No more duplicate serial numbers

Every unit eControl builds carries a unique serial number, and under busy conditions two orders could occasionally be handed the same one. We fixed it with a belt-and-braces approach: a dedicated service now generates each number with a secure random generator and checks it against the database before committing, retrying if it has to.

Then we backed the whole thing with a unique constraint at the database level — so even in the rare case something slips past the application, the database itself refuses to store a duplicate. Two guarantees where there used to be none.