Merge branch 'claude/angry-villani-8ae757' — Phase N.1 WorldBuilder rendering migration

Roadmap updates after Phase N.1 ship:
- Marks N.0 (submodule + project refs setup) as ✓ SHIPPED with the
  c8782c9 commit reference
- Updates N.2-N.9 effort estimates with realistic post-N.1 numbers
  (originals were 1-2 days / 1 week / 2 weeks; realistic numbers
  factor in conformance-test discovery, ACME-vs-Chorizite delta
  hunts, and the visual-verification-then-revert cycle that ate
  most of N.1's calendar time)
- Adds a "Lessons from N.1" subsection so future N phases benefit
  from the rotation-bug-conformance-test pattern, the ACME divergence
  insight, and the "whackamole = stop" rule
- Updates total calendar estimate to 3-4 months / 10-12 engineering
  weeks for N.2-N.9 (was 2-3 months / 6-8 weeks)

New handoff doc at docs/research/2026-05-08-phase-n3-handoff.md
captures everything a fresh agent picking up N.3 (texture decoding)
needs: phase context, what to read first, suggested task decomposition,
watchouts (especially the ACME-divergence and conformance-test
lessons), and where to start.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -18,7 +18,11 @@ packages/
 Thumbs.db
 
 # Reference repos and retail client (large, not our code, separate licenses)
-references/
+# WorldBuilder is exempt — it's a load-bearing dependency tracked as a git
+# submodule pointing at our fork (Phase N, see docs/architecture/worldbuilder-inventory.md).
+references/*
+!references/WorldBuilder
+!references/WorldBuilder/
 
 # Claude Code session state
 .claude/

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "references/WorldBuilder"]
+	path = references/WorldBuilder
+	url = git@github.com:eriknihlen/WorldBuilder.git
+	branch = acdream

CLAUDE.md

@@ -25,6 +25,19 @@ single source of truth for how the client is structured. All work must
 align with this document. When the architecture doc and reality diverge,
 update one or the other — never leave them out of sync.
 
+**WorldBuilder is acdream's rendering + dat-handling base** as of
+2026-05-08. Before re-implementing any AC-specific rendering or
+dat-handling algorithm, **read `docs/architecture/worldbuilder-inventory.md`
+FIRST**. If WorldBuilder has it, port from WorldBuilder (or call into
+our fork once wired up), not from retail decomp. WorldBuilder is
+MIT-licensed, verified to render the world correctly, and uses the same
+Silk.NET stack we target. Re-porting from retail decomp when WB already
+has a tested port is how subtle bugs (the scenery edge-vertex bug, the
+triangle-Z bug) keep slipping in. Retail decomp remains the oracle for
+network, physics, animation, movement, UI, plugin, audio, chat — see
+the inventory doc's 🔴 list for the full scope of "we still write this
+ourselves".
+
 **Execution phases:** R1→R8 in the architecture doc. Each phase has clear
 goals, test criteria, and builds on the previous. Don't skip phases.
 
@@ -625,11 +638,18 @@ these, ideally all four:
   for the palette-indexed formats. See
   `ACViewer/Render/TextureCache.cs::IndexToColor` for the canonical
   subpalette overlay algorithm.
-- **`references/WorldBuilder/`** — C# + Silk.NET dat editor. Exact-stack
-  match to acdream for rendering approaches: terrain blending, texture
-  atlases, shader patterns. Most useful for "how do I do this GL thing
-  with Silk.NET on net10 idiomatically?" Less useful for protocol or
-  character appearance (dat editor, not game client).
+- **`references/WorldBuilder/`** — **acdream's rendering + dat-handling
+  BASE (not just a reference).** As of 2026-05-08 acdream is moving to
+  fork WorldBuilder upstream and depend on the fork for terrain,
+  scenery, static objects, EnvCells, portals, sky, particles, texture
+  decoding, mesh extraction, visibility/culling. WorldBuilder is
+  MIT-licensed, exact-stack match (Silk.NET + .NET), and verified to
+  render the world correctly. **Before re-porting any rendering or
+  dat-handling algorithm from retail decomp, check
+  `docs/architecture/worldbuilder-inventory.md` first.** If WB has it,
+  use WB's port. If WB doesn't have it (network, physics, animation,
+  movement, UI, plugin, audio, chat), port from retail decomp as
+  before.
 - **`references/Chorizite.ACProtocol/`** — clean-room C# protocol
   library generated from a protocol XML description. Useful sanity check
   on field order, packed-dword conventions, type-prefix handling. The
@@ -684,12 +704,15 @@ decompiled client code and would have fixed it in minutes.
 
 | Domain | Primary Oracle | Secondary | Notes |
 |--------|---------------|-----------|-------|
-| **Any AC-specific algorithm** | **`docs/research/named-retail/`** (PDB-named decomp + verbatim retail header structs from Sept 2013 EoR build) | the existing references below | The retail client itself, fully named. 18,366 functions + 5,371 struct types + 1.4 M lines of pseudo-C in one searchable tree. Beats every other reference for "what does the real client do." |
-| **Terrain** (split direction, height sampling, palCode, vertex position, normals) | **ACME `ClientReference.cs`** — decompiled retail client with exact offsets | ACME `TerrainGeometryGenerator.cs` (matches the mesh index buffer) | WorldBuilder original is SUPERSEDED for terrain algorithms. AC2D confirms the same formula. |
-| **Terrain blending** (texture atlas, alpha masks, road overlays) | **ACME `LandSurfaceManager.cs`** | WorldBuilder original `LandSurfaceManager.cs` (same code, less tested) | Both use the same TexMerge pipeline. ACME has conformance tests. |
-| **GfxObj / Setup rendering** (mesh extraction, multi-part assembly, ObjDesc) | **ACME `StaticObjectManager.cs`** — includes CreaturePalette, GfxObjRemapping, HiddenParts | ACViewer `Render/` namespace | ACME has the complete creature appearance pipeline in one file. |
-| **Texture decoding** (INDEX16, P8, DXT, BGRA, alpha) | **ACME `TextureHelpers.cs`** | ACViewer `Render/TextureCache.cs` (palette overlay = `IndexToColor`) | For subpalette overlay specifically, ACViewer's `IndexToColor` is the canonical algorithm. |
-| **EnvCell / dungeon rendering** (cell geometry, portal visibility, collision mesh) | **ACME `EnvCellManager.cs`** — portal traversal, mixed landblock detection, collision cache | ACViewer `Physics/Common/EnvCell.cs` | ACME is significantly more complete than original WorldBuilder for dungeons. |
+| **Any AC-specific algorithm** | **`docs/research/named-retail/`** (PDB-named decomp + verbatim retail header structs from Sept 2013 EoR build) | the existing references below | The retail client itself, fully named. 18,366 functions + 5,371 struct types + 1.4 M lines of pseudo-C in one searchable tree. Beats every other reference for "what does the real client do." Use for everything in the 🔴 list (network, physics, animation, movement, UI, plugin, audio, chat). |
+| **Terrain** (split direction, height sampling, palCode, vertex position, normals) | **WorldBuilder `TerrainGeometryGenerator.cs` + `TerrainUtils.cs`** | retail decomp for cross-check | WB is acdream's terrain base. ACME's port is older/SUPERSEDED by WB. |
+| **Terrain blending** (texture atlas, alpha masks, road overlays) | **WorldBuilder `LandSurfaceManager.cs`** | ACME `LandSurfaceManager.cs` (same algo, less complete) | WB is acdream's blending base. |
+| **Scenery** (procedural placement: trees, bushes, rocks, fences) | **WorldBuilder `SceneryRenderManager.cs` + `SceneryHelpers.cs`** | retail decomp `CLandBlock::get_land_scenes` | WB is acdream's scenery base. Re-porting from retail decomp is what caused the edge-vertex bug. |
+| **GfxObj / Setup rendering** (mesh extraction, multi-part assembly, ObjDesc) | **WorldBuilder `StaticObjectRenderManager.cs` + `ObjectMeshManager.cs`** | ACME `StaticObjectManager.cs` (includes CreaturePalette, GfxObjRemapping, HiddenParts — useful for character appearance which WB doesn't cover) | WB for static objects, ACME for character appearance. |
+| **Texture decoding** (INDEX16, P8, DXT, BGRA, alpha) | **WorldBuilder `TextureHelpers.cs`** | ACME `TextureHelpers.cs`; ACViewer's `IndexToColor` is canonical for subpalette overlay | WB is acdream's decode base. |
+| **EnvCell / dungeon rendering** (cell geometry, portal visibility, collision mesh) | **WorldBuilder `EnvCellRenderManager.cs` + `PortalRenderManager.cs`** | ACME `EnvCellManager.cs` (more complete for collision); ACViewer `Physics/Common/EnvCell.cs` | WB is acdream's geometry base; ACME for collision until ported. |
+| **Particles / sky** (particle systems, weather, sky particles) | **WorldBuilder `SkyboxRenderManager.cs` + `ParticleEmitterRenderer.cs` + `ParticleBatcher.cs`** | retail decomp | WB is acdream's particle base. |
+| **Visibility / culling** (frustum, cell visibility) | **WorldBuilder `VisibilityManager.cs` + `Frustum.cs`** | — | WB. |
 | **Network protocol** (wire format, packet framing, fragment assembly, ISAAC) | **holtburger** `crates/holtburger-session/` | AC2D `cNetwork.cpp` (simpler, good for cross-check) | ACE shows the server side; holtburger + AC2D show the client side. |
 | **Client behavior** (what to send when, login flow, ack pattern, keepalive) | **holtburger** `crates/holtburger-core/src/client/` | AC2D `cNetwork.cpp` + `cInterface.cpp` | holtburger is the most complete; AC2D is simpler but confirmed working. |
 | **Movement** (MoveToState format, AutonomousPosition, sequence counters, speed) | **holtburger** `client/movement/` | AC2D `cNetwork.cpp:2592-2664` (0xF61C format) | See `docs/research/2026-04-12-movement-deep-dive.md` for the full cross-reference. |

docs/ISSUES.md

@@ -46,6 +46,50 @@ Copy this block when adding a new issue:
 
 # Active issues
 
+## #50 — Road-edge tree at 0xA9B1 visible in acdream but not retail
+
+**Status:** OPEN
+**Severity:** LOW (cosmetic; one spawned tree near the road in Holtburg)
+**Filed:** 2026-05-08
+**Component:** scenery placement / Phase N (WorldBuilder rendering migration)
+
+**Description:** With `ACDREAM_USE_WB_SCENERY=1` (default since commit `b84ecbd`),
+a tree at landblock 0xA9B1 around `(lx=85.08, ly=190.97)` appears in acdream but
+neither retail nor ACME WorldBuilder render it. Upstream Chorizite/WorldBuilder
+DOES render it, so our migration to WB's helpers (Phase N.1) inherited this
+discrepancy from upstream.
+
+**Root cause (suspected):** ACME WorldBuilder includes a per-vertex road check that
+skips the entire vertex when its road bit is set (see
+`references/WorldBuilder-ACME-Edition/WorldBuilder/Editors/Landscape/GameScene.cs:1074`).
+The current vertex (4,8) has a road bit set in the dat. ACME skips it;
+Chorizite/WorldBuilder doesn't; we don't.
+
+**Fix attempt that didn't work:** commit `e279c46` added the per-vertex road check
+directly to our `GenerateViaWb` (and legacy `Generate` for parity). It successfully
+removed the offending tree but over-suppressed scenery in other landblocks (visual
+regressions during user testing). Reverted in commit `677a726`. ACME's check likely
+interacts with other factors (per-vertex building check, or something else in ACME's
+pipeline) that we'd need to port together, not the road check alone.
+
+**Next steps:**
+1. Investigate ACME's full per-vertex filter set (road + building + anything else)
+   and port them as a coherent unit, not piecemeal.
+2. OR upstream the per-vertex road check to Chorizite/WorldBuilder (which is now our
+   submodule fork) so it lands as a generic ACME-conformance improvement.
+3. OR consider switching fork target from Chorizite/WorldBuilder to ACME WorldBuilder
+   for future phases (N.2+).
+
+Visually undetectable to most users; one extra tree at one landblock. Defer until
+other Phase N work catches a similar issue and a coherent fix becomes obvious.
+
+**Files:**
+- `src/AcDream.Core/World/SceneryGenerator.cs` — `GenerateInternal` is the active path
+- `src/AcDream.Core/World/WbSceneryAdapter.cs` — adapter used by `GenerateInternal`
+- `references/WorldBuilder-ACME-Edition/WorldBuilder/Editors/Landscape/GameScene.cs:1074` — ACME's per-vertex road filter
+
+---
+
 ## #49 — Scenery (X, Y) placement drifts from retail at some landblocks
 
 **Status:** OPEN

docs/architecture/worldbuilder-inventory.md

@@ -0,0 +1,250 @@
+# WorldBuilder Inventory — what we take, adapt, or leave
+
+**Status:** load-bearing reference. As of 2026-05-08 acdream's strategy is
+to **rely heavily on WorldBuilder** for rendering and dat-handling rather
+than re-port retail algorithms ourselves. WorldBuilder is MIT-licensed, is
+verified by visual inspection to render the AC world correctly (terrain,
+scenery, slabs, dungeons, slopes, particles), and uses the same Silk.NET
++ .NET stack we already target.
+
+**Integration model:** **fork upstream WorldBuilder** at
+`github.com/Chorizite/WorldBuilder`, depend on our fork, delete editor-only
+code, expose hooks for our network state to feed scene data in. Sync with
+upstream via merge so we inherit fixes. This document tells you, before
+you write code, whether the thing you're about to port already exists in
+WorldBuilder.
+
+**Workflow change:** Before re-implementing any AC-specific rendering or
+dat-handling algorithm, **check this inventory first**. If WorldBuilder
+has it, port from WorldBuilder (or call into our fork once it's wired
+up), not from retail decomp. Retail decomp remains the oracle for things
+WorldBuilder lacks — animation, motion, physics collision, networking.
+
+---
+
+## Repo layout (as of cloned snapshot under `references/WorldBuilder/`)
+
+- **`Chorizite.OpenGLSDLBackend/`** — full OpenGL renderer (Silk.NET).
+- **`WorldBuilder.Shared/`** — data models, dat parsers, landscape module.
+- **`WorldBuilder/`** — Avalonia desktop app shell (NOT taken).
+- **`WorldBuilder.{Windows,Linux,Mac}/`** — platform entry points (NOT taken).
+- **`WorldBuilder.Server/`** — collab editing backend (NOT taken).
+- **`Tests/` + `WorldBuilder.Shared.Benchmarks/`** — test harness (study).
+
+**Upstream NuGet dependencies** (these stay as NuGet packages, we don't
+vendor them):
+
+| Package | Version | Purpose |
+|---|---|---|
+| `Chorizite.Core` | 0.0.18 | Plugin framework — contains `Chorizite.Core.Lib.BoundingBox`, `Chorizite.Core.Render.*` interfaces used by every render manager |
+| `Chorizite.DatReaderWriter` | 2.1.x | dat parsing (we already use 2.1.7) |
+| `Chorizite.DatReaderWriter.Extensions` | 1.1.x | extra dat helpers |
+| `BCnEncoder.Net` | 2.2.x | DXT decode (we already use) |
+| `SixLabors.ImageSharp` | 3.1.x | image loading |
+| `Silk.NET.OpenGL` + `Silk.NET.SDL` | 2.23.x | GL + windowing (we use Silk's own windowing, they use SDL) |
+| `MP3Sharp` | 1.0.5 | MP3 decode |
+
+---
+
+## 🟢 RENDERING — take wholesale or adapt
+
+These are what makes WB "perfect". Anything in this section, we should
+use from WB rather than re-implement.
+
+### Terrain
+
+| Component | What it does |
+|---|---|
+| `TerrainRenderManager` | Full pipeline (per-chunk GPU buffers, draw orchestration) |
+| `LandSurfaceManager` | Texture blending atlas (palCode, alpha masks, road overlays) |
+| `TerrainGeometryGenerator` | Heightmap → mesh, normals, OnRoad, GetHeight, GetNormal |
+| `TerrainChunk` | 16×16 landblock chunk geometry |
+| `TextureAtlasManager` | Texture atlas builder |
+| `VertexLandscape` | Terrain vertex format |
+
+### Scenery (procedural placement: trees, bushes, rocks, fences)
+
+| Component | What it does |
+|---|---|
+| `SceneryRenderManager` | Generate + render per-vertex scenery |
+| `SceneryHelpers` | Displace / RotateObj / ScaleObj / ObjAlign / CheckSlope |
+| `SceneryInstance` | Per-spawn instance data |
+
+### Static objects (buildings, slabs, props — Setup + GfxObj + ObjDesc)
+
+| Component | What it does |
+|---|---|
+| `StaticObjectRenderManager` | Master pipeline for static objects |
+| `ObjectRenderManagerBase` + `BaseObjectRenderManager` | Common render base |
+| `ObjectMeshManager` | Mesh extraction from Setup/GfxObj, ObjDesc application |
+
+### Dungeons / interiors
+
+| Component | What it does |
+|---|---|
+| `EnvCellRenderManager` | Dungeon interior cell geometry |
+| `PortalRenderManager` | Portal traversal / visibility |
+
+### Sky + atmosphere
+
+| Component | What it does |
+|---|---|
+| `SkyboxRenderManager` | Skybox rendering |
+| `ParticleEmitterRenderer` + `ParticleBatcher` + `ActiveParticleEmitter` | Particle systems (sky particles, weather, magic) |
+
+### Visibility / culling
+
+| Component | What it does |
+|---|---|
+| `VisibilityManager` + `VisibilitySnapshot` | Frustum + cell visibility |
+| `Frustum` | Frustum-cull math |
+
+### Other rendering helpers
+
+| Component | What it does |
+|---|---|
+| `MinimapRenderer` | Top-down minimap |
+| `GlobalMeshBuffer` | Shared GPU mesh buffer |
+| `GpuResourceManager` | GPU resource lifecycle |
+| `InstanceData` | Instanced draw data |
+| `TextureHelpers` | INDEX16, P8, BGRA, DXT decode + alpha (canonical port) |
+| `DebugRenderer` + `DebugRendererLineDrawer` + `EdgeLineBuilder` | Debug primitives |
+
+### Shaders (22 total)
+
+Located at `Chorizite.OpenGLSDLBackend/Shaders/`:
+
+`Landscape.{vert,frag}` · `StaticObject.{vert,frag}` · `StaticObjectModern.{vert,frag}` · `Particle.{vert,frag}` · `PortalStencil.{vert,frag}` · `Outline.{vert,frag}` · `Simple3D.{vert,frag}` · `InstancedLine.{vert,frag}` · `Text.{vert,frag}` · `UI.{vert,frag}` · `Gizmo.{vert,frag}` (editor-only)
+
+---
+
+## 🟢 LOW-LEVEL GL / FRAMEWORK — take or replace with our own
+
+Either take WB's wrappers wholesale, or keep our own and adapt the
+render managers to use ours. These wrappers are stateless or
+near-stateless and are the easiest to swap.
+
+| Component | What it does |
+|---|---|
+| `OpenGLGraphicsDevice` | Silk.NET.OpenGL wrapper |
+| `OpenGLRenderer` | Render orchestration |
+| `GLSLShader` | Shader compile/link/uniforms |
+| `GLHelpers` + `GLStateScope` | GL state utility |
+| `ManagedGLFrameBuffer` / `ManagedGLIndexBuffer` / `ManagedGLTexture` / `ManagedGLTextureArray` / `ManagedGLUniformBuffer` / `ManagedGLVertexArray` / `ManagedGLVertexBuffer` | GL resource wrappers |
+| `TextureParameters` | Sampler config |
+| `GpuMemoryTracker` | Memory tracking |
+| `Camera2D` / `Camera3D` / `CameraBase` / `ICamera` / `CameraController` | Camera primitives |
+| `GameScene` + `SingleObjectScene` + `SceneData` + `ModernRenderData` + `RenderPass` | Scene / pass structures |
+
+---
+
+## 🟢 GEOMETRY / MATH UTILS — take wholesale
+
+| Component | File |
+|---|---|
+| `TerrainUtils` (OnRoad, GetNormal, GetHeight, GetRoad, palCode) | `WorldBuilder.Shared/Modules/Landscape/Lib/TerrainUtils.cs` |
+| `TerrainCacheManager` | `…/Lib/TerrainCacheManager.cs` |
+| `TerrainRaycast` | `…/Lib/TerrainRaycast.cs` |
+| `GeometryUtils` | `WorldBuilder.Shared/Lib/GeometryUtils.cs` |
+| `RaycastingUtils` (ray-vs-sphere/AABB/triangle) | `WorldBuilder.Shared/Lib/RaycastingUtils.cs` |
+| `DoubleNumerics` (double-precision Vector/Matrix) | `WorldBuilder.Shared/Lib/DoubleNumerics.cs` |
+| `DatUtils` | `WorldBuilder.Shared/Lib/DatUtils.cs` |
+| `BoundingBoxExtensions` | `Chorizite.OpenGLSDLBackend/Lib/BoundingBoxExtensions.cs` |
+
+---
+
+## 🟢 DATA MODELS — take selectively
+
+| Component | What it does |
+|---|---|
+| `RegionInfo` | Landblock metadata wrapper (LandblockSizeInUnits, CellSizeInUnits, etc.) |
+| `TerrainEntry` | Per-vertex terrain (Type/Scenery/Road/Height) |
+| `MergedLandblock` | Merged dat data |
+| `CellSplitDirection` | SW-NE vs NE-SW |
+| `Cell` | Generic cell wrapper |
+| `ObjectId` | Object identifier |
+| `Position` | World position |
+| `ACEnums` | AC-specific enums |
+| `WbBuildingPortal` / `WbCellPortal` | Portal structures |
+| `BuildingObject` | Building data |
+
+---
+
+## 🟡 EDITOR-ONLY — leave behind / delete in fork
+
+These exist for the editor experience and have no place in a game
+client. Delete in fork.
+
+- **`Modules/Landscape/Tools/*`** — `BrushTool`, `BucketFillTool`,
+  `RoadLineTool`, `RoadVertexTool`, `InspectorTool`,
+  `ObjectManipulationTool`, `Gizmo*` (DragHandler, HitTester, Renderer,
+  State), `TexturePainting*`, `SceneRaycaster`,
+  `LandscapeBrush`, `LandscapeToolBase`, `LandscapeToolContext`,
+  `IToolSettingsProvider`, `ILandscapeBrush`, `ILandscapeEditorService`,
+  `ILandscapeRaycastService`, `ILandscapeTool`, `ITexturePaintingTool`
+- **`Modules/Landscape/Commands/*`** — undo/redo command pattern for
+  editor (Add/Delete/Move/Rename/Reorder/etc.)
+- **`LandscapeDocument` + `LandscapeLayer` + `LandscapeLayerGroup` + `LandscapeChunk` + `LandscapeLayerChunk` + `LandscapeLayerBase`** — editor document model
+- **`Modules/Landscape/Models/TerrainPatch*` + `LandblockChangedEventArgs`** — editor mutation events
+- **`Modules/Landscape/Services/ILandscapeCacheService` + `ILandscapeDataProvider` + `ILandscapeObjectService` + impls** — editor data flow
+- **All `Migrations/*`** — SQLite schema migrations (project file format)
+- **`Repositories/*`** + **`Services/*`** — project storage, dat repository, AceDb, SignalR sync, document manager, undo stack, world coordinates, keyword DB, project migration, semantic kernel AI helpers
+- **`Hubs/*`** — collaborative editing via SignalR
+- **`StaticObject` (editor model)** — replace with our own scene-state data model fed from network
+- **`BackendGizmoDrawer` + `GizmoRenderer`** — editor gizmos
+- **`ProjectStructures, IProject, Project`** — editor project files
+- **`KeyBinding`** — editor input binding
+- **`ViewportInputEvent[Extensions]`** — editor viewport input
+- **`EditorState`** — editor state container
+
+---
+
+## 🟡 AUDIO / FONT — we already have alternatives
+
+Keep ours; don't take theirs.
+
+- **`AudioPlaybackEngine`** — uses MP3Sharp. We have OpenAL.
+- **`FontRenderer`** — uses ImageSharp. We have BitmapFont/StbTrueTypeSharp + ImGui.
+
+---
+
+## 🔴 NOT IN WORLDBUILDER — port from retail decomp ourselves
+
+WorldBuilder is a dat editor; it does not have:
+
+- **Network protocol** — UDP framing, ISAAC, packet codec, ACE message
+  layer (we have this; oracle is `references/holtburger`)
+- **Physics** — collision (CPhysicsObj transitions, BSP queries, sphere
+  sweeps), step-up, walkable validation (we have partial; oracle is the
+  retail decomp at `docs/research/named-retail/`)
+- **Animation** — motion sequencer, cycle/non-cycle parts, animation
+  frame interpolation (we have this; oracle is retail decomp)
+- **Movement** — local player WASD → MoveToState wire, remote-entity
+  motion via UpdateMotion + dead-reckoning (we have this; oracle is
+  `references/holtburger` + retail decomp)
+- **Game UI** — chat, vitals, inventory, spell book, allegiance, options
+  (we have this; ImGui-based today, custom-toolkit later)
+- **Plugin API** — `IGameState`, `IEvents`, `IActions`, `IPacketPipeline`,
+  `IOverlay` (we have this — acdream-unique)
+- **Game events** — combat, allegiance, spell casting, quest events
+  (we have this; oracle is ACE for opcodes + retail for client behavior)
+- **Audio** — OpenAL pipeline, sound triggers (we have this)
+- **TurbineChat** + **slash commands** (we have this)
+- **Login + character selection flow** (we have this)
+
+---
+
+## What this means for the workflow
+
+The CLAUDE.md "grep named → decompile → verify → port" workflow stays
+the rule for everything in the 🔴 list (network, physics, animation,
+movement, UI, plugin, audio, chat). For anything in 🟢, the new rule is:
+**check this inventory FIRST**. If WB has it, port from WB. Re-porting
+from retail decomp when WB already has a tested port is no longer
+appropriate — that's how we got the scenery edge-vertex bug.
+
+When the inventory says "take wholesale or adapt" and we discover a
+behavior mismatch with retail (rare — WB is verified), the resolution
+is: reconcile WB ↔ retail decomp ↔ holtburger ↔ ACE ↔ ACViewer (the
+existing reference hierarchy in CLAUDE.md). WorldBuilder ranks at the
+top of that hierarchy for anything 🟢.

docs/plans/2026-04-11-roadmap.md

@@ -57,6 +57,7 @@
 | K | Input architecture — `Action` enum, `KeyChord`, `KeyBindings`, multicast `InputDispatcher` with scope-stack + modal capture, retail-default keymap (152 bindings), `keybinds.json` persistence, F11 Settings panel with click-to-rebind + conflict detection, main menu bar + View menu | Live ✓ |
 | L.0 | Full retail-style Settings interface — F11 tabbed panel with 6 tabs (Keybinds + Display + Audio + Gameplay + Chat + Character). `settings.json` at `%LOCALAPPDATA%\acdream\`, per-toon `Character` keying (swapped on EnterWorld). Display GL knobs (Resolution / Fullscreen / VSync / FOV / ShowFps) + Audio (Master / SFX) live-wired; Gameplay / Chat / Character settings persist for server-sync wiring later. Tab API extension to `IPanelRenderer`; chat Copy mode (read-only multi-line); per-panel layout reset; FramebufferResize handler keeps GL viewport + camera aspect + panel positions in sync. | Live ✓ |
 | C.1 | PES particle system + sky-pass refinements — retail-faithful `ParticleEmitterInfo` unpack with all 13 motion integrators (`Particle::Init`/`Update` ports of `0x0051c290`/`0x0051c930`), `PhysicsScriptRunner` with `CallPES` self-loop semantics, `ParticleHookSink` with `EmitterDied` cleanup, instanced billboard `ParticleRenderer` with material-derived blend (DAT emitters never default additive — pulled from particle GfxObj surface), global back-to-front sort, BC clipmap alpha-keying, AttachLocal `is_parent_local=1` live-parent follow via `UpdateEmitterAnchor`. Sky pass: `Translucent+ClipMap` → alpha-blend cloud sheet (matches `D3DPolyRender::SetSurface` `0x0059c4d0`), raw-`Additive` fog-skip (matches `0x0059c882`), per-keyframe `SkyObjectReplace` Translucency/Luminosity/MaxBright divide-by-100, bit `0x01` pre/post-scene split (matches `GameSky::CreateDeletePhysicsObjects` `0x005073c0`), Setup-backed (`0x020xxxxx`) sky objects via `SetupMesh.Flatten`, persistent GL sampler objects (Wrap + ClampToEdge) replace per-frame wrap-mode mutation (ported from WorldBuilder's `OpenGLGraphicsDevice`), post-scene Z-offset gated on `(Properties & 4) != 0 && (Properties & 8) == 0` per `GameSky::UpdatePosition` `0x00506dd0`. Sky-PES playback disabled by default (named-retail proves `GameSky` drops `pes_id`); `ACDREAM_ENABLE_SKY_PES=1` opens the experimental path. 1325 → 1331 tests. | Live ✓ |
+| N.1 | WorldBuilder-backed scenery (Chorizite/WorldBuilder fork as submodule, SceneryHelpers + TerrainUtils replace our inline ports) | Live ✓ |
 
 Plus polish that doesn't get its own phase number:
 - FlyCamera default speed lowered + Shift-to-boost
@@ -498,6 +499,146 @@ before porting.
 
 ---
 
+### Phase N — WorldBuilder Rendering Migration
+
+**Goal:** Stop re-porting AC-specific rendering / dat-handling
+algorithms. Depend on a fork of `Chorizite/WorldBuilder` (MIT) for
+terrain, scenery, static objects, EnvCells, portals, sky, particles,
+texture decoding, mesh extraction, and visibility. Acdream keeps its
+own network, physics, animation, motion, UI, plugin, audio, chat
+layers (those aren't in WB).
+
+**Why now (2026-05-08):** the scenery edge-vertex bug at landblock
+`0xA9B1` was the third subtle porting bug in a quarter (after the
+triangle-Z bug and the hover-over-terrain bug). Even when our code
+looked byte-identical to WB's, our output diverged. WB renders the
+world correctly; the cost of "we re-port retail algorithms" is now
+higher than "we depend on WB's tested port."
+
+**Design + inventory:**
+
+- `docs/architecture/worldbuilder-inventory.md` — full taxonomy of
+  what WB has and what we keep porting ourselves.
+- `docs/superpowers/specs/2026-05-08-phase-n-worldbuilder-migration-design.md` —
+  parent design doc.
+- `docs/superpowers/specs/2026-05-08-phase-n1-scenery-via-wb-helpers-design.md` —
+  N.1 detailed design.
+
+**Integration model:** fork at
+`https://github.com/eriknihlen/WorldBuilder` (already created), git
+submodule replacing `references/WorldBuilder/` snapshot, project
+references in our solution. Long-lived `acdream` branch in the fork
+for our deletions/additions; merge upstream `master` periodically.
+
+**Lessons from N.1 (apply to N.2-N.10):**
+
+1. **Per-helper conformance tests work.** The N.1 conformance test caught a
+   ~180° rotation bug in our retail port that had been silently wrong
+   forever. Write the conformance test BEFORE the substitution in each
+   sub-phase.
+
+2. **ACME ≠ Chorizite/WorldBuilder.** ACME is a downstream fork of WB with
+   additional retail-faithful filters that upstream WB (our submodule)
+   doesn't have. When a visual discrepancy appears, check ACME's source
+   (`references/WorldBuilder-ACME-Edition/`) for delta filters BEFORE
+   investigating retail decomp directly. ACME's deltas tend to come as
+   coherent units — porting one filter without its companions can
+   over-suppress.
+
+3. **"Whackamole" is the warning sign.** If a phase generates 3+ visual
+   regressions on default-on, stop, accept the cosmetic deltas as
+   ISSUES.md entries, ship the migration. Bugs we leave behind are
+   debuggable; bugs we never ship are forgotten.
+
+4. **Subagent-driven execution holds up at this scope.** Fresh subagent
+   per task with the full task text inline keeps quality high without
+   polluting the controller's context. Each task should be self-contained
+   enough that a subagent without session history can complete it.
+
+**Sub-phases (strangler-fig with feature flags):**
+
+- **✓ SHIPPED — N.0 — Setup.** Shipped 2026-05-08 (commit `c8782c9`).
+  WorldBuilder fork at `github.com/eriknihlen/WorldBuilder.git` registered
+  as git submodule at `references/WorldBuilder/` tracking the `acdream`
+  branch. `AcDream.Core.csproj` references `WorldBuilder.Shared` +
+  `Chorizite.OpenGLSDLBackend`. Build green, all 28 scenery/terrain tests
+  passing.
+- **✓ SHIPPED — N.1 — Scenery algorithm calls.** Shipped 2026-05-08.
+  Replaced `IsOnRoad` / `DisplaceObject` / slope-normal calc / rotation /
+  scale inside `SceneryGenerator.Generate()` with calls to WB's
+  `SceneryHelpers` + `TerrainUtils`. Adapter `WbSceneryAdapter` produces
+  `TerrainEntry[]`. Visual verification at Holtburg confirmed Issue #49's
+  previously missing edge-vertex trees still visible after the migration;
+  rotation bug fixed (our retail port's `yawDeg = -(450-degrees)%360`
+  formula was ~180° off from retail's actual `Frame::set_heading` atan2
+  round-trip). One known cosmetic difference filed in ISSUES.md
+  (road-edge tree at landblock 0xA9B1).
+- **N.2 — Terrain math helpers.** Refactor `TerrainSurface.SampleZ` /
+  `SampleNormal` / `SampleSurface` to call WB's `TerrainUtils.GetHeight`
+  / `GetNormal` internally. ~1-2 days. Smallest remaining N phase, low
+  risk after N.1's conformance proof on GetNormal.
+- **N.3 — Texture decoding.** Replace our `TextureCache` decode
+  pipeline (`src/AcDream.App/Rendering/TextureCache.cs`) with WB's
+  `TextureHelpers` (INDEX16, P8, BGRA, DXT, alpha). Touches every
+  texture path. **Realistic estimate: 3-5 days** (was 2-3) — the GL
+  upload path needs adapting and we'll need conformance tests per
+  texture format. Handoff doc:
+  `docs/research/2026-05-08-phase-n3-handoff.md`.
+- **N.4 — Object meshing.** Replace `SetupMesh.cs` + `GfxObjMesh.cs`
+  with calls to WB's `ObjectMeshManager`. Character-appearance
+  behaviors (CreaturePalette / GfxObjRemapping / HiddenParts) remain
+  ours — ACME is the secondary oracle. **Realistic estimate: 1.5-2
+  weeks** (was 1) — character appearance edge cases like N.1's
+  rotation bug will surface.
+- **N.5 — Terrain rendering.** Replace `TerrainChunkRenderer` +
+  `TerrainAtlas` + `TerrainBlending` with WB's `TerrainRenderManager` +
+  `LandSurfaceManager` + `TerrainGeometryGenerator`. **Realistic
+  estimate: 3-4 weeks** (was 2) — largest single phase, GPU-buffer
+  ownership shifts, integration with our streaming loader is
+  non-trivial.
+- **N.6 — Static objects rendering.** Replace `StaticMeshRenderer` +
+  `InstancedMeshRenderer` with WB's `StaticObjectRenderManager`.
+  **Realistic estimate: 2-3 weeks** (was 2) — interacts with N.4
+  output.
+- **N.7 — EnvCells / dungeons.** Replace EnvCell rendering with WB's
+  `EnvCellRenderManager` + `PortalRenderManager`. **Realistic
+  estimate: 2-3 weeks** (was 2).
+- **N.8 — Sky + particles.** Replace sky rendering + particle pipeline
+  (#36 / C.1 work) with WB's `SkyboxRenderManager` +
+  `ParticleEmitterRenderer`. **Realistic estimate: 1.5-2 weeks**
+  (was 1) — visual continuity matters; we just shipped C.1 and that
+  work flows through here.
+- **N.9 — Visibility / culling.** Replace `CellVisibility` +
+  `FrustumCuller` with WB's `VisibilityManager`. **Realistic
+  estimate: 1 week** (was 3-5 days) — affects perf and what gets
+  drawn.
+- **N.10 — GL infrastructure consolidation (optional).** Replace our
+  `Shader` / `TextureCache` / `SamplerCache` plumbing with WB's
+  `ManagedGL*` wrappers + `OpenGLGraphicsDevice`. ~1 week.
+
+**Estimated calendar:** **3-4 months / 10-12 engineering weeks for
+N.2-N.9 (skipping N.10).** (Was 2-3 months / 6-8 weeks — revised
+upward after N.1 landed; realistic per-phase numbers above.)
+
+**Each sub-phase:**
+- Ships behind `ACDREAM_USE_WB_<NAME>=1` flag.
+- Has its own conformance test (side-by-side against existing path).
+- Visual verification before flag becomes default-on.
+- Old code deleted after default-on lands cleanly.
+
+**N.2-N.10 detailed specs are NOT yet written** — each gets its own
+brainstorm + spec when we reach it.
+
+**Acceptance:**
+- All 10 sub-phases shipped, feature flags removed, old rendering code
+  paths deleted.
+- Visual verification at Holtburg + Foundry statue + a representative
+  dungeon shows no regression vs Phase C.1.
+- WB upstream merges into our `acdream` branch are clean (or have
+  documented conflict-resolution patterns).
+
+---
+
 ### Phase J — Long-tail (deferred / low-priority)
 
 Not detailed here; each gets its own brainstorm when it becomes relevant.

docs/research/2026-05-08-phase-n3-handoff.md

@@ -0,0 +1,132 @@
+# Phase N.3 handoff — texture decoding via WorldBuilder
+
+**Use this whole document as the prompt** when handing off to a fresh
+agent. Everything they need to pick up cold is below.
+
+---
+
+## Background you'll need
+
+You're working in `acdream`, a from-scratch C# .NET 10 reimplementation
+of Asheron's Call's retail client. The project's house rule (in
+`CLAUDE.md`) is **the code is modern, the behavior is retail**.
+
+acdream just shipped **Phase N.1** (commits `26cf2b8` through `ad8b931`),
+the first sub-phase of a strategic migration to fork WorldBuilder
+(`github.com/Chorizite/WorldBuilder`, MIT) and depend on its tested
+rendering + dat-handling code instead of porting algorithms from retail
+decomp ourselves.
+
+**Read first:**
+- `docs/architecture/worldbuilder-inventory.md` — the full taxonomy of
+  what WB has and what we keep porting ourselves
+- `docs/superpowers/specs/2026-05-08-phase-n-worldbuilder-migration-design.md`
+  — the parent design doc for Phase N
+- `CLAUDE.md` — especially the "Reference repos" section (now points at
+  WB as the rendering BASE) and the workflow rules
+
+**Phase N.1 commit history (just shipped):** read
+`git log --oneline c8782c9..ad8b931` to see how N.0 + N.1 were
+structured. The pattern repeats for N.3.
+
+## What N.3 is
+
+Replace acdream's texture decoding pipeline with WorldBuilder's
+`Chorizite.OpenGLSDLBackend.Lib.TextureHelpers`. WB handles INDEX16,
+P8, BGRA, DXT, and alpha-channel decoding. Our existing implementations
+of these are scattered across `src/AcDream.App/Rendering/TextureCache.cs`
+and possibly `src/AcDream.Core/Meshing/` — find them with
+`grep -rln "INDEX16\|P8 decode\|DXT\|BGRA" src/`.
+
+## Acceptance criteria
+
+- Build green (`dotnet build`)
+- All existing tests green (the 8 pre-existing `DispatcherToMovementIntegrationTests`
+  failures don't count — they exist on main)
+- New conformance tests added per format that's substituted (one xUnit
+  Theory per: INDEX16, P8, BGRA, DXT). Each compares a fixed input byte
+  array decoded by our path vs WB's path; assertions on output pixel array.
+- Visual verification at Holtburg (or wherever) shows no texture
+  regressions: terrain texturing, mesh texturing, particle textures all
+  look the same.
+- ISSUES.md updated with any known cosmetic deltas (the N.1 pattern —
+  if WB and retail disagree on something subtle, file it, don't try
+  to fix it inline).
+
+## Tasks (suggested decomposition)
+
+Follow the N.1 plan structure (`docs/superpowers/plans/2026-05-08-phase-n1-scenery-via-wb-helpers.md`)
+as the template. Concretely:
+
+1. **Audit our texture decode paths.** Grep, list every file/method that
+   decodes a texture. Map each to the WB equivalent in
+   `references/WorldBuilder/Chorizite.OpenGLSDLBackend/Lib/TextureHelpers.cs`
+   (read it end to end first).
+2. **Per-format conformance test.** TDD style: write the test, run it
+   to fail, then plumb the substitution. Conformance test fixture inputs
+   should include real-dat byte sequences (read a known-good texture from
+   a dat, encode the bytes as a hex blob in the test).
+3. **Substitution.** Replace each decode site with the WB call. Keep our
+   GL upload pathways — those are NOT WB's responsibility.
+4. **Visual verification.** Launch the client at Holtburg, walk around,
+   look at a tree (mesh texture), the ground (atlas texture), particles
+   (the recent C.1 rain/clouds/aurora work), and a building (composite
+   texture). Compare against retail or against a screenshot before the
+   change.
+5. **Delete legacy decoders** once visual verification passes.
+6. **Update roadmap + ISSUES** as the final commit.
+
+## Watchouts (lessons from N.1)
+
+- **ACME has a downstream fork with extra filters** (`references/WorldBuilder-ACME-Edition/`).
+  WB's `TextureHelpers` may have ACME-specific patches not yet in upstream.
+  Compare both before assuming WB's version is canonical. We forked
+  upstream WB; ACME is reference-only.
+- **Conformance tests are non-negotiable.** Phase N.1's rotation bug was
+  caught by the conformance test. Don't skip them. If a test fails, it's
+  a real divergence — investigate before "fixing" the test.
+- **Whackamole stops the migration.** If 3+ visual regressions appear on
+  default-on, stop, file as ISSUES, ship. The migration goal is "use WB's
+  tested code"; pixel-perfect equivalence with our broken hand-ports is
+  not the goal.
+- **`Setup.SortingSphere` ≠ `Setup.CylSphere`.** The N.1 attempt at
+  `obj_within_block` over-suppressed because we used the wrong radius
+  source (sorting sphere too large). For texture decoding this likely
+  doesn't matter, but the general lesson is: read WB's full source
+  carefully before adapting; don't assume parallel methods do parallel
+  things.
+- **Per-vertex road check — STOP signal.** If you find yourself reading
+  ACME for "what's missing" and considering a per-vertex filter, STOP.
+  N.1 tried this (commit `e279c46`), regressed visually, reverted in
+  `677a726`. ACME's filter set works as a coherent unit; pick-and-choose
+  fails. If the N.3 work uncovers a similar ACME-only filter, file it
+  in ISSUES and move on, don't port it inline.
+
+## Where to start
+
+1. `git pull` on main to get the latest (Phase N.1 just merged).
+2. Create a new worktree for the work:
+   `git worktree add .claude/worktrees/<your-name> -b claude/<your-name>`.
+3. Read the three "read first" docs above.
+4. Run `dotnet build && dotnet test` to confirm clean baseline.
+5. Read `references/WorldBuilder/Chorizite.OpenGLSDLBackend/Lib/TextureHelpers.cs`
+   end to end. Take notes on the public API surface.
+6. Run the audit task (#1 in Tasks above). Output should be a markdown
+   table of "our function / file:line / WB equivalent / format covered."
+7. Use `superpowers:writing-plans` to convert the audit into a concrete
+   per-format plan. Then use `superpowers:subagent-driven-development`
+   to execute it with fresh subagents per format.
+
+## Useful greps
+
+- `grep -rln "INDEX16\|IndexedSurface\|P8\|DXT\|BGRA\|TextureFormat" src/` — find decode paths
+- `grep -rln "TextureCache" src/` — find our cache layer
+- `grep -n "public static.*Decode\|public static.*Convert" references/WorldBuilder/Chorizite.OpenGLSDLBackend/Lib/TextureHelpers.cs` — WB's public API
+
+## Open question to resolve early
+
+Does `Chorizite.OpenGLSDLBackend.Lib.TextureHelpers` cover ALL the
+formats we use, or does it have gaps? Audit our texture types against
+WB's API in step 1. If WB is missing a format we need, the migration for
+that format gets deferred (file in ISSUES; keep our decoder for it; note
+in the roadmap).

docs/superpowers/specs/2026-05-08-phase-n-worldbuilder-migration-design.md

@@ -0,0 +1,223 @@
+# Phase N — WorldBuilder Rendering Migration: Design
+
+**Date:** 2026-05-08
+**Status:** Design complete, awaiting plan generation for N.1.
+
+## Goal
+
+Stop re-porting AC-specific rendering and dat-handling algorithms from
+retail decomp. Instead, depend on a fork of WorldBuilder
+(`github.com/Chorizite/WorldBuilder`, MIT) for terrain, scenery, static
+objects, EnvCells, portals, sky, particles, texture decoding, mesh
+extraction, and visibility / culling. Acdream keeps its own network,
+physics, animation, motion, UI, plugin, audio, and chat layers — those
+are not in WorldBuilder.
+
+## Why
+
+acdream has accumulated a recurring pattern of subtle porting bugs in
+its own rendering algorithms (the latest: a tree near the road at
+landblock `0xA9B1` that retail and WorldBuilder do not show but our
+re-port did, despite the algorithm code looking byte-identical to
+WorldBuilder's). The triangle-Z bug, the hover-over-terrain bug, and
+the edge-vertex spawn bug are all in the same family: small porting
+errors that survive surface-level review.
+
+WorldBuilder is verified by visual inspection to render the AC world
+correctly. It uses the same Silk.NET + .NET stack we already target.
+It is MIT-licensed. It has fewer subtle bugs because its developers
+have run it against the entire client_cell + client_portal dat content
+and fixed everything users have reported.
+
+The cost of "we re-port retail algorithms ourselves" is now higher than
+the cost of "we depend on someone else's tested port and inherit their
+fixes." Migrating the rendering+dat layer to WorldBuilder is the
+right call.
+
+## Inventory reference
+
+The full taxonomy of "what WorldBuilder has, what we keep porting
+ourselves" lives at
+[`docs/architecture/worldbuilder-inventory.md`](../../architecture/worldbuilder-inventory.md).
+Before re-implementing any rendering or dat-handling algorithm, **check
+the inventory first**. CLAUDE.md is updated to enforce this.
+
+## Architecture
+
+### Integration model
+
+**Fork upstream WorldBuilder, depend on the fork via git submodule.**
+
+- Fork: `https://github.com/eriknihlen/WorldBuilder` (already created;
+  upstream: `Chorizite/WorldBuilder`).
+- Long-lived branch in fork: `acdream`. Upstream `master` merges into
+  `acdream` periodically; our acdream-specific changes (delete editor
+  files, expose hooks for our scene state) live on `acdream`.
+- The current read-only snapshot at `references/WorldBuilder/` is
+  **replaced** by a git submodule pointing at the fork's `acdream`
+  branch. Existing CLAUDE.md path references and research docs that
+  cite `references/WorldBuilder/...` keep working.
+- Our solution adds two `<ProjectReference>`s:
+  - `references/WorldBuilder/Chorizite.OpenGLSDLBackend/Chorizite.OpenGLSDLBackend.csproj`
+  - `references/WorldBuilder/WorldBuilder.Shared/WorldBuilder.Shared.csproj`
+- Transitive NuGet dependencies (`Chorizite.Core`,
+  `Chorizite.DatReaderWriter.Extensions`, `BCnEncoder.Net`,
+  `SixLabors.ImageSharp`, `Silk.NET.SDL`, `MP3Sharp`) flow through.
+- Editor-only files in WorldBuilder (Modules/Landscape/{Tools,
+  Commands, Services, Migrations, Hubs}, LandscapeDocument, etc.) stay
+  in the fork's source tree but are simply not referenced by acdream.
+  They impose no runtime cost. We can prune later if upstream stays
+  well-organized.
+
+### Phasing — strangler fig, subsystem by subsystem
+
+Each sub-phase is independently shippable behind a feature flag
+(`ACDREAM_USE_WB_<NAME>=1`). After visual verification the flag becomes
+default-on, then is removed and the old code is deleted. This gives us
+a one-line revert if a phase regresses.
+
+| # | Sub-phase | Effort | Risk |
+|---|---|---|---|
+| **N.0** | Submodule + project references + build green | 1-2 hrs | Low |
+| **N.1** | Scenery algorithm calls | 1-2 days | Low |
+| **N.2** | Terrain math helpers | 1-2 days | Low |
+| **N.3** | Texture decoding | 2-3 days | Medium |
+| **N.4** | Object meshing (Setup/GfxObj) | 1 week | Medium |
+| **N.5** | Terrain rendering (full pipeline) | 2 weeks | High |
+| **N.6** | Static objects rendering | 2 weeks | High |
+| **N.7** | EnvCells / dungeons | 2 weeks | High |
+| **N.8** | Sky + particles | 1 week | Medium |
+| **N.9** | Visibility / culling | 3-5 days | Medium |
+| **N.10** | GL infrastructure consolidation (optional) | 1 week | Medium |
+
+Total estimated calendar: 2-3 months. Engineering effort: 6-8 weeks.
+
+### What WorldBuilder does NOT cover (keep porting from retail decomp)
+
+- Network protocol (UDP, ISAAC, ACE messages) — keep ours
+- Physics: collision, BSP queries, sphere sweeps, walkable validation
+  — keep ours (partial), continue porting from retail decomp
+- Animation: motion sequencer, cycle/non-cycle parts — keep ours
+- Movement: WASD → MoveToState wire, remote-entity motion via
+  UpdateMotion + dead-reckoning — keep ours
+- Game UI: chat, vitals, inventory, spell book — keep ours (ImGui
+  today, custom-toolkit later)
+- Plugin API: IGameState, IEvents, IActions, IPacketPipeline,
+  IOverlay — keep ours (acdream-unique)
+- Game events: combat, allegiance, spell casting — keep ours
+- Audio (OpenAL pipeline) — keep ours
+- TurbineChat + slash commands — keep ours
+- Login + character selection flow — keep ours
+
+Per CLAUDE.md update, these still follow the
+"grep named → decompile → verify → port" workflow against retail decomp
+at `docs/research/named-retail/`.
+
+### Network reference posture
+
+`references/Chorizite.ACProtocol/` (separate Chorizite repo) remains
+the Primary Oracle for protocol field order and packed-dword
+conventions per CLAUDE.md's reference table. No fork needed there. We
+will lean on it harder during future network-conformance phases (Phase
+M is already on the roadmap for that).
+
+## Components
+
+### N.0 — Setup (must land before N.1)
+
+**Files / actions:**
+- Remove `references/WorldBuilder/` from working tree (it's currently a
+  checked-in snapshot). Add it back as a submodule pointing at
+  `git@github.com:eriknihlen/WorldBuilder.git` tracking the `acdream`
+  branch (created off `master`).
+- Add `<ProjectReference>` entries in
+  `src/AcDream.Core/AcDream.Core.csproj` and
+  `src/AcDream.App/AcDream.App.csproj` for the two WB projects.
+- Update `.gitmodules` to reflect the new submodule.
+- Verify `dotnet build` and `dotnet test` are green.
+- Commit.
+
+**Done criteria:**
+- `git submodule status` shows `references/WorldBuilder` at the fork's
+  `acdream` HEAD.
+- Solution builds clean with no new warnings.
+- Existing 870+ tests still pass.
+
+### N.1 — Scenery algorithm calls
+
+See companion design doc:
+[`2026-05-08-phase-n1-scenery-via-wb-helpers-design.md`](2026-05-08-phase-n1-scenery-via-wb-helpers-design.md).
+
+Brief: replace the algorithm guts inside `SceneryGenerator.Generate()`
+with calls to WB's `SceneryHelpers` (Displace, RotateObj, ScaleObj,
+ObjAlign, CheckSlope) and `TerrainUtils` (OnRoad, GetNormal). Keep our
+data flow, our `ScenerySpawn` shape, our renderer integration. Add a
+small adapter `LandBlock → TerrainEntry[]`.
+
+### N.2-N.10 — separately brainstormed when we get there
+
+Each sub-phase will get its own brainstorm + spec when we reach it.
+Estimating ahead is unreliable for the bigger phases (N.5, N.6, N.7);
+we'll know more after N.1 ships and we have hands-on experience with
+the WB integration.
+
+## Risks
+
+1. **Chorizite.Core dependency footprint.** Each render manager we
+   take pulls in `Chorizite.Core.Lib` and `Chorizite.Core.Render`.
+   Mitigation: take the NuGet dep, don't try to strip it. Risk is
+   mostly cosmetic (an extra package).
+
+2. **WB's data-flow is editor-shaped.** `LandscapeDocument`,
+   `LandscapeChunk`, etc. are editor concepts. Mitigation: write small
+   adapters that produce the editor-shaped data from our dat reads.
+   Phase N.1 is intentionally chosen to avoid this — we use only the
+   stateless helpers, not the full `SceneryRenderManager`. Larger
+   phases (N.5+) will need real adapter layers.
+
+3. **Upstream divergence.** WB's `master` will keep moving. Mitigation:
+   merge upstream `master` into our `acdream` branch periodically (at
+   minimum, before each new phase starts). Our acdream-specific
+   changes are isolated to deletions and additions on the `acdream`
+   branch, which merges cleanly with upstream most of the time.
+
+4. **Behaviors WB doesn't have.** WB is a dat editor; some
+   in-game-only behaviors (creature appearance via CreaturePalette /
+   GfxObjRemapping / HiddenParts) aren't in WB and we'll still need to
+   handle them ourselves at the integration boundary. Mitigation:
+   ACME's `StaticObjectManager.cs` covers these and is documented in
+   CLAUDE.md as the secondary oracle for character appearance.
+
+5. **Visual regression during migration.** Mitigation: feature flag
+   per phase. Visual verification at known-good locations (Holtburg,
+   Foundry statue, dungeon entrances) before flag becomes default-on.
+
+## Testing
+
+- **N.0:** existing 870+ tests stay green; `dotnet build` clean.
+- **N.1:** new conformance test that runs both our `SceneryGenerator`
+  and a parallel call into WB's helpers against the same fixture data,
+  asserts identical spawn list. Visual verification at landblock
+  `0xA9B1` — the offending tree should be gone, Issue #49's missing
+  scenery should still be visible.
+- **N.2-N.10:** each phase will define its own conformance and visual
+  verification criteria when brainstormed.
+
+## Documentation impact
+
+- [x] `docs/architecture/worldbuilder-inventory.md` — created.
+- [x] `CLAUDE.md` — updated with new posture (top-level rule + reference
+  table + per-domain oracle hierarchy).
+- [ ] `docs/plans/2026-04-11-roadmap.md` — add Phase N entry alongside
+  L, M, etc. (this happens in the same commit as the spec).
+- [ ] `docs/architecture/acdream-architecture.md` — needs an
+  acknowledging note that the rendering layer is now WB-backed; can
+  follow in a later commit, not blocking.
+
+## Out of scope for this design
+
+- Phase N.2-N.10 detailed scope (each gets own brainstorm).
+- Network conformance work (separate Phase M).
+- Animation, physics, motion ports (continue against retail decomp,
+  not WB).
+- UI, plugin, chat work (separate phases, not affected).

docs/superpowers/specs/2026-05-08-phase-n1-scenery-via-wb-helpers-design.md

@@ -0,0 +1,191 @@
+# Phase N.1 — Scenery via WorldBuilder Helpers: Design
+
+**Date:** 2026-05-08
+**Parent design:** [`2026-05-08-phase-n-worldbuilder-migration-design.md`](2026-05-08-phase-n-worldbuilder-migration-design.md)
+**Status:** Design complete, awaiting plan generation.
+
+## Goal
+
+Replace the algorithm guts of `SceneryGenerator.Generate()` with calls
+to WorldBuilder's stateless `SceneryHelpers` and `TerrainUtils`. Keep
+our data flow, our `ScenerySpawn` shape, and our renderer integration
+unchanged.
+
+## Why scenery first
+
+1. **Active bug source.** Issues #48, #49 are scenery-related; the
+   investigation in this session uncovered another (the road-edge tree
+   at `0xA9B1`) we couldn't easily root-cause despite our code looking
+   identical to WB's.
+2. **Smallest coherent slice.** Scenery placement uses only stateless
+   helpers from WB (Displace, OnRoad, GetNormal, CheckSlope, RotateObj,
+   ScaleObj). No need to take WB's `SceneryRenderManager`, no need for
+   editor-shaped data flow.
+3. **Proves the integration pattern.** Phase N.0 wires up the
+   submodule + project references. N.1 uses them with a tiny surface
+   area. If something is wrong with the dependency model, we discover
+   it cheaply.
+
+## Architecture
+
+### What changes
+
+`src/AcDream.Core/World/SceneryGenerator.cs`:
+- Remove our private `IsOnRoad(LandBlock, float, float)` helper.
+- Remove our private `DisplaceObject(ObjectDesc, uint, uint, uint)` helper.
+- Remove the `RoadHalfWidth` constant.
+- Replace inline algorithm calls with WB equivalents (see table below).
+
+New file `src/AcDream.Core/World/WbSceneryAdapter.cs` (or similar
+location — TBD during implementation):
+- Helper `BuildTerrainEntries(LandBlock block) → TerrainEntry[]`
+  converting our `DatReaderWriter.DBObjs.LandBlock` (the dat type) into
+  the `TerrainEntry[]` shape WB's `TerrainUtils` expects (9×9 grid,
+  Type/Scenery/Road/Height fields per vertex).
+- Helper for `RegionInfo` if needed (small wrapper over our
+  `Region` dat).
+
+### Algorithm-call substitution table
+
+| Today (ours) | Phase N.1 (WB) |
+|---|---|
+| `IsRoadVertex(raw)` (kept; small util) | unchanged — small predicate, no benefit to swap |
+| `IsOnRoad(block, lx, ly)` | `TerrainUtils.OnRoad(new Vector3(lx, ly, 0), terrainEntries)` |
+| `DisplaceObject(obj, gx, gy, j)` | `SceneryHelpers.Displace(obj, gx, gy, j)` |
+| Slope normal: `TerrainSurface.SampleNormalZFromHeightmap(...)` | `TerrainUtils.GetNormal(region, terrainEntries, lbX, lbY, lbOffset).Z` |
+| Slope check: `nz < obj.MinSlope \|\| nz > obj.MaxSlope` | `SceneryHelpers.CheckSlope(obj, normal.Z)` (returns bool) |
+| Rotation logic (`AFrame::set_heading` reproduction) | `SceneryHelpers.RotateObj(obj, gx, gy, j, localPos)` (returns Quaternion) |
+| Scale logic (LCG + Pow + clamp) | `SceneryHelpers.ScaleObj(obj, gx, gy, j)` (returns float) |
+
+### What does NOT change
+
+- The 9×9 vertex loop (`for (x = 0; x < 9; x++) for (y = 0; y < 9; y++)`).
+- Scene selection hash.
+- Frequency roll.
+- `obj.WeenieObj != 0` skip (weenie entries are dynamic spawns).
+- Bounds check `lx, ly ∈ [0, 192)`.
+- Per-spawn building check using our `buildingCells` HashSet.
+- `BaseLoc.Z` offset application.
+- `ScenerySpawn` record shape returned to the renderer.
+- `Generate()` method signature — same parameters, same return type.
+
+### What about `obj_within_block`?
+
+We attempted this during the bug investigation but it's too aggressive
+when applied with the model's actual sorting sphere radius (rejects
+trees that should be there). WB also doesn't apply it. The retail
+behavior we couldn't reproduce stays unreproduced for now — we accept
+that as a known minor cosmetic discrepancy and move on. The point of
+N.1 is matching WB's behavior, not retail's. If WB and retail
+disagree, that's a WB-upstream problem to file separately.
+
+## Components
+
+### Files modified
+
+- `src/AcDream.Core/World/SceneryGenerator.cs` — algorithm-call swap.
+- `src/AcDream.Core/AcDream.Core.csproj` — already has WB project ref
+  from N.0.
+
+### Files added
+
+- `src/AcDream.Core/World/WbSceneryAdapter.cs` — `LandBlock →
+  TerrainEntry[]` and any other small adapters needed.
+- `tests/AcDream.Core.Tests/World/SceneryGeneratorWbConformanceTests.cs`
+  — side-by-side test asserting our generator's output equals what
+  comes out when the same algorithms are called via WB directly.
+
+### Files deleted (eventually, after flag is on by default)
+
+- The deleted helpers in `SceneryGenerator.cs` mentioned above.
+
+### Feature flag
+
+Phase 1 of the rollout: `ACDREAM_USE_WB_SCENERY=1` (default off — old
+path runs). When the env var is set, the new WB-backed path runs.
+
+Phase 2 (after visual verification at Holtburg / `0xA9B1`): flag
+default-on. Old path can still be reached via
+`ACDREAM_USE_WB_SCENERY=0`.
+
+Phase 3 (one or two sessions later, after no regressions): delete the
+flag and the old code paths entirely.
+
+## Done criteria
+
+1. `dotnet build` green with no new warnings.
+2. All existing tests pass (870+).
+3. New conformance test passes: `SceneryGeneratorWbConformanceTests`
+   runs both code paths against fixture LandBlock data and asserts
+   identical spawn lists (same ObjectId, same LocalPosition within
+   1e-4, same Rotation within 1e-4, same Scale within 1e-4).
+4. Visual verification at landblock `0xA9B1` (Holtburg area):
+   - The offending tree near the road that retail/WB do not show is
+     **gone** in our render.
+   - Issue #49's previously missing scenery (the tree from the 9×9
+     loop expansion) is **still visible**.
+   - No new visual regressions in surrounding landblocks during a
+     brief flight around Holtburg.
+5. Issue #49 stays closed; no new issues filed.
+
+## Risks (Phase-N.1-specific)
+
+1. **`TerrainEntry` field semantics.** WB packs Type/Scenery/Road/
+   Height into the `TerrainEntry` struct in a specific format. Getting
+   the adapter wrong means OnRoad / scenery selection produces
+   different results than ours. Mitigation: read
+   `WorldBuilder.Shared/Modules/Landscape/Models/TerrainEntry.cs`
+   carefully; cross-check against WB's `TerrainUtils.GetRoad` /
+   `GetTerrainEntryForCell` to confirm field encoding.
+2. **`RegionInfo` dependencies.** WB's `TerrainUtils.GetNormal` takes
+   a `RegionInfo` parameter. We need to either build a minimal
+   `RegionInfo` from our `Region` dat or call WB's normal calc
+   differently. Mitigation: investigate during implementation; expect
+   this is a small wrapper.
+3. **`obj.MaxScale / obj.MinScale` divide-by-zero.** Our code checks
+   `if (obj.MinScale == obj.MaxScale)` first; WB's `ScaleObj` does the
+   same per-line review of `references/WorldBuilder/Chorizite.OpenGLSDLBackend/Lib/SceneryHelpers.cs:42-51`. Should be a non-issue.
+4. **Rotation quaternion convention.** Our rotation produces
+   `headingQuat * baseLoc.Orientation`. WB's `RotateObj` calls
+   `SetHeading` which does its own composition. Need to confirm the
+   resulting quaternion is the same convention our renderer expects.
+   Mitigation: the conformance test catches this if it's wrong.
+
+## Testing
+
+### Conformance test (new)
+
+`SceneryGeneratorWbConformanceTests`:
+- Construct a synthetic `LandBlock` with known terrain data.
+- Run `SceneryGenerator.Generate(...)` with `ACDREAM_USE_WB_SCENERY=0`
+  and again with `=1`.
+- Assert spawn counts equal.
+- Assert each spawn's ObjectId, LocalPosition (within 1e-4), Rotation
+  (within 1e-4 per component), Scale (within 1e-4) are equal.
+
+### Existing tests
+
+`SceneryGeneratorTests` covers: road-vertex predicate, edge-vertex
+displacement bounds, interior-vertex displacement bounds. These tests
+exercise our internal helpers (`IsRoadVertex`, `DisplaceObject`).
+After N.1, the `DisplaceObject` test must be either deleted (if we
+delete the helper) or replaced (if we keep `IsRoadVertex` as a small
+predicate — it's only one bit-test).
+
+### Visual verification
+
+User runs the client against ACE locally:
+- Navigate to landblock `0xA9B1` (Holtburg). Verify offending tree
+  near road is gone.
+- Confirm Issue #49's tree is still visible.
+- Fly around Holtburg, scan visible scenery for any obvious
+  regression.
+
+## Out of scope for N.1
+
+- Replacing our `SceneryRenderManager` (we don't have one — we have
+  `SceneryGenerator` producing `ScenerySpawn[]` and the renderer
+  consuming it directly). N.1 only touches the generator.
+- Replacing our terrain math helpers (that's N.2).
+- Replacing the static-object renderer (that's N.6).
+- Anything in N.2-N.10.

references/WorldBuilder

@@ -0,0 +1 @@
+Subproject commit 167788be6fce65f5ebe79eef07a0b7d28bd7aa81

src/AcDream.Core/AcDream.Core.csproj

@@ -18,5 +18,13 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\AcDream.Plugin.Abstractions\AcDream.Plugin.Abstractions.csproj" />
+    <!-- Phase N: WorldBuilder is acdream's rendering + dat-handling base.
+         See docs/architecture/worldbuilder-inventory.md for the inventory of
+         what we use from WB vs port from retail decomp ourselves.
+         WorldBuilder.Shared = stateless helpers (TerrainUtils, TerrainEntry, RegionInfo).
+         Chorizite.OpenGLSDLBackend = render managers + SceneryHelpers + ParticleEmitterRenderer
+         (full GL pipeline; we currently use only the stateless SceneryHelpers from it). -->
+    <ProjectReference Include="..\..\references\WorldBuilder\WorldBuilder.Shared\WorldBuilder.Shared.csproj" />
+    <ProjectReference Include="..\..\references\WorldBuilder\Chorizite.OpenGLSDLBackend\Chorizite.OpenGLSDLBackend.csproj" />
   </ItemGroup>
 </Project>

src/AcDream.Core/Physics/TerrainSurface.cs

@@ -198,6 +198,73 @@ public sealed class TerrainSurface
         return InterpolateZInTriangle(hBL, hBR, hTR, hTL, tx, ty, splitSWtoNE);
     }
 
+    /// <summary>
+    /// Sample the terrain triangle's surface-normal Z component at (localX, localY)
+    /// from a raw heightmap. Returns the upward component of the unit normal for
+    /// the specific triangle the point lies in — flat ground returns 1.0, steeper
+    /// slopes return smaller values. Used by <see cref="SceneryGenerator"/> for
+    /// the retail slope filter (<c>CLandCell::find_terrain_poly → polygon.plane.N.z</c>).
+    /// </summary>
+    public static float SampleNormalZFromHeightmap(
+        byte[] heights, float[] heightTable,
+        uint landblockX, uint landblockY,
+        float localX, float localY)
+    {
+        ArgumentNullException.ThrowIfNull(heights);
+        ArgumentNullException.ThrowIfNull(heightTable);
+        if (heights.Length < 81)
+            throw new ArgumentException("heights must have 81 entries", nameof(heights));
+        if (heightTable.Length < 256)
+            throw new ArgumentException("heightTable must have 256 entries", nameof(heightTable));
+
+        float fx = Math.Clamp(localX / CellSize, 0f, CellsPerSide - 0.001f);
+        float fy = Math.Clamp(localY / CellSize, 0f, CellsPerSide - 0.001f);
+        int cx = (int)fx;
+        int cy = (int)fy;
+        cx = Math.Clamp(cx, 0, CellsPerSide - 1);
+        cy = Math.Clamp(cy, 0, CellsPerSide - 1);
+
+        float tx = fx - cx;
+        float ty = fy - cy;
+
+        float hBL = heightTable[heights[cx     * HeightmapSide + cy    ]];
+        float hBR = heightTable[heights[(cx+1) * HeightmapSide + cy    ]];
+        float hTR = heightTable[heights[(cx+1) * HeightmapSide + (cy+1)]];
+        float hTL = heightTable[heights[cx     * HeightmapSide + (cy+1)]];
+
+        bool splitSWtoNE = IsSplitSWtoNE(landblockX, (uint)cx, landblockY, (uint)cy);
+
+        float dzdx, dzdy;
+        if (splitSWtoNE)
+        {
+            if (tx > ty)
+            {
+                dzdx = (hBR - hBL) / CellSize;
+                dzdy = (hTR - hBR) / CellSize;
+            }
+            else
+            {
+                dzdx = (hTR - hTL) / CellSize;
+                dzdy = (hTL - hBL) / CellSize;
+            }
+        }
+        else
+        {
+            if (tx + ty <= 1f)
+            {
+                dzdx = (hBR - hBL) / CellSize;
+                dzdy = (hTL - hBL) / CellSize;
+            }
+            else
+            {
+                dzdx = (hTR - hTL) / CellSize;
+                dzdy = (hTR - hBR) / CellSize;
+            }
+        }
+
+        return 1f / MathF.Sqrt(dzdx * dzdx + dzdy * dzdy + 1f);
+    }
+
     /// <summary>
     /// Pick the cell's triangle for the chosen diagonal and barycentric-
     /// interpolate Z. Single source of truth shared by both

src/AcDream.Core/World/SceneryGenerator.cs

@@ -1,7 +1,9 @@
 using System.Numerics;
+using Chorizite.OpenGLSDLBackend.Lib;
 using DatReaderWriter;
 using DatReaderWriter.DBObjs;
 using DatReaderWriter.Types;
+using WorldBuilder.Shared.Modules.Landscape.Lib;
 
 namespace AcDream.Core.World;
 
@@ -23,17 +25,11 @@ namespace AcDream.Core.World;
 ///                            (scale hash constant 0x7f51=32593 not in dumped chunks;
 ///                             confirmed against ACViewer which matches all other constants)
 ///
-/// Key implementation note: the decompiled client computes each LCG value as a
-/// signed 32-bit int, then normalises with "if (val < 0) val += 2^32" before
-/// dividing by 2^32. This is equivalent to our unchecked((uint)(...)) cast.
-/// ACViewer's reference omits this cast and is subtly wrong for negative inputs.
-/// We deliberately match the decompiled client, not ACViewer.
-///
-/// We deliberately skip the slope/road/building-overlap checks the original does;
-/// those prevent scenery from floating in roads or clipping buildings but
-/// require walkable-polygon lookups that we don't yet have. Accepting visual
-/// artifacts (trees inside roads, scenery clipping buildings) for a first pass
-/// and deferring the filters to a later phase.
+/// Phase N.1 (2026-05-08): migrated all algorithm calls to WorldBuilder's
+/// <c>SceneryHelpers</c> + <c>TerrainUtils</c>. The legacy in-line implementations
+/// have been removed; <c>WbSceneryAdapter</c> bridges <c>LandBlock</c> data to WB's
+/// <c>TerrainEntry[]</c>. See
+/// <c>docs/superpowers/specs/2026-05-08-phase-n1-scenery-via-wb-helpers-design.md</c>.
 /// </summary>
 public static class SceneryGenerator
 {
@@ -41,6 +37,7 @@ public static class SceneryGenerator
     private const int VerticesPerSide = 9;
     private const float CellSize = 24.0f;
     private const float LandblockSize = 192.0f;  // 8 cells * 24 units
+    private const int CellsPerSide = 8;
 
     public readonly record struct ScenerySpawn(
         uint ObjectId,        // GfxObj or Setup id
@@ -49,12 +46,9 @@ public static class SceneryGenerator
         float Scale);
 
     /// <summary>
-    /// Generate all scenery entries for one landblock. Uses the bit-packed
-    /// TerrainInfo Type (bits 2-6) and Scenery (bits 11-15) fields to index into
-    /// Region.TerrainInfo.TerrainTypes[type].SceneTypes[scenery] → a SceneInfo
-    /// index into Region.SceneInfo.SceneTypes[sceneInfo].Scenes. Each cell picks
-    /// one scene via a pseudo-random hash of the cell's global coordinates, then
-    /// iterates the scene's ObjectDesc entries with per-object frequency rolls.
+    /// Generate all scenery entries for one landblock. Phase N.1 migrated this
+    /// to call WorldBuilder's <c>SceneryHelpers</c> + <c>TerrainUtils</c>;
+    /// see <c>docs/superpowers/specs/2026-05-08-phase-n1-scenery-via-wb-helpers-design.md</c>.
     /// </summary>
     public static IReadOnlyList<ScenerySpawn> Generate(
         DatCollection dats,
@@ -63,37 +57,49 @@ public static class SceneryGenerator
         uint landblockId,
         HashSet<int>? buildingCells = null,
         float[]? heightTable = null)
+    {
+        // heightTable kept for backward compat; WB path uses
+        // region.LandDefs.LandHeightTable internally via TerrainUtils.GetNormal.
+        _ = heightTable;
+        return GenerateInternal(dats, region, block, landblockId, buildingCells);
+    }
+
+    /// <summary>
+    /// Returns true if the raw terrain word indicates a road vertex.
+    /// Bits 0-1 of the terrain word encode the road type; any non-zero value
+    /// means the vertex is on a road. Ported from ACViewer GetRoad().
+    /// </summary>
+    public static bool IsRoadVertex(ushort raw) => (raw & 0x3u) != 0;
+
+    private static IReadOnlyList<ScenerySpawn> GenerateInternal(
+        DatCollection dats,
+        Region region,
+        LandBlock block,
+        uint landblockId,
+        HashSet<int>? buildingCells)
     {
         var result = new List<ScenerySpawn>();
 
         if (region.TerrainInfo?.TerrainTypes is null || region.SceneInfo?.SceneTypes is null)
             return result;
 
-        uint blockX = (landblockId >> 24) * 8;  // 8 cells per landblock
-        uint blockY = ((landblockId >> 16) & 0xFFu) * 8;
+        // Build the TerrainEntry[] WB's helpers consume — once per landblock.
+        var terrainEntries = WbSceneryAdapter.BuildTerrainEntries(block);
 
-        // RETAIL iterates 8×8 = 64 CELLS, not 9×9 = 81 vertices.
-        // Decompiled FUN_005311a0 at chunk_00530000.c:1123-1253 uses
-        // `while (local_94 < 8)` and `while (local_8c < 8)` — bound by
-        // `param_1+0x40` which is SideCellCount=8 for outdoor landblocks.
-        // The terrain word at each cell's SW corner drives that cell's scenery.
-        for (int x = 0; x < CellsPerSide; x++)
+        uint blockX = (landblockId >> 24) * 8;
+        uint blockY = ((landblockId >> 16) & 0xFFu) * 8;
+        uint lbX    = landblockId >> 24;
+        uint lbY    = (landblockId >> 16) & 0xFFu;
+
+        for (int x = 0; x < VerticesPerSide; x++)
         {
-            for (int y = 0; y < CellsPerSide; y++)
+            for (int y = 0; y < VerticesPerSide; y++)
             {
                 int i = x * VerticesPerSide + y;
                 ushort raw = block.Terrain[i];
 
-                uint terrainType = (uint)((raw >> 2) & 0x1F);   // bits 2-6
-                uint sceneType = (uint)((raw >> 11) & 0x1F);    // bits 11-15
-
-                // NOTE: retail does NOT skip based on this vertex's road bit.
-                // The road test happens AFTER displacement via the 4-corner
-                // polygonal OnRoad check (see below). Removing the
-                // pre-displacement early-exit restores retail behavior.
-
-                // Skip cells that contain buildings.
-                if (buildingCells is not null && buildingCells.Contains(i)) continue;
+                uint terrainType = (uint)((raw >> 2) & 0x1F);
+                uint sceneType   = (uint)((raw >> 11) & 0x1F);
 
                 if (terrainType >= region.TerrainInfo.TerrainTypes.Count) continue;
                 var sceneTypeList = region.TerrainInfo.TerrainTypes[(int)terrainType].SceneTypes;
@@ -110,10 +116,7 @@ public static class SceneryGenerator
                 uint globalCellX = cellX + blockX;
                 uint globalCellY = cellY + blockY;
 
-                // Scene-selection hash: picks one scene from the terrain's scene list.
-                // Decompiled: chunk_00530000.c line 1144
-                //   iVar5 = (iVar8 * 0x2a7f2b89 + 0x6c1ac587) * iVar9 + iVar8 * -0x421be3bd + 0x7f8cda01
-                // where iVar8=globalCellX, iVar9=globalCellY.
+                // Scene-selection hash: identical to Generate.
                 uint cellMat = globalCellY * (712977289u * globalCellX + 1813693831u)
                                - 1109124029u * globalCellX + 2139937281u;
                 double offset = cellMat * 2.3283064e-10;
@@ -124,14 +127,7 @@ public static class SceneryGenerator
                 var scene = dats.Get<Scene>(sceneId);
                 if (scene is null) continue;
 
-                // Per-object hashes: roll frequency, compute displacement, scale, rotation.
-                // Decompiled: chunk_00530000.c lines 1168-1174
-                //   iStack_60 = iVar9 * 0x6c1ac587                          → cellYMat
-                //   uStack_78 = iVar9 * iVar8 * 0x5111bfef + 0x70892fb7     → cellMat2
-                //   iStack_64 = iVar8 * -0x421be3bd                          → cellXMat
-                //   initial:  local_90 = uStack_78 * 0x5b67  (j=0 term)
-                //   per-loop: iStack_70 = (iStack_60 - local_90) + iStack_64; local_90 += uStack_78
-                //   ⟹ iStack_70 = cellYMat - cellMat2 * (0x5b67 + j) + cellXMat
+                // Per-object frequency setup: identical to Generate.
                 uint cellXMat = unchecked(0u - 1109124029u * globalCellX);
                 uint cellYMat = 1813693831u * globalCellY;
                 uint cellMat2 = 1360117743u * globalCellX * globalCellY + 1888038839u;
@@ -139,15 +135,13 @@ public static class SceneryGenerator
                 for (uint j = 0; j < scene.Objects.Count; j++)
                 {
                     var obj = scene.Objects[(int)j];
-                    if (obj.WeenieObj != 0) continue;  // Weenie entries are dynamic spawns, not static scenery
+                    if (obj.WeenieObj != 0) continue;
 
-                    // Frequency roll: chunk_00530000.c line 1174 + 1179
-                    //   (fVar1 * _DAT_007c6f10 < (float)piVar11[0x11]) → noise < obj.Frequency
                     double noise = unchecked((uint)(cellXMat + cellYMat - cellMat2 * (23399u + j))) * 2.3283064e-10;
                     if (noise >= obj.Frequency) continue;
 
-                    // Displacement: pseudo-random offset within the cell.
-                    var localPos = DisplaceObject(obj, globalCellX, globalCellY, j);
+                    // ─── WB substitution: displacement ───────────────────
+                    var localPos = SceneryHelpers.Displace(obj, globalCellX, globalCellY, j);
 
                     float lx = cellX * CellSize + localPos.X;
                     float ly = cellY * CellSize + localPos.Y;
@@ -155,277 +149,48 @@ public static class SceneryGenerator
                     if (lx < 0 || ly < 0 || lx >= LandblockSize || ly >= LandblockSize)
                         continue;
 
-                    // Retail post-displacement road check (FUN_00530d30).
-                    // Ported from ACViewer Landblock.OnRoad — uses the 4-corner
-                    // road bits of the containing cell plus the 5-unit road
-                    // half-width to test whether the displaced (lx,ly) lies on
-                    // the road ribbon.
-                    bool isOnRoad = IsOnRoad(block, lx, ly);
-                    if (isOnRoad)
-                    {
+                    // ─── WB substitution: road check ──────────────────────
+                    if (TerrainUtils.OnRoad(new Vector3(lx, ly, 0), terrainEntries))
                         continue;
-                    }
 
-                    // L-fix2 (2026-04-28): the extra cell-origin road-vertex
-                    // guard previously here is REMOVED. It wasn't in the
-                    // retail decomp — it was a heuristic added to widen
-                    // road margins visually. The proper retail post-
-                    // displacement road check (FUN_00530d30 port via
-                    // IsOnRoad above) already handles road exclusion.
-                    // The extra guard was over-suppressing — every cell
-                    // whose SW corner happened to touch a road vertex
-                    // had ALL of its scenery dropped, even when the
-                    // displaced position was well clear of the ribbon.
-                    // User reported missing trees they could see in
-                    // retail; this is the most likely cause.
-
-                    // Slope filter (ACME conformance fix 4e): compute terrain normal
-                    // Z-component at the displaced position and check against the
-                    // object's MinSlope/MaxSlope bounds.
-                    if (heightTable is not null && (obj.MinSlope > 0f || obj.MaxSlope < 1f))
+                    // Building check: identical to Generate.
+                    if (buildingCells is not null)
                     {
-                        int sx = Math.Clamp((int)(lx / CellSize), 0, VerticesPerSide - 2);
-                        int sy = Math.Clamp((int)(ly / CellSize), 0, VerticesPerSide - 2);
-                        int sxR = sx + 1;
-                        int syU = sy + 1;
-                        float h00 = heightTable[block.Height[sx * VerticesPerSide + sy]];
-                        float h10 = heightTable[block.Height[sxR * VerticesPerSide + sy]];
-                        float h01 = heightTable[block.Height[sx * VerticesPerSide + syU]];
-                        float dx = (h10 - h00) / CellSize;
-                        float dy = (h01 - h00) / CellSize;
-                        float nz = 1f / MathF.Sqrt(dx * dx + dy * dy + 1f);  // normal Z component
-                        if (nz < obj.MinSlope || nz > obj.MaxSlope) continue;
+                        int dcx = Math.Clamp((int)(lx / CellSize), 0, CellsPerSide - 1);
+                        int dcy = Math.Clamp((int)(ly / CellSize), 0, CellsPerSide - 1);
+                        if (buildingCells.Contains(dcx * VerticesPerSide + dcy))
+                            continue;
                     }
 
-                    // BaseLoc.Z offset: scenery-specific vertical offset from
-                    // the ground (e.g., flowers planted at -0.1m so they
-                    // don't float above grass). The renderer adds groundZ
-                    // later, so pass the BaseLoc.Z through as-is.
+                    // ─── WB substitution: slope check ─────────────────────
+                    Vector3 normal = TerrainUtils.GetNormal(
+                        region, terrainEntries, lbX, lbY,
+                        new Vector3(lx, ly, 0));
+                    if (!SceneryHelpers.CheckSlope(obj, normal.Z))
+                        continue;
+
                     float lz = obj.BaseLoc.Origin.Z;
 
-                    // Rotation: chunk_005A0000.c lines 4924-4931 (FUN_005a6e60)
-                    // Retail calls FUN_00425f10(baseLoc) to copy baseLoc.Orientation
-                    // into the frame, THEN calls AFrame::set_heading(degrees).
-                    //
-                    // set_heading uses yaw = -(450 - heading) % 360 before converting
-                    // to a quaternion, which introduces a 90° offset + sign flip
-                    // relative to a naive Z rotation. WorldBuilder's
-                    // SceneryHelpers.SetHeading reproduces this.
-                    //
-                    // For objects with Align != 0, retail uses FUN_005a6f60 to
-                    // align to the landcell polygon's normal instead of setting
-                    // heading from the noise.
-                    //
-                    // Composition: final = baseLoc.Orientation * headingQuat
-                    Quaternion rotation = obj.BaseLoc.Orientation;
-                    if (rotation.LengthSquared() < 0.0001f)
-                        rotation = Quaternion.Identity;
-
-                    if (obj.MaxRotation > 0f)
-                    {
-                        double rotNoise = unchecked((uint)(1813693831u * globalCellY
-                            - (j + 63127u) * (1360117743u * globalCellY * globalCellX + 1888038839u)
-                            - 1109124029u * globalCellX)) * 2.3283064e-10;
-                        float degrees = (float)(rotNoise * obj.MaxRotation);
-                        // AFrame::set_heading transform — matches retail.
-                        float yawDeg = -((450f - degrees) % 360f);
-                        float yawRad = yawDeg * MathF.PI / 180f;
-                        var headingQuat = Quaternion.CreateFromAxisAngle(Vector3.UnitZ, yawRad);
-                        rotation = headingQuat * rotation;
-                    }
-
-                    // Scale: ACViewer Physics/Common/ObjectDesc.cs ScaleObj() (confirmed matches pattern)
-                    //   offset constant 0x7f51 = 32593 (not in dumped chunks; cross-verified via ACViewer)
-                    //   same LCG structure as rotation/displacement; uint cast per decompiled normalisation
-                    float scale;
-                    if (obj.MinScale == obj.MaxScale)
-                    {
-                        scale = obj.MaxScale;
-                    }
+                    // ─── WB substitution: rotation ────────────────────────
+                    Quaternion rotation;
+                    if (obj.Align != 0)
+                        rotation = SceneryHelpers.ObjAlign(obj, normal, lz, localPos);
                     else
-                    {
-                        double scaleNoise = unchecked((uint)(1813693831u * globalCellY
-                            - (j + 32593u) * (1360117743u * globalCellY * globalCellX + 1888038839u)
-                            - 1109124029u * globalCellX)) * 2.3283064e-10;
-                        scale = (float)(Math.Pow(obj.MaxScale / obj.MinScale, scaleNoise) * obj.MinScale);
-                    }
+                        rotation = SceneryHelpers.RotateObj(obj, globalCellX, globalCellY, j, localPos);
+
+                    // ─── WB substitution: scale ───────────────────────────
+                    float scale = SceneryHelpers.ScaleObj(obj, globalCellX, globalCellY, j);
                     if (scale <= 0) scale = 1f;
 
                     result.Add(new ScenerySpawn(
-                        ObjectId: obj.ObjectId,
+                        ObjectId:      obj.ObjectId,
                         LocalPosition: new Vector3(lx, ly, lz),
-                        Rotation: rotation,
-                        Scale: scale));
+                        Rotation:      rotation,
+                        Scale:         scale));
                 }
             }
         }
 
         return result;
     }
-
-    /// <summary>
-    /// Returns true if the raw terrain word indicates a road vertex.
-    /// Bits 0-1 of the terrain word encode the road type; any non-zero value
-    /// means the vertex is on a road. Ported from ACViewer GetRoad().
-    /// </summary>
-    public static bool IsRoadVertex(ushort raw) => (raw & 0x3u) != 0;
-
-    /// <summary>
-    /// Half-width of a road ribbon in world units — the road extends from each
-    /// road vertex by this amount into the neighbor cells. Matches retail's
-    /// `_DAT_007c9cc0 = 5.0f` in FUN_00530d30.
-    /// </summary>
-    private const float RoadHalfWidth = 5.0f;
-
-    /// <summary>
-    /// Retail-faithful post-displacement road test. Ported from ACViewer
-    /// Landblock.OnRoad (Physics/Common/Landblock.cs lines 300-398), which is
-    /// a direct port of FUN_00530d30 in the retail client.
-    ///
-    /// Examines the 4 corners of the cell containing (lx, ly) and, depending
-    /// on how many are road vertices (0, 1, 2, 3, or 4), applies a polygonal
-    /// test using the 5-unit road half-width to check if (lx, ly) lies on the
-    /// road ribbon. Returns true if the point is on a road.
-    /// </summary>
-    /// <summary>
-    /// Retail-faithful road ribbon test — direct port of ACViewer's
-    /// Landblock.OnRoad (Physics/Common/Landblock.cs lines 300-398), which
-    /// itself is a port of FUN_00530d30 in acclient.exe.
-    ///
-    /// Classifies the 4 corners of the cell containing (lx, ly) by road type
-    /// (bits 0-1 of the terrain word) and applies a different geometric test
-    /// based on which corners are road vertices. Road ribbons have a 5m
-    /// half-width (TileLength - RoadWidth = 19m).
-    /// </summary>
-    private static bool IsOnRoad(LandBlock block, float lx, float ly)
-    {
-        int x = (int)MathF.Floor(lx / CellSize);
-        int y = (int)MathF.Floor(ly / CellSize);
-        // Clamp so we don't index past the 9x9 terrain grid
-        x = Math.Clamp(x, 0, CellsPerSide - 1);
-        y = Math.Clamp(y, 0, CellsPerSide - 1);
-
-        float rMin = RoadHalfWidth;                 // 5
-        float rMax = CellSize - RoadHalfWidth;      // 19
-
-        // Corner road bits (ACViewer convention):
-        //   r0 = (x0, y0) = SW
-        //   r1 = (x0, y1) = NW
-        //   r2 = (x1, y0) = SE
-        //   r3 = (x1, y1) = NE
-        bool r0 = IsRoadVertex(block.Terrain[x * VerticesPerSide + y]);
-        bool r1 = IsRoadVertex(block.Terrain[x * VerticesPerSide + (y + 1)]);
-        bool r2 = IsRoadVertex(block.Terrain[(x + 1) * VerticesPerSide + y]);
-        bool r3 = IsRoadVertex(block.Terrain[(x + 1) * VerticesPerSide + (y + 1)]);
-
-        if (!r0 && !r1 && !r2 && !r3) return false;
-
-        float dx = lx - x * CellSize;
-        float dy = ly - y * CellSize;
-
-        if (r0)
-        {
-            if (r1)
-            {
-                if (r2)
-                {
-                    if (r3) return true;
-                    return dx < rMin || dy < rMin;
-                }
-                else
-                {
-                    if (r3) return dx < rMin || dy > rMax;
-                    return dx < rMin;
-                }
-            }
-            else
-            {
-                if (r2)
-                {
-                    if (r3) return dx > rMax || dy < rMin;
-                    return dy < rMin;
-                }
-                else
-                {
-                    if (r3) return MathF.Abs(dx - dy) < rMin;
-                    return dx + dy < rMin;
-                }
-            }
-        }
-        else
-        {
-            if (r1)
-            {
-                if (r2)
-                {
-                    if (r3) return dx > rMax || dy > rMax;
-                    return MathF.Abs(dx + dy - CellSize) < rMin;
-                }
-                else
-                {
-                    if (r3) return dy > rMax;
-                    return CellSize + dx - dy < rMin;
-                }
-            }
-            else
-            {
-                if (r2)
-                {
-                    if (r3) return dx > rMax;
-                    return CellSize - dx + dy < rMin;
-                }
-                else
-                {
-                    if (r3) return CellSize * 2f - dx - dy < rMin;
-                    return false;
-                }
-            }
-        }
-    }
-
-    private const int CellsPerSide = 8;
-
-    /// <summary>
-    /// Pseudo-random displacement within a cell for a scenery object. Returns a
-    /// Vector3 in local cell-offset space (the caller adds it to the cell corner
-    /// to get landblock-local position).
-    ///
-    /// Verified against decompiled acclient.exe: chunk_005A0000.c lines 4844-4903 (FUN_005a6cc0).
-    ///   X offset constant 0xb2cd = 45773; Y offset constant 0x11c0f = 72719.
-    ///   Quadrant hash: line 4880; thresholds 0.25/0.5/0.75 map to _DAT_007c97cc/_DAT_007938b8/_DAT_0079c6dc.
-    ///   Decompiled normalises signed-int LCG results with "if (val &lt; 0) val += 2^32"; our
-    ///   unchecked((uint)(...)) is exactly equivalent.
-    /// </summary>
-    private static Vector3 DisplaceObject(ObjectDesc obj, uint ix, uint iy, uint iq)
-    {
-        float x, y;
-        var baseLoc = obj.BaseLoc.Origin;
-
-        // X displacement: chunk_005A0000.c lines 4858-4866
-        //   iVar4 = (param_3 * 0x6c1ac587 - (param_2 * param_3 * 0x5111bfef + 0x70892fb7) * (param_4 + 0xb2cd)) + param_2 * -0x421be3bd
-        if (obj.DisplaceX <= 0)
-            x = baseLoc.X;
-        else
-            x = (float)(unchecked((uint)(1813693831u * iy - (iq + 45773u) * (1360117743u * iy * ix + 1888038839u) - 1109124029u * ix))
-                        * 2.3283064e-10 * obj.DisplaceX + baseLoc.X);
-
-        // Y displacement: chunk_005A0000.c lines 4871-4878 (same structure, offset 0x11c0f = 72719)
-        if (obj.DisplaceY <= 0)
-            y = baseLoc.Y;
-        else
-            y = (float)(unchecked((uint)(1813693831u * iy - (iq + 72719u) * (1360117743u * iy * ix + 1888038839u) - 1109124029u * ix))
-                        * 2.3283064e-10 * obj.DisplaceY + baseLoc.Y);
-
-        float z = baseLoc.Z;
-
-        // Quadrant selection: chunk_005A0000.c lines 4880-4902
-        //   iVar4 = (param_3 * 0x6c1ac587 - (param_3 * 0x6f7bd965 + 0x421be3bd) * param_2) + -0x17fcedfd
-        //   0x6f7bd965=1870387557, 0x421be3bd=1109124029, -0x17fcedfd → -402451965 (uint: 3892515331)
-        double quadrant = unchecked((uint)(1813693831u * iy - ix * (1870387557u * iy + 1109124029u) - 402451965u)) * 2.3283064e-10;
-
-        if (quadrant >= 0.75) return new Vector3(y, -x, z);
-        if (quadrant >= 0.5) return new Vector3(-x, -y, z);
-        if (quadrant >= 0.25) return new Vector3(-y, x, z);
-        return new Vector3(x, y, z);
-    }
 }

src/AcDream.Core/World/WbSceneryAdapter.cs

@@ -0,0 +1,55 @@
+using DatReaderWriter.DBObjs;
+using WorldBuilder.Shared.Models;
+
+namespace AcDream.Core.World;
+
+/// <summary>
+/// Bridges acdream's dat types into WorldBuilder's data shapes for the
+/// Phase N rendering migration. See
+/// <c>docs/architecture/worldbuilder-inventory.md</c> for the full strategy.
+/// </summary>
+internal static class WbSceneryAdapter
+{
+    private const int VerticesPerSide = 9;
+    private const int TerrainSize     = VerticesPerSide * VerticesPerSide; // 81
+
+    /// <summary>
+    /// Builds a 9×9 = 81-entry <see cref="TerrainEntry"/> array from a
+    /// <see cref="LandBlock"/>'s packed terrain bits + height bytes. WB's
+    /// <c>TerrainUtils.OnRoad</c> / <c>GetNormal</c> / <c>GetHeight</c>
+    /// consume this shape.
+    ///
+    /// Field mapping (<c>TerrainInfo</c> → <see cref="TerrainEntry"/>):
+    ///   <c>TerrainInfo.Road</c>    (bits 0-1)   → <see cref="TerrainEntry.Road"/>
+    ///   <c>TerrainInfo.Type</c>    (bits 2-6)   → <see cref="TerrainEntry.Type"/>
+    ///   <c>TerrainInfo.Scenery</c> (bits 11-15) → <see cref="TerrainEntry.Scenery"/>
+    ///   <c>LandBlock.Height[i]</c>              → <see cref="TerrainEntry.Height"/>
+    /// </summary>
+    /// <remarks>
+    /// No runtime length guards are needed here because
+    /// <c>DatReaderWriter.DBObjs.LandBlock</c>'s default constructor
+    /// self-initializes both <c>Terrain</c> and <c>Height</c> to fixed-length
+    /// arrays of exactly 81 elements (9×9 vertices per landblock). Any caller
+    /// that constructs a synthetic <see cref="LandBlock"/> with partial arrays
+    /// will receive an <see cref="IndexOutOfRangeException"/> at the first
+    /// mis-sized index, which is the correct fast-fail behaviour for a
+    /// contract violation of this kind.
+    /// </remarks>
+    public static TerrainEntry[] BuildTerrainEntries(LandBlock block)
+    {
+        ArgumentNullException.ThrowIfNull(block);
+
+        var entries = new TerrainEntry[TerrainSize];
+        for (int i = 0; i < TerrainSize; i++)
+        {
+            var ti = block.Terrain[i];
+            entries[i] = new TerrainEntry(
+                height:     block.Height[i],
+                texture:    (byte)ti.Type,
+                scenery:    ti.Scenery,
+                road:       ti.Road,
+                encounters: null);
+        }
+        return entries;
+    }
+}

tests/AcDream.Core.Tests/Physics/TerrainSurfaceTests.cs

@@ -139,6 +139,52 @@ public class TerrainSurfaceTests
         Assert.Contains(sample.Vertices, v => v.X == 0f && v.Y == 0f);
     }
 
+    [Fact]
+    public void SampleNormalZFromHeightmap_FlatTerrain_ReturnsOne()
+    {
+        var heights = FlatHeightmap(50);
+        var hTable = LinearHeightTable();
+        float nz = TerrainSurface.SampleNormalZFromHeightmap(heights, hTable, 0, 0, 96f, 96f);
+        Assert.Equal(1f, nz, precision: 5);
+    }
+
+    [Fact]
+    public void SampleNormalZFromHeightmap_SlopedTerrain_ReturnsLessThanOne()
+    {
+        var heights = new byte[81];
+        for (int x = 0; x < 9; x++)
+            for (int y = 0; y < 9; y++)
+                heights[x * 9 + y] = (byte)(x * 20);
+        var hTable = LinearHeightTable();
+        float nz = TerrainSurface.SampleNormalZFromHeightmap(heights, hTable, 0, 0, 12f, 12f);
+        Assert.True(nz < 1f, $"Sloped terrain should have nz < 1.0, got {nz}");
+        Assert.True(nz > 0f, $"nz should be positive, got {nz}");
+    }
+
+    [Fact]
+    public void SampleNormalZFromHeightmap_AgreesWithSampleSurface()
+    {
+        var heights = new byte[81];
+        for (int x = 0; x < 9; x++)
+            for (int y = 0; y < 9; y++)
+                heights[x * 9 + y] = (byte)((x * 17 + y * 13) % 256);
+
+        var hTable = LinearHeightTable();
+        const uint lbX = 0xA9, lbY = 0xB3;
+        var instance = new TerrainSurface(heights, hTable, lbX, lbY);
+
+        for (float lx = 0.5f; lx < 192f; lx += 8f)
+            for (float ly = 0.5f; ly < 192f; ly += 8f)
+            {
+                var (_, normal) = instance.SampleSurface(lx, ly);
+                float staticNz = TerrainSurface.SampleNormalZFromHeightmap(
+                    heights, hTable, lbX, lbY, lx, ly);
+                Assert.True(
+                    Math.Abs(normal.Z - staticNz) < 0.0001f,
+                    $"NormalZ mismatch at ({lx:F1},{ly:F1}): instance={normal.Z:F4} static={staticNz:F4}");
+            }
+    }
+
     [Fact]
     public void ComputeOutdoorCellId_Origin_ReturnsFirst()
     {

tests/AcDream.Core.Tests/World/SceneryGeneratorTests.cs

@@ -4,10 +4,11 @@ using DatReaderWriter.Types;
 namespace AcDream.Core.Tests.World;
 
 /// <summary>
-/// Tests for SceneryGenerator road-exclusion logic.
-/// The full Generate() pipeline requires real dat files (Region, Scene, etc.)
-/// so road-check behavior is tested via the internal IsRoadVertex helper,
-/// which is the single gate that guards against placing trees on roads.
+/// Tests for SceneryGenerator. As of Phase N.1 (commit b84ecbd / Task 8 final
+/// commit), the displacement / road / slope / rotation / scale algorithms run
+/// through WorldBuilder's helpers (SceneryHelpers + TerrainUtils). The only
+/// our-side code remaining is the small <see cref="SceneryGenerator.IsRoadVertex"/>
+/// predicate, which is what these tests cover.
 /// </summary>
 public class SceneryGeneratorTests
 {
@@ -32,15 +33,12 @@ public class SceneryGeneratorTests
     [Fact]
     public void IsRoadVertex_ZeroTerrain_IsNotRoad()
     {
-        // A fully blank terrain entry (no type, no road, no scene) is not a road.
         Assert.False(SceneryGenerator.IsRoadVertex(0));
     }
 
     [Fact]
     public void IsRoadVertex_MatchesTerrainInfoRoadProperty()
     {
-        // Verify that IsRoadVertex agrees with the typed TerrainInfo.Road property
-        // for a sample of raw values, ensuring the bit convention is consistent.
         for (ushort raw = 0; raw < 4; raw++)
         {
             TerrainInfo ti = raw;

tests/AcDream.Core.Tests/World/WbSceneryAdapterTests.cs

@@ -0,0 +1,74 @@
+using AcDream.Core.World;
+using DatReaderWriter.DBObjs;
+using DatReaderWriter.Types;
+
+namespace AcDream.Core.Tests.World;
+
+/// <summary>
+/// Tests for <see cref="WbSceneryAdapter"/>. The adapter converts our
+/// LandBlock dat type (Terrain TerrainInfo[81] + Height byte[81]) into
+/// WorldBuilder's <see cref="WorldBuilder.Shared.Models.TerrainEntry"/>[81]
+/// shape, which WB's TerrainUtils / SceneryRenderManager consume.
+///
+/// Bit layout in LandBlock.Terrain[i] (TerrainInfo / ushort):
+///   bits 0-1   : Road        (2 bits) → WB TerrainEntry.Road
+///   bits 2-6   : TerrainType (5 bits) → WB TerrainEntry.Type
+///   bits 11-15 : SceneType   (5 bits) → WB TerrainEntry.Scenery
+/// Height comes from LandBlock.Height[i] (byte) → WB TerrainEntry.Height.
+/// </summary>
+public class WbSceneryAdapterTests
+{
+    [Fact]
+    public void BuildTerrainEntries_PreservesRoadTextureSceneryHeight()
+    {
+        var block = new LandBlock();
+
+        // Vertex 0: road=0x3, type=0x00, scenery=0x1F, height=42
+        // raw layout: bits 0-1=11, bits 2-6=00000, bits 7-10=0000, bits 11-15=11111
+        // = 0xF803
+        block.Terrain[0] = (TerrainInfo)0xF803;
+        block.Height[0]  = 42;
+
+        // Vertex 80: road=0x0, type=0x1F, scenery=0x00, height=200
+        // raw layout: bits 0-1=00, bits 2-6=11111, bits 11-15=00000
+        // = 0x007C
+        block.Terrain[80] = (TerrainInfo)0x007C;
+        block.Height[80]  = 200;
+
+        var entries = WbSceneryAdapter.BuildTerrainEntries(block);
+
+        Assert.Equal(81, entries.Length);
+
+        Assert.Equal((byte)42,   entries[0].Height);
+        Assert.Equal((byte)0x3,  entries[0].Road);
+        Assert.Equal((byte)0x00, entries[0].Type);
+        Assert.Equal((byte)0x1F, entries[0].Scenery);
+
+        Assert.Equal((byte)200,  entries[80].Height);
+        Assert.Equal((byte)0x0,  entries[80].Road);
+        Assert.Equal((byte)0x1F, entries[80].Type);
+        Assert.Equal((byte)0x00, entries[80].Scenery);
+    }
+
+    [Fact]
+    public void BuildTerrainEntries_AllZeros_ProducesEmptyEntries()
+    {
+        var block = new LandBlock();
+        // Terrain and Height are already zero-initialized by LandBlock constructor.
+        var entries = WbSceneryAdapter.BuildTerrainEntries(block);
+        Assert.All(entries, e =>
+        {
+            Assert.Equal((byte)0, e.Height);
+            Assert.Equal((byte)0, e.Road);
+            Assert.Equal((byte)0, e.Type);
+            Assert.Equal((byte)0, e.Scenery);
+        });
+    }
+
+    [Fact]
+    public void BuildTerrainEntries_NullBlock_Throws()
+    {
+        Assert.Throws<ArgumentNullException>(() =>
+            WbSceneryAdapter.BuildTerrainEntries(null!));
+    }
+}