Systematic Debugging

Path convention: Commands below assume cwd is $CLAUDE_PROJECT_DIR (project root). Prefix paths with "$CLAUDE_PROJECT_DIR/" when invoking from subdirectories.

Iron Law: NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST.

Skill wiring

• Reads memory: .claude/memory/fixes.md, .claude/memory/architecture-decisions.md
• Writes memory: .claude/memory/fixes.md via direct Edit (diagnosis records only — ##note: is a user-typed keyboard shortcut that does NOT fire from agent output; the fix itself is persisted by mk:fix). See .claude/skills/memory/references/capture-architecture.md.

Plan-First Gate

Investigation precedes planning for bug fixes:

1. Confirm root cause FIRST (Iron Law)
2. After root cause confirmed → invoke mk:plan-creator --type bugfix if fix affects > 2 files

Skip: Investigation itself doesn't need a plan — it produces the input for planning.

When to Use

• User reports errors, bugs, unexpected behavior
• "debug this", "fix this bug", "why is this broken"
• "investigate this error", "root cause analysis"
• Troubleshooting why something stopped working

Process

1. Run preamble — load references/preamble.md and execute the startup bash block
2. Collect symptoms — read error messages, stack traces, reproduction steps
3. Investigate root cause — load references/debugging-methodology.md and follow Phase 1-3. For recurring patterns or complex failures, load references/rca-method-selection.md for methodology selection. Load references/rca-anti-patterns.md to avoid common RCA mistakes.
4. Lock scope — optionally invoke mk:freeze <target-dir> first to restrict edits to the affected module. The check-freeze.sh hook is installed but without an explicit mk:freeze invocation it is a no-op (all edits allowed).
5. Implement fix — follow Phase 4 from debugging methodology
6. Verify — reproduce original scenario, run test suite, output DEBUG REPORT
7. Run shared protocols — load references/shared-protocols.md for completion status + telemetry

References

Load only when executing the corresponding step — not upfront.

Specialized Techniques (load based on bug type)

Constraints

• Read-only until hypothesis confirmed — no edits until root cause identified
• 3-strike rule — if 3 hypotheses fail, STOP and escalate
• Minimal diff — fix root cause with fewest files/lines possible
• Regression test required — must fail without fix, pass with fix
• >5 files touched — AskUserQuestion about blast radius before proceeding

Hooks

• Iron Law enforcement: No fixes without confirmed root cause — this is a process constraint, not a technical hook
• The skill gates Phase 3 (Fix) behind Phase 1 (Investigate) completion
• If root cause cannot be confirmed after 3 hypotheses, escalate to human
• Scope-locking hook: Installs a PreToolUse hook on Edit/Write that delegates to mk:freeze to scope edits to the investigation target. Deactivation follows freeze's semantics — end the session or start a new one to clear it.
• Interaction with mk:careful: If mk:careful is active, debugging commands that touch state will still prompt for confirmation. This is expected — do not bypass.

Gotchas

• Confirming hypothesis without disproving alternatives: Finding evidence FOR a theory doesn't mean it's correct → Actively test at least one alternative hypothesis before concluding
• Log timestamps in wrong timezone: Server logs in UTC, local comparison in local time → Normalize all timestamps to UTC before correlation

Delegation: mk:web-to-markdown

When investigation requires fetching an arbitrary external URL (e.g. a vendor error page, a remote log endpoint, a referenced issue URL), this skill delegates to mk:web-to-markdown via the --wtm-accept-risk flag.

• Without --wtm-accept-risk: mk:web-to-markdown refuses cross-skill delegation. External URL resolution falls back to Context7 / chub / WebSearch only.
• With --wtm-accept-risk: delegation proceeds through all security layers (SSRF guard, injection scanner, DATA boundary, secret scrub). The flag is a conscious trust-boundary crossing — the caller acknowledges the target URL may contain prompt injection and that the skill's defenses are best-effort.
• Delegation example: .claude/skills/.venv/bin/python3 .claude/skills/web-to-markdown/scripts/fetch_as_markdown.py "<url>" --wtm-accept-risk --caller mk:investigate