Over the past two decades, STEREO has fundamentally reshaped our understanding of solar-heliospheric connectivity, establishing multi-viewpoint observations as a cornerstone of the field. Crucially, STEREO bridged remote sensing and in situ observations in a way not previously possible, expanding our understanding of coronal transients, energetic particles and the solar wind. This integration transformed how we interpret propagation, validate models, and understand the evolution of heliospheric structures from the Sun to the observer. We invite contributions that span:
Advances enabled by STEREO in remote and in-situ CME reconstruction and heliospheric imaging;
Integration of remote sensing and in situ observations for understanding solar wind and CME evolution;
Insights from deep-sky observations and high-sensitivity campaigns;
Comparative and complementary approaches to 3D inference, including stereoscopy, polarization, tomography, and data assimilation;
Connections to current and future missions, including PUNCH, as part of a broader observational progression;
Implications for modeling, validation, and predictive capabilities.