Resize_MappedScalar2D_t Subroutine

  subroutine Resize_MappedScalar2D_t(this,interp,nVar,nElem)
    !! Rebind to a new element count, reusing storage where it fits (AMR Stage 6b). The mortar
    !! staging buffer is sized by mesh%nMortars rather than nElem, and nMortars changes with the
    !! mesh independently of the element count, so it is invalidated here and lazily re-created
    !! at the correct size by the next mortar exchange.
    implicit none
    class(MappedScalar2D_t),intent(inout) :: this
    type(Lagrange),intent(in),target :: interp
    integer,intent(in) :: nVar
    integer,intent(in) :: nElem

    call Resize_Scalar2D_t(this,interp,nVar,nElem)
    if(allocated(this%mortarBuff)) deallocate(this%mortarBuff)

    ! The geometry binding refers to the PREVIOUS mesh's geometry, which the caller is
    ! about to destroy. It must be dropped here so the AssociateGeometry that follows a
    ! regrid actually rebinds: AssociateGeometry is a no-op when a geometry is already
    ! associated, so leaving the stale one in place silently kept every mapped operation
    ! reading freed metric terms - observed as NaN entropy on the first step after an
    ! adaptation. Free + Init used to hide this by nulling the pointer.
    call this%DissociateGeometry()

  endsubroutine Resize_MappedScalar2D_t