Minimal reproduction
Also called Reduced test case, Delta debugging
The smallest input or program that still shows the bug. You get there by removing things until the failure goes away, then putting the last thing back. What remains is often close to an explanation.
A small reproduction is cheap to hand to an agent and leaves it nothing irrelevant to chase, so you get a better answer for less.
Say it to your agent
“This 4,000 row CSV crashes the import. Write a script that deletes rows and reruns the import until it has the fewest rows that still crash, and save them as tests/fixtures/import-crash.csv.”