FlowWM/causal_droidstd/base_vs_causal/README.md

BASE Ctrl-World vs CAUSAL checkpoint-20000 — same 4 val episodes, same seed

SIDEBYSIDE_*.mp4: TOP half = base, BOTTOM half = causal. Within each half: GT over prediction.

val	task	BASE	CAUSAL-20k	delta
99	pull the wooden handle	19.28	16.92	-2.36
199	move the green towel	20.68	16.86	-3.82
299	(unlabelled)	23.05	18.42	-4.63
399	wipe with a napkin	16.92	15.22	-1.70
	mean	20.0	16.9	-3.1

Base wins on 4/4, by 1.7-4.6 dB. That is a systematic per-episode gap, not the 3.2 dB episode-to-episode spread, so it is a real effect.

Two competing explanations -- NOT separable from this data

(a) The Phi branch is costing appearance quality (the original concern: a shared UNet asked to emit both a sharp frame and a smooth flow field). (b) Plain fine-tuning loss: base was trained on the FULL DROID corpus; the causal run fine-tunes on 387 trajectories, ~200x narrower. Any fine-tune on a set that much smaller degrades PSNR even with no Phi at all (catastrophic forgetting).

Deciding between them needs the ablation-table baseline row that has never been run: Ctrl-World fine-tuned on these same 387 trajectories with lambda_flow=0. Until that exists, this table does not show that the causal design is harmful -- only that this checkpoint is worse than the corpus-trained base.

Also note the causal run is at 33% of its schedule (20k/60k).