# User Action Edge Cases

> Use when finishing anything that depends on external state a person controls - a file, a record, a folder.

- Skill: `fergius-engineering/user-action-edge-cases` (Agent Skill)
- Install (CLI): `npx skillmds@latest add fergius-engineering/user-action-edge-cases`
- Raw SKILL.md: https://api.skillmd.com/api/skills/fergius-engineering/user-action-edge-cases/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: Fergius-Engineering (https://skillmd.com/u/fergius-engineering)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/fergius-engineering/user-action-edge-cases

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## The rule

Anything you depend on that a user can touch will get renamed, moved, deleted, and duplicated. If your code assumes a fixed path or a single copy, it breaks the first time the user does something ordinary. Before you finish, run those four actions through your head.

## Fires when

Your code reads, writes, or depends on a file, a record, a document, or any state the user can edit outside your code.

## How to apply

For each thing you depend on, ask the four questions: renamed? moved? deleted? duplicated?

Prefer finding things by type or id over a hardcoded path or name. Decide what happens in each case instead of assuming it won't happen.

## Worked example

Your app stores its settings in a file at a hardcoded path. It works on your machine. Then a user renames the file, and the app silently writes a fresh one with defaults, losing their config. Or they copy the project folder, and now two copies fight over the same path. Looking the file up by a stable marker instead of a fixed name, and handling "not found" and "more than one" on purpose, turns four silent bugs into defined behavior.

## Red flags

| Thought | Reality |
|---|---|
| "The file is always at this path" | Until the user moves it. |
| "There's only ever one" | Until they duplicate it. |
| "They won't rename it" | They will. |