Port Flat and Void Age terrain to Minecraft 26.3 beta

docs/MINECRAFT_26_3_PORT.md

@@ -480,6 +480,21 @@ symbol-page data and authoring pipeline, not just drawing more placeholders.
 The local `1.0.1.15-alpha.1` follow-up changes the missing-panel cue to the
 Link Panel's 16×16 item icon while preserving its red pulse and tooltip.
 
+The local `1.0.1.33-beta.1` slice adds Flat and Void terrain to authored Binder
+books. Flat uses vanilla superflat layers and can use one authored Biome; Void
+generates no terrain but can use one authored Biome for environmental behavior.
+Without a Biome page, Void uses `minecraft:the_void`. Books with multiple Biome
+pages and Flat/Void terrain remain unassembled until their custom distribution
+generator is ported. The dedicated-server smoke creates, samples, and reloads
+both terrain families in a disposable world.
+
+The local `1.0.1.34-beta.1` follow-up moves Flat ground to Y=0 and targets its
+surface for travel. `1.0.1.35-beta.1` enables the selected biome's decoration
+on Flat. `1.0.1.36-beta.1` ports a multi-biome Flat/Void chunk generator and
+accepts the existing authored distribution pages for those terrains. New Flat
+chunks can vary vegetation by biome; Void keeps biome climate without adding
+a floor or decorations. These are beta-port slices, not full 1.21.1 parity.
+
 ## Verification of this first slice
 
 The 1.21.1 `compileJava` and `build` tasks passed offline after the backend