name: code-investigator
description: "Investigate code to confirm specifications and provide evidence-based reports. Use for questions like 'what does this do?', 'how is this implemented?', 'where is the spec?', 'explain this behavior', or any request requiring code investigation with documented evidence. Also use for bug investigation requiring current specification understanding."

Code Investigator

Systematically investigate code to understand specifications and provide evidence-based reports with file/line references. Saves findings to persistent memory for future reference.

Core Capabilities

1. Evidence-based specification confirmation: Trace code to confirm actual behavior with file/line references
2. Visual flow documentation: Generate Mermaid diagrams for multi-file/complex flows
3. Persistent memory storage: Save investigation results in searchable format for future use
4. Uncertainty tracking: Clearly distinguish confirmed facts from unknowns

Investigation Workflow

Step 0: Plan (Brief)

State what to investigate and where to start (1-3 lines). Prevents scope drift.

Step 1: Identify Entry Point

Locate the starting point: routing, CLI entry, UI event, main function, service initialization, etc.

Step 2: Trace Call Chain (Shortest Path Only)

Follow function/class/module calls related to the specification. Identify:
- Data structures (DTO/Model/State) and transformation points
- Conditional logic, defaults, exception handling, retries, caching, persistence

Step 3: Extract Confirmed Specifications

Document facts that can be determined from code:
- "When/If [condition] then [action]"
- Default values, timeout settings, retry counts, etc.

Step 4: Handle Uncertainties

List runtime dependencies (env vars, config files, external APIs) that cannot be confirmed from code alone:
- Mark as "Unconfirmed"
- Suggest additional investigation methods

Step 5: Generate Diagram (Conditional)

Create Mermaid diagram when:
- 3+ files are involved
- Async/event-driven/state transitions are present
- Dependency direction is unclear (DI, plugins, hooks)

Output Format

Use this template for all investigation reports:

Report Template

## TL;DR
[1-2 sentence conclusion]

## Confirmed Specifications
[Bulleted list, each with evidence]

- **Spec**: [When/If/Then format]
  - **Evidence**: [path/to/file.ts:L10-L42](path/to/file.ts#L10-L42) - [Why this code proves the spec]
  - **Notes**: [Optional: exceptions, config dependencies, related locations]

## Implementation Evidence
[Key implementation details by file]

### [path/to/file.ts](path/to/file.ts)
- Lines X-Y: [What this code does]
- Lines A-B: [What this code does]

## Flow Diagram (Optional)
[Mermaid diagram if applicable]

## Open Questions / Unknowns
[What could not be confirmed and why]
- [Unconfirmed item]: [What additional investigation is needed]

Evidence Linking Rules

• Always link files with markdown: [path/to/file.ts](path/to/file.ts#L10-L42)
• Use line numbers when available: #L10-L42
• If line numbers unavailable, use: #functionName or just (file.ts)

Specification Item Format

Every specification MUST follow this structure:
- Spec: Specification statement (prefer When/If/Then format)
- Evidence: File reference + one-line justification
- Notes (optional): Exceptions, config dependencies, related code

Diagram Guidelines

Use appropriate diagram types:
- Process flow: sequenceDiagram
- Module dependencies: flowchart LR
- State transitions: stateDiagram-v2

Diagram policy:
- Show shortest path only (no comprehensive views)
- Use File::Symbol format for node names (e.g., src/foo.ts::createPlayer)

Example:

sequenceDiagram
    participant UI as app/routes/_app.tsx::handleClick
    participant Store as app/stores/player.ts::Player
    participant Service as app/lib/player/service.ts::updateState

    UI->>Store: dispatch(action)
    Store->>Service: updateState(data)
    Service-->>Store: newState

Memory Storage

All confirmed investigations are saved to: .claude/skills/code-investigator/memories/

Storage Timing

• Save when specification is confirmed (even partial)
• Save incomplete results with status in-progress

File Naming Convention

YYYY-MM-DD__topic__short-slug.md

Example: 2026-01-08__player__loop-behavior.md

Memory File Format

---
summary: "Brief description of investigation topic and findings"
created: YYYY-MM-DD
updated: YYYY-MM-DD  # optional
status: confirmed | in-progress | blocked  # optional
tags: [feature-area, component]  # optional
related: [path/to/file.ts, path/to/other.ts]  # optional
---

# [Investigation Topic]

## Question
[Original user question or investigation goal]

## Confirmed Specifications
[Same format as report above]

## Implementation Evidence
[Same format as report above]

## Flow Diagram
[Mermaid if applicable]

## Open Questions
[Unconfirmed items and next steps]

Language: All memory files MUST be written in English (per project standards). Chat responses can be in Japanese.

Memory Search Workflow

When asked to recall previous investigations:

# 1. List investigations
ls .claude/skills/code-investigator/memories/

# 2. View all summaries
rg "^summary:" .claude/skills/code-investigator/memories/ --no-ignore --hidden

# 3. Search summaries by keyword
rg "^summary:.*keyword" .claude/skills/code-investigator/memories/ --no-ignore --hidden -i

# 4. Search by tag
rg "^tags:.*keyword" .claude/skills/code-investigator/memories/ --no-ignore --hidden -i

# 5. Full-text search (when summary insufficient)
rg "keyword" .claude/skills/code-investigator/memories/ --no-ignore --hidden -i

# 6. Read specific memory if relevant

Note: Memory files are gitignored, use --no-ignore --hidden flags.

Quality Standards

Prohibited

• No speculation as fact: Use "likely" / "probably" only in "Open Questions", never in "Confirmed Specifications"
• No baseless evidence: Every specification claim must have file:line reference

Required

• Primary vs supplementary evidence: When multiple locations support one spec, separate "primary" and "supplementary" evidence
• Config/env dependencies: Always note when behavior depends on ENV vars, config files, or runtime values

References

For detailed guidance on specific patterns, see:
- references/report-templates.md - Detailed report format examples
- references/diagram-patterns.md - Mermaid diagram examples for common scenarios

scripts/

Executable code (Python/Bash/etc.) that can be run directly to perform specific operations.

Examples from other skills:
- PDF skill: fill_fillable_fields.py, extract_form_field_info.py - utilities for PDF manipulation
- DOCX skill: document.py, utilities.py - Python modules for document processing

Appropriate for: Python scripts, shell scripts, or any executable code that performs automation, data processing, or specific operations.

Note: Scripts may be executed without loading into context, but can still be read by Codex for patching or environment adjustments.

references/

Documentation and reference material intended to be loaded into context to inform Codex's process and thinking.

Examples from other skills:
- Product management: communication.md, context_building.md - detailed workflow guides
- BigQuery: API reference documentation and query examples
- Finance: Schema documentation, company policies

Appropriate for: In-depth documentation, API references, database schemas, comprehensive guides, or any detailed information that Codex should reference while working.

assets/

Files not intended to be loaded into context, but rather used within the output Codex produces.

Examples from other skills:
- Brand styling: PowerPoint template files (.pptx), logo files
- Frontend builder: HTML/React boilerplate project directories
- Typography: Font files (.ttf, .woff2)

Appropriate for: Templates, boilerplate code, document templates, images, icons, fonts, or any files meant to be copied or used in the final output.

Not every skill requires all three types of resources.