Per-gesture context passed to behaviors. current is the running pose
map; behaviors mutate proposed poses by returning new TPose values from
onMove. scratch is per-gesture key/value storage that resets at the
next gesture start.
Per-gesture mutable store. Keys should be namespaced by behavior name to avoid
collisions: 'behaviorName' for a single value, 'behaviorName.field' for
sub-keys. Two behaviors sharing a key will silently clobber each other.
Per-gesture context passed to behaviors.
currentis the running pose map; behaviors mutate proposed poses by returning new TPose values from onMove.scratchis per-gesture key/value storage that resets at the next gesture start.