What RoR Can Write under Privileged Supervision: Decoder Expressivity for Continuous-Time 3D Gaussians

Open-loop continuous-time 3D Gaussian extrapolators forecast well under continuous observation, yet under intermittent reveals they still need a correctable write of off-screen geometric change. We run a controlled write-path diagnostic on NVFi Visible–Disappear–Reappear: GT-render reveals, constant-rate hidden change (translation or centroid rotation), and dense 3D attribute supervision—isolating which components of an image-space Reconcile-on-Reobservation (RoR) stack can record the change, not claiming a transferable real-camera world model. A co-evolving latent drift-rate is inert; a frozen translation-only head fails under in-place rotation (fan). Unfreezing the Stage-2 decoder so RoR can express quaternion updates accounts for most of the rotational sign flip vs. an honest static-memory baseline ($+7.8\pm 1.3\%$ RoR-only at occ$=$10 over training seeds); gated typed on-manifold residuals add only a small, seed-sensitive margin at this operating point (typed $+8.3\pm 1.7\%$), but that margin triples as the hidden rotation grows along either occlusion length or rotation rate ($+0.9\to +2.7$ pp), so the typed channel is operating-point dependent rather than negligible. The same residual family specialized to translation remains useful for relocation ($+34.3\pm 6.8\%$ inj-seed mean on bat @ occ$=$10), and adding the SO(3) channel converts fan's relocation deficit from $-12.5\%$ to $-1.9\%$, confirming that its residual error there is rotational. Photometric-only finetuning (state weight $0$) collapses the flip ($-13.6\%$ at occ$=$10), and freezing the reconcile path localizes that collapse to a single operator while recovering a positive write ($+3.2\%$); a weak state weight ($0.1$) suffices to learn the write from scratch with no privileged initialization ($+11.0\%$ vs. $+12.1\%$ for full supervision), so image-only calibration of the reveal reconcile is the specific open problem, not privilege in the attribute signal.