Two owner-reported symptoms, one mechanism (verified frame-by-frame on a
zero-model-call fixture): the position machine read its OWN growth-driven
scroll lag as the learner leaving.
1. Probe arrival at the bottom: the form opened, the reserve grew, the
smooth catch-up lagged (d peaked ~405px > COLLAPSE_DIST 96) → phantom
fold → bar shrink morph → re-expand at bottom. FORM→BAR→FORM, ~600ms.
Fix: the at-bottom arrival now runs under the SAME fold suppression
the teach reveal uses (suppressFoldDuringReveal, extracted) — the
arrival's open and its scroll-to-bottom are the same motion class.
2. Probe arrival scrolled up: one stale-open frame painted before the
after-paint effect collapsed it. Fix: probeArrivalExpanded — the
open/closed state decided DURING RENDER (open iff at bottom), like
the teach seam; the effect keeps only the reveal scroll.
3. Dictation stop flush into the pending question: the field grows on
its own render (capped 192px), the reserve lands on the NEXT
DockOverlay render (~1s later live), and the spacer's growth spiked
d≈152 → fold → bar → re-expand. Fix: the offer stamps the geometry
mute when the reserve GROWS while pending — the spacer is the
phantom-scroll source, so the mute covers exactly its scroll events.
Shrinks never stamp (the resize round's stuck-collapsed regression).
Live-verified on :3001 (job-settle fixture, abort-channel settle, no
model calls): A at-bottom arrival FORM-only; B scrolled-up arrival
straight to BAR with zero FORM frames and no scroll-down; C dictation
flush FORM-only through the +152px reserve growth.
Owner report (2026-09-25): in the teaching phase a new question arrives
collapsed behind the reveal button, but the transcript scrolled up as if
it had OPENED — the room it made was the expanded form's height, never
shown. Root cause: the expanded state is stale-true from the previous
question (nothing resets it when the dock returns to the composer), so
the new question's FIRST paint rendered open; the dock measured itself
tall and offered that height to the spacer, and the collapse one tick
later could never give it back (fold immunity refuses drops while a
question pends). Collapsed bar, tall reserve — scroll as-if-opened.
Fix (owner-shaped, deliberately minimal): apply the arrival state DURING
RENDER, before the first paint (the render-time state adjustment
pattern) — revealArrival(wasQuestion) decides how a teach question
lands: after the composer → collapsed (the learner reads the teaching
first); after ANOTHER question (a queued parallel check) → OPEN — the
reading already happened, and the height it already has is the honest
height. The paint measures the truth, so the reserve never learns a
height that isn't on screen. Probe arrivals are untouched — instant-open
at the bottom stays. The old [pendingId] effect keeps only its probe
branch.
Live-verified on :3001 with a fabricated teach-phase session driven
through the real settle/adoption path (zero model calls): composer→teach
arrival lands as the 59px bar with the spacer growing 206→211 (+5) and
the transcript scrolling only 77px (the new message itself) — the
previous behavior jumped the reserve +339px and scrolled 660px;
teach-check reveal click still expands (425px) and scrolls to bottom;
a queued parallel question arrives open with the reserve unchanged
(577→577) and +40px scroll.
Pins: tests/reveal-arrival.test.ts — revealArrival(false) = collapsed,
revealArrival(true) = open (the owner ruling). 946/946.
amosblomqvist