DRAFT pre-reg: disk-position draws — the target moves, the success zone moves with it

Drafted 2026-08-12 ~11:0xZ (work session; real date -u at write: 10:52). STATUS: DRAFT — not registered. This is the (c) leg the content-diversity pre-reg scoped out as task semantics — the disk is the task target, so moving it is an eval-protocol change, not an appearance draw. It holds for owner sign-off (the queue item pins it to the rerun call); nothing is implemented or launched from this document. Evidence base: content-diversity close (the record-only disk fact) · sim100 v0 close · spot20 v3 results.

Plain words

Our simulator glues the wooden target disk to one spot on the table, episode after episode. The real rig doesn’t: measuring the 26 real reference episodes, the disk sits somewhere different almost every time — the operator nudges it around a region about 20 by 29 centimeters. Worse, the one spot the sim glues it to turns out to be a place the real disk never actually sat — it’s just outside the measured range. This plan makes the sim draw the disk’s position fresh every episode from the real measured spread, with the boat spawned in front of the disk wherever it lands and the success zone following it. Beyond realism, that upgrade turns the eval into a question the pinned disk can never ask: does the policy look for the disk, or does it just drive to the memorized spot? A policy that only memorized will dump the boat where the disk used to be; a policy that sees will track it. The plan sits in draft until the owner signs it off — and it deliberately stays out of the v3 rerun, which must measure one change (visuals) at a time.

The measured baseline (banked, bank_manifest.json)

• Disk detected in 21/26 A-episodes (disk_record_only, per-object centroid-bias-calibrated camera model, same pipeline the v3 clutter draws use). The 5 absences are detection misses / occlusions — a diskless place-task is undefined, so presence is pinned at 1 in this protocol.
• Absolute world frame (follower base = origin): x 0.083–0.288, y −0.193–0.097, median (0.199, −0.048); radius from the follower base 0.107–0.288 m, median 0.217.
• The sim pins the disk at (0.22, 0.11) — radius 0.246, and y = 0.11 is outside the entire measured y range (max 0.097). The pinned eval measures a target placement the real rig never exhibited.
• Frame alignment is trusted on the mouse precedent: its measured absolute box (x 0.485–0.555, y −0.233..−0.075) brackets its sim canonical (0.50, −0.085), so the calibrated world frame IS the sim frame. The laptop needed delta-mode only because its real center sits past the frame edge; the disk has 21 clean in-frame detections and no such excuse.

Design — six decisions, stated so they can be objected to

D1 — draw mode: ABSOLUTE, not delta-about-canonical. Uniform in the measured box (x 0.083–0.288, y −0.193–0.097) intersected with the validity region (D4), rejection-redrawn until valid. Absolute is the fidelity-first choice given the frame alignment above; delta-about-canonical would re-center the real spread on a pinned position the real disk never occupied, dragging ~38% of the empirical draws beyond even the farthest radius the real rig ever demonstrated (0.288 m). One draw per episode, presence 1.

D2 — success geometry follows the drawn disk. Mechanism: the reset writes model.geom_pos["disk"] and updates self.disk_center (today read once at init, so101_sim.py:238). success(), benchy_disk_distance(), and the initial/min/final cm metrics all key off disk_center, so progress_final stays “distance recovered toward the (drawn) disk” with no metric change. Note the disk — unlike the contype-0 clutter stand-ins — has real collision (the boat physically rests on it at success). Moving it is a physics change, and that is the point.

D3 — benchy spawn goes DISK-RELATIVE. The current absolute spawn box was hand-placed for the pinned disk (mean boat→disk gap ~9.5 cm, boat “in front of” the disk at −y). Keep exactly that relationship: spawn = drawn disk + delta, delta-x ∈ [−0.025, 0.05], delta-y ∈ [−0.115, −0.07], yaw uniform — the current box expressed relative to the disk. This preserves the initial_cm scale (episodes stay ~9.5 cm tasks) and the task difficulty distribution; an absolute spawn box under a wandering disk would smear initial distance over ~2–25 cm and make per-seed numbers incomparable in a useless way (difficulty, not ability, would drive the spread).

D4 — joint validity clamp, by rejection redraw. A drawn (disk, spawn) pair is valid iff: disk radius from base ∈ [0.12, 0.28] (brackets 20/21 real draws; the far real outlier at 0.288 is marginal); disk edge ≥ 7 cm from the parked jaw tip (0.155, 0.01) (the settle would strike it); every spawn-box corner at x ≥ 0.17, y ≥ −0.19, radius ≤ 0.30 (jaw clearance, leader-arm clearance — the leader mounts at y=−0.25 and the raw delta box would push spawns to y=−0.31 under the most down-table real draws — and reach). Invalid → redraw both. Constants are proposals, finalized by the policy-free 1000-seed reset sweep at implementation (gates: reset strikes = 0 on every seed, settle displacement nominal); the sweep also reports the truncation fraction — how much of the measured real support the clamp cuts — so nothing is silently capped.

D5 — comparability: banked rows DIE under this protocol. The choice, stated plainly: with disk-relative spawn, the same seed no longer produces the same boat world pose as banked sim100/spot20 rows — and the frames differ regardless (the disk is elsewhere). No number produced under disk draws may be compared to a banked pinned-disk row, paired or otherwise. This is protocol v2 of the sim eval (“sim100-D”); any registered run under it re-runs its own hold floor and baselines from scratch. What pairing survives is the within-run kind — and fully: same seed → same disk + same spawn across arms AND render styles, so arm-vs-arm per-seed deltas keep their full power. The alternative (absolute spawn box, banked spawn-stream bit-match preserved) was rejected: the banked comparison it preserves is vacuous anyway (different disk → different initial_cm → progress_final not comparable), and it costs the difficulty-controlled task (D3).

D6 — stream discipline. Both draws live on the SPAWN stream (seeded by seed, untouched by appearance_seed): disk draw first, then the relative spawn draws, then yaw. The appearance stream is not consumed → the protocol is orthogonal to render style (v0/v2/v3 all see the same drawn geometry for a given seed). A disk_draws flag (default off) guards the whole path: off = today’s behavior, bit-identical, oracle-pinned.

The grounding probe (the payoff read)

The pinned-disk eval cannot distinguish “drives to the memorized spot” from “sees the disk” — the two policies act identically. Under draws they diverge, and the divergence is registered as a diagnostic: per seed, compare the boat’s final distance to the drawn disk against its distance to the canonical location. Summary read: across seeds, the regression slope of final-boat displacement on disk-draw offset — slope ≈ 1 is a tracker, slope ≈ 0 with finals clustered at canonical is a memorizer. Priors to be registered per-arm at the run-specific pre-reg (not here), but the shape expected from spot20: teacher80k (the one confirmed visual responder) is the candidate tracker; er60k’s reach-over-and-miss fingerprint predicts slope ≈ 0.

Implementation plan + oracles (the follow-up item, CPU-only)

Implementation is NOT this item; when signed off it lands with:

1. Guard oracle: disk_draws=False → settled qpos, spawn xy, and frames bit-identical to today across seeds (extends tests/test_sim_appearance.py).
2. Pairing oracle: same seed → identical (disk xy, spawn xy, settled qpos) across appearance seeds AND render styles.
3. Geometry oracle: teleport boat onto the drawn disk → success() true; onto the canonical location (disk drawn elsewhere) → false; benchy_disk_distance tracks the drawn center.
4. Determinism oracle: rejection redraws are a pure function of seed — same seed, same draw count, same result, any process.
5. Render oracle: the drawn disk appears at its drawn position in BOTH cameras under v2/v3 composites (it is a V2_DYNAMIC_STATIC — rendered, never plate content; the plates median it out).
6. The 1000-seed policy-free reset sweep (D4 gates + truncation report).

Cost and sequencing

• Implementation + oracles + sweep: ~1 CPU session, no GPU.
• Any registered eval under sim100-D prices exactly like the v3 rerun: parallel-oracle GREEN → ~2–3 GPU-h for 4 arms × 100 seeds; sequential fallback ~6–9 h wall. Owner-gated, separate pre-reg.
• Sequencing (registered intent): AFTER the v3 rerun reads out. The rerun isolates the visual overhaul at n=100; stacking a task change into it would confound both reads. Disk draws are the next protocol step, with the rerun’s v3 numbers as its pinned baseline context.

Owner decision points

1. Sign off the protocol change at all (it retires banked-row comparability for future runs — D5).
2. D3’s disk-relative spawn (the alternative preserves banked spawn bit-match but was rejected above — overrule if the banked-row link matters more than difficulty control).
3. Whether the pinned-disk protocol stays available as a registered variant (the disk_draws flag keeps it one boolean away) or is deprecated for anything but reproduction runs.

Finalization checklist (at sign-off)

1. Owner call on the three points above.
2. Implementation session lands the six oracles + sweep; truncation fraction and final clamp constants appended HERE with a dated edit note.
3. Run-specific pre-reg (arms, per-arm grounding-probe priors, GPU gate) posted with param sheet in-channel + objection window.