Drop the injectable `topEdgePx` knob (one caller, one constant) so the
threshold has a single home, and fold the two-branch tail of
shouldAutoShowEarlier into one predicate. Comments keep the WHY: wheel is
the only signal at a clamped scrollTop 0, and the gates name the states
where scrollTop is near 0 without meaning "read earlier".
Tests: collapse the 11-case matrix into one invariant test on the pure
gate, and add a rendered-list test that mounts the real Thread against a
transcript heavier than RENDER_BUDGET, escapes the bottom lock, wheels up
at the clamped top and asserts more turn groups mount — while an upward
wheel mid-transcript mounts none. Red on origin/main (28 groups stay 28),
green with the fix.
Teknium
474143da81