Port dry Cave Ages and safe landing to 26.3 beta

ports/mc263/README.md

@@ -3,7 +3,7 @@
 This is an **experimental beta port** for issues #97–#104, not gameplay parity
 with the Minecraft 1.21.1 release. The 26.3 backend persists separate Ages and
 their seeds. Books, the Book Binder, and the Ink Mixer work, and the Binder can
-author Standard, Amplified, Island, Flat, or Void terrain with supported
+author Standard, Amplified, Island, Flat, Void, or Cave terrain with supported
 biome-distribution pages. Other terrain families, feature/material effects,
 portals, and much of
 the 1.21.1 gameplay remain unported. Use a test world and keep a backup; do not
@@ -177,6 +177,23 @@ surface decoration in Flat. Void continues to generate no floor or biome
 decoration. The operator-only `age create_multi` probe creates two-biome test
 Ages for the dedicated-server smoke test.
 
+The local `1.0.1.37-beta.1` slice adds the Cave terrain page to Binder
+authoring. It uses Minecraft's caves noise settings, accepts Cave and Nether
+biome pages (including multi-biome distribution), and searches below Y=64 for
+a safe arrival instead of landing on the roof. The 26.3 vanilla Cave preset
+defaults to water below Y=32, so this port derives a dry Cave setting with
+air as its default fluid and the sea level below the world floor. This applies
+to newly generated Cave chunks; it does not drain existing chunks. Cave-specific Nether surface
+materials from 1.21.1 are not ported yet. The dedicated-server smoke now
+creates and reloads Cave Ages alongside the other terrain families.
+
+The dry-Cave follow-up is packaged as `1.0.1.38-beta.1`; no 26.3 release is
+published until the in-game check passes and publication is explicitly requested.
+
+The local `1.0.1.39-beta.1` follow-up rejects fluid at both feet and head
+height during safe-landing searches. It also refuses to carve the fallback
+platform into submerged space if no dry footing can be found.
+
 From the repository root:
 
 ```sh