  We present a 1d lattice model that mimics the boundary of the conventional 2d
quantum spin-Hall insulator (QSHI) with $U(1)$ symmetry and time-reversal $T$,
satisfying $T^2 = (-1)^F$. Our construction utilizes a local tensor product
Hilbert space of finite site dimension with a non-onsite symmetry action. We
discuss how several signature properties of the QSHI, such as the fractional
charge on $T$-domain walls and Kramers parity switching upon $\pi$-flux
threading, are manifested in our treatment. We also present a 1d Hamiltonian
whose ground state realizes the conventional Luttinger-liquid phase of the QSHI
edge.
