System commands are a fixed list. There is no way to run something of one's own.
Scope
- A saved command kind that holds a shell command, edited and reviewed before it is saved.
- Run it and show the output in the palette, or copy it.
- Arguments from the query, with the same escaping discipline used for the existing scripts.
- Destructive commands ask first.
Constraints
This is directly at odds with the current rule that nothing a user types is ever run as code, and with the sandboxed build. It likely cannot ship in the Store build at all. Decide whether it is a direct-download-only capability before building. Related: #5.