ufv_weights_consistent
======================

.. py:function:: t3toolbox.backend.ufv_operations.ufv_weights_consistent(variations, weights)

   .. code-block:: python

      def ufv_weights_consistent(
              variations: typ.Tuple,            # UT3Variations .data: (tkv, ttv, shape, masks), stack = K + C
              weights:    UT3FrameWeightsData,  # (up, down, left, right, masks), stack = C
      ) -> bool:                                # True iff `weights` can be absorbed into `variations`


   True iff the four weight families fit ``variations`` (non-raising): padded widths match, the weight
   stack is the **trailing part** of the variation stack, and the weight's masks -- broadcast constant
   over the excess ``K`` -- equal the variations' masks.

   Two checks ragged does not need, both because uniform pads:

   - **The trailing-stack rule** is ragged's too (a weight is frame-like: it carries ``C``, the variations
     carry ``K + C``; ``fv_weights_consistent``), but here it must be spelled out against padded shapes.
   - **Mask equality** is uniform-only. Ragged catches a rank mismatch as an einsum shape error; uniform
     pads both to the common ``(nU, nD, rL, rR)``, so a mismatch is invisible to the shapes and would
     silently corrupt -- a weight whose mask calls slot ``i`` padding carries a canonical zero there, so
     absorbing it **zeroes a real variation slot**. The mask comparison mirrors ``check_ufv_pair``'s
     (the variation masks are constant along ``K``).