Function config_tab 

fn config_tab(kind: &str, title: &str, choices: &[String]) -> String

One config-editor tab: a file dropdown, the editor, and Reload / Save.

Reload includes #{kind}-path alone rather than the whole form. The form holds the editor too, and on a GET that would ride up the query string — a megabyte-class config (some in configs/ are over 1 MB) then pushes the URI past what the server accepts and Reload silently does nothing. Save is a POST, so it can and must include the whole form.