systematic-debugging

name	systematic-debugging
description	Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes. Enforces a 4-phase root-cause process with a 3-attempt escalation to architectural review. Invoke when the operator says 'debug', 'investigate', 'figure out why', or pastes an error message / failing test.
source	{"upstream":"obra/superpowers","tag":"v5.0.7","commit":"1f20bef3f59b85ad7b52718f822e37c4478a3ff5","path":"skills/systematic-debugging/SKILL.md","license":"MIT"}

Systematic Debugging

Overview

Random fixes waste time and create new bugs. Quick patches mask underlying issues.

Core principle: find the root cause before attempting any fix. Symptom fixes are failure.

Violating the letter of this process is violating the spirit of debugging.

NovaCore adaptations (vendored from Superpowers v5.0.7):

• For general structured reasoning (architecture trade-offs, multi-phase planning), prefer sequential-thinking. This skill is specifically for bug/failure/incident investigation.
• The 3-attempt escalation routes to the Critic agent (AGENTS/critic/AGENT.md) via Task dispatch, and the root-cause summary is logged via memory-store with memory_type: research and tag debug. See the "3+ Failed Fixes — Escalation" section below.
• Upstream phrasing "your human partner" is rendered here as "operator".

The Iron Law

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

If you haven't completed Phase 1, you cannot propose fixes.

When to Use

Use for any technical issue:

• Test failures
• Bugs in production
• Unexpected behavior
• Performance problems
• Build failures
• Integration issues

Use this especially when:

• Under time pressure (emergencies make guessing tempting)
• "Just one quick fix" seems obvious
• You've already tried multiple fixes
• The previous fix didn't work
• You don't fully understand the issue

Don't skip when:

• Issue seems simple (simple bugs have root causes too)
• You're in a hurry (rushing guarantees rework)
• The operator wants it fixed now (systematic is faster than thrashing)

The Four Phases

Complete each phase before proceeding to the next.

Phase 1: Root Cause Investigation

Before attempting any fix:

1. Read error messages carefully. Don't skip past errors or warnings. They often contain the exact solution. Read stack traces completely. Note line numbers, file paths, error codes.

2. Reproduce consistently. Can you trigger it reliably? What are the exact steps? Does it happen every time? If not reproducible → gather more data, don't guess.

3. Check recent changes. What changed that could cause this? git diff, recent commits, new dependencies, config changes, environmental differences.

4. Gather evidence in multi-component systems. When the system has multiple layers (CI → build → signing, API → service → database), add diagnostic instrumentation at each component boundary before proposing fixes:

   For each component boundary:
     - Log what data enters the component
     - Log what data exits the component
     - Verify environment/config propagation
     - Check state at each layer
   
   Run once to gather evidence showing WHERE it breaks.
   Then analyze evidence to identify the failing component.
   Then investigate that specific component.
   

5. Trace data flow. When the error is deep in the call stack, trace backward: where does the bad value originate? What called this with a bad value? Keep tracing up until you find the source. Fix at the source, not at the symptom.

Phase 2: Pattern Analysis

Find the pattern before fixing:

1. Find working examples. Locate similar working code in the same codebase.
2. Compare against references. Read reference implementations completely — don't skim.
3. Identify differences. List every difference, however small. Don't assume "that can't matter".
4. Understand dependencies. What other components does this need? What settings, config, environment? What assumptions does it make?

Phase 3: Hypothesis and Testing

Scientific method:

1. Form a single hypothesis. State it clearly: "I think X is the root cause because Y." Write it down. Be specific.
2. Test minimally. Make the smallest possible change to test the hypothesis. One variable at a time.
3. Verify before continuing. Did it work? Yes → Phase 4. Didn't work? Form a new hypothesis. Don't pile fixes on top.
4. When you don't know. Say "I don't understand X". Don't pretend. Ask for help. Research more.

Phase 4: Implementation

Fix the root cause, not the symptom:

1. Create a failing test case. Simplest possible reproduction. Use test-driven-development for proper failing tests. This is required before fixing.

2. Implement a single fix. Address the root cause identified. One change at a time. No "while I'm here" improvements.

3. Verify the fix. Test passes? No other tests broken? Issue actually resolved?

4. If the fix doesn't work:

   • Stop.
   • Count: how many fixes have you tried?
   • If < 3: return to Phase 1, re-analyze with new information.
   • If ≥ 3: stop and question the architecture (step 5 below).
   • Do not attempt fix #4 without architectural discussion.

5. If 3+ fixes failed — escalate (see "3+ Failed Fixes — Escalation" below).

   Pattern indicating architectural problem:

   • Each fix reveals new shared state / coupling / problem in a different place
   • Fixes require "massive refactoring" to implement
   • Each fix creates new symptoms elsewhere

   This is not a failed hypothesis — this is a wrong architecture. Do not attempt fix #4 without escalating.

3+ Failed Fixes — Escalation

When you cross the 3-attempt threshold, do both of the following before proposing any further fix:

Step A — Dispatch the Critic agent

Use Task (subagent dispatch) with subagent_type matching NovaCore's Critic agent (see AGENTS/critic/AGENT.md for the contract). The prompt is self-contained and includes:

• The original symptom and every reproduction step
• All three failed hypotheses with evidence showing why each failed
• Code diffs for each attempted fix
• The specific question: is this pattern architecturally sound, or are we fighting the design?

Task(
  subagent_type="critic",
  description="3-fix architectural escalation: <short symptom>",
  prompt="""
  Bug: <symptom + repro>
  Attempt 1 hypothesis: <X because Y>. Result: <what happened>. Diff: <paths>.
  Attempt 2 hypothesis: <...>. Result: <...>. Diff: <...>.
  Attempt 3 hypothesis: <...>. Result: <...>. Diff: <...>.

  Verdict requested: is this pattern fundamentally sound? Should we continue
  fixing symptoms or refactor the architecture? What is the minimum refactor
  that would make this class of bug impossible?
  """
)

The Critic is independent of this session's context — it sees only what you pass in. Include the raw evidence, not your interpretation.

Step B — Log the root-cause finding via memory-store

Whether the Critic says "refactor" or "continue fixing", persist the finding. Use mcp__nova-memory__upsert_memory (or invoke the memory-store skill, which wraps it):

mcp__nova-memory__upsert_memory(
  content="<concrete root-cause statement — one concept, self-contained. "
          "Example: 'retry_operation() in src/worker.py shares mutable state "
          "between concurrent invocations via module-level cache; 3 fix "
          "attempts confirmed the coupling is architectural, not a lock bug.'>",
  metadata={
    "memory_type": "research",
    "project": "<project slug>",
    "tags": ["debug", "root-cause", "<component>"],
    "session_id": "<current session id>"
  }
)

One atomic fact per upsert_memory call. If the Critic returns multiple independent findings, use bulk_upsert_memory. Never store secrets or raw stack traces — distill to the insight.

Step C — Present to the operator

After dispatching the Critic and logging the finding, summarise for the operator:

"Hit the 3-fix threshold on <symptom>. Critic verdict: <summary>. Root cause logged to Fusion Memory as <memory_id>. Recommended next step: <refactor X> / <one more targeted fix>. Proceed?"

Wait for a decision. Do not attempt fix #4 without operator approval.

Red Flags — STOP and Follow Process

Catching yourself thinking:

• "Quick fix for now, investigate later"
• "Just try changing X and see if it works"
• "Add multiple changes, run tests"
• "Skip the test, I'll manually verify"
• "It's probably X, let me fix that"
• "I don't fully understand but this might work"
• "Pattern says X but I'll adapt it differently"
• "Here are the main problems: [lists fixes without investigation]"
• Proposing solutions before tracing data flow
• "One more fix attempt" (after 2+ already)
• Each fix reveals a new problem in a different place

All of these mean: stop. Return to Phase 1.

If 3+ fixes failed: question the architecture (see Phase 4, step 5).

Operator Signals You're Doing It Wrong

Watch for these redirections:

• "Is that not happening?" — you assumed without verifying
• "Will it show us…?" — you should have added evidence gathering
• "Stop guessing" — you're proposing fixes without understanding
• "Ultrathink this" — question fundamentals, not just symptoms
• "We're stuck?" (frustrated) — your approach isn't working

When you see these: stop. Return to Phase 1.

Common Rationalizations

Excuse	Reality
"Issue is simple, don't need process"	Simple issues have root causes too. Process is fast for simple bugs.
"Emergency, no time for process"	Systematic debugging is faster than guess-and-check thrashing.
"Just try this first, then investigate"	First fix sets the pattern. Do it right from the start.
"I'll write a test after confirming the fix works"	Untested fixes don't stick. Test first proves it.
"Multiple fixes at once saves time"	Can't isolate what worked. Causes new bugs.
"Reference too long, I'll adapt the pattern"	Partial understanding guarantees bugs. Read it completely.
"I see the problem, let me fix it"	Seeing symptoms ≠ understanding root cause.
"One more fix attempt" (after 2+ failures)	3+ failures = architectural problem. Question the pattern.

Quick Reference

Phase	Key Activities	Success Criteria
1. Root Cause	Read errors, reproduce, check changes, gather evidence	Understand WHAT and WHY
2. Pattern	Find working examples, compare	Identify differences
3. Hypothesis	Form theory, test minimally	Confirmed or new hypothesis
4. Implementation	Create test, fix, verify	Bug resolved, tests pass

When Process Reveals "No Root Cause"

If investigation reveals a truly environmental, timing-dependent, or external issue:

1. You've completed the process.
2. Document what you investigated.
3. Implement appropriate handling (retry, timeout, error message).
4. Add monitoring/logging for future investigation.

But: 95% of "no root cause" cases are incomplete investigation.

Related NovaCore Skills

• test-driven-development — for creating the failing test (Phase 4, Step 1)
• self-verification — verify the fix worked before claiming success
• sequential-thinking — general structured reasoning (not bug-specific)
• memory-store — log root-cause findings (see "3+ Failed Fixes — Escalation", Step B)
• Critic agent (AGENTS/critic/AGENT.md) — escalation target after 3+ failed fixes (see "3+ Failed Fixes — Escalation", Step A)