One row emitted by the Configurable derive’s integration_descriptor()
method on structs annotated with #[integration(...)]. Used for nested
toggleable configs (e.g. BrowserConfig, CronConfig) where the
integration is “active” iff a named bool field on the struct is true.
Stable wire-form for an addable section — a HashMap<String, T> (Map) or
Vec<T> (List) field whose value type implements Configurable. The
dashboard / CLI use this to surface + Add affordances without
hardcoding the section list. Auto-discovered by the Configurable derive.
Sentinel rendered for unset / None / empty config values during display.
Never a valid stored value: the write path rejects it so it cannot round-trip
into persisted config.