Function make_loft_skinned_closed 

pub fn make_loft_skinned_closed(
    model: &mut Model,
    sections: &[Shape],
    tolerance: f64,
    tol: Tolerances,
) -> OgeomResult<Built>

Loft a ring through closed planar sections that loop back to the first.

make_loft_skinned’s closed sibling: the sections are sampled the same way, the skin runs through all of them and back to the start, C1 across the loop, and there are no caps: the result bounds itself the way a torus does. The sections are not repeated: the loop-back is the construction’s own.

The closed join costs freedom: a sparse loop fits only loosely, and the refusal quotes the deviation it honestly reached. A loop that wants a tight tolerance wants sections dense enough to bend around: in practice, a dozen and up.

Errors

As make_loft_skinned, needing at least three sections; OgeomError::NotDone if the closed skin cannot reach the tolerance.