Machine Coding: Build a Small CLI Tool With Tests

Question

## Problem

Pair-programming/machine-coding round: build a small CLI (e.g., a config linter or a simple `kv` client) with clean structure and unit tests, then extend it.

## Example
```
parse args -> validate config -> report errors; add a new subcommand
```

## Constraints
- Idiomatic Go, testable, extensible

## What HashiCorp looks for
Real-world engineering: modular packages, error handling, and tests — not algorithmic tricks.