Apply authored Age environment symbols (#34)

docs/AGE_PROFILES.md

@@ -47,9 +47,11 @@ in the Binder. Bundled controls are Native, Single, Tiled, Grid, and Tiny throug
 Huge regions. Single needs one distinct biome; Tiled/Grid and Tiny–Huge need
 two. An authored book receives seeded filler only when it falls below that
 minimum, while extra authored pages are retained as weighted entries. A book
-with no biome pages selects a seeded count from 2–4 for Tiled/Grid or 2–6 for
-Tiny–Huge, capped by the number of eligible terrain biomes. Single uses one;
-Native uses its preset biome pool. These random-age maximums do not truncate
+with no biome pages selects a seeded count from two up to the number of
+eligible biomes for Tiled/Grid and Tiny–Huge. The eligible pool comes from the
+terrain's biome preset, or `#rivencraft:cave_biomes` for Cave terrain, so future
+biome integrations can expand it without changing the count rule. Single uses
+one; Native uses its preset biome pool. This random-age maximum does not truncate
 authored pages: the Binder's 27 symbol-page positions bound an authored book.
 Native cannot be paired with explicit biome pages. Legacy filled Tiny–Huge to
 three; Rivencraft deliberately uses two so a pair of written biome pages stays
@@ -79,6 +81,28 @@ eligible fallback for that load; restoring the biome recovers the original
 selection. Generation-version-15 Ages keep their prior registry-wide biome
 selection algorithm instead of being silently regenerated.
 
+## Written environment
+
+Lighting pages select Normal, Dark, or Bright lighting for the new Age. A Sky
+page selects Minecraft's Overworld, Nether, or End sky effects; the chosen
+effects also determine the destination preview backdrop. Overworld sky tint
+continues to come from the destination biome. A written sky changes only that
+Age's dimension type, not the source world or other Ages.
+
+Normal, Fast, Slow, Off, Always, and Storm weather pages use the existing Age
+weather controller. Zero, Half, Full, and Double Length pages set the day-cycle
+period, and Nadir, Rising, Zenith, and Setting pages set its initial phase.
+Repeated numeric modifiers combine in written order. A Zero Length Age keeps
+the nonzero minimum clock rate that avoids client skybox bounce. Pages for
+Cloudy, forced Rain, and Snow are not offered: vanilla precipitation rendering
+cannot reproduce those Legacy distinctions yet, and Snow remains planned for
+the optional season integrations. A data pack that supplies these unsupported
+weather choices receives a binding error rather than a false success.
+
+The Pages creative tab and optional JEI page ingredients use the same generated
+index of bundled environment symbols. Existing Age definitions and page-free
+random Ages retain their saved or seeded environment unchanged.
+
 ## Persistence and reload behavior
 
 An Age permanently stores its selected profile ID, generation version, seed,