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/Public/VoxelSettings.h

@@ -13,6 +13,7 @@
 
 // IWYU : pointeur seulement (VoxelMaterial). / Pointer-only use.
 class UMaterialInterface;
+class UVoxelSeasonAsset;
 
 UCLASS(BlueprintType)
 class UVoxelSettings : public UPrimaryDataAsset
@@ -21,6 +22,12 @@ class UVoxelSettings : public UPrimaryDataAsset
 
 public:
 
+    /** Season seed/radius replace the mutable authored values only when Season is assigned. */
+    int32 GetEffectiveWorldSeed() const;
+    float GetEffectiveOriginSpineRadius() const;
+    float GetEffectiveWorldRadiusVoxels() const;
+    int32 GetEffectiveSeasonNumber() const;
+
 	//=========================================================================
 	// STREAMING (distance de vue)
 	//=========================================================================
@@ -350,6 +357,11 @@ public:
 	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Voxel|Strates")
 	int32 Seed = 0;
 
+	// Optional reviewed/cooked season. When set, its manifest owns layout, seed, bounds and
+	// density recipes; the authored StratePool/FixedStrates path remains untouched when unset.
+	UPROPERTY(EditAnywhere, BlueprintReadOnly, Category = "Voxel|Strates")
+	TSoftObjectPtr<UVoxelSeasonAsset> Season;
+
 	// Numéro de saison (incrementé par ChangeSeed). Purement informatif côté gameplay.
 	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Voxel|Strates")
 	int32 CurrentSeason = 1;