Fix failing tests

Reproduce and diagnose a bug before fixing it

This skill gives a coding agent a diagnose-first process for bug reports, regressions, runtime errors, failing builds and broken tests. It reproduces the problem as narrowly as it can, tests hypotheses that can be proven wrong, finds the shared root cause and checks the smallest change that would fix it. It only applies a fix when you authorize one; otherwise it stops at the diagnosis and a structured report. You get a reproduced bug, its root cause and a proposed fix you choose whether to apply.