Diagnose

A discipline for hard bugs. Skip phases only when explicitly justified.

Scope: a bug report, failing command or test, error message, performance complaint, reproduction steps, or affected scope. If no repro is provided, build an agent-runnable feedback loop first (Phase 1).

When exploring the codebase, use the project's domain glossary to get a clear mental model of the relevant modules, and check ADRs in the area you're touching.

User clarifications (Cursor)

When you need a discrete decision with a small set of clear options (about 2–6), prefer the AskQuestion tool so the user gets structured choices. Ask one decision at a time when this skill already sequences questions that way.

If AskQuestion is unavailable in the current environment, ask the same choices in ordinary chat (same options, same ordering).

Use plain chat (not forced multiple-choice) when the answer is inherently free-form—for example pasted logs, a paragraph describing a custom tracker workflow, or an open-ended design explanation.

Phase 1 — Build a feedback loop

This is the skill. Everything else is mechanical. If you have a fast, deterministic, agent-runnable pass/fail signal for the bug, you will find the cause — bisection, hypothesis-testing, and instrumentation all just consume that signal. If you don't have one, no amount of staring at code will save you.