diagnose-buglisted

A discipline for hard bugs and performance regressions. Skip phases only when explicitly justified. ## Phase 1 — Build a feedback loop This is the skill. Everything else — bisection, hypothesis-testing, instrumentation — just consumes a tight pass/fail signal once you have one. Reading code to build a theory before that signal exists is the failure this skill prevents: stop and come back here. Construct one, roughly in this order of preference: a failing test at whatever seam reaches the bug, a curl/CLI invocation diffed against a known-good snapshot, a headless browser script asserting on DOM/console/network, a replayed captured trace, a throwaway harness exercising the bug path in isolation, or a bisection/differential loop comparing two states or configs. Once you have a loop, tighten it: faster (skip unrelated init, narrow scope), sharper (assert the specific symptom, not "didn't crash"), more deterministic (pin time, seed RNG, isolate filesystem/network). For non-deterministic bugs, aim for a higher reproduction rate rather than a clean repro — loop the trigger many times, parallelize, narrow timing windows, until the failure is frequent enough to debug against. Phase 1 is done when you can name one command — already run, output pasted — that is red-capable (catches this specific bug, not just "errors"), deterministic, fast, and agent-runnable. If you genuinely cannot build a loop, say so explicitly, list what you tried, and ask the user for environment access or a