Function resolve_source_bounds 

pub fn resolve_source_bounds(
    source: &dyn DataSource,
    variable_name: &str,
    x_axis: &str,
    y_axis: &str,
    requested: NumericBounds,
) -> Result<Bounds, BoundsError>

Resolve bounds for a data-source variable using its selected x/y axes. Coordinate access is performed by the caller’s worker, not a TUI reducer.