Robot Critics that Sweat the Small Stuff: the trained pole of the selector family

Lit slice 2026-08-09 (work session 14:1xZ, skim-to-place per the queue item — read, placed, parked). Robot Critics (2606.21572). Fed #19/#6 (the selector ledger’s trained pole, priced) — sibling of RoVer and the Q-guided flow critic.

The paper in plain words

If a robot policy proposes several candidate actions, something has to judge which one to execute. Off-the-shelf vision-language models are bad judges of the small things that decide manipulation — a gripper a centimeter off, a block not quite seated. This paper fine-tunes a VLM into a critic using pairs of success and failure snapshots from the policy’s own rollouts, so it learns exactly those small visual differences, and adds an action-conditioned video model that imagines the outcome of each candidate before the critic judges it. Executing the critic’s pick improves success by ~11 points on their real-robot tasks and ~6 in simulation.

Placement, and why it parks

This is the trained-critic pole of the selection family we have now measured from the free end: our #6/#19 arc showed the label-free scorer family anti-selects or nulls on our stacks (masked-contrast rung (c), jerk-pick/SDN), and the selection-ceiling reads bound what ANY selector could buy — real but small for AR draws, ~null for flow fresh-noise. Robot Critics is evidence the trained pole works where the free pole fails — consistent with RoVer, and with its price tag stated plainly:

• Supervision we don’t have: pairwise success/failure labels from policy rollouts — closed-loop artifacts. Our stack is offline; rollout labels arrive only with the #16 rig bench.
• A second model we don’t have: the action-conditioned video predictor doing the imagining. That is a bigger build than the selector it serves.
• A payoff our ceiling reads cap: +11% real-world is against policies with selection headroom. Our measured oracle gaps say the headroom on our decodes is small (AR) to absent (flow) — the ceiling read is exactly the number that says whether this machinery could ever pay before building any of it.

Verdict

Placed and parked: the trained-critic pole stays priced-not-built until (a) #16 exists and produces rollout labels, and (b) a ceiling read on the deployment-relevant decode shows headroom worth a trained judge. No idea page changes rank; the selector ledger gains one more data point that learning the judge is what makes judging work.