We analyze the post-perihelion coma of the Great Comet of 2024, C/2023 A3 (Tsuchinshan–ATLAS), to characterize its dust activity and assess the contribution of sublimating icy grains to a candidate near-nucleus halo. Using archival Zwicky Transient Facility images obtained between 15 February and 26 May 2025, we performed aperture photometry within a fixed projected radius of 40,000 km and derived azimuthally averaged surface-brightness profiles from annular photometry. Over the observed interval, the comet faded from 12.86 to 14.77 mag as its heliocentric distance increased from 2.64 to 3.90 au, although two short-lived brightenings were superimposed on the secular decline. The effective dust cross-section decreased by about a factor of 2.4 and followed C_ ̊m e ∝ r_ ̊m h ^ -3.1 , while the dust mass production rate scaled as dot M _ ̊m d ∝ r_ ̊m h ^ -3.41 . These dependences are compatible with a contribution from water-ice-driven activity. Extrapolating the fitted post-perihelion relation back to perihelion gives a model-dependent cumulative dust mass loss of 3.0 kg, corresponding to a globally averaged erosion depth of ∼ 1.4 m for an assumed nucleus radius of 5.9 km. The coma profiles are shallower than the canonical steady-state expectation, indicating radial evolution in the dust distribution or scattering properties, with delayed aggregate fragmentation as one possible contributor. In addition, a persistent central excess, spatially coincident with a less-red inner-coma color, supports the presence of an additional near-nucleus component consistent with an icy-grain halo. Among the cases explored, icy grains with radii of ∼ 10 μm and a carbon fraction of ∼ 0.1 % yield model halo radii comparable to the observed halo scale during the enhanced-activity interval between 21 and 25 February 2025, with model grain lifetimes ranging from 2.8 to 3.2 s. Although no single model with both grain size and composition held fixed reproduces the full halo evolution, an increase in the carbon fraction of the released icy-grain population provides one possible explanation for the broad halo-radius trend and may reflect progressive refractory enrichment of the evolving near-surface material.