Allow floorless leafy link destinations

docs/PORTING.md

@@ -142,6 +142,9 @@ Version 0.1.20 uses a cubic 18-by-18-by-18 snapshot. The renderer remaps the
 link point within that cube so its existing target-centered camera framing is
 unchanged.
 
+Version 0.1.21 treats air and leaf blocks as passable linking destinations;
+links no longer require a solid floor beneath the player.
+
 The preview code is separated behind a renderer interface and uses an isolated
 Ponder level populated from server-authoritative destination snapshots.