systematic-debugging

Systematic Debugging

Overview

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

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

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
• 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)
• Manager wants it fixed NOW (systematic is faster than thrashing)

The Four Phases

You MUST 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
   • For workflow-level issues (blocked beads, stuck execution): bd ready --explain shows dependency reasoning
   • Check the knowledge store for this symptom before investigating further: bd memories <symptom-keywords> (prior root-cause/lesson memories) and bd list --label <topic> --status all (+ bd search "<symptom>" --status all for decision/design knowledge-beads; error strings are body terms: add --desc-contains "<error-string>"; >10 hits: narrow the query, never triage truncated titles). Then read — hits are pointers, not knowledge: bd show <ids> every plausibly-matching prior decision/design, and bd recall <key> every plausibly-matching memory (bd memories prints truncated previews) — full bodies, before investigating further. 0 relevant does not mean none exist — re-angle the query once before emitting KB check: none. Emit KB check: N hits, M read + a one-line disposition each. If a prior root cause or decision already covers this, use it — don't re-debug something already understood.