Measured by the Decoder with the full-quad reader: at the snap frame both sweeps
enter at their DECLARED OPENING alphas -- pteff03 at 255, pteff03a at 0 rising
1,2,3,4,6,11,17 from x=1721. Those are the leaves' own t=0 poses.
My implementation advanced the shared clock and left the leaf phase untouched, so
the sweeps would have sat mid-travel at the right clock value and the wrong
position. A defect visible only in a film -- no still and no clock reading would
show it, because the clock was correct.
The field already existed (leaf_start_units, from the F6 work); it simply was not
being set at the snap.
VERIFIED, pre-registered, via --probe-leaf on a real boot with a real press:
snap frame -> leaf_t 0.0, pteff03 x=-639, pteff03a x=1721 (declared t=0)
next frame -> leaf_t 0.5, both advanced by 2 px
Their separate note on my snap target: 236.0 survives their challenge -- at the
snap the sweeps are at alpha 255, putting the title clock in [100,238) -- but
their data cannot separate 236 from 200. Recorded as surviving, not confirmed;
the bound in the code comment already says so.
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