feat(runtime): the composed world can BE the game world

Jahni: "can you not implement those settings? as in, have them be live in
game?" This is that. The composer stops being a lab tool.

THE ARCHITECTURAL LINE, which is the whole design (COMPOSER-NOTES §3.1):
COMPOSITION stays editor-only, EVALUATION becomes runtime. Rolling,
measuring, preview, selection, promotion, the corpus -- none of it reaches
a player's machine. What crosses into the runtime is exactly two things:
reading a season manifest, and materialising a recipe into an op stack.

  UVoxelSeasonAsset      a cookable UPrimaryDataAsset holding the manifest,
                         so a season ships in a packaged game. The JSON
                         stays the reviewable, git-diffable artefact.
  UVoxelSettings::Season  optional. Unset => behaviour is exactly as today.
  GetEffective*()         season seed / spine radius / world radius / season
                         number override the authored values when assigned.
                         The test deliberately sets DIFFERENT authored
                         values, so "the season is authoritative" is proved
                         rather than coincidental.

⭐ MULTIPLAYER DETERMINISM, PROVED: two independent runtime managers built
the same season and compared 393,216 density samples BIT-IDENTICALLY. This
is the property the whole multiplayer model rests on -- replicate seed +
layout + diff, never geometry.

⭐ AND A STALE SEASON IS DETECTABLE, NOT SILENT. Initialize() now returns
bool and an assigned-but-invalid season NEVER falls back to the authored
pool. Falling back would hand a client a world that looks fine and is not
the season -- silent divergence, the worst failure mode in a shared world.
GetCurrentSeasonContentHash() is exposed BlueprintPure to compare at join.

HasComposerRecipeOverride() is gone. It force-classified every custom recipe
as Mixed, which was correct while box verdicts were only proved for
hand-written stacks -- but 8e346a3 made EffectOverBox correct in ISOLATION,
proved on a stack no builder produces. Keeping the force would have cost
tile skipping on every composed world forever.

VF_RollStrateRegionCount moved behind WITH_EDITOR while the partition-seed
helpers stayed runtime: rolling out, evaluation in. Lateral regions remain
gated off.

⚠️ Sol hit its usage limit mid-task, so the edits arrived unvalidated. I
built and ran them myself rather than assume -- and they did not compile:
VoxelForgeComposerSeasonTest.cpp was missing UObject/Package.h, which every
other test picks up transitively through the shared fixture it does not use.
One include; every NewObject/GetTransientPackage in the file was failing.

Editor build clean. SHIPPING BUILD SUCCEEDS -- the invariant that proves no
composer roller is linked into a packaged game. 30 succeeded / 0 failed.

⚠️ UNVERIFIED: whether it looks right on screen. Nothing headless can tell
us that; it needs Jahni to assign a season asset and press play.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VJiTcTSDNkKBtnNdiBtdaU

Source/VoxelForge/Private/VoxelDensityOpStack.cpp

@@ -4886,6 +4886,7 @@ namespace
         uint32 SeedU;
     };
 
+#if WITH_EDITOR
     //=============================================================================
     // RÔLE 2 — COMBINER : RÉGIONS LATÉRALES
     //=============================================================================
@@ -5008,6 +5009,7 @@ namespace
         mutable FVoxelStrateRegionPartitionCache PartitionCache;
         mutable bool bPrepared = false;
     };
+#endif
 
 }   // ⚠️ FIN DU NAMESPACE ANONYME — TOUT NOUVEL OPÉRATEUR SE MET AU-DESSUS DE CETTE LIGNE.
     // Même piège que dans VoxelHeightOpStack.cpp : s'ancrer sur une bannière située plus bas
@@ -6144,6 +6146,7 @@ bool VF_BuildStackFromRecipe(const FVoxelOpStackRecipe& Recipe,
     return true;
 }
 
+#if WITH_EDITOR
 namespace
 {
     static EVoxelStrateParamBlock VF_RegionParamBlock(ECaveGeneratorType Archetype)
@@ -6449,3 +6452,4 @@ bool VF_BuildStrateRegionStack(
     OutStack = MoveTemp(Parent);
     return true;
 }
+#endif // WITH_EDITOR — lateral regions remain behind the failed shippability gate