Chesterton's Fence Investigation

Enforce epistemic humility before changing existing systems. Requires understanding original purpose before proposing changes.

Triggers

Phrase	Context
why does this exist	Investigating existing code or patterns
chestertons fence	Explicit investigation request
before removing	Planning deletion or replacement
historical context	Researching original rationale
prior art investigation	ADR-required investigation

Quick Reference

Input	Output	Destination
File path or ADR number	Investigation report	.agents/analysis/NNN-chestertons-fence-TOPIC.md
Component description	Historical context summary	stdout (JSON)

When to Use

Use this skill BEFORE proposing changes to existing:

• Code patterns or architectural decisions
• ADRs, constraints, or protocol rules
• Workflow configurations or CI pipelines
• Skills, hooks, or agent prompts

Process

1. Identify Structure    What exists? Where?
       |
       v
2. Git Archaeology       git log/blame to find origin
       |
       v
3. PR/ADR Search         Find original rationale
       |
       v
4. Dependency Analysis   What references this?
       |
       v
5. Generate Report       Fill investigation template
       |
       v
6. Decision              REMOVE / MODIFY / PRESERVE / REPLACE

Usage

# Investigate a file or pattern
python3 scripts/investigate.py --target path/to/file.py --change "remove unused validation"

# Investigate an ADR
python3 scripts/investigate.py --target .agents/architecture/ADR-005.md --change "allow bash scripts"

# Output as JSON (for automation)
python3 scripts/investigate.py --target path/to/file.py --change "description" --format json

Integration with Agent Workflows

Analyst Agent

When investigating changes to existing systems, run this skill first. The investigation report becomes a prerequisite for any change proposal.

Architect Agent

ADRs that deprecate or replace existing patterns MUST include a "Prior Art Investigation" section. Use this skill to generate it.

Implementer Agent

Before implementing deletions or major refactoring, verify that an investigation report exists. If missing, route to analyst.

Critic Agent

When validating plans that remove or replace existing systems, check for investigation evidence. Auto-reject proposals without historical context.

Template

Investigation reports use the template at .agents/templates/chestertons-fence-investigation.md.