, and `checkDbError()` for manual queries. Multi-table writes wrap `$this->db->transStart()/transComplete()` with status checks. Lookups leverage `App\\Libraries\\Lookups` and JSON files in `app/Libraries/Data/valuesets/`. Routes stay in `app/Config/Routes.php` grouped by resource; filters like `auth` guard protected routes. Audits/logging use `log_message` with sanitized data. Tests live under `tests/Feature` and `tests/Unit`, use PHPUnit 10.5+ conventions, and expect status assertions per HTTP semantics.