What problem does it solve? Hard bugs and performance regressions stall when developers stare at code without a reproducible signal. This Skill enforces a disciplined diagnosis loop — build a feedback loop, reproduce, hypothesise, instrument, fix, and regression-test — so root causes are found systematically instead of by guesswork. ## Core Features & Use Cases - Feedback loop construction: Builds a fast, deterministic pass/fail signal using failing tests, curl scripts, CLI fixtures, headless browsers, trace replay, fuzz loops, or git bisect harnesses. - Ranked hypothesis testing: Generates 3-5 falsifiable hypotheses with explicit predictions, then instruments one variable at a time with tagged debug logs for clean removal. - Regression locking and post-mortem: Writes the regression test before the fix at a correct seam, verifies the original repro is gone, and documents the confirmed root cause. - Use Case: A user reports that the export endpoint intermittently returns empty files. The Skill builds a loop replaying the failing request 100 times, ranks hypotheses, instruments the boundary, fixes the race condition, and locks it with a regression test. ## Quick Start Ask the agent to diagnose the bug where the export endpoint intermittently returns empty files and follow the structured diagnosis loop.
