jerry/buzz

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npub17jjz49l9jjmhhk7cac63j8yt9z555n9cw8vk7v5jz4vzw4ppld5qgj57cc 32e41e78e0 T1.1 upscroll-jitter gate: reframe to motion-consistency (comp-sensitive)

Dawn found the RED gate from 33e73511 was mathematically invariant to the
fix: its residual subtracted the REALIZED scrollTop delta, which includes
the fix-writer's compensating scrollBy, so the writer cancelled out and the
gate scored raw estimate error R (only T3 can move it), not motion
smoothness. Quinn and Eva re-derived and confirmed. Co-visible and any
row-vs-row differential share the disease: compensation is a uniform global
offset, so it cancels out of any quantity not referenced to the input.

Reframe (converged with Dawn/Quinn/Eva; ratified event 63f5e6e1):

- Metric is now per-notch MOTION CONSISTENCY: the reading row's viewport
  motion (rowMove = after.top - before.top; NO scrollTop reference) scored
  as deviation from the run median. This references the row's own motion
  ACROSS notches (temporal self-reference), never a neighbour (spatial) or
  scrollTop, so the writer's scrollBy survives into the metric and is SEEN.
- Actuation is a fixed synchronous step (scrollTop -= STEP) so the input
  delta is constant by construction, bypassing Blink's wheel-scaling (a
  wheel notch applies 218/220/222...; median-of-run would misread that
  per-notch scaling as jitter). Dawn independently confirmed even the
  actuated scrollTop delta is post-writer contaminated (48-75px spread
  under sync) — rowMove is the only clean measurable.
- Anti-cheat floor: mean rowMove must be > STEP*0.75 so a frozen or
  half-applying scroller (near-zero variance, would false-green) is caught.
- Old scrollTop-referenced residual kept as a printed NON-GATING diagnostic
  (= estimate error R = T3's estimator acceptance number).
- Second non-gating diagnostic: one wheel-actuated pass of the same metric
  (Tyler's real input is a wheel), on the record every run.
- RED-at-tip is a HARD gate with a VOID comment: median-of-run is only
  valid while the corpus produces varying realization, and the tip run
  being RED IS the proof of that dispersion.

RED at tip: peak-dev 41px / rms 24px (gate <=2 / <=0.6). GREEN target is
Dawn's real T2 writer: peak-dev 0.00 / rms 0.00, reproducible over 3 sync
runs. A synthetic per-notch-varying oracle drives 74/77 notches to exactly
STEP; the real writer re-pins in the same ResizeObserver cycle and closes
the synthetic-only outliers.

Co-authored-by: Tyler Longwell <tlongwell@block.xyz>
Signed-off-by: Tyler Longwell <tlongwell@block.xyz>

2026-07-08 14:04:08 -04:00