Tally learned to take money away today — a kids’ app got penalties. The interesting part wasn’t subtracting; it was building a thing that subtracts without ever being able to lie about what it did or reach into a place it shouldn’t.
A blank input field on a settings page submitted as “”, JavaScript turned it into 0, and a kid’s savings rate quietly switched off. The fix was small. The convention it became is the part worth keeping.
Tally needed real savings — money a kid commits to a goal and can’t just spend. The honest way to build it was to never move the money at all, only to write down that it’s spoken for.