Debug

Debug

Overview

Fuses systematic root-cause debugging with verification-before-completion.

Core principle: evidence before fixes; evidence before "fixed" claims.

Announce: "Using debug to …"

When to Use

• Any bug, flaky test, build/CI failure, unexpected behavior, performance mystery
• Especially under time pressure ("just one quick fix")
• Before claiming "done" / "passing" / "fixed"

When NOT to use: pure greenfield feature with no failure (use grill / write-plan / tdd).

The Iron Law

1. NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST.
2. NO "FIXED" / "PASSING" / "DONE" CLAIMS WITHOUT FRESH VERIFICATION EVIDENCE IN THIS TURN.

Violating the letter is violating the spirit.

Workflow (phases — do in order)

Phase 1 — Investigate (no fix yet)

1. Read the full error / stack / logs (don't skim)
2. Reproduce consistently — if you can't, gather data, don't guess
3. Check recent changes (git diff, commits, config, env)
4. Multi-component systems: instrument boundaries (in → out) to see where it breaks
5. Trace bad values backward to the source; plan to fix at source

Create todos for these steps; do not edit production logic until Phase 1 has a stated root cause.

Phase 2 — Pattern

• Find a working similar path in-repo
• Diff working vs broken; list every difference
• Note dependencies / assumptions

Phase 3 — Hypothesis

• One hypothesis: "X is root cause because Y"
• Design the smallest test/probe that would falsify it
• If wrong → new hypothesis (don't stack random changes)

Phase 4 — Fix via TDD

1. tdd + test-design: write a failing regression that locks the bug
2. Watch RED for the right reason
3. Minimal fix → GREEN
4. Verify (below) before any success language

Phase 5 — Verify before claims (mandatory)

Before saying fixed/passing/done/complete:

1. IDENTIFY the command that proves the claim
2. RUN it fresh (full command)
3. READ exit code and failures
4. ONLY THEN claim, with the evidence

Claim	Requires
Tests pass	Test run output, 0 failures
Bug fixed	Original symptom re-tested + regression green
Build OK	Build exit 0
Requirements met	Checklist against plan/spec

Red-green proof for the regression: fail without fix → pass with fix (mentally or actually revert-check when feasible).

Rationalization Table

Excuse	Reality
"Obvious one-liner"	Still need cause + regression test.
"Should work now"	RUN verification.
"I'm confident / tired"	Confidence ≠ evidence.
"Logged something, good enough"	Boundary evidence must show where.
"Fix first, understand later"	That's how you get two bugs.

Red Flags — STOP

• Proposing a fix before stating root cause
• "Should", "probably", "seems" success wording
• Commit/PR of a fix without fresh test/symptom proof
• Shotgun changes across unrelated files
• Skipping the failing regression test

Checklist

• Root cause stated with evidence
• Failing regression (tdd) observed RED then GREEN
• Fresh verification command run this turn
• Claim includes that evidence
• No unrelated drive-by edits

Hand-off

• Structure was the cause → solid
• Ship the fix → review + commit-and-push