RLM Systematic Debugging (Phase 1.5)

Overview

When a requirement involves fixing a bug or investigating unexpected behavior, ad-hoc fixes waste time and create new bugs. Systematic debugging finds the root cause before any fix is attempted.

Core Principle: ALWAYS find root cause before attempting fixes. Symptom fixes are failure.

The Iron Law for RLM Debugging:

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

Trigger examples

• Tests are failing after the last change; debug it
• Fix crash on empty input
• Investigate why the API returns wrong data
• Do a root cause analysis before making changes

When to Use

Mandatory Phase 1.5 when:

• Requirement is a bug fix
• Test failures need investigation
• Unexpected behavior reported
• Performance problems
• Integration issues

Use ESPECIALLY when:

• Under time pressure (emergencies make guessing tempting)
• "Just one quick fix" seems obvious
• Previous fix attempts failed
• 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)
• Manager wants it fixed NOW (systematic is faster than thrashing)

Phase 1.5 Insertion

Phase 1.5 is inserted between Phase 1 (AS-IS) and Phase 2 (TO-BE Plan) when debugging is required:

Phase 0: 00-requirements.md
    ->
Phase 1: 01-as-is.md (captures current behavior)
    ->
Phase 1.5: 01.5-root-cause.md <- NEW (this skill)
    ->
Phase 2: 02-to-be-plan.md (includes fix plan based on root cause)

The Four Phases of Systematic Debugging

digraph debugging_phases {
    rankdir=TB;
    
    phase1 [label="Step 1:\nRoot Cause Investigation", shape=box, style=filled, fillcolor="#ffcccc"];
    phase2 [label="Step 2:\nPattern Analysis", shape=box, style=filled, fillcolor="#ffffcc"];
    phase3 [label="Step 3:\nHypothesis & Testing", shape=box, style=filled, fillcolor="#ccffcc"];
    phase4 [label="Step 4:\nFix Implementation", shape=box, style=filled, fillcolor="#ccccff"];
    
    phase1 -> phase2 -> phase3 -> phase4;
    
    // Feedback loops
    phase3 -> phase1 [label="hypothesis\nfailed", style=dashed];
    phase4 -> phase1 [label="fix\nfailed", style=dashed];
}

Step 1: Root Cause Investigation

BEFORE attempting ANY fix:

1.1 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

Record in Phase 1.5 artifact:

## Error Analysis

**Error Message:** [verbatim]
**Stack Trace:** [key frames]
**File:Line:** [locations]
**Error Code:** [if applicable]
**Key Insight:** [what the error is telling you]

1.2 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

Record in Phase 1.5 artifact:

## Reproduction Verification

**Steps:**
1. [exact step]
2. [exact step]
3. [exact step]

**Reproducible:** Yes / No / Intermittent
**Frequency:** [X out of Y attempts]
**Deterministic:** Yes / No

1.3 Check Recent Changes

• What changed that could cause this?
• Git diff, recent commits
• New dependencies, config changes
• Environmental differences

Record in Phase 1.5 artifact:

## Recent Changes Analysis

**Git History:** [relevant commits]
**Dependency Changes:** [package.json, requirements.txt, etc.]
**Config Changes:** [relevant files]
**Environment:** [OS, runtime versions]
**Likely Culprit:** [most suspicious change]

1.4 Gather Evidence in Multi-Component Systems

WHEN system has multiple components (CI -> build -> signing, API -> service -> database):

BEFORE proposing fixes, add diagnostic instrumentation:

For EACH component boundary:

• Log what data enters component
• Log what data exits component
• Verify environment/config propagation
• Check state at each layer

Run once to gather evidence showing WHERE it breaks, THEN analyze evidence.

Record in Phase 1.5 artifact:

## Multi-Layer Evidence

**Layer 1: [Component Name]**
- Input: [data]
- Output: [data]
- Status: ✅ Working / ❌ Broken

**Layer 2: [Component Name]**
- Input: [data from Layer 1]
- Output: [data]
- Status: ✅ Working / ❌ Broken

**Failure Boundary:** Layer X -> Layer Y
**Root Cause Location:** [specific component]

1.5 Trace Data Flow

WHEN error is deep in call stack:

Trace backward:

• Where does bad value originate?
• What called this with bad value?
• Keep tracing up until you find the source
• Fix at source, not at symptom

Record in Phase 1.5 artifact:

## Data Flow Trace

**Error Location:** [file:line - function]
**Bad Value:** [what was wrong]

**Call Stack Trace:**
1. [deepest] `functionA()` at fileA:line - received [value]
2. `functionB()` at fileB:line - passed [value]
3. `functionC()` at fileC:line - passed [value]
4. [source] `functionD()` at fileD:line - ORIGIN of bad value

**Root Cause:** [source location] - [explanation]

Step 2: Pattern Analysis

Find the pattern before fixing:

2.1 Find Working Examples

• Locate similar working code in same codebase
• What works that's similar to what's broken?

2.2 Compare Against References

• If implementing pattern, read reference implementation COMPLETELY
• Don't skim - read every line
• Understand the pattern fully before applying

2.3 Identify Differences

• What's different between working and broken?
• List every difference, however small
• Don't assume "that can't matter"

2.4 Understand Dependencies

• What other components does this need?
• What settings, config, environment?
• What assumptions does it make?

Record in Phase 1.5 artifact:

## Pattern Analysis

**Working Example:** [file:location]
**Broken Code:** [file:location]

**Key Differences:**
| Aspect | Working | Broken |
|--------|---------|--------|
| [X] | [value] | [value] |
| [Y] | [value] | [value] |

**Likely Cause:** [difference that explains the bug]
**Dependencies:** [what the code needs to work]

Step 3: Hypothesis and Testing

Scientific method:

3.1 Form Single Hypothesis

• State clearly: "I think X is the root cause because Y"
• Write it down
• Be specific, not vague

3.2 Test Minimally

• Make the SMALLEST possible change to test hypothesis
• One variable at a time
• Don't fix multiple things at once

3.3 Verify Before Continuing

• Did it work? Yes -> Phase 4
• Didn't work? Form NEW hypothesis
• DON'T add more fixes on top

3.4 When You Don't Know

• Say "I don't understand X"
• Don't pretend to know
• Ask for help
• Research more

Record in Phase 1.5 artifact:

## Hypothesis Testing

### Hypothesis 1
**Statement:** [clear hypothesis]
**Rationale:** [why you think this]
**Test:** [minimal change to verify]
**Result:** [confirmed/rejected]
**Evidence:** [output/observation]

### Hypothesis 2 (if needed)
[...]

**Confirmed Root Cause:** [final hypothesis]

Step 4: Fix Summary (Handoff to Phase 2 Planning)

Fix the root cause, not the symptom:

4.1 Create Failing Test Case

• Simplest possible reproduction
• Automated test if possible
• One-off test script if no framework
• MUST have before fixing
• This becomes part of Phase 3's test plan

4.2 Root Cause Summary for Phase 2

• Summarize root cause found
• Document the fix approach
• Reference evidence from Phase 1.5

Record in Phase 1.5 artifact:

## Root Cause Summary

**Root Cause:** [one sentence]
**Location:** [file:line]
**Explanation:** [paragraph explaining why]
**Fix Approach:** [high-level]
**Test Strategy:** [how to verify fix]

## Phase 1.5 Gate

Coverage: [Did we find root cause?]
Approval: [Ready to proceed to Phase 3 with fix plan?]

Red Flags - STOP and Follow Process

If you catch 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"
• Proposing solutions before tracing data flow
• "One more fix attempt" (when already tried 2+)

ALL of these mean: STOP. Return to Phase 2.

Common Process Shortcuts (STOP)

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 test after confirming fix"	Untested fixes don't stick. Test first proves it.
"Multiple fixes at once saves time"	Can't isolate what worked. Causes new bugs.
"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 pattern, don't fix again.

If 3+ Fix Attempts Failed

Pattern indicating architectural problem:

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

STOP and question fundamentals:

• Is this pattern fundamentally sound?
• Are we "sticking with it through sheer inertia"?
• Should we refactor architecture vs. continue fixing symptoms?

Document in Phase 1.5:

## Architectural Concern

**Fix Attempts:** [number]
**Pattern:** [what happens with each fix]
**Recommendation:** [architectural change vs. symptom fix]
**Next Steps:** [escalate, refactor, or accept risk]

Phase 1.5 Artifact Template

File: /.codex/rlm/<run-id>/01.5-root-cause.md

Run: `/.codex/rlm/<run-id>/`
Phase: `01.5 Root Cause Analysis`
Status: `DRAFT` | `LOCKED`
Inputs:
- `/.codex/rlm/<run-id>/01-as-is.md`
- [relevant addenda]
Outputs:
- `/.codex/rlm/<run-id>/01.5-root-cause.md`
Scope note: This document records systematic debugging process and identified root cause.

## Error Analysis

[Section 2.1 - verbatim errors, stack traces]

## Reproduction Verification

[Section 2.2 - exact steps, reproducibility]

## Recent Changes Analysis

[Section 2.3 - git history, dependencies]

## Evidence Gathering

[Section 2.4 - multi-layer diagnostics if applicable]

## Data Flow Trace

[Section 2.5 - backward trace to source]

## Pattern Analysis

[Section 3 - working vs broken comparison]

## Hypothesis Testing

[Section 4 - scientific method log]

## Root Cause Summary

**Root Cause:** [one sentence]
**Location:** [file:line]
**Detailed Explanation:** [paragraph]
**Fix Strategy:** [approach for Phase 3]
**Test Plan:** [how to verify]

## Traceability

- R1 (Bug fix requirement) -> Root cause identified at [location] | Evidence: [section]

## Coverage Gate

- [ ] Error messages analyzed
- [ ] Reproduction verified
- [ ] Recent changes reviewed
- [ ] Data flow traced to source
- [ ] Pattern analysis completed
- [ ] Hypothesis tested and confirmed
- [ ] Root cause documented
- [ ] Fix strategy defined

Coverage: PASS / FAIL

## Approval Gate

- [ ] Root cause identified (not just symptom)
- [ ] Fix approach clear
- [ ] Test strategy defined
- [ ] No "quick fixes" attempted
- [ ] Ready to proceed to Phase 3

Approval: PASS / FAIL

LockedAt: [when locked]
LockHash: [sha256]

Integration with RLM

Phase 1 -> 1.5 Transition

When Phase 1 (AS-IS) identifies a bug/issue that needs fixing:

1. Lock Phase 1 (01-as-is.md)
2. Create Phase 1.5 (01.5-root-cause.md) with Status: DRAFT
3. Execute systematic debugging
4. Lock Phase 1.5 when root cause found
5. Proceed to Phase 3 with root cause knowledge

Phase 1.5 -> 3 Transition

Phase 3 (02-to-be-plan.md) builds ON Phase 1.5:

## Root Cause Reference

Root cause identified in `01.5-root-cause.md`:
- Location: [file:line]
- Cause: [summary]
- Full analysis: [reference]

## Fix Plan

Based on root cause analysis:
1. [specific fix steps]
2. [test strategy from Phase 1.5]

References

• REQUIRED: Use this skill for all bug-fix requirements
• TRIGGERS: When requirement involves debugging/fixing
• OUTPUT: 01.5-root-cause.md artifact
• NEXT: Phase 3 (TO-BE Plan) incorporates findings