require_concrete_masks
======================

.. py:function:: t3toolbox.backend.common.require_concrete_masks(*masks)

   .. code-block:: python

      def require_concrete_masks(
              *masks: NDArray,  # HOST bool, static -- the uniform structure masks (must NOT be traced)
      ) -> None:


   Guard the uniform-mask contract: masks are concrete host (numpy) arrays, never jax tracers.

   Under jit any ``jnp`` op on a mask returns a tracer, which breaks the layer two ways: host-int
   shape/rank extraction (``int(mask.sum())``) raises ``ConcretizationTypeError``, and recomputed masks
   leak as tracers into the (identity-hashed, never-inspected) output ``aux_data`` -- silently invalid.
   So a traced mask here means the masks were passed *among* the traced jit args; the fix is functional,
   not numerical (raise, per the structural-vs-numerical philosophy). See
   ``docs/contributor/uniform_pytree_composition.md``.

   Infrastructure, not part of the ``ut3_*`` family (``docs/naming_conventions.md``): it guards the mask
   representation itself, so it serves every uniform object -- plain, frame, variations, and weights.