Struct SettingKey 

pub struct SettingKey {
    pub key: &'static str,
    pub default: Option<&'static str>,
}

One entry of the canonical setting registry.

Carrying the default alongside the key is what lets config doctor derive its whole listing from SETTING_KEYS instead of repeating a hand-written table. GAP-SG-85 was exactly that divergence: a 14-entry manual list next to a 44-key registry, missing the one key that redirects the database.

Fields

key: &'static str

Dotted key accepted by config set.

default: Option<&'static str>

Literal default applied when neither a CLI flag nor the XDG config supplies a value.

None marks a default that cannot be a static string because it is derived from the host at runtime — an XDG directory, the CPU count, or a probe. config doctor reports those as derived rather than inventing a number that would not match what the process actually uses.