feat(editor): walk a composed candidate in PIE + why rooms read angular

PART B -- the thing Jahni asked for: "any way to test those in game?"
A candidate existed only as measurements and PNGs. Now he can stand in one.

  Select the VoxelWorld actor in PIE -> Live Edit|Composer ->
  ComposerSeed / ComposerCandidateIndex / ComposerTargetStrateIndex /
  bComposerRollStructure -> click Apply Composer Candidate.

The button and the automation tests call the SAME roll wrapper, which was
the load-bearing requirement: a second roll path could drift, and then he
would be judging a different world than the contact sheet describes. A
determinism sample is logged on apply (seed, index, recipe, archetype,
metrics, epoch, eight-point density verdict) so drift is caught the day it
happens rather than in a month.

Hazards handled, since this is the first composer code to touch the live
runtime path: preflight materialisation before any live mutation, generation
and decoration tasks drained, PassagesVersion bumped to invalidate
thread_local caches, reuse of the existing RegenerateAllChunks / Epoch
invalidation rather than a new path, no Initialize() or GeneratePassages()
during apply (the re-entrancy trap), DiffLayer locks untouched, and custom
recipes conservatively force ClassifyTile to Mixed.

Scope is deliberate: a DENSITY-ONLY overlay. Layout height, authored
passages, content, water and biome metadata stay from the existing slot;
RebuildStrates() clears it. A full composed layout replacement needs a safe
rebuild path that does not exist yet.

Editor-only, verified: a Shipping build succeeds with the bridge excluded
(96/96 actions), so §3.1's "offline only, never on a player's machine"
still holds.

⚠️ UNVERIFIED BY DESIGN: a button cannot be tested headlessly and Codex was
told not to claim it works. Jahni presses it and confirms the visual plus
the "determinism=PASS" log line.

PART A -- why rooms read angular, measured not guessed. One of three room
shapes is VoxelSDF::RoundedBox:
  ShapeA = (.8 Rxy, .8 Rxy, .8 Rz)   ShapeR = .25 Rxy
so rounding is 31% of the horizontal half-extent but 78% of the vertical.
Corners are rounded; the broad planar FACES survive. SmoothMin (blend 4)
softens room/tunnel junctions not isolated corners; the cave warp bends
geometry but preserves flat regions; roughness is surface-scale only.
The name is accurate -- "rounded box" is not "blob".

NOT ACTED ON. Jahni corrected his own read: the angular archetype is Maze
(lattice source, rectilinear BY DESIGN and correct), and TunnelNetwork is
"alright-ish". Codex's recommendation is recorded for if he ever wants it:
~5-10% boxes, 10-20% capsules, rest ellipsoids, or a larger ShapeR.

Also closed REVIEW_FINDINGS EVoxelPassageType/Style as WONTFIX, enacting a
2026-08-16 judgement that recommended closure and was left open.

Build clean (Editor + Shipping), 25 succeeded / 0 failed, run by me.

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

ARCHITECTURE.md

@@ -118,6 +118,15 @@ Provided per chunk by `StrateManager::GetDisturbanceParamsForChunk`.
 **If you add a connectivity rule with longer edges, the COLLECT region must still cover the
 max edge reach, and decisions must not depend on the stored window.**
 
+The editor composer walk-through preserves this invariant by avoiding a layout rebuild. AVoxelWorld::ApplyComposerCandidate
+pauses and drains active generation, installs one temporary override on an existing slot, increments
+the manager's layout/passages version, and then reuses RegenerateAllChunks to bump GenerationEpoch.
+The slot's Z range and passages therefore remain stable; worker tasks copy the immutable override during
+their versioned refetch. A parameter candidate uses the production native stack mapping, while a
+structure candidate uses VF_BuildStackFromRecipe; custom recipes conservatively return Mixed from
+ClassifyTile so no unproven box bound can skip their mesh. The bridge and its editable properties are
+WITH_EDITOR/WITH_EDITORONLY_DATA only and do not exist in a shipping build.
+
 ### 8.5 Content scatter & water — `VoxelContentManager.h/.cpp` (NEW)
 `UVoxelContentManager` (owned by `AVoxelWorld`, game-thread). TWO INDEPENDENT subsystems:
 
@@ -658,6 +667,14 @@ driven by `EditorBrush*` props.
 ### 8.11 Live tuning & debug (`AVoxelWorld`, CallInEditor / PIE)
 - `RebuildStrates` — re-reads ALL of `VoxelSettings` and rebuilds layout/gap/passages/spine +
   regenerates. Use after changing those (plain `RegenerateAllChunks` keeps the old layout/passages).
+- ApplyComposerCandidate — editor-only PIE walk-through for one offline candidate. Set
+  ComposerSeed, ComposerCandidateIndex, ComposerTargetStrateIndex (0 = topmost), and
+  bComposerRollStructure in Live Edit|Composer, then click Apply Composer Candidate. It uses the
+  shared composer roll, overlays density on the existing slot, pauses/drains workers, bumps the
+  manager version, and reuses RegenerateAllChunks for the epoch/re-stream. It does not rebuild
+  passages or change the authoritative Settings->Seed; RebuildStrates removes the overlay. The
+  action logs recipe, archetype, air/largest-component/walkable/feature metrics, and an eight-point
+  bit-level density verdict. The button itself still requires owner verification in PIE.
 - `ValidateDeterminism` (F2) — one-click §8.4 regression test: samples chunk-boundary points under
   two different thread_local cache alignments (left-chunk warm vs right-chunk warm) + a repeat
   pass; every delta must be EXACTLY 0. Run it after any hot-path refactor that claims

CODEMAP.md

@@ -413,13 +413,14 @@ Maps depth→strate at runtime; owns passages.
 | `AnyPassageNearBox` | — | Conservative sphere-vs-AABB test of every passage's bound against a voxel box (+carve blend pad). Per TILE (ClassifyTile guard), never per voxel. |
 | `FindSlotIndexForChunkZ` | 427 | Z → layout index. |
 | `GetStrateAt` / `GetStrateIndex` | 443 / 455 | World-Z queries. |
-| `GetLayoutVersion` | h:161 (inline) | Layout/passage generation counter (= `PassagesVersion`, bumped by every `Initialize`). Hot-path callers key `thread_local` memos on it (strate-index memo in `GetDensityWithParams`, passage shortlist) so editor rebuilds never serve stale data. |
+| `GetLayoutVersion` | h:161 (inline) | Layout/passage generation counter (= `PassagesVersion`, bumped by every `Initialize` and by the editor composer override). Hot-path callers key `thread_local` memos on it (strate-index memo in `GetDensityWithParams`, passage shortlist) so live changes never serve stale data. |
 | `GetStrateForChunk` | 466 | Chunk → definition. |
 | `GetGeneratorTypeForChunk` | 476 | Chunk → generator type. |
 | `UsesOperatorStackForChunk` | 559 | Chunk → should `GetDensityAt` take the operator stack? `bUseOperatorStack` on the definition **AND** archetype in the ported list — **now all 8 of 8** (Maze, FlatPlain, CrystalChamber, SurfaceWorld, VerticalShafts, FloatingIslands, TunnelNetwork, Underwater). **That list is written down here and nowhere else.** With every archetype ported the flag is now the *only* thing that decides the path, so ticking the box is no longer a no-op anywhere — it is a real switch onto the operator stack for that strate. |
 | `GetSlabParamsForChunk` | 490 | Slab params with runtime Z bounds (no blend — slabs use Hard). |
 | `GetBiomeContextForChunk` | — | Flatten the strate's `Biomes[]` + `BiomeMapParams` into a POD `FBiomeContext` for the biome field. Empty ⇒ biomes disabled. §8.14. |
 | `GetGenerationParams` | 515 | **Blended** TunnelNetwork params (handles Gradient/Hard/Interleaved transitions). |
+| `SetComposerOverrideForStrate` / `GetComposerOverrideForChunk` | editor-only | Temporary density-only candidate overlay for one existing slot. Copies immutable params/recipe into the worker refetch path, leaves layout/content/passages intact, and bumps `PassagesVersion` to invalidate generator memos. |
 | `BuildParamsFromDefinition` (static) | 1399 | Returns the definition's base `GenerationParams` only. Terrain-op assets are passed separately to `BuildChunkCache`, which applies one selected op per room and pre-bakes Column/Pit/Chimney features. |
 
 **`Public/VoxelTerrainOpDefinition.h` + `.cpp`** — `UVoxelTerrainOpDefinition : UPrimaryDataAsset`
@@ -462,7 +463,8 @@ selection → `FStrateGenerationParams::Lerp` or reflected native-family blend
 field range jitter (or the season-zero ±25% own-magnitude bootstrap for near-zero ranges) →
 editor-reflection clamps → ordered-pair repair. Bool
 `bTunnelsFlowTowardOrigin` inherits from the dominant parent; integer/enum SNAP fields are not
-jittered. This API is not called by runtime generation. The settings audit found **one unique path**,
+jittered. Normal runtime generation never calls this API; the editor-only AVoxelWorld bridge does so
+only from its PIE button. The settings audit found **one unique path**,
 `/Game/VoxelForge/DA_Strate3`, which explains the old one-vector corpus; the project assets were
 never in that pool.
 
@@ -475,6 +477,13 @@ it. `RequiredResources` / `ProvidedResources` close the room-state hole that cha
 could not express. `VoxelForgeComposerStructureRollTest` rolls 64 candidates, measures them through
 the offline sampler, and brute-forces every uniform box verdict from the novel stack itself.
 
+Public/VoxelWorld.h + Private/VoxelWorld.cpp — ApplyComposerCandidate exposes the four
+Live Edit|Composer properties and the CallInEditor button. It preflights the candidate, pauses
+generation before installing the manager override, and calls the existing epoch-aware full reset.
+The post-apply check compares eight densities against the shared native/recipe stack where the live
+world has no extra diff, disturbance, or biome context. It reports SKIPPED rather than comparing
+unlike fields.
+
 **`Public/VoxelStratePreview.h` + `Private/VoxelStratePreview.cpp`** — editor/automation-only PNG
 renderer and self-contained contact sheet. It consumes `FVoxelStrateSampleGrid` from the measurement
 pass, emits deterministic centre-Y XZ and data-selected XY slices via `IImageWrapper`, and shows filled-cell

COMPOSER-NOTES.md

@@ -84,7 +84,10 @@ a model over the candidates at zero runtime cost. **And Jahni reviews and vetoes
 publishes** — the system does the work, he keeps the veto.
 
 **What ships is small:** the season's seed plus the chosen strates' parameter vectors. Clients generate
-terrain from those, deterministically, exactly as today. **No runtime composition anywhere.**
+terrain from those, deterministically, exactly as today. **No composition is shipped or run in the
+normal game path.** The editor-only PIE inspection button described below is a deliberate debugging
+exception: it overlays one already-built slot so the owner can walk a measured candidate; it is not
+cooked, does not compose a season, and is cleared by RebuildStrates.
 
 ### 3.2 Structure: how a stack gets assembled
 
@@ -194,6 +197,26 @@ through the offline Tier 2 sampler; no runtime generation path calls this API. T
 test took **76.466 s**. The complete `VoxelForge` namespace then passed **24/24 tests (0 failed,
 0 not run)** in **339.797 s**.
 
+### 3.2a Editor walk-through hand-off (not a runtime composer)
+
+AVoxelWorld::ApplyComposerCandidate is the one editor-only bridge from this offline API to a live
+PIE world. It calls VF_RollStrateCandidate(Corpus, ComposerSeed, ComposerCandidateIndex,
+bComposerRollStructure). That wrapper delegates to the exact parameter/recipe calls exercised by
+the offline composer tests, then installs the result
+as a temporary density override on ComposerTargetStrateIndex. The layout slot's authored definition,
+height, content, and generated passages are intentionally unchanged; this avoids calling
+GeneratePassages while Initialize is half-built. The action pauses/drains generation, bumps the
+manager layout version, and reuses RegenerateAllChunks so GenerationEpoch invalidates stale mesh
+results and the normal streamer rebuilds the world.
+
+The Details-panel properties are ComposerSeed, ComposerCandidateIndex, ComposerTargetStrateIndex,
+and bComposerRollStructure, under Live Edit|Composer. The button is Apply Composer Candidate; it
+is usable only during PIE. RebuildStrates clears the temporary override. A post-apply eight-point
+density check compares the live generator with the same prepared candidate stack bit-for-bit when
+no diff edits, disturbance post, or surface-biome context makes the standalone oracle incomplete.
+The log line carries the recipe/archetype and the coarse metrics so it can be matched to a
+contact-sheet row. This hand-off is editor-only and is not part of the shipped composer contract.
+
 ### 3.3 Parameters: the range problem
 
 **Verified facts, not remembered:** `FStrateGenerationParams` has **73 scalar fields** (+1 bool) — not

REVIEW_FINDINGS.md

@@ -90,7 +90,10 @@ Legend: ✅ verified against code · ◻️ checklist box.
   like Box/Capsule already did (one diff-layer + remesh dispatch). *(2026-07-04)*
 - [x] **`VoxelContentManager.cpp`** — duplicated drain/reset loops → `DrainDecoResults()` +
   `ResetGridBuildState(FDecoGrid&)`. *(2026-07-04)*
-- [ ] **`EVoxelPassageType` vs `EVoxelPassageStyle`** — two overlapping passage-shape enums, both in
+- [x] **`EVoxelPassageType` vs `EVoxelPassageStyle`** — ✅ **CLOSED 2026-09-04 as WONTFIX**, enacting
+  the 2026-08-16 judgement below, which recommended closure and was then left open by oversight. No
+  code change; the two enums stay.
+  Two overlapping passage-shape enums, both in
   active use (11 refs). Consider consolidating to one. *(judgment call, not dead)*
   **JUDGED 2026-08-16 — LEAVE THEM. Recommendation: close this item rather than act on it.** They
   read as duplicates from the index and are not: `EVoxelPassageType` (`VoxelStrateTypes.h` ~42) is

Source/VoxelForge/Private/Tests/VoxelForgeComposerParameterRollTest.cpp

@@ -816,8 +816,18 @@ bool FVoxelForgeComposerParameterRollTest::RunTest(const FString& Parameters)
     const double RollAndMeasureStartSeconds = FPlatformTime::Seconds();
     for (int32 CandidateIndex = 0; CandidateIndex < NumCandidates; ++CandidateIndex)
     {
+#if WITH_EDITOR
+        // The PIE hand-off and this test deliberately cross the same seam. The wrapper only
+        // packages the exact parameter-roll call below; it must not grow a second RNG path.
+        const FVoxelStrateComposerCandidate Candidate = VF_RollStrateCandidate(
+            Corpus, AuthoredSettings->Seed, CandidateIndex, false);
+        const FVoxelStrateRollInfo& Roll = Candidate.ParameterRoll;
+        TestTrue(FString::Printf(TEXT("candidate %d hand-off roll is valid"), CandidateIndex),
+                 Candidate.bValid && Roll.bValid);
+#else
         const FVoxelStrateRollInfo Roll = VF_RollStrateParamsDetailed(
             Corpus, AuthoredSettings->Seed, CandidateIndex);
+#endif
         TestTrue(FString::Printf(TEXT("candidate %d roll is valid"), CandidateIndex), Roll.bValid);
 
         TotalBootstrapJitterFields += Roll.BootstrapJitterFieldCount;

Source/VoxelForge/Private/Tests/VoxelForgeComposerStructureRollTest.cpp

@@ -367,8 +367,17 @@ bool FVoxelForgeComposerStructureRollTest::RunTest(const FString& Parameters)
     const double RollAndMeasureStartSeconds = FPlatformTime::Seconds();
     for (int32 CandidateIndex = 0; CandidateIndex < NumCandidates; ++CandidateIndex)
     {
+#if WITH_EDITOR
+        // Keep the editor hand-off and the structure test on the same recipe/block roll seam.
+        const FVoxelStrateComposerCandidate Candidate = VF_RollStrateCandidate(
+            Corpus, AuthoredSettings->Seed, CandidateIndex, true);
+        TestTrue(FString::Printf(TEXT("candidate %d hand-off roll is valid"), CandidateIndex),
+                 Candidate.bValid);
+        const FVoxelOpStackRecipe Recipe = Candidate.Recipe;
+#else
         const FVoxelOpStackRecipe Recipe = VF_RollStrateStructure(
             AuthoredSettings->Seed, CandidateIndex);
+#endif
         const FVoxelOpStackRecipe RepeatRecipe = VF_RollStrateStructure(
             AuthoredSettings->Seed, CandidateIndex);
         TestTrue(FString::Printf(TEXT("candidate %d recipe reroll is identical"), CandidateIndex),
@@ -404,11 +413,24 @@ bool FVoxelForgeComposerStructureRollTest::RunTest(const FString& Parameters)
         FVoxelStrateArchetypeParams CandidateParams;
         bool bParameterRollsValid = true;
         double CandidateDistanceSquared = 0.0;
-        for (const FBlockSpec& Spec : GBlockSpecs)
+        for (int32 BlockIndex = 0; BlockIndex < UE_ARRAY_COUNT(GBlockSpecs); ++BlockIndex)
         {
+#if WITH_EDITOR
+            const FBlockSpec& Spec = GBlockSpecs[BlockIndex];
+            if (!Candidate.StructureBlockRolls.IsValidIndex(BlockIndex))
+            {
+                bParameterRollsValid = false;
+                AddError(FString::Printf(TEXT("candidate %d missing parameter block %d"),
+                                         CandidateIndex, static_cast<int32>(Spec.Block)));
+                continue;
+            }
+            const FVoxelStrateRollInfo& BlockRoll = Candidate.StructureBlockRolls[BlockIndex];
+#else
+            const FBlockSpec& Spec = GBlockSpecs[BlockIndex];
             const FVoxelStrateRollInfo BlockRoll = VF_RollStrateParamsDetailedForArchetype(
                 Corpus, Spec.Archetype,
                 AuthoredSettings->Seed ^ static_cast<int32>(Spec.SeedSalt), CandidateIndex);
+#endif
             if (!BlockRoll.bValid)
             {
                 bParameterRollsValid = false;

Source/VoxelForge/Private/VoxelGenerator.cpp

@@ -18,6 +18,10 @@
 #include "VoxelHeightOp.h"            // IVoxelBiomeField — the adapter below implements it
 #include "VoxelStats.h"
 
+#if WITH_EDITOR
+#include "VoxelStrateComposer.h"
+#endif
+
 #include <atomic>
 
 //=============================================================================
@@ -589,6 +593,63 @@ namespace
     }
 }
 
+#if WITH_EDITOR
+bool VF_BuildNativeStrateStackForCandidate(
+    ECaveGeneratorType Archetype,
+    const FVoxelStrateArchetypeParams& Params,
+    int32 InSeed,
+    float SpineRadius,
+    float InWorldRadiusVoxels,
+    float InEdgeSealThickness,
+    const UVoxelStrateManager* StrateManager,
+    FVoxelOpStack& OutStack,
+    FVoxelOpContext& OutContext)
+{
+    FVoxelStackParamRefs Refs;
+    switch (Archetype)
+    {
+    case ECaveGeneratorType::FlatPlain:
+    case ECaveGeneratorType::CrystalChamber:
+        Refs.Slab = &Params.SlabParams;
+        break;
+    case ECaveGeneratorType::Maze:
+        Refs.Maze = &Params.MazeParams;
+        break;
+    case ECaveGeneratorType::SurfaceWorld:
+        // The live surface path can additionally carry biome-specific parameter arrays and a
+        // generator-owned biome field. The editor sanity check deliberately handles the exact
+        // no-biome/native case only; the caller reports a biome target as unavailable rather than
+        // comparing unlike fields.
+        Refs.Surface = &Params.SurfaceParams;
+        break;
+    case ECaveGeneratorType::VerticalShafts:
+        Refs.Vert = &Params.VerticalShaftParams;
+        break;
+    case ECaveGeneratorType::FloatingIslands:
+        Refs.Float = &Params.FloatingIslandParams;
+        break;
+    case ECaveGeneratorType::Underwater:
+    case ECaveGeneratorType::TunnelNetwork:
+        Refs.Tunnel = &Params.TunnelNetworkParams;
+        break;
+    default:
+        return false;
+    }
+
+    OutContext = FVoxelOpContext();
+    OutContext.Seed = static_cast<uint32>(InSeed);
+    OutContext.LayoutVersion = StrateManager != nullptr ? StrateManager->GetLayoutVersion() : 0;
+    OutContext.WorldRadiusVoxels = InWorldRadiusVoxels;
+    OutContext.EdgeSealThickness = InEdgeSealThickness;
+    if (!VF_BuildOpStackForChunk(Archetype, Refs, InSeed, SpineRadius, StrateManager,
+                                 OutStack, OutContext))
+    {
+        return false;
+    }
+    return true;
+}
+#endif
+
 UVoxelGenerator::UVoxelGenerator()
     : DensityCacheOwnerId(GNextDensityCacheOwnerId.fetch_add(1, std::memory_order_relaxed) + 1)
 {
@@ -675,6 +736,15 @@ float UVoxelGenerator::GetDensityAt(float WorldX, float WorldY, float WorldZ) co
         // la strate n'a pas coché `bUseOperatorStack` ET que son archétype n'est pas porté.
         thread_local FVoxelOpStack            CP_OpStack;
         thread_local bool                     CP_UseOpStack = false;
+#if WITH_EDITOR
+        // Editor-only composer override. The candidate recipe is copied into this worker-local
+        // cache on the same versioned refetch as the native params; no worker reads mutable editor
+        // state while the world is applying a new candidate.
+        thread_local bool                       CP_UseComposerRecipe = false;
+        thread_local int32                      CP_ComposerSeed = 0;
+        thread_local FVoxelStrateArchetypeParams CP_ComposerParams;
+        thread_local FVoxelOpStackRecipe        CP_ComposerRecipe;
+#endif
 
         const uint32 LayoutVersion = StrateManager->GetLayoutVersion();
         const bool bOwnerChanged = DensityCacheOwnerId != CP_OwnerId;
@@ -691,6 +761,18 @@ float UVoxelGenerator::GetDensityAt(float WorldX, float WorldY, float WorldZ) co
             CP_Version = LayoutVersion;
             CP_Chunk   = ChunkCoord;
             CP_GenType = StrateManager->GetGeneratorTypeForChunk(ChunkCoord);
+#if WITH_EDITOR
+            CP_UseComposerRecipe = false;
+            ECaveGeneratorType ComposerArchetype = ECaveGeneratorType::TunnelNetwork;
+            bool bComposerUseRecipe = false;
+            if (StrateManager->GetComposerOverrideForChunk(
+                ChunkCoord, CP_ComposerSeed, ComposerArchetype, CP_ComposerParams,
+                bComposerUseRecipe, CP_ComposerRecipe))
+            {
+                CP_GenType = ComposerArchetype;
+                CP_UseComposerRecipe = bComposerUseRecipe;
+            }
+#endif
             switch (CP_GenType)
             {
             case ECaveGeneratorType::FlatPlain:
@@ -725,6 +807,35 @@ float UVoxelGenerator::GetDensityAt(float WorldX, float WorldY, float WorldZ) co
             if (CP_UseOpStack)
             {
                 CP_OpStack = FVoxelOpStack();   // move-assign : libère l'ancienne pile
+#if WITH_EDITOR
+                if (CP_UseComposerRecipe)
+                {
+                    FVoxelOpContext ComposerContext;
+                    if (VF_BuildStackFromRecipe(
+                        CP_ComposerRecipe, CP_ComposerParams, Seed,
+                        OriginSpineRadius, StrateManager, CP_OpStack, ComposerContext, nullptr))
+                    {
+                        ComposerContext.ChunkCoord = ChunkCoord;
+                        ComposerContext.Step = 1;
+                        ComposerContext.LayoutVersion = LayoutVersion;
+                        // The recipe builder supplies the candidate's vertical seal to the
+                        // structural post. The XY edge seal is global and uses live settings.
+                        ComposerContext.WorldRadiusVoxels = WorldRadiusVoxels;
+                        ComposerContext.EdgeSealThickness = EdgeSealThickness;
+                        CP_OpStack.PrepareChunk(ComposerContext);
+                    }
+                    else
+                    {
+                        // The editor action validates before installing the override. Keep this
+                        // fallback safe if a future recipe changes underneath PIE: the native
+                        // candidate params remain available instead of yielding an uninitialised
+                        // stack or a hole.
+                        CP_UseOpStack = false;
+                    }
+                }
+                else
+#endif
+                {
                 FVoxelOpContext OpCtx;
                 OpCtx.ChunkCoord    = ChunkCoord;
                 OpCtx.Seed          = (uint32)Seed;
@@ -773,6 +884,7 @@ float UVoxelGenerator::GetDensityAt(float WorldX, float WorldY, float WorldZ) co
                 // which is the point: the first op that hoists real per-chunk work must find the
                 // call already here.
                 if (CP_UseOpStack) { CP_OpStack.PrepareChunk(OpCtx); }
+                }
             }
         }
 
@@ -2784,6 +2896,16 @@ EVoxelTileClass UVoxelGenerator::ClassifyTile(const FIntVector& OriginVoxels, in
 
     if (!StrateManager) return EVoxelTileClass::Mixed;
 
+#if WITH_EDITOR
+    // A custom recipe is deliberately not fed to the native ClassifyBox proof yet. Returning
+    // Mixed keeps the live walk-through hole-safe: GenerateMesh samples the exact recipe stack,
+    // while no optimistic AllAir/AllSolid result can skip a candidate tile.
+    if (StrateManager->HasComposerRecipeOverride())
+    {
+        return EVoxelTileClass::Mixed;
+    }
+#endif
+
     bool bCanSolid = true;   // "tout le treillis est solide" encore prouvable
     bool bCanAir   = true;   // "tout le treillis est air" encore prouvable
 

Source/VoxelForge/Private/VoxelStrateComposer.cpp

@@ -2270,6 +2270,131 @@ FVoxelOpStackRecipe VF_RollStrateStructure(int32 Seed, int32 Index)
     return Recipe;
 }
 
+#if WITH_EDITOR
+namespace
+{
+    struct FComposerStructureBlockSpec
+    {
+        EVoxelStrateParamBlock Block;
+        ECaveGeneratorType Archetype;
+        uint32 SeedSalt;
+    };
+
+    // Keep these salts in the composer implementation so the editor action and the offline
+    // structure test cannot silently acquire different block streams.
+    static const FComposerStructureBlockSpec GComposerStructureBlocks[] =
+    {
+        { EVoxelStrateParamBlock::TunnelNetwork,  ECaveGeneratorType::TunnelNetwork,  0x1001u },
+        { EVoxelStrateParamBlock::Slab,            ECaveGeneratorType::FlatPlain,       0x1003u },
+        { EVoxelStrateParamBlock::Maze,            ECaveGeneratorType::Maze,            0x1005u },
+        { EVoxelStrateParamBlock::Surface,         ECaveGeneratorType::SurfaceWorld,    0x1007u },
+        { EVoxelStrateParamBlock::VerticalShaft,   ECaveGeneratorType::VerticalShafts,  0x1009u },
+        { EVoxelStrateParamBlock::FloatingIsland,  ECaveGeneratorType::FloatingIslands, 0x100Bu },
+    };
+
+    void VF_CopyComposerBlock(FVoxelStrateArchetypeParams& OutParams,
+                              const FVoxelStrateRollInfo& Roll,
+                              ECaveGeneratorType Archetype)
+    {
+        switch (Archetype)
+        {
+        case ECaveGeneratorType::TunnelNetwork:
+        case ECaveGeneratorType::Underwater:
+            OutParams.TunnelNetworkParams = Roll.ArchetypeParams.TunnelNetworkParams;
+            break;
+        case ECaveGeneratorType::FlatPlain:
+        case ECaveGeneratorType::CrystalChamber:
+            OutParams.SlabParams = Roll.ArchetypeParams.SlabParams;
+            break;
+        case ECaveGeneratorType::Maze:
+            OutParams.MazeParams = Roll.ArchetypeParams.MazeParams;
+            break;
+        case ECaveGeneratorType::SurfaceWorld:
+            OutParams.SurfaceParams = Roll.ArchetypeParams.SurfaceParams;
+            break;
+        case ECaveGeneratorType::VerticalShafts:
+            OutParams.VerticalShaftParams = Roll.ArchetypeParams.VerticalShaftParams;
+            break;
+        case ECaveGeneratorType::FloatingIslands:
+            OutParams.FloatingIslandParams = Roll.ArchetypeParams.FloatingIslandParams;
+            break;
+        default:
+            break;
+        }
+    }
+
+    ECaveGeneratorType VF_ComposerArchetypeForRecipe(const FVoxelOpStackRecipe& Recipe)
+    {
+        switch (Recipe.StructuralParamBlock)
+        {
+        case EVoxelStrateParamBlock::TunnelNetwork: return ECaveGeneratorType::TunnelNetwork;
+        case EVoxelStrateParamBlock::Slab:           return ECaveGeneratorType::FlatPlain;
+        case EVoxelStrateParamBlock::Maze:           return ECaveGeneratorType::Maze;
+        case EVoxelStrateParamBlock::Surface:        return ECaveGeneratorType::SurfaceWorld;
+        case EVoxelStrateParamBlock::VerticalShaft:  return ECaveGeneratorType::VerticalShafts;
+        case EVoxelStrateParamBlock::FloatingIsland: return ECaveGeneratorType::FloatingIslands;
+        default:                                     return ECaveGeneratorType::TunnelNetwork;
+        }
+    }
+}
+
+FVoxelStrateComposerCandidate VF_RollStrateCandidate(
+    const FVoxelStrateCorpus& Corpus, int32 Seed, int32 Index, bool bRollStructure)
+{
+    FVoxelStrateComposerCandidate Candidate;
+    Candidate.Seed = Seed;
+    Candidate.Index = Index;
+    Candidate.bStructureRoll = bRollStructure;
+
+    if (!bRollStructure)
+    {
+        // This is the exact Tier 4a call used by the parameter-roll measurement test.
+        Candidate.ParameterRoll = VF_RollStrateParamsDetailed(Corpus, Seed, Index);
+        if (!Candidate.ParameterRoll.bValid)
+        {
+            Candidate.FailureReason = Candidate.ParameterRoll.FailureReason;
+            return Candidate;
+        }
+
+        Candidate.Archetype = Candidate.ParameterRoll.Archetype;
+        Candidate.ArchetypeParams = Candidate.ParameterRoll.ArchetypeParams;
+        Candidate.bValid = true;
+        return Candidate;
+    }
+
+    // This is the exact Tier 4b structure call plus the six independent native-family rolls used
+    // to materialise every structure candidate in the offline test.
+    Candidate.Recipe = VF_RollStrateStructure(Seed, Index);
+    Candidate.Archetype = VF_ComposerArchetypeForRecipe(Candidate.Recipe);
+    Candidate.StructureBlockRolls.Reserve(UE_ARRAY_COUNT(GComposerStructureBlocks));
+
+    bool bAllBlocksValid = true;
+    for (const FComposerStructureBlockSpec& Spec : GComposerStructureBlocks)
+    {
+        const FVoxelStrateRollInfo Roll = VF_RollStrateParamsDetailedForArchetype(
+            Corpus, Spec.Archetype, Seed ^ static_cast<int32>(Spec.SeedSalt), Index);
+        Candidate.StructureBlockRolls.Add(Roll);
+        if (!Roll.bValid)
+        {
+            bAllBlocksValid = false;
+            if (Candidate.FailureReason.IsEmpty())
+            {
+                Candidate.FailureReason = FString::Printf(
+                    TEXT("parameter block %d (%s) failed: %s"),
+                    static_cast<int32>(Spec.Block),
+                    VF_GetStrateArchetypeName(Spec.Archetype),
+                    *Roll.FailureReason);
+            }
+            continue;
+        }
+        VF_CopyComposerBlock(Candidate.ArchetypeParams, Roll, Spec.Archetype);
+    }
+
+    Candidate.bValid = bAllBlocksValid;
+    return Candidate;
+}
+#endif
+
 FString VF_FormatStrateStructureRecipe(const FVoxelOpStackRecipe& Recipe)
 {
     FString Modifiers;

Source/VoxelForge/Private/VoxelStrateManager.cpp

@@ -9,6 +9,36 @@
 #include "VoxelTerrainOpDefinition.h"  // For UVoxelTerrainOpDefinition::ApplyTo
 #include "VoxelBiomeDefinition.h"  // For UVoxelBiomeDefinition (biome context flatten)
 
+#if WITH_EDITOR
+#include "VoxelStrateComposer.h"
+
+struct FVoxelStrateComposerSlotOverride
+{
+    int32 CandidateSeed = 0;
+    ECaveGeneratorType Archetype = ECaveGeneratorType::TunnelNetwork;
+    FVoxelStrateArchetypeParams Params;
+    bool bUseRecipe = false;
+    FVoxelOpStackRecipe Recipe;
+};
+
+static void VF_SetComposerRuntimeBounds(
+    FVoxelStrateArchetypeParams& Params, float TopWorldZ, float BottomWorldZ)
+{
+    Params.TunnelNetworkParams.StrateTopWorldZ = TopWorldZ;
+    Params.TunnelNetworkParams.StrateBottomWorldZ = BottomWorldZ;
+    Params.SlabParams.StrateTopWorldZ = TopWorldZ;
+    Params.SlabParams.StrateBottomWorldZ = BottomWorldZ;
+    Params.MazeParams.StrateTopWorldZ = TopWorldZ;
+    Params.MazeParams.StrateBottomWorldZ = BottomWorldZ;
+    Params.SurfaceParams.StrateTopWorldZ = TopWorldZ;
+    Params.SurfaceParams.StrateBottomWorldZ = BottomWorldZ;
+    Params.VerticalShaftParams.StrateTopWorldZ = TopWorldZ;
+    Params.VerticalShaftParams.StrateBottomWorldZ = BottomWorldZ;
+    Params.FloatingIslandParams.StrateTopWorldZ = TopWorldZ;
+    Params.FloatingIslandParams.StrateBottomWorldZ = BottomWorldZ;
+}
+#endif
+
 // Fractal Brownian Motion (layered Perlin) along a 1D parameter, ~[-1,1].
 // Independent octaves at increasing frequency / decreasing amplitude give an organic,
 // non-repeating wander — the key to a worm that SQUIRMS instead of zig-zagging (1D) or
@@ -35,6 +65,11 @@ void UVoxelStrateManager::Initialize(UVoxelSettings* Settings, int32 WorldSeed)
     }
 
     StrateLayout.Empty();
+#if WITH_EDITOR
+    // A full layout rebuild discards any temporary walk-through candidate. The world calls this
+    // under FScopedGenerationPause, so no worker can observe the map while it is being cleared.
+    ComposerOverrides.Reset();
+#endif
 
     const int32 TotalStrates = Settings->TotalStrates;
 
@@ -240,6 +275,125 @@ void UVoxelStrateManager::Initialize(UVoxelSettings* Settings, int32 WorldSeed)
     GeneratePassages();
 }
 
+#if WITH_EDITOR
+const FVoxelStrateComposerSlotOverride* UVoxelStrateManager::FindComposerOverride(
+    int32 StrateIndex) const
+{
+    const TSharedPtr<FVoxelStrateComposerSlotOverride>* Found = ComposerOverrides.Find(StrateIndex);
+    return Found != nullptr ? Found->Get() : nullptr;
+}
+
+bool UVoxelStrateManager::SetComposerOverrideForStrate(
+    int32 StrateIndex, int32 CandidateSeed, ECaveGeneratorType Archetype,
+    const FVoxelStrateArchetypeParams& Params, bool bUseRecipe,
+    const FVoxelOpStackRecipe* Recipe, FString& OutError)
+{
+    OutError.Reset();
+
+    const FStrateSlot* TargetSlot = nullptr;
+    for (const FStrateSlot& Slot : StrateLayout)
+    {
+        if (Slot.StrateIndex == StrateIndex)
+        {
+            TargetSlot = &Slot;
+            break;
+        }
+    }
+    if (TargetSlot == nullptr || TargetSlot->Definition == nullptr)
+    {
+        OutError = FString::Printf(TEXT("Strate index %d is not present in the live layout."), StrateIndex);
+        return false;
+    }
+
+    switch (Archetype)
+    {
+    case ECaveGeneratorType::TunnelNetwork:
+    case ECaveGeneratorType::FlatPlain:
+    case ECaveGeneratorType::CrystalChamber:
+    case ECaveGeneratorType::Maze:
+    case ECaveGeneratorType::SurfaceWorld:
+    case ECaveGeneratorType::VerticalShafts:
+    case ECaveGeneratorType::FloatingIslands:
+    case ECaveGeneratorType::Underwater:
+        break;
+    default:
+        OutError = TEXT("The composer returned an unsupported strate archetype.");
+        return false;
+    }
+
+    if (bUseRecipe && Recipe == nullptr)
+    {
+        OutError = TEXT("A structure candidate did not provide a recipe.");
+        return false;
+    }
+
+    TSharedPtr<FVoxelStrateComposerSlotOverride> Override =
+        MakeShared<FVoxelStrateComposerSlotOverride>();
+    Override->CandidateSeed = CandidateSeed;
+    Override->Archetype = Archetype;
+    Override->Params = Params;
+    VF_SetComposerRuntimeBounds(
+        Override->Params,
+        (float)(TargetSlot->TopChunkZ + 1) * CHUNK_SIZE,
+        (float)TargetSlot->BottomChunkZ * CHUNK_SIZE);
+    Override->bUseRecipe = bUseRecipe;
+    if (Recipe != nullptr)
+    {
+        Override->Recipe = *Recipe;
+    }
+
+    // Only one slot is overridden at a time. Keeping this map small also makes the worker-side
+    // copy-on-chunk-refetch cheap. Passage geometry is deliberately not regenerated: the layout
+    // and its passages are unchanged, and this is the same manager state used by the offline
+    // candidate measurement harness.
+    ComposerOverrides.Reset();
+    ComposerOverrides.Add(StrateIndex, MoveTemp(Override));
+
+    // This is both the passage-shortlist invalidation counter and the cache key used by the
+    // generator's per-chunk params/stack memos. The world has already paused all readers.
+    ++PassagesVersion;
+    return true;
+}
+
+bool UVoxelStrateManager::GetComposerOverrideForChunk(
+    const FIntVector& ChunkCoord, int32& OutCandidateSeed,
+    ECaveGeneratorType& OutArchetype, FVoxelStrateArchetypeParams& OutParams,
+    bool& bOutUseRecipe, FVoxelOpStackRecipe& OutRecipe) const
+{
+    const int32 SlotIdx = FindSlotIndexForChunkZ(ChunkCoord.Z);
+    if (SlotIdx < 0)
+    {
+        return false;
+    }
+
+    const FVoxelStrateComposerSlotOverride* Override =
+        FindComposerOverride(StrateLayout[SlotIdx].StrateIndex);
+    if (Override == nullptr)
+    {
+        return false;
+    }
+
+    OutCandidateSeed = Override->CandidateSeed;
+    OutArchetype = Override->Archetype;
+    OutParams = Override->Params;
+    bOutUseRecipe = Override->bUseRecipe;
+    OutRecipe = Override->Recipe;
+    return true;
+}
+
+bool UVoxelStrateManager::HasComposerRecipeOverride() const
+{
+    for (const TPair<int32, TSharedPtr<FVoxelStrateComposerSlotOverride>>& Pair : ComposerOverrides)
+    {
+        if (Pair.Value.IsValid() && Pair.Value->bUseRecipe)
+        {
+            return true;
+        }
+    }
+    return false;
+}
+#endif
+
 //=============================================================================
 // PASSAGE GENERATION
 //=============================================================================
@@ -935,6 +1089,14 @@ ECaveGeneratorType UVoxelStrateManager::GetGeneratorTypeForChunk(const FIntVecto
         return ECaveGeneratorType::TunnelNetwork;
     }
 
+#if WITH_EDITOR
+    if (const FVoxelStrateComposerSlotOverride* Override =
+        FindComposerOverride(StrateLayout[SlotIdx].StrateIndex))
+    {
+        return Override->Archetype;
+    }
+#endif
+
     return StrateLayout[SlotIdx].Definition->GeneratorType;
 }
 
@@ -943,6 +1105,15 @@ bool UVoxelStrateManager::UsesOperatorStackForChunk(const FIntVector& ChunkCoord
     const int32 SlotIdx = FindSlotIndexForChunkZ(ChunkCoord.Z);
     if (SlotIdx < 0 || !StrateLayout[SlotIdx].Definition) { return false; }
 
+#if WITH_EDITOR
+    if (FindComposerOverride(StrateLayout[SlotIdx].StrateIndex) != nullptr)
+    {
+        // Temporary composer candidates are measured through the stack path. Do not inherit an
+        // unrelated asset flag from the slot being replaced.
+        return true;
+    }
+#endif
+
     const UVoxelStrateDefinition* Def = StrateLayout[SlotIdx].Definition;
     if (!Def->bUseOperatorStack) { return false; }
 
@@ -1018,8 +1189,23 @@ FSlabGenerationParams UVoxelStrateManager::GetSlabParamsForChunk(const FIntVecto
 
     const FStrateSlot& Slot = StrateLayout[SlotIdx];
 
-    // Copy the designer-authored slab params from the strate definition.
-    FSlabGenerationParams Result = Slot.Definition->SlabParams;
+    // Copy the designer-authored slab params from the strate definition, unless an editor
+    // composer candidate owns this slot.
+    FSlabGenerationParams Result;
+#if WITH_EDITOR
+    if (const FVoxelStrateComposerSlotOverride* Override =
+        FindComposerOverride(Slot.StrateIndex))
+    {
+        Result = (Override->Archetype == ECaveGeneratorType::FlatPlain
+                  || Override->Archetype == ECaveGeneratorType::CrystalChamber)
+            ? Override->Params.SlabParams
+            : Slot.Definition->SlabParams;
+    }
+    else
+#endif
+    {
+        Result = Slot.Definition->SlabParams;
+    }
 
     // Fill in the runtime Z bounds (voxel coordinates, same convention as
     // FStrateGenerationParams::StrateTopWorldZ / StrateBottomWorldZ).
@@ -1034,32 +1220,111 @@ FSlabGenerationParams UVoxelStrateManager::GetSlabParamsForChunk(const FIntVecto
 // PER-ARCHETYPE PARAM GETTERS
 //=============================================================================
 // Each mirrors GetSlabParamsForChunk: copy designer params, fill runtime Z bounds.
-// No cross-boundary blending — archetypes meet at Hard boundaries. A macro keeps
-// the boilerplate (slot lookup + fallback + Z bounds) in one place.
+// No cross-boundary blending — archetypes meet at Hard boundaries.
 
-#define VF_ARCHETYPE_PARAMS_GETTER(FnName, StructType, DefMember)                       \
-StructType UVoxelStrateManager::FnName(const FIntVector& ChunkCoord) const              \
-{                                                                                      \
-    int32 SlotIdx = FindSlotIndexForChunkZ(ChunkCoord.Z);                              \
-    if (SlotIdx < 0 || !StrateLayout[SlotIdx].Definition)                              \
-    {                                                                                  \
-        StructType Empty;                                                              \
-        Empty.BaseDensity = -1.0f;                                                     \
-        return Empty;                                                                  \
-    }                                                                                  \
-    const FStrateSlot& Slot = StrateLayout[SlotIdx];                                   \
-    StructType Result = Slot.Definition->DefMember;                                    \
-    Result.StrateTopWorldZ    = (float)(Slot.TopChunkZ + 1) * CHUNK_SIZE;              \
-    Result.StrateBottomWorldZ = (float)(Slot.BottomChunkZ)  * CHUNK_SIZE;              \
-    return Result;                                                                     \
+FMazeGenerationParams UVoxelStrateManager::GetMazeParamsForChunk(const FIntVector& ChunkCoord) const
+{
+    const int32 SlotIdx = FindSlotIndexForChunkZ(ChunkCoord.Z);
+    if (SlotIdx < 0 || !StrateLayout[SlotIdx].Definition)
+    {
+        FMazeGenerationParams Empty;
+        Empty.BaseDensity = -1.0f;
+        return Empty;
+    }
+
+    const FStrateSlot& Slot = StrateLayout[SlotIdx];
+    FMazeGenerationParams Result = Slot.Definition->MazeParams;
+#if WITH_EDITOR
+    if (const FVoxelStrateComposerSlotOverride* Override = FindComposerOverride(Slot.StrateIndex))
+    {
+        if (Override->Archetype == ECaveGeneratorType::Maze)
+        {
+            Result = Override->Params.MazeParams;
+        }
+    }
+#endif
+    Result.StrateTopWorldZ = (float)(Slot.TopChunkZ + 1) * CHUNK_SIZE;
+    Result.StrateBottomWorldZ = (float)Slot.BottomChunkZ * CHUNK_SIZE;
+    return Result;
 }
 
-VF_ARCHETYPE_PARAMS_GETTER(GetMazeParamsForChunk,           FMazeGenerationParams,    MazeParams)
-VF_ARCHETYPE_PARAMS_GETTER(GetSurfaceParamsForChunk,        FSurfaceGenerationParams, SurfaceParams)
-VF_ARCHETYPE_PARAMS_GETTER(GetVerticalShaftParamsForChunk,  FVerticalShaftParams,     VerticalShaftParams)
-VF_ARCHETYPE_PARAMS_GETTER(GetFloatingIslandParamsForChunk, FFloatingIslandParams,    FloatingIslandParams)
+FSurfaceGenerationParams UVoxelStrateManager::GetSurfaceParamsForChunk(const FIntVector& ChunkCoord) const
+{
+    const int32 SlotIdx = FindSlotIndexForChunkZ(ChunkCoord.Z);
+    if (SlotIdx < 0 || !StrateLayout[SlotIdx].Definition)
+    {
+        FSurfaceGenerationParams Empty;
+        Empty.BaseDensity = -1.0f;
+        return Empty;
+    }
 
-#undef VF_ARCHETYPE_PARAMS_GETTER
+    const FStrateSlot& Slot = StrateLayout[SlotIdx];
+    FSurfaceGenerationParams Result = Slot.Definition->SurfaceParams;
+#if WITH_EDITOR
+    if (const FVoxelStrateComposerSlotOverride* Override = FindComposerOverride(Slot.StrateIndex))
+    {
+        if (Override->Archetype == ECaveGeneratorType::SurfaceWorld)
+        {
+            Result = Override->Params.SurfaceParams;
+        }
+    }
+#endif
+    Result.StrateTopWorldZ = (float)(Slot.TopChunkZ + 1) * CHUNK_SIZE;
+    Result.StrateBottomWorldZ = (float)Slot.BottomChunkZ * CHUNK_SIZE;
+    return Result;
+}
+
+FVerticalShaftParams UVoxelStrateManager::GetVerticalShaftParamsForChunk(const FIntVector& ChunkCoord) const
+{
+    const int32 SlotIdx = FindSlotIndexForChunkZ(ChunkCoord.Z);
+    if (SlotIdx < 0 || !StrateLayout[SlotIdx].Definition)
+    {
+        FVerticalShaftParams Empty;
+        Empty.BaseDensity = -1.0f;
+        return Empty;
+    }
+
+    const FStrateSlot& Slot = StrateLayout[SlotIdx];
+    FVerticalShaftParams Result = Slot.Definition->VerticalShaftParams;
+#if WITH_EDITOR
+    if (const FVoxelStrateComposerSlotOverride* Override = FindComposerOverride(Slot.StrateIndex))
+    {
+        if (Override->Archetype == ECaveGeneratorType::VerticalShafts)
+        {
+            Result = Override->Params.VerticalShaftParams;
+        }
+    }
+#endif
+    Result.StrateTopWorldZ = (float)(Slot.TopChunkZ + 1) * CHUNK_SIZE;
+    Result.StrateBottomWorldZ = (float)Slot.BottomChunkZ * CHUNK_SIZE;
+    return Result;
+}
+
+FFloatingIslandParams UVoxelStrateManager::GetFloatingIslandParamsForChunk(const FIntVector& ChunkCoord) const
+{
+    const int32 SlotIdx = FindSlotIndexForChunkZ(ChunkCoord.Z);
+    if (SlotIdx < 0 || !StrateLayout[SlotIdx].Definition)
+    {
+        FFloatingIslandParams Empty;
+        Empty.BaseDensity = -1.0f;
+        return Empty;
+    }
+
+    const FStrateSlot& Slot = StrateLayout[SlotIdx];
+    FFloatingIslandParams Result = Slot.Definition->FloatingIslandParams;
+#if WITH_EDITOR
+    if (const FVoxelStrateComposerSlotOverride* Override = FindComposerOverride(Slot.StrateIndex))
+    {
+        if (Override->Archetype == ECaveGeneratorType::FloatingIslands)
+        {
+            Result = Override->Params.FloatingIslandParams;
+        }
+    }
+#endif
+    Result.StrateTopWorldZ = (float)(Slot.TopChunkZ + 1) * CHUNK_SIZE;
+    Result.StrateBottomWorldZ = (float)Slot.BottomChunkZ * CHUNK_SIZE;
+    return Result;
+}
 
 FBiomeContext UVoxelStrateManager::GetBiomeContextForChunk(const FIntVector& ChunkCoord) const
 {
@@ -1156,6 +1421,20 @@ FStrateGenerationParams UVoxelStrateManager::GetGenerationParams(const FIntVecto
     }
 
     const FStrateSlot& Slot = StrateLayout[SlotIdx];
+
+#if WITH_EDITOR
+    if (const FVoxelStrateComposerSlotOverride* Override =
+        FindComposerOverride(Slot.StrateIndex))
+    {
+        FStrateGenerationParams Result = Override->Params.TunnelNetworkParams;
+        Result.StrateTopWorldZ = (float)(Slot.TopChunkZ + 1) * CHUNK_SIZE;
+        Result.StrateBottomWorldZ = (float)Slot.BottomChunkZ * CHUNK_SIZE;
+        // A candidate is a hard replacement of this slot. Do not blend its rolled vector with an
+        // authored neighbour at a boundary; this is also how the offline fixture measures it.
+        return Result;
+    }
+#endif
+
     FStrateGenerationParams BaseParams = BuildParamsFromDefinition(Slot.Definition);
 
     //=========================================================================

Source/VoxelForge/Private/VoxelWorld.cpp

@@ -33,6 +33,11 @@
 #include "Misc/Paths.h"
 #include "ProfilingDebugging/CpuProfilerTrace.h"   // Unreal Insights scopes (Perf 0)
 
+#if WITH_EDITOR
+#include "VoxelStrateComposer.h"
+#include "VoxelStrateMeasure.h"
+#endif
+
 AVoxelWorld::AVoxelWorld()
 {
     PrimaryActorTick.bCanEverTick = true;
@@ -127,6 +132,228 @@ private:
     bool bAcquired = false;
 };
 
+#if WITH_EDITOR
+namespace
+{
+    void VF_SetComposerRuntimeBounds(FVoxelStrateArchetypeParams& Params,
+                                     float TopWorldZ, float BottomWorldZ)
+    {
+        Params.TunnelNetworkParams.StrateTopWorldZ = TopWorldZ;
+        Params.TunnelNetworkParams.StrateBottomWorldZ = BottomWorldZ;
+        Params.SlabParams.StrateTopWorldZ = TopWorldZ;
+        Params.SlabParams.StrateBottomWorldZ = BottomWorldZ;
+        Params.MazeParams.StrateTopWorldZ = TopWorldZ;
+        Params.MazeParams.StrateBottomWorldZ = BottomWorldZ;
+        Params.SurfaceParams.StrateTopWorldZ = TopWorldZ;
+        Params.SurfaceParams.StrateBottomWorldZ = BottomWorldZ;
+        Params.VerticalShaftParams.StrateTopWorldZ = TopWorldZ;
+        Params.VerticalShaftParams.StrateBottomWorldZ = BottomWorldZ;
+        Params.FloatingIslandParams.StrateTopWorldZ = TopWorldZ;
+        Params.FloatingIslandParams.StrateBottomWorldZ = BottomWorldZ;
+    }
+
+    float VF_ComposerBoundarySeal(const FVoxelStrateArchetypeParams& Params,
+                                  ECaveGeneratorType Archetype)
+    {
+        switch (Archetype)
+        {
+        case ECaveGeneratorType::FlatPlain:
+        case ECaveGeneratorType::CrystalChamber:
+            return Params.SlabParams.BoundarySealThickness;
+        case ECaveGeneratorType::Maze:
+            return Params.MazeParams.BoundarySealThickness;
+        case ECaveGeneratorType::SurfaceWorld:
+            return Params.SurfaceParams.BoundarySealThickness;
+        case ECaveGeneratorType::VerticalShafts:
+            return Params.VerticalShaftParams.BoundarySealThickness;
+        case ECaveGeneratorType::FloatingIslands:
+            return Params.FloatingIslandParams.BoundarySealThickness;
+        case ECaveGeneratorType::Underwater:
+        case ECaveGeneratorType::TunnelNetwork:
+        default:
+            return Params.TunnelNetworkParams.BoundarySealThickness;
+        }
+    }
+
+    class FComposerStackDensitySampler final : public IVoxelStrateDensitySampler
+    {
+    public:
+        explicit FComposerStackDensitySampler(const FVoxelOpStack& InStack)
+            : Stack(InStack) {}
+
+        float SampleDensity(float WorldX, float WorldY, float WorldZ) const override
+        {
+            return Stack.EvalMC(WorldX, WorldY, WorldZ);
+        }
+
+    private:
+        const FVoxelOpStack& Stack;
+    };
+
+    bool VF_BuildComposerReferenceStack(
+        const FVoxelStrateComposerCandidate& Candidate,
+        const UVoxelGenerator& Generator,
+        const UVoxelStrateManager& StrateManager,
+        int32 TargetTopChunkZ,
+        int32 TargetBottomChunkZ,
+        FVoxelOpStack& OutStack,
+        FVoxelOpContext& OutContext,
+        FString& OutError)
+    {
+        const float TopWorldZ = (float)(TargetTopChunkZ + 1) * CHUNK_SIZE;
+        const float BottomWorldZ = (float)TargetBottomChunkZ * CHUNK_SIZE;
+        FVoxelStrateArchetypeParams Params = Candidate.ArchetypeParams;
+        VF_SetComposerRuntimeBounds(Params, TopWorldZ, BottomWorldZ);
+
+        bool bBuilt = false;
+        if (Candidate.bStructureRoll)
+        {
+            bBuilt = VF_BuildStackFromRecipe(
+                Candidate.Recipe, Params, Generator.Seed, Generator.OriginSpineRadius,
+                &StrateManager, OutStack, OutContext, &OutError);
+        }
+        else
+        {
+            bBuilt = VF_BuildNativeStrateStackForCandidate(
+                Candidate.Archetype, Params, Generator.Seed, Generator.OriginSpineRadius,
+                Generator.WorldRadiusVoxels, Generator.EdgeSealThickness, &StrateManager,
+                OutStack, OutContext);
+            if (!bBuilt && OutError.IsEmpty())
+            {
+                OutError = TEXT("The production native candidate stack could not be materialised.");
+            }
+        }
+        if (!bBuilt)
+        {
+            return false;
+        }
+
+        // The recipe builder deliberately defaults the world-edge context to 0 for offline
+        // measurements. A live candidate must use the actual world's edge law, while its
+        // vertical bounds and structural seal remain candidate-owned.
+        const int32 MidChunkZ = TargetBottomChunkZ
+            + (TargetTopChunkZ - TargetBottomChunkZ) / 2;
+        OutContext.ChunkCoord = FIntVector(0, 0, MidChunkZ);
+        OutContext.Step = 1;
+        OutContext.LayoutVersion = StrateManager.GetLayoutVersion();
+        OutContext.WorldRadiusVoxels = Generator.WorldRadiusVoxels;
+        OutContext.EdgeSealThickness = Generator.EdgeSealThickness;
+        OutStack.PrepareChunk(OutContext);
+        return true;
+    }
+
+    bool VF_ComposerReferenceIsComparable(
+        const AVoxelWorld& World,
+        const FStrateSlot& TargetSlot,
+        ECaveGeneratorType Archetype,
+        const FIntVector& RepresentativeChunk,
+        FString& OutReason)
+    {
+        OutReason.Reset();
+        if (World.DiffLayer && World.DiffLayer->HasAnyMods())
+        {
+            OutReason = TEXT("diff-layer-modifications-present");
+            return false;
+        }
+
+        const FStrateDisturbanceParams Disturbances =
+            World.StrateManager->GetDisturbanceParamsForChunk(RepresentativeChunk);
+        if (Disturbances.ChasmDensity > 0.0f
+            || Disturbances.BridgeDensity > 0.0f
+            || Disturbances.RidgeDensity > 0.0f)
+        {
+            OutReason = TEXT("live-disturbance-post-present");
+            return false;
+        }
+
+        // The production SurfaceWorld stack may include a generator-owned biome field and
+        // per-biome params. The standalone candidate stack intentionally does not invent that
+        // context; fall back to the live metric and mark the density check as unavailable.
+        if (Archetype == ECaveGeneratorType::SurfaceWorld
+            && TargetSlot.Definition != nullptr
+            && TargetSlot.Definition->Biomes.Num() > 0)
+        {
+            OutReason = TEXT("surface-biome-context-present");
+            return false;
+        }
+        return true;
+    }
+
+    FVoxelStrateMeasureSettings VF_ComposerMeasureSettings()
+    {
+        FVoxelStrateMeasureSettings Settings;
+        Settings.SampleStep = 4;
+        Settings.RadiusInVoxels = 256;
+        Settings.CenterXY = FVector2D::ZeroVector;
+        Settings.MaxCells = 8000000;
+        Settings.MaxRouteRetries = 16;
+        Settings.HeadroomCells = 2;
+        Settings.InteriorMarginVoxels = -1;
+        return Settings;
+    }
+
+    bool VF_ComposerDensitySanityCheck(
+        const UVoxelGenerator& Generator,
+        const FVoxelOpStack& ReferenceStack,
+        int32 TargetTopChunkZ,
+        int32 TargetBottomChunkZ,
+        float& OutMaxDelta,
+        int32& OutMismatches,
+        int32& OutSamples)
+    {
+        // Keep all probes inside one representative chunk column where possible. This exercises
+        // both the live thread-local refetch and the prepared reference stack without making the
+        // check depend on a particular room being present at a hand-picked coordinate.
+        static const FIntVector Offsets[] =
+        {
+            FIntVector(1, 1, -15),
+            FIntVector(7, 13, -7),
+            FIntVector(17, 3, 1),
+            FIntVector(29, 27, 9),
+            FIntVector(3, 23, 17),
+            FIntVector(19, 19, 25),
+            FIntVector(11, 29, 31),
+            FIntVector(27, 5, -23),
+        };
+
+        const int32 MidChunkZ = TargetBottomChunkZ
+            + (TargetTopChunkZ - TargetBottomChunkZ) / 2;
+        const int32 BottomWorldZ = TargetBottomChunkZ * CHUNK_SIZE;
+        const int32 TopWorldZExclusive = (TargetTopChunkZ + 1) * CHUNK_SIZE;
+        const int32 MidWorldZ = MidChunkZ * CHUNK_SIZE + CHUNK_SIZE / 2;
+
+        OutMaxDelta = 0.0f;
+        OutMismatches = 0;
+        OutSamples = 0;
+        for (const FIntVector& Offset : Offsets)
+        {
+            const float X = (float)Offset.X;
+            const float Y = (float)Offset.Y;
+            const float Z = (float)FMath::Clamp(
+                MidWorldZ + Offset.Z, BottomWorldZ + 1, TopWorldZExclusive - 1);
+            const float Live = Generator.GetDensityAt(X, Y, Z);
+            const float Reference = ReferenceStack.EvalMC(X, Y, Z);
+
+            uint32 LiveBits = 0;
+            uint32 ReferenceBits = 0;
+            FMemory::Memcpy(&LiveBits, &Live, sizeof(LiveBits));
+            FMemory::Memcpy(&ReferenceBits, &Reference, sizeof(ReferenceBits));
+            const bool bBitEqual = LiveBits == ReferenceBits;
+            if (!bBitEqual)
+            {
+                ++OutMismatches;
+            }
+
+            const float Delta = (FMath::IsFinite(Live) && FMath::IsFinite(Reference))
+                ? FMath::Abs(Live - Reference) : FLT_MAX;
+            OutMaxDelta = FMath::Max(OutMaxDelta, Delta);
+            ++OutSamples;
+        }
+        return OutMismatches == 0;
+    }
+}
+#endif
+
 //=============================================================================
 // LIVE EDIT — regenerate all chunks when params change in the Details panel
 //=============================================================================
@@ -270,6 +497,210 @@ void AVoxelWorld::ValidateDeterminism()
 }
 
 #if WITH_EDITOR
+void AVoxelWorld::ApplyComposerCandidate()
+{
+    UWorld* World = GetWorld();
+    if (World == nullptr || !World->IsPlayInEditor())
+    {
+        UE_LOG(LogTemp, Warning,
+            TEXT("[VoxelWorld] ApplyComposerCandidate: run this button from a PIE world."));
+        return;
+    }
+    if (bShuttingDown.load(std::memory_order_acquire)
+        || bGenerationPaused.load(std::memory_order_acquire))
+    {
+        UE_LOG(LogTemp, Warning,
+            TEXT("[VoxelWorld] ApplyComposerCandidate: generation is already stopping or paused."));
+        return;
+    }
+    if (!Settings || !Generator || !StrateManager)
+    {
+        UE_LOG(LogTemp, Warning,
+            TEXT("[VoxelWorld] ApplyComposerCandidate: BeginPlay has not initialized Settings, Generator, and StrateManager."));
+        return;
+    }
+
+    const TArray<FStrateSlot>& Layout = StrateManager->GetLayout();
+    const FStrateSlot* TargetSlot = nullptr;
+    for (const FStrateSlot& Slot : Layout)
+    {
+        if (Slot.StrateIndex == ComposerTargetStrateIndex)
+        {
+            TargetSlot = &Slot;
+            break;
+        }
+    }
+    if (TargetSlot == nullptr || TargetSlot->Definition == nullptr)
+    {
+        UE_LOG(LogTemp, Warning,
+            TEXT("[VoxelWorld] ApplyComposerCandidate: ComposerTargetStrateIndex=%d is not a live layout slot (layout has %d slots)."),
+            ComposerTargetStrateIndex, Layout.Num());
+        return;
+    }
+
+    FVoxelStrateCorpus Corpus;
+    FString CorpusReport;
+    if (!Corpus.LoadFromAssetRegistry(CorpusReport))
+    {
+        UE_LOG(LogTemp, Error,
+            TEXT("[VoxelWorld] ApplyComposerCandidate: composer corpus is unavailable: %s"),
+            *CorpusReport);
+        return;
+    }
+
+    const FVoxelStrateComposerCandidate Candidate = VF_RollStrateCandidate(
+        Corpus, ComposerSeed, ComposerCandidateIndex, bComposerRollStructure);
+    if (!Candidate.bValid)
+    {
+        UE_LOG(LogTemp, Error,
+            TEXT("[VoxelWorld] ApplyComposerCandidate: seed=%d index=%d roll failed: %s"),
+            ComposerSeed, ComposerCandidateIndex, *Candidate.FailureReason);
+        return;
+    }
+
+    const int32 TargetTopChunkZ = TargetSlot->TopChunkZ;
+    const int32 TargetBottomChunkZ = TargetSlot->BottomChunkZ;
+    const float TargetTopWorldZ = (float)(TargetTopChunkZ + 1) * CHUNK_SIZE;
+    const float TargetBottomWorldZ = (float)TargetBottomChunkZ * CHUNK_SIZE;
+    const FIntVector RepresentativeChunk(
+        0, 0, TargetBottomChunkZ + (TargetTopChunkZ - TargetBottomChunkZ) / 2);
+
+    // Materialise before mutating the live manager. A bad recipe or unsupported native family
+    // therefore leaves the running world untouched.
+    FVoxelStrateArchetypeParams PreflightParams = Candidate.ArchetypeParams;
+    VF_SetComposerRuntimeBounds(PreflightParams, TargetTopWorldZ, TargetBottomWorldZ);
+    FVoxelOpStack PreflightStack;
+    FVoxelOpContext PreflightContext;
+    FString PreflightError;
+    bool bPreflightBuilt = false;
+    if (Candidate.bStructureRoll)
+    {
+        bPreflightBuilt = VF_BuildStackFromRecipe(
+            Candidate.Recipe, PreflightParams, Generator->Seed, Generator->OriginSpineRadius,
+            StrateManager, PreflightStack, PreflightContext, &PreflightError);
+    }
+    else
+    {
+        bPreflightBuilt = VF_BuildNativeStrateStackForCandidate(
+            Candidate.Archetype, PreflightParams, Generator->Seed, Generator->OriginSpineRadius,
+            Generator->WorldRadiusVoxels, Generator->EdgeSealThickness, StrateManager,
+            PreflightStack, PreflightContext);
+        if (!bPreflightBuilt)
+        {
+            PreflightError = TEXT("The production native candidate stack could not be materialised.");
+        }
+    }
+    if (!bPreflightBuilt)
+    {
+        UE_LOG(LogTemp, Error,
+            TEXT("[VoxelWorld] ApplyComposerCandidate: seed=%d index=%d was not applied: %s"),
+            ComposerSeed, ComposerCandidateIndex, *PreflightError);
+        return;
+    }
+
+    FString ApplyError;
+    {
+        // The manager override is a density-only replacement. It does not call Initialize or
+        // GeneratePassages while the layout is half-built: the existing slot Z span, content
+        // definition, and passage geometry remain stable. The pause drains current workers before
+        // the map is changed, and the subsequent RegenerateAllChunks supplies the epoch bump.
+        FScopedGenerationPause Guard(this);
+        if (!Guard.Acquired())
+        {
+            UE_LOG(LogTemp, Error,
+                TEXT("[VoxelWorld] ApplyComposerCandidate: generation pause timed out; no mutation applied."));
+            return;
+        }
+
+        if (!StrateManager->SetComposerOverrideForStrate(
+            ComposerTargetStrateIndex, Candidate.Seed, Candidate.Archetype,
+            Candidate.ArchetypeParams, Candidate.bStructureRoll,
+            Candidate.bStructureRoll ? &Candidate.Recipe : nullptr, ApplyError))
+        {
+            UE_LOG(LogTemp, Error,
+                TEXT("[VoxelWorld] ApplyComposerCandidate: seed=%d index=%d was not applied: %s"),
+                ComposerSeed, ComposerCandidateIndex, *ApplyError);
+            return;
+        }
+
+        // These are the same game-thread-owned side systems reset by RebuildStrates. The full
+        // chunk reset below also resets the density volume and preserves DiffLayer edits.
+        if (AtmosphereManager) { AtmosphereManager->Reset(); }
+        if (ContentManager)    { ContentManager->ClearAll(); }
+    }
+
+    // Reuse the established seed/live-edit invalidation path: GenerationEpoch increments here,
+    // stale ProcessQueue results are dropped, and the normal Tick submits a fresh stream around
+    // the player. No async worker can observe the half-applied manager state.
+    RegenerateAllChunks();
+
+    FVoxelOpStack ReferenceStack;
+    FVoxelOpContext ReferenceContext;
+    FString ReferenceError;
+    const bool bReferenceBuilt = VF_BuildComposerReferenceStack(
+        Candidate, *Generator, *StrateManager, TargetTopChunkZ, TargetBottomChunkZ,
+        ReferenceStack, ReferenceContext, ReferenceError);
+
+    FString ComparableReason;
+    const bool bReferenceComparable = bReferenceBuilt
+        && VF_ComposerReferenceIsComparable(
+            *this, *TargetSlot, Candidate.Archetype, RepresentativeChunk, ComparableReason);
+
+    const FVoxelStrateMeasureSettings MeasureSettings = VF_ComposerMeasureSettings();
+    FVoxelStrateMetrics Metrics;
+    FString MetricSource;
+    if (bReferenceComparable)
+    {
+        FComposerStackDensitySampler Sampler(ReferenceStack);
+        Metrics = VF_MeasureStrateWithSampler(
+            Sampler, (int32)TargetBottomWorldZ, (int32)TargetTopWorldZ,
+            VF_ComposerBoundarySeal(PreflightParams, Candidate.Archetype), MeasureSettings);
+        MetricSource = TEXT("candidate-stack");
+    }
+    else
+    {
+        // A live diff, disturbance post, or surface biome context makes a standalone stack an
+        // unlike oracle. Keep the owner's metric useful by measuring the actual applied generator;
+        // the log records why the bit-level oracle was skipped.
+        Metrics = VF_MeasureStrate(
+            *Generator, *StrateManager, ComposerTargetStrateIndex, MeasureSettings);
+        MetricSource = TEXT("live-generator");
+    }
+
+    float MaxDensityDelta = 0.0f;
+    int32 DensityMismatches = 0;
+    int32 DensitySamples = 0;
+    bool bDensityMatch = false;
+    if (bReferenceComparable)
+    {
+        bDensityMatch = VF_ComposerDensitySanityCheck(
+            *Generator, ReferenceStack, TargetTopChunkZ, TargetBottomChunkZ,
+            MaxDensityDelta, DensityMismatches, DensitySamples);
+    }
+
+    const FString RecipeText = Candidate.bStructureRoll
+        ? VF_FormatStrateStructureRecipe(Candidate.Recipe)
+        : TEXT("parameter-roll");
+    const FString DeterminismText = !bReferenceBuilt
+        ? FString::Printf(TEXT("UNAVAILABLE(%s)"), *ReferenceError)
+        : !bReferenceComparable
+            ? FString::Printf(TEXT("SKIPPED(%s)"), *ComparableReason)
+            : FString::Printf(TEXT("%s/%d"), bDensityMatch ? TEXT("PASS") : TEXT("FAIL"),
+                              DensitySamples);
+    const float AirFraction = Metrics.bValid ? Metrics.AirFraction : -1.0f;
+    const float LargestShare = Metrics.bValid ? Metrics.LargestComponentShare : -1.0f;
+    const float WalkableFraction = Metrics.bValid ? Metrics.WalkableFraction : -1.0f;
+    const float FeatureScale = Metrics.bValid ? Metrics.MedianFeatureScale : -1.0f;
+
+    UE_LOG(LogTemp, Log,
+        TEXT("[VoxelWorld] ComposerCandidate applied seed=%d index=%d target=%d recipe=%s archetype=%s metrics=%s air=%.6f largest=%.6f walkable=%.6f feature=%.3f components=%d determinism=%s max_delta=%.9g mismatches=%d epoch=%u"),
+        Candidate.Seed, Candidate.Index, ComposerTargetStrateIndex, *RecipeText,
+        VF_GetStrateArchetypeName(Candidate.Archetype), *MetricSource,
+        AirFraction, LargestShare, WalkableFraction, FeatureScale,
+        Metrics.bValid ? Metrics.NumAirComponents : -1,
+        *DeterminismText, MaxDensityDelta, DensityMismatches, GenerationEpoch);
+}
+
 void AVoxelWorld::PostEditChangeProperty(FPropertyChangedEvent& PropertyChangedEvent)
 {
     Super::PostEditChangeProperty(PropertyChangedEvent);

Source/VoxelForge/Public/VoxelStrateComposer.h

@@ -15,6 +15,7 @@
 
 class UVoxelSettings;
 class UVoxelStrateDefinition;
+class UVoxelStrateManager;
 
 /** The one-bit identity choice at the root of a rolled structure. */
 UENUM(BlueprintType)
@@ -211,6 +212,32 @@ struct VOXELFORGE_API FVoxelStrateRollInfo
     TArray<FString> BootstrapJitterFieldNames;
 };
 
+#if WITH_EDITOR
+/**
+ * One candidate materialised by the same deterministic calls used by the offline composer tests.
+ * This is an editor-only hand-off object: it is never a reflected asset and never part of the
+ * shipping generation contract.
+ */
+struct VOXELFORGE_API FVoxelStrateComposerCandidate
+{
+    bool bValid = false;
+    FString FailureReason;
+
+    int32 Seed = 0;
+    int32 Index = 0;
+    bool bStructureRoll = false;
+
+    ECaveGeneratorType Archetype = ECaveGeneratorType::TunnelNetwork;
+    FVoxelStrateArchetypeParams ArchetypeParams;
+    FVoxelOpStackRecipe Recipe;
+
+    // Kept so automation/editor callers can audit the exact six independent structure blocks
+    // without re-rolling them through a second implementation.
+    FVoxelStrateRollInfo ParameterRoll;
+    TArray<FVoxelStrateRollInfo> StructureBlockRolls;
+};
+#endif
+
 /**
  * Known-good strate vectors plus their measured field spread.
  *
@@ -293,6 +320,32 @@ VOXELFORGE_API FVoxelStrateRollInfo VF_RollStrateParamsDetailedForArchetype(
 /** Pure structure roll: no retained RNG state and no corpus/runtime dependency. */
 VOXELFORGE_API FVoxelOpStackRecipe VF_RollStrateStructure(int32 Seed, int32 Index);
 
+#if WITH_EDITOR
+/**
+ * Roll one candidate for the editor walk-through path. Parameter rolls call
+ * VF_RollStrateParamsDetailed; structure rolls call VF_RollStrateStructure and the exact six
+ * VF_RollStrateParamsDetailedForArchetype block rolls used by the structure test.
+ */
+VOXELFORGE_API FVoxelStrateComposerCandidate VF_RollStrateCandidate(
+    const FVoxelStrateCorpus& Corpus, int32 Seed, int32 Index, bool bRollStructure);
+
+/**
+ * Build a parameter-roll candidate through the same archetype-to-stack mapping used by production
+ * GetDensityAt/ClassifyTile. This is editor-only so the offline composer remains absent from a
+ * shipping build; the result is used only for the post-apply density sanity check.
+ */
+VOXELFORGE_API bool VF_BuildNativeStrateStackForCandidate(
+    ECaveGeneratorType Archetype,
+    const FVoxelStrateArchetypeParams& Params,
+    int32 Seed,
+    float SpineRadius,
+    float WorldRadiusVoxels,
+    float EdgeSealThickness,
+    const UVoxelStrateManager* StrateManager,
+    FVoxelOpStack& OutStack,
+    FVoxelOpContext& OutContext);
+#endif
+
 /** Stable compact representation and equality/hash helpers for manifests and reports. */
 VOXELFORGE_API FString VF_FormatStrateStructureRecipe(const FVoxelOpStackRecipe& Recipe);
 VOXELFORGE_API uint32 VF_HashStrateStructureRecipe(const FVoxelOpStackRecipe& Recipe);

Source/VoxelForge/Public/VoxelStrateManager.h

@@ -24,6 +24,12 @@
 
 class UVoxelSettings;
 
+#if WITH_EDITOR
+struct FVoxelStrateArchetypeParams;
+struct FVoxelOpStackRecipe;
+struct FVoxelStrateComposerSlotOverride;
+#endif
+
 /**
  * FVoxelPassage — A navigable connection between two strates.
  *
@@ -143,6 +149,27 @@ public:
      */
     void Initialize(UVoxelSettings* Settings, int32 WorldSeed);
 
+#if WITH_EDITOR
+    /**
+     * Install an editor-only candidate over one already-built slot. The slot's definition,
+     * dimensions, content, and passages remain intact; only the density archetype/parameters
+     * (or the materialised recipe) are replaced. The caller must hold the world's generation pause.
+     */
+    bool SetComposerOverrideForStrate(
+        int32 StrateIndex, int32 CandidateSeed, ECaveGeneratorType Archetype,
+        const FVoxelStrateArchetypeParams& Params, bool bUseRecipe,
+        const FVoxelOpStackRecipe* Recipe, FString& OutError);
+
+    /** Read the immutable editor override for a chunk into worker-local storage. */
+    bool GetComposerOverrideForChunk(
+        const FIntVector& ChunkCoord, int32& OutCandidateSeed,
+        ECaveGeneratorType& OutArchetype, FVoxelStrateArchetypeParams& OutParams,
+        bool& bOutUseRecipe, FVoxelOpStackRecipe& OutRecipe) const;
+
+    /** Custom recipes cannot be safely classified by the native ClassifyBox proof yet. */
+    bool HasComposerRecipeOverride() const;
+#endif
+
     //=========================================================================
     // QUERIES
     //=========================================================================
@@ -326,9 +353,9 @@ protected:
     // Passages connecting consecutive strates
     TArray<FVoxelPassage> Passages;
 
-    // Bumped every time Passages is rebuilt (GeneratePassages). EvaluateModifierSDF keeps a
-    // thread_local per-chunk shortlist of nearby passages and uses this to invalidate it when
-    // the passage set changes — so stale indices are never read after a rebuild.
+    // Bumped every time Passages is rebuilt (GeneratePassages), and for an editor composer
+    // override. EvaluateModifierSDF and all generator thread_local memos use this to invalidate
+    // cached passage/strate data after either kind of live change.
     uint32 PassagesVersion = 0;
 
     // How many chunks at strate boundaries are blended (transition zone)
@@ -360,6 +387,11 @@ protected:
     // Returns INDEX into StrateLayout, or -1 if not found.
     int32 FindSlotIndexForChunkZ(int32 ChunkZ) const;
 
+#if WITH_EDITOR
+    const FVoxelStrateComposerSlotOverride* FindComposerOverride(int32 StrateIndex) const;
+    TMap<int32, TSharedPtr<FVoxelStrateComposerSlotOverride>> ComposerOverrides;
+#endif
+
     // Build FStrateGenerationParams from a strate definition:
     // copies base GenerationParams, then applies all referenced terrain op assets.
     // This is the single point where terrain op data assets are merged into params.

Source/VoxelForge/Public/VoxelWorld.h

@@ -452,6 +452,30 @@ public:
     UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Live Edit")
     bool bLiveEditStrates = false;
 
+#if WITH_EDITORONLY_DATA
+    /** Seed passed to the deterministic offline composer roll. This does not change Settings->Seed. */
+    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Live Edit|Composer")
+    int32 ComposerSeed = 0;
+
+    /** Candidate row passed to VF_RollStrateCandidate (the offline tests use the same index). */
+    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Live Edit|Composer", meta = (ClampMin = "0"))
+    int32 ComposerCandidateIndex = 0;
+
+    /** Existing layout slot to replace; 0 is the topmost strate. */
+    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Live Edit|Composer", meta = (ClampMin = "0"))
+    int32 ComposerTargetStrateIndex = 0;
+
+    /** False rolls one native parameter vector; true rolls the structure recipe and its six blocks. */
+    UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Live Edit|Composer")
+    bool bComposerRollStructure = false;
+#endif
+
+#if WITH_EDITOR
+    /** Roll and apply the selected offline composer candidate to one live PIE slot. */
+    UFUNCTION(CallInEditor, Category = "Live Edit|Composer")
+    void ApplyComposerCandidate();
+#endif
+
     /** Click to force-regenerate all chunks right now (useful during PIE). */
     UFUNCTION(CallInEditor, BlueprintCallable, Category = "Live Edit")
     void RegenerateAllChunks();