Restore Zero Length frozen Age time

docs/PORTING.md

@@ -299,6 +299,11 @@ later loads continue from saved world time. Celestial angle remains persisted
 for a future custom sky renderer because vanilla dimension data cannot rotate
 the sun's render plane.
 
+Version 0.2.20.1 restores Legacy's Zero Length celestial modifier as a rarer
+random outcome using its effective one-in-seven grammar weight. Zero Length
+freezes an Age at its generated phase without changing the global daylight
+cycle, while nonzero Ages retain their independently scaled clocks.
+
 Version 0.2.14.0 restores the legacy Linking and Descriptive Book artwork for
 inventory items and gives each book its matching open-book texture when placed
 on a Book Stand. Return Linking Books created inside another Age also retain and