test the full demo before presenting
what happened
MAKE SURE THE THING WORKS BEFORE GOING INTO THE PRESENTATION. tested individual pieces, assumed they'd work together. they didn't.
why it's a gotcha
integration bugs only show up when you run the full flow. you'll discover that step 3 breaks step 5 right in front of the judges. individual components working does not mean the system works. AI-generated code you didn't test is a common cause — and environmental differences between your machine and the demo machine make it worse.
the fix
run the complete user flow at least twice before presenting. start from a clean state each time — restart services to make sure you're not running stale code. if something breaks, you want to find it now, not on stage. and have a backup plan for when it breaks anyway. testing the demo is one thing; testing the presentation itself is another.