G7: a moving pane casts a shadow, a retargeted move keeps its speed, a dissolve crossfades

- Track.launch: a move retargeted mid-way (Presentation.sync) starts at
  the old move's speed along the new one's longest side (carriedLaunch,
  Motion.easeFrom/speedFrom), so a second change during a slide bends the
  motion instead of stopping it dead. The macOS track ABI grows the float
  (pardes.h, 48 bytes; its reserved byte is named motion, as in Zig).
- A pane that slides, zooms or rises casts Lift's soft shadow at
  sin(pi x progress) of its strength, on the other panes' bodies and
  rails alone, under the same contrast ceiling, carried by its track.
- The GUI's PanelDissolve is a crossfade: the new cell drawn first, the
  old one over it at 1 - progress, premultiplied, on the blending cell
  pipeline for such groups (new cells now emitted before old ones, as the
  old layers already came after the new). sRGB blend, not linear light
  (documented). The tty keeps its per-cell swap.

Presentation.zig's and animation.zig's tests were not in any test root;
pardes.zig's test block now takes them in.

Tests: a retargeted move carries its speed and still lands exactly; a
moving pane's shadow is clipped off every tag, grip and its own body,
none at the start or the landing, most mid-way. GUI golden 18 changes by
the shadow (frame 6 of a slide). Gates as G6. Feel review:
.scratch/render/transitions/.

1 files changed, 15 insertions, 0 deletions

diff --git a/docs/effects.md b/docs/effects.md
index 04757aca..58c0098e 100644
--- a/docs/effects.md
+++ b/docs/effects.md
@@ -40,6 +40,7 @@ why. The verdict is the user's.
 | G4 bloom, vignette, grain | `Bloom`, `Vignette`, `Grain` `0..3` (off) | bundled post passes; none touches a tag, grip, notice or the cursor (pardesSpare); each capped per theme (pardesCap) | .scratch/render/{bloom,vignette,grain}/ (levels 0-3 on forge, dusk, acme; crops; mp4 stepping through the levels) | pending |
 | G5 lapis | `Theme lapis` (its `decor`) | a native theme with ornament: tag plaques with hard shadows inside their bands (the focused one striped), dots, rail checker, title shadow | .scratch/render/lapis/ (whole window at 1x and 2x, crops, a slide mp4) | pending |
 | G6 smooth scroll | follows `Motion` (on through the default smooth; `Motion off` lands at once) | a mouse wheel's notch glides, a touchpad follows the finger | .scratch/render/scroll/ (glide-<flavour>.mp4, quarter speed, strips) | pending |
+| G7 panel transitions | `PanelSlide`, `PanelZoom`, `PanelVertical`, `PanelDissolve` (off) with `Motion` | a moving pane casts a shadow; a retargeted move keeps its speed; the GUI's dissolve is a crossfade | .scratch/render/transitions/ (slide smooth, bouncy, retargeted; dissolve) | pending |
 
 ## Motion flavours
 
@@ -161,3 +162,17 @@ continuous path (Pardes.shell_continuous), so the shell draws every loop
 while it moves and a virtual clock moves with it; idle, it costs nothing.
 A PDF page scrolls as before. The test feed takes wheel events
 (ESC]777;mouse;wheel;<amount>;<x>;<y>BEL).
+
+Notes on G7: the geometry already followed the Motion flavour's spring
+(sxrrwplk); a move retargeted mid-way now carries its speed on
+(Track.launch, from the old move's speed along the new one's longest
+side), so a second Newcol during a slide bends the motion instead of
+stopping it dead. A pane that slides, zooms or rises stands off the page
+while it moves: a soft shadow as Lift's, at sin(pi x progress) of its
+strength (none as it sets out or lands), on the other panes' bodies and
+rails alone and under the same contrast ceiling, moving with the pane. The
+GUI's PanelDissolve is a crossfade: a changed cell's new form drawn whole,
+its old one over it at 1 - progress; the blend is in sRGB, not linear
+light (a two-colour mix in linear light needs both in one shader; open
+point 3). The tty keeps its per-cell swap. GUI golden 18-mid-transition
+changes (the slide's shadow at frame 6).