  Given a compact Lagrangian $L$ in a semipositive convex-at-infinity
symplectic manifold $W$, we establish a cup-length estimate for the action
values of $L$ associated to a Hamiltonian isotopy whose spectral norm is
smaller than some $\hbar(L)$. When $L$ is rational, this implies a cup-length
estimate on the number of intersection points. This Chekanov-type result
generalizes a theorem of Kislev and Shelukhin proving non-displaceability in
the case when $W$ is closed and monotone. The method of proof is to deform the
pair-of-pants product on Hamiltonian Floer cohomology using the Lagrangian $L$.
