Port Spheres and Spikes features (#48, #49)

docs/AGE_PROFILES.md

@@ -53,9 +53,10 @@ which already forms its own islands. Cave terrain rejects it. A page-free random
 Age may also roll Floating Islands as one of its material features.
 
 An unpaired Block or Fluid page chooses a compatible feature from the Age seed:
-full blocks can become Rocks or Floating Islands; source fluids can become one
-of the lake features. Flat and Void terrain can only use Floating Islands from
-this pool, while Cave terrain has no compatible material feature. A page-free
+full blocks can become Rocks, Floating Islands, Tendrils, Spheres, or Spikes; source fluids can become one
+of the lake features. Flat terrain can use Floating Islands, Tendrils, Spheres,
+or Spikes; Void can use Floating Islands, Tendrils, or Spheres; Cave can use
+Spheres or Tendrils. A page-free
 random Age rolls zero, one, or two distinct compatible material features, choosing each
 material from the Block or Fluid Pages pool. The choices are saved on the Age
 definition, so opening the Age again does not reroll them.
@@ -101,6 +102,25 @@ including on Cave terrain where the surface material features are unavailable.
 The shape and placement use only the Age seed and source-chunk coordinates, so
 revisiting an Age recreates the same geometry.
 
+**Spheres** and **Spikes** are two separate Feature pages. Spheres adds
+winding chains of solid sphere nodes within terrain generation; like Tendrils,
+it works on all terrain families, even Void and Cave. Spikes is a later,
+rarer surface decoration (roughly one attempt per 18 chunks) that rises from
+solid ground on Standard, Amplified, Sky Islands, or Flat terrain. Cave and
+Void reject the Spikes page because they do not provide a suitable exposed
+surface. Each page accepts its own immediately preceding full-collision Block
+page; without one, the Age seed chooses a compatible material. The pages
+remain distinct in the catalog, Creative menu, JEI, ordered writing, and
+saved Age definition. Page-free random Ages can select either where compatible.
+
+For an in-game check, make separate Void/Spheres and Flat/Spikes books with
+Glowstone Block pages directly before their respective Feature pages. Spheres
+should form connected bright globes across chunk boundaries in Void; Spikes
+should appear as rare upward clusters rooted on the Flat surface. Revisit the
+same Ages to confirm stable locations. Check that a Void/Spikes book is
+rejected, and that Spheres and Spikes remain two independently selectable
+pages in Creative and JEI.
+
 For a clear visual check, bind a Void Age with a Glowstone Block page followed
 by Tendrils. Fly around world Y=0–120 across several chunks: branching solid
 forms should appear in the otherwise empty dimension, continue across chunk