Function check_shape_if_available 

pub fn check_shape_if_available(
    cx: &mut Cx,
    shape_ref: Ref,
    input: Value,
) -> Result<()>

Checks input against a shape reference, passing silently only when the shape reference explicitly accepts anything.

Used by invoke_op to validate operation arguments. Missing symbols, unresolved refs, and registered non-shape values fail closed.