What problem does it solve? Hard bugs and performance regressions stall when developers jump straight to hypotheses without a reproducible signal. This Skill enforces a disciplined diagnosis loop that builds a tight pass/fail feedback signal first, then reproduces, minimises, hypothesises, instruments, fixes, and cleans up. ## Core Features & Use Cases - Feedback loop construction: Ten ranked strategies for building a red-capable reproduction command, from failing tests and curl scripts to headless browser runs, trace replay, fuzz loops, and git bisect harnesses. - Structured hypothesis testing: Generates 3-5 ranked, falsifiable hypotheses before testing, then maps each instrumentation probe to a specific prediction with tagged debug logs for easy cleanup. - Regression test and post-mortem: Turns the minimised repro into a failing regression test at a correct seam, verifies the fix, removes instrumentation, and records the confirmed root cause. - Use Case: A user reports that an export endpoint intermittently returns corrupted data. The Skill guides building a deterministic loop that reproduces the corruption, minimising the input, ranking hypotheses, and landing a fix with a regression test. ## Quick Start Ask the agent to diagnose the bug where the export endpoint intermittently returns corrupted data and have it build a reproduction loop first.