P2. A keyframe is the start of a linear ramp toward the next; `ScreenView` walks
them at `time_units` and `boot.gd` advances that in real time, or freezes it with
`--time=<seconds>`.
`authored/timing.json` holds the ONE constant this needs. HANDOFF Q1 is answered
-- linear, 2 units per rendered frame, 1 unit = 1/60 s -- but that conversion was
MEASURED off the running game, not read from a file, so it is authored rather
than exported and it says so at length. Expressed as units-per-second, because
60 is exact and 0.01666... is a decimal a reader has to recognise.
The timeline stops at the last TIMED keyframe and never plays the exit. Every
group's final keyframe carries no `t` -- across this export it is a fade-out for
116 of 134 elements, a scale-and-slide exit for 12, and identical for 6 -- so
playing into it would mean inventing how long the ramp takes. That duration is
the screen transition, it is measured at ~0.4 s, and it is P3's to author with
its own evidence. `exit_ramp_seconds` is therefore null on purpose, not missing.
`--pose=rest` keeps the P1 behaviour available: since the port's default is now
the timeline and the two DISAGREE, renderer-vs-renderer diffing has to be able to
ask for the same assumption the reference renderer makes.
The interpolation is checked by where it lands: on 8 of the 12 screens the
settled timeline is byte-identical to the rest render.
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