Module editor 

Editor resolution + argv parsing.

Precedence ladder (FR-009):

1. --editor=<cmd> flag (Default mode only); empty value falls through.
2. $VISUAL
3. $EDITOR
4. /usr/bin/editor (Unix only; existence + executable check)
5. vi (Unix) / notepad.exe (Windows)

Structs

Resolved

Result of resolving the editor command: the argv to spawn (NOT yet including the tempfile path) plus the resolved source for diagnostics.

Functions

parse_editor_value

Parse an editor command string into argv using shell-words rules. Returns Error::InvalidEditorCommand(value.to_string()) on parse failure (per FR-010 + STF-003).

resolve

Walk the resolution ladder. Returns the editor argv (without tempfile) and the matched source rung.