  We investigate the order of the QCD chiral transition in the limit of
vanishing bare up/down quark masses and variations of the bare strange-quark
mass $0 \le m_{\mathrm{s}} \le \infty$. In this limit and due to universality
long range correlations with the quantum numbers of pseudoscalar and scalar
mesons may dominate the physics. In order to study the interplay between the
microscopic quark and gluon degrees of freedom and the long range correlations
we extend a combination of lattice Yang--Mills theory and a (truncated) version
of Dyson--Schwinger equations by also taking back-reactions of mesonic degrees
of freedom into account. Both this system and the meson backcoupling approach
have been studied extensively in the past but this is the first work in a full
$(2 + 1)$-flavor setup. Starting from the physical point, we determine the
chiral susceptibilities for decreasing up/down quark masses and find good
agreement with both lattice and functional renormalization group results. We
then proceed to determine the order of the chiral transition along the
left-hand side of the Columbia plot, for chemical potentials in the range $-(30
\,\textrm{MeV})^2 \le \mu_q^2 \le (30 \,\textrm{MeV})^2$. We find a
second-order phase transition throughout and no trace of a first-order region
in the $N_{f} = 3$ corner of the Columbia plot. This result remains unchanged
when an additional Goldstone boson due to a restored axial $\mathrm{U_A}(1)$ is
taken into account.
