Function primitive_shape 

pub fn primitive_shape(
    op: &Op,
    input_shapes: &[Shape],
    input_dtypes: &[DType],
) -> Result<(Shape, DType), Error>

The single source of truth for primitive-Op shape+dtype inference. Given a primitive Op (its params live on the variant) plus its input shapes and dtypes, returns the (output_shape, output_dtype) the op produces. Reads params off the Op, not off OpAttrs. Never panics: a malformed op/shape, a leaf/bookkeeping op with no pure inference, or a higher-order/basis-gap op is an honest Err.

M-2: on the emit path this fn is intentionally more permissive than the NodeHandle builders — it computes the output shape/dtype but does NOT re-run every builder-side precondition (broadcast-compatibility for BroadcastTo/ ReduceSumTo/ReduceMaxTo, the size-1 check for Squeeze, the elem-count check for Reshape, duplicate-axis for Permute). The builders validate those before calling in (Task 6), and emit re-emits already-validated recipes, so the derived-shape math is the only thing needed here. It still range-checks the arithmetic it performs (dim bounds, matmul inner dim, …) so a malformed authored region is an Err, never an out-of-bounds panic.