Bug Killer -- Hypothesis-Driven Debugging Workflow

Execute a systematic debugging workflow that enforces investigation before fixes. Every bug gets a hypothesis journal, evidence gathering, and root cause confirmation before any code changes.

Phase Overview

1. Triage and Reproduction -- Understand, reproduce, route to quick or deep track
2. Investigation -- Gather evidence with language-specific techniques
3. Root Cause Analysis -- Confirm root cause through hypothesis testing
4. Fix and Verify -- Fix with proof, regression test, quality check
5. Wrap-up and Report -- Document trail, capture learnings

Nested Agents

• bug-investigator (agents/bug-investigator.md) -- Executes diagnostic investigation tasks to test debugging hypotheses. Runs tests, traces execution, checks git history, and reports evidence. Used in Phase 3 (deep track).
• code-explorer (cross-reference: ../../core-tools/skills/deep-analysis/agents/code-explorer.md from the core-tools package) -- Read-only exploration agent for investigating codebase areas related to the bug. Used in Phase 2 (deep track).

Phase 1: Triage and Reproduction

Goal: Understand the bug, reproduce it, and decide the investigation track.

1.1 Parse Context

Extract from $ARGUMENTS and conversation context:

• Bug description: What's failing? Error messages, symptoms
• Reproduction steps: How to trigger the bug (test command, user action, etc.)
• Environment: Language, framework, test runner, relevant config
• Prior attempts: Has the user already tried fixes? What didn't work?
• Deep flag: If --deep is present, skip triage and go directly to deep track (jump to Phase 2 deep track)

1.2 Reproduce the Bug

Attempt to reproduce before investigating:

1. If a failing test was mentioned, run it:

   # Run the specific test to confirm the failure
   <test-runner> <test-file>::<test-name>
   

2. If an error was described, find and trigger it
3. If neither, search for related test files and run them

Capture the exact error output -- this is your primary evidence.

If the bug cannot be reproduced:

• Prompt the user for more context
• Check if it's environment-specific or intermittent
• Note "not yet reproduced" in the hypothesis journal

1.3 Form Initial Hypothesis

Based on the error message and context, form your first hypothesis:

### H1: [Title]
- Hypothesis: [What you think is causing the bug]
- Evidence for: [What supports this -- error message, stack trace, etc.]
- Evidence against: [Anything that contradicts it -- if none yet, say "None yet"]
- Test plan: [Specific steps to confirm or reject]
- Status: Pending

1.4 Route to Track

Quick-fix signals (ALL must be true):

• Clear, specific error message pointing to exact location
• Localized to 1-2 files (not spread across the codebase)
• Obvious fix visible from reading the error location
• No concurrency, timing, or state management involved

Deep-track signals (ANY one triggers deep track):

• Bug spans 3+ files or modules
• Root cause unclear from the error message alone
• Intermittent or environment-dependent failure
• Involves concurrency, timing, shared state, or async behavior
• User already tried fixes that didn't work
• Generic error message (e.g., "null reference" without clear origin)
• Stack trace points to library/framework code rather than application code

Present your assessment. Prompt the user to choose:

• Summarize the bug and your initial hypothesis
• Recommend quick or deep track with justification
• Options: "Quick track (Recommended)" / "Deep track" or "Deep track (Recommended)" / "Quick track" -- depending on your assessment
• Let the user override your recommendation

Track escalation rule: If during quick track execution, 2 hypotheses are rejected, automatically escalate to deep track. Preserve all hypothesis journal entries when escalating.

Phase 2: Investigation

Goal: Gather evidence systematically, guided by language-specific techniques.

2.1 Load Language Reference

Detect the primary language of the bug's context and load the appropriate reference:

Always also consult the General Debugging Reference as a supplement when using a language-specific reference.

2.2 Quick Track Investigation

For quick-track bugs, investigate directly:

1. Read the error location -- the file and function where the error occurs
2. Read the immediate callers -- 1-2 files up the call chain
3. Check recent changes -- git log --oneline -5 -- <file> for the affected files
4. Update hypothesis -- does the evidence support H1? Add evidence for/against

Proceed to Phase 3 (quick track).

2.3 Deep Track Investigation

For deep-track bugs, use parallel exploration agents:

1. Plan exploration areas -- identify 2-3 focus areas based on the bug:

   • Focus 1: The error site and immediate code path
   • Focus 2: Data flow and state management leading to the error
   • Focus 3: Related subsystems, configuration, or external dependencies

2. Launch exploration agents:

   This step uses the code-explorer agent from the deep-analysis skill in the core-tools package (see ../../core-tools/skills/deep-analysis/agents/code-explorer.md).

   Spawn 2-3 exploration agents with distinct focus areas:

   Prompt for each agent:
   Bug context: [description of the bug and error]
   Focus area: [specific area for this agent]
   
   Investigate this focus area in relation to the bug:
   - Find all relevant files
   - Trace the execution/data path
   - Identify where behavior diverges from expected
   - Note any suspicious patterns, recent changes, or known issues
   - Report structured findings
   

   Launch agents in parallel for independent focus areas.

3. Synthesize exploration results:

   • Collect findings from all agents
   • Identify convergence (multiple agents pointing to same area)
   • Update hypothesis journal with new evidence
   • Form additional hypotheses if evidence warrants (aim for 2-3 total)

Proceed to Phase 3 (deep track).

Phase 3: Root Cause Analysis

Goal: Confirm the root cause through systematic hypothesis testing.

3.1 Quick Track Root Cause

For quick-track bugs:

1. Verify the hypothesis:

   • Read the specific code identified in Phase 2
   • Trace the logic step-by-step
   • Confirm that the hypothesized cause produces the observed error

2. If confirmed (Status -> Confirmed):

   • Update H1 with confirming evidence
   • Proceed to Phase 4

3. If rejected (Status -> Rejected):

   • Update H1 with evidence against and reason for rejection
   • Form a new hypothesis (H2) based on what you learned
   • Investigate H2 following Phase 2 quick track steps
   • If H2 is also rejected, escalate to deep track
   • Preserve all journal entries, continue with Phase 2 deep track

3.2 Deep Track Root Cause

For deep-track bugs:

1. Prepare hypotheses for testing:

   • You should have 2-3 hypotheses from Phase 2
   • Each needs a concrete test plan (how to confirm or reject)

2. Launch investigator agents:

   Delegate to 1-3 investigator agents (see agents/bug-investigator.md for instructions) to test hypotheses in parallel:

   Prompt for each agent:
   Bug context: [description of the bug and error]
   
   Hypothesis to test: [specific hypothesis]
   Test plan:
   1. [Step 1 -- e.g., run this specific test with these arguments]
   2. [Step 2 -- e.g., check git blame for this function]
   3. [Step 3 -- e.g., trace the data from input to error site]
   
   Report your findings with v