Wrist-transfer screen: closed F-instrument — the control couldn’t referee its own match

2026-08-15 02:4xZ. Consolidated results page for the wrist-transfer screen (FINAL pre-reg, stage 1 executed 22:24Z 08-14 → rc 01:32Z 08-15, boundary read closed at 01:3xZ per the frozen §4; the 01:34Z Discord post is the short record, this page is the full one). Reads: wrist_stage1_reads.py → reports/analysis__wrist_screen_stage1.json; charts recompute the same paired recipe and abort on mismatch.

Plain words. Our robot policy watches two cameras: one overhead, one on its own wrist. We suspected the simulated wrist view looks fake enough (it films our simulated robot arm up close, and an encoder can tell sim from real there easily) that the policy ignores or misuses it. The screen’s plan: corrupt the wrist view in controlled ways (black it out, blur just the arm’s pixels out of it) and measure whether behavior changes. To trust “no change means the channel doesn’t matter,” we included a positive control — corrupting the top camera, which we know the policy needs: if the instrument can’t detect even that, the instrument is broken. That is exactly what happened: with only 25 episodes, the control’s confidence interval was too wide to certify anything. The screen therefore closed F-instrument — no conclusion about the wrist channel in either direction — and its ~10 remaining GPU-hours were returned. One genuinely interesting side-finding survives (recorded, not certified): blurring the arm out of the wrist view made the policy touch the boat more often, a paired effect whose interval excludes zero at n=100.

What ran (stage 1, one detached unit, ~3.1 GPU-h of the ≤14 gate)

ftrig4k @ step_004000, euler-1 deterministic, 30 s episodes, the frozen sim100 substrate. Cells: determinism entry gate (W0 twice, seeds 0–9, per-seed rows bit-equal — PASS), hold floor (25 seeds — PASS, 0.0000 mean progress, 0 strikes), then W0 classic / W1 wrist blackout / W3 wrist arm-blur at n=100 paired seeds and T1 top-blackout at n=25.

Validity receipts, all green before any treatment read: W0 sanity band (+0.054 cm mean progress, 44/100 moved, inside the registered bands), spawn-xy pairing bit-equal across arms, honesty-placement and none-bit-replay receipts from stage 0 (c5be36f), hook consumption receipted (24/25 T1 top frames bit-differ; the 25th episode ended before its second replan).

The frozen gate that failed

The §3 T1 gate: the top-blackout control must move at least one of paired Δengagement / Δ|progress| with a CI95 excluding zero.

Blacking out the camera the policy demonstrably uses produced point estimates in the expected directions — and intervals too wide to certify either. Per the frozen §4 that is F-instrument: the screen cannot referee the wrist arms, stages 2/3 never launch, and no transfer-link claim is made in either direction.

The power analysis (the successor lesson)

The control was priced at n=25 against effect sizes nobody had measured yet. Stage 1 measured them: the W3 arm shows an engagement flip of +0.18 with CI half-width ±0.115 at n=100. The control’s half-width at n=25 was ±0.28 — about 2× the point estimates the wrist arms actually produce. A control that needs the effect to be ~2× the treatment effects to fire is not a control; it is decoration. The successor rule is mechanical: price the control at the same n as the treatment arms (T1 at n=100 ≈ 1.2 extra GPU-h — the cheapest insurance in the ladder).

The record-only finding that wants a successor

W3 (arm-blur) raises engagement: +18 flips/100, paired CI95 [+0.06, +0.29], excludes zero — the only registered read in the whole screen that does. Blurring the robot’s own arm out of the wrist view makes the policy touch the boat more often (44→62/100 moved), while final progress stays null (+0.14 cm [−0.47, +0.74]). Under F-instrument this stays record-only, but the shape is suggestive: the sim’s wrist-view arm rendering may actively inhibit engagement — consistent with the honesty probe’s 0.877 AUROC saying the arm pixels are the wrist view’s most sim-vs-real-separable content.

It is not certified because with a dead control, a wrist read that fires could be instrument artifact — that asymmetry (treatment fires, control can’t) is precisely why the gate exists.

What this cost and what it returned

~3.3 GPU-h total (stage 0 receipts + stage 1) of the ≤14 gate; the F-instrument close at the stage-1 boundary returned the ~10 GPU-h stages 2/3 would have spent on an instrument that cannot certify them.

What a successor screen needs

1. A competence floor first. At ~1–2 successes/100 the behavior metrics ride on touches and near-misses, which is why engagement — not success — is where W3 shows up. The grasp-SFT bootstrap (running now) is that floor; re-screen wrist fidelity on a policy whose success rate can actually move.
2. Control at treatment n (above).
3. Keep the paired-seed + determinism-gate design verbatim — it worked exactly as intended: every read above is paired per-seed with bit-equal spawns, and the failure it caught was real.