Aggregate movie rays through time slabs

README.md

@@ -45,9 +45,12 @@ mkdir -p output/imgs
 This writes `minkowski_accel_000000.png` through
 `minkowski_accel_000060.png`.  The renderer treats the CSV as its observer
 input; the acceleration generator is only a reproducible flat-spacetime test
-fixture.  The current movie path still renders frames independently while the
-time-slab/RayPool scheduler is implemented next, so it must not yet be used
-as a performance measurement for numerical-relativity data.  The current
+fixture.  Movie mode collects all current frame-mesh vertices into a single
+SoA ray pool, activates rays as a newest-to-oldest coordinate-time scan reaches
+their observer event, and advances active rays to each slab boundary.  The
+analytic backends use logical slabs with no metric I/O; nmesh slab loading is
+the next backend step.  `--slab-duration` sets the coordinate-time width
+(default `64`) for this current fixed-mesh pass.  The current
 synthetic test catalog uses global default exposure `1e-3`; the accelerated
 benchmark explicitly uses `1e-5` because its physical Doppler blue shift
 otherwise clips the later frames.