We investigate the impact of spatial curvature ${\mathrm{\Omega }}_k$ and dynamical dark energy on the cosmological constraints of the neutrino mass sum, $\sum m_{\nu }$. Using a joint analysis of the latest cosmic microwave background (Planck and ACT DR6), baryon acoustic oscillation (DESI Data Release 2), and Type Ia supernovae (DESY5 and DES-Dovekie) datasets, we perform a systematic exploration of the neutrino mass parameter space. To mitigate prior-driven biases near the physical boundary, we implement a symmetric extension wrapper that allows for effective negative masses. We find that the inclusion of spatial curvature modifies the posterior distributions, exhibiting a smooth transition across the $\sum m_{\nu }=0$ threshold. In the $\mathrm{\Lambda }\mathrm{CDM}+{\mathrm{\Omega }}_k+\sum m_{\nu ,\mathrm{eff}}$ framework, we obtain $\sum m_{\nu ,\mathrm{eff}}=-0.011_{-0.050}^{+0.052}$, reducing the tension with the terrestrial lower limit of 0.06 eV from $2.59\sigma$ for the $\mathrm{\Lambda }\mathrm{CDM}+\sum m_{\nu ,\mathrm{eff}}$ model to $1.17\sigma$. For the most flexible scenario ${\omega }_0{\omega }_a\mathrm{CDM}+{\mathrm{\Omega }}_k+\sum m_{\nu ,\mathrm{eff}}$, we find $\sum m_{\nu ,\mathrm{eff}}=-0.07\pm 0.11$ with a tension of $1.13\sigma$, illustrating how the increased parameter freedom notably degrades the precision of the mass estimate compared to simpler extensions. Our results demonstrate that current cosmological bounds on $\sum m_{\nu }$ are influenced by boundary effects and geometric degeneracies.

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• Cosmological parameters
• Neutrino mass