Function validate_date_range 

pub fn validate_date_range(
    since: Option<NaiveDateTime>,
    until: Option<NaiveDateTime>,
) -> Result<(), Error>

Validate that a (since, until) date range is well-ordered.

Extracted so the HTTP handler and CLI can share the check without constructing a full backend context.

Errors

[Error::BadRequest] when both bounds are supplied and since > until. Returns Ok(()) whenever either bound is None, including when they are equal.