Use whenever the user writes SQL DDL for a Perfex CRM module, adds a foreign key referencing `tblcontacts`, `tblstaff`, `tblclients`, `tblinvoices`, or any `tbl*` core table, designs `tbl<module>_<entity>` schema, writes `install.php` / `uninstall.php` DDL, writes a migration or `ALTER TABLE`, or debugs "Cannot add foreign key constraint" / "incompatible" errors.
