Investigate

Systematic debugging skill that enforces the Iron Law: never fix without a confirmed root cause. Produces a structured debug report with full evidence chain, minimal fix, and regression test.

Iron Law Principle

No fix without confirmed root cause. Every investigation follows a strict evidence chain:

1. Reproduce the bug with concrete evidence
2. Analyze patterns to assess scope
3. Form and test hypotheses (max 3 strikes)
4. Implement minimal fix ONLY after root cause is confirmed
5. Verify fix and generate structured report

Violation of the Iron Law (skipping to Phase 4 without Phase 3 confirmation) is prohibited.

Key Design Principles

1. Evidence-First: Collect before theorizing. Logs, stack traces, and reproduction steps are mandatory inputs.
2. Minimal Fix: Change only what is necessary. Refactoring is not debugging.
3. 3-Strike Escalation: If 3 consecutive hypothesis tests fail, STOP and escalate with a diagnostic dump.
4. Regression Coverage: Every fix must include a test that fails without the fix and passes with it.
5. Structured Output: All findings are recorded in machine-readable JSON for future reference.

Execution Flow

Phase 1: Root Cause Investigation
  Reproduce bug, collect evidence (errors, logs, traces)
  Use ccw cli --tool gemini --mode analysis for initial diagnosis
  Output: investigation-report.json
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Phase 2: Pattern Analysis
  Search codebase for similar patterns (same error, module, antipattern)
  Assess scope: isolated vs systemic
  Output: pattern-analysis section in report
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Phase 3: Hypothesis Testing
  Form max 3 hypotheses from evidence
  Test each with minimal read-only probes
  3-strike rule: STOP and escalate on 3 consecutive failures
  Output: confirmed root cause with evidence chain
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Phase 4: Implementation  [GATE: requires Phase 3 confirmed root cause]
  Implement minimal fix
  Add regression test
  Verify fix resolves reproduction case
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Phase 5: Verification & Report
  Run full test suite
  Check for regressions
  Generate structured debug report to .workflow/.debug/

Directory Setup

mkdir -p .workflow/.debug

Output Structure

.workflow/.debug/
  debug-report-{YYYY-MM-DD}-{slug}.json    # Structured debug report

Completion Status Protocol

This skill follows the Completion Status Protocol defined in _shared/SKILL-DESIGN-SPEC.md sections 13-14.

Status	When
DONE	Root cause confirmed, fix applied, regression test passes, no regressions
DONE_WITH_CONCERNS	Fix applied but partial test coverage or minor warnings
BLOCKED	Cannot reproduce bug, or 3-strike escalation triggered in Phase 3
NEEDS_CONTEXT	Missing reproduction steps, unclear error conditions

Reference Documents

Document	Purpose
phases/01-root-cause-investigation.md	Evidence collection and reproduction
phases/02-pattern-analysis.md	Codebase pattern search and scope assessment
phases/03-hypothesis-testing.md	Hypothesis formation, testing, and 3-strike rule
phases/04-implementation.md	Minimal fix with Iron Law gate
phases/05-verification-report.md	Test suite, regression check, report generation
specs/iron-law.md	Iron Law rules definition
specs/debug-report-format.md	Structured debug report JSON schema

CLI Integration

This skill leverages ccw cli for multi-model analysis at key points:

Phase	CLI Usage	Mode
Phase 1	Initial diagnosis from error evidence	--mode analysis
Phase 2	Cross-file pattern search	--mode analysis
Phase 3	Hypothesis validation assistance	--mode analysis

All CLI calls use --mode analysis (read-only). No write-mode CLI calls during investigation phases 1-3.