System-size dependence of the $D^0$--$D_s^{+}$ flow splitting from early $D_s^{+}$ formation at $\sqrt{s_{NN}}=5.36$~TeV

We investigate the elliptic-flow splitting between prompt $D^0$ and $D_s^{+}$ mesons within a heavy-quark transport framework with sequential hadronization, in which $D_s^{+}$ forms at $1.2T_c$ and $D^0$ at $T_c$. We present predictions for the $p_T$-differential $v_2$ and $D_s^{+}\mathrm{/}{D}^0$ yield ratio in O–O $0$–$20\mathrm{\%}$ collisions at $\sqrt{s_{NN}}=5.36$~TeV, where preliminary ALICE data are available. The sequential scenario reproduces the observed $v_2(D^0)>v_2(D_s^{+})$ ordering and predicts an enhanced $D_s^{+}\mathrm{/}{D}^0$ ratio at low $p_T$, whereas a simultaneous baseline yields the opposite ordering. Decomposing the hadronic splitting into its partonic components, we show that the $v_2$ ordering is driven by the late-stage flow accumulated by $D^0$-parent charm quarks during the $1.2T_c\to T_c$ interval, with hadronic rescattering essential to preserve the signal in small systems. A systematic scan across nine collision configurations spanning O–O and Pb–Pb centralities reveals a universal linear scaling between the hadronic splitting and the partonic flow increment accumulated during this window. This establishes the $D^0$–$D_s^{+}$ flow splitting as a hadronization chronometer of the QGP at $\sqrt{s_{NN}}=5.36$~TeV.