From 2d15c7ab8d3af45e3b86ddb70b073c99368ae819 Mon Sep 17 00:00:00 2001
From: Toad <toad@sigitex.com>
Date: Mon, 24 Aug 2026 15:17:53 +0200
Subject: [PATCH] refactor: move world concepts into engine

---
 .agents/history/jerklint-01/review.md       | 137 ----
 .agents/plans/gpu.md                        | 714 ++++++++++++++++++
 .agents/plans/levels-and-editor.md          |  15 +-
 .agents/rules/forge-sync.md                 |  29 -
 .agents/rules/openspec.md                   |  19 -
 .claude/skills                              |   1 -
 AGENTS.md                                   | 143 ++--
 CLAUDE.md                                   |  10 -
 CONTEXT.md                                  |  29 +
 app/main.ts                                 | 205 ++---
 app/render-worker.ts                        |  88 +--
 app/renderer.ts                             | 228 ++++--
 docs/adr/0001-engine-owns-world-concepts.md |   3 +
 engine/math/Mat4.ts                         |   2 +-
 engine/render/Chunk.ts                      |  29 +
 engine/render/ChunkBuilder.ts               | 123 +++
 engine/render/Rasterizer.ts                 |   6 +-
 engine/render/RenderConfig.ts               |   6 +-
 engine/render/RenderProtocol.ts             | 123 +++
 engine/render/RenderScene.ts                | 224 ++++++
 engine/scene/Actor.ts                       |  68 +-
 engine/scene/MeshBuilder.ts                 |  80 ++
 engine/scene/Prefab.ts                      |  38 +
 engine/world/CharacterController.ts         |  89 +++
 engine/world/Collider.ts                    | 116 +++
 engine/world/CollisionWorld.ts              |  62 ++
 engine/world/Level.ts                       | 123 +++
 engine/world/Terrain.ts                     | 121 +++
 game/Terrain.ts                             | 106 ---
 game/actors/Boulder.ts                      |  37 +-
 game/actors/Bush.ts                         |  18 +-
 game/actors/Flower.ts                       |  46 +-
 game/actors/Mob.ts                          |  86 +--
 game/actors/Tree.ts                         |  43 --
 game/actors/mobs/Bee.ts                     |  37 +-
 game/actors/mobs/Frog.ts                    |  37 +-
 game/actors/mobs/Robin.ts                   |  37 +-
 game/actors/mobs/mobkit.ts                  |  59 +-
 game/actors/trees/Birch.ts                  |  66 +-
 game/actors/trees/Oak.ts                    |  55 +-
 game/actors/trees/Spruce.ts                 |  51 +-
 game/actors/trees/treekit.ts                |   5 +-
 game/level.ts                               | 794 ++++++++++----------
 game/player.ts                              | 181 +----
 game/renderScene.ts                         | 133 ----
 meat.code-workspace                         |   5 +-
 tests/actors.test.ts                        |  38 +
 tests/layering.test.ts                      |  42 +-
 tests/level.test.ts                         |  72 ++
 tests/mobs.test.ts                          |  21 -
 tests/render-protocol.test.ts               |  38 +
 tests/trees.test.ts                         |  18 -
 52 files changed, 3298 insertions(+), 1558 deletions(-)
 delete mode 100644 .agents/history/jerklint-01/review.md
 create mode 100644 .agents/plans/gpu.md
 delete mode 100644 .agents/rules/forge-sync.md
 delete mode 100644 .agents/rules/openspec.md
 delete mode 120000 .claude/skills
 delete mode 100644 CLAUDE.md
 create mode 100644 CONTEXT.md
 create mode 100644 docs/adr/0001-engine-owns-world-concepts.md
 create mode 100644 engine/render/Chunk.ts
 create mode 100644 engine/render/ChunkBuilder.ts
 create mode 100644 engine/render/RenderProtocol.ts
 create mode 100644 engine/render/RenderScene.ts
 create mode 100644 engine/scene/MeshBuilder.ts
 create mode 100644 engine/scene/Prefab.ts
 create mode 100644 engine/world/CharacterController.ts
 create mode 100644 engine/world/Collider.ts
 create mode 100644 engine/world/CollisionWorld.ts
 create mode 100644 engine/world/Level.ts
 create mode 100644 engine/world/Terrain.ts
 delete mode 100644 game/Terrain.ts
 delete mode 100644 game/renderScene.ts
 create mode 100644 tests/actors.test.ts
 create mode 100644 tests/level.test.ts
 delete mode 100644 tests/mobs.test.ts
 create mode 100644 tests/render-protocol.test.ts
 delete mode 100644 tests/trees.test.ts

diff --git a/.agents/history/jerklint-01/review.md b/.agents/history/jerklint-01/review.md
deleted file mode 100644
index de6ccb8..0000000
--- a/.agents/history/jerklint-01/review.md
+++ /dev/null
@@ -1,137 +0,0 @@
-# Jerklint Review 01
-
-Reviewed 2026-08-04. Scope: handwritten source under `engine/`, `app/`,
-`server/`, `shared/`, and `scripts/`; root runtime, build, lint, editor, and
-project configuration; `README.md`. Generated assets, build output,
-dependencies, and lockfile were excluded.
-
-**Jerklint Findings**
-
-1. **High** `engine/render/Color.ts:37-43`,
-   `engine/render/Texture.ts:46-56`, `engine/render/Rasterizer.ts:199-203`,
-   `engine/render/RenderConfig.ts:104-114`, `scripts/gen-assets.ts:136-143`:
-   `Color.lerp` promises to interpolate a `Color` but omits alpha, so `Color.rgb`
-   silently supplies `255`. Every bilinear sample therefore becomes opaque.
-   The `clean` preset enables linear filtering, while the NPC asset has a
-   transparent background and alpha cutout happens after sampling. This is a
-   false generic abstraction with a direct behavior change hidden behind an
-   unrelated render knob. Smallest fix: interpolate alpha in `Color.lerp`; add
-   an explicitly named RGB-only blend only if fog or sky ever needs one.
-
-2. **High** `engine/render/RenderConfig.ts:16-58`,
-   `engine/render/RenderConfig.ts:64-115`, `app/main.ts:19-29`,
-   `engine/render/Framebuffer.ts:43-73`: live render configuration has no
-   authoritative validity or application boundary. Public presets are mutable
-   singleton objects, `useConfig` retains the supplied alias, dimensions are
-   snapshotted into framebuffer resources, and documented numeric ranges are
-   not enforced. A direct width change leaves resources stale; values such as
-   `colorDepth = 0` make quantization divide by zero. This will become immediate
-   pressure when planned live sliders arrive. Smallest fix: make presets
-   readonly templates, create a fresh validated config for each update, and
-   route updates through one app-side apply function that rebuilds resources
-   when dimensions change.
-
-
-4. **Medium** `app/level.ts:18-27`, `app/level.ts:66-105`,
-   `app/player.ts:2`, `app/player.ts:19-31`, `app/player.ts:61-97`,
-   `app/main.ts:48-52`: collision policy has no single owner. `Player.update`
-   accepts the render-heavy `Level`, then reconstructs gameplay facts using a
-   hardcoded ground height and NPC radius; NPC visual size lives in `main.ts`.
-   `buildLevel` also constructs geometry, collision, NPC placement, and sky in
-   one body. NPC or floor changes therefore require cross-file agreement and
-   isolated player tests need unrelated render data. Smallest fix: let `Level`
-   own a compact NPC descriptor and a narrow collision world containing ground,
-   boxes, and circles; pass only that collision value to `Player.update`.
-
-5. **Medium** `app/main.ts:54-69`, `app/player.ts:23-55`: browser key codes are
-   the player simulation API. Physics owns WASD and Space bindings, receives a
-   mutable `Set<string>`, cannot represent a press edge, and therefore treats a
-   held jump key as a fresh jump whenever landing. Lost `keyup` events also
-   leave state stuck because no blur path clears the set. Rebinding, gamepad
-   input, and deterministic tests all require physics edits. Smallest fix: map
-   browser events in `main.ts` to a semantic `PlayerInput` value with movement
-   axes and `jumpPressed`; clear raw input on blur.
-
-6. **Medium** `engine/scene/Camera.ts:27-33`,
-   `engine/math/Mat4.ts:23-34`, `engine/render/Rasterizer.ts:9-19`,
-   `engine/render/Rasterizer.ts:58-68`, `engine/render/Rasterizer.ts:77-115`:
-   projection limits and clipping have separate authorities. Camera projection
-   declares near/far values of `0.05` and `100`, but `Rasterizer.project`
-   discards clip-space `z` and clips only against unrelated `w >= 0.01`; far
-   clipping is absent. `Rasterizer.draw` looks matrix-generic while relying on
-   perspective-specific `w` semantics for clipping, depth, and fog. Smallest
-   fix: retain clip-space `z` and clip against canonical near/far planes, or
-   narrow and name the API so its perspective-matrix contract is explicit.
-
-7. **Medium** `engine/render/RenderConfig.ts:48-54`,
-   `engine/render/Texture.ts:36-38`, `engine/render/Rasterizer.ts:51-57`,
-   `engine/render/Sky.ts:34-36`, `engine/render/Sky.ts:93-98`,
-   `engine/render/Sky.ts:121-128`: closed option unions fail open. New texture
-   filters silently become nearest, new lighting modes silently become unlit,
-   and new cloud kinds silently become basic because each dispatcher uses a
-   binary predicate plus fallback. `basicCumulus` accepts the full `CloudLayer`
-   union, preventing TypeScript from exposing the missing branch. Smallest fix:
-   use exhaustive switches with a `never` check and narrow cloud helpers to
-   their concrete variant types.
-
-11. **Low** `engine/scene/Sprite.ts:9-23`, `app/main.ts:48-52`,
-    `app/main.ts:107-112`: `Sprite.texture` is assigned but never read; drawing
-    separately reaches back to `textures.npc`. Two sources can diverge, and the
-    type promises ownership the render path ignores. Smallest fix: draw with
-    `npc.texture`, or remove the field if material binding is intentionally
-    external.
-
-12. **Low** `engine/scene/Camera.ts:4-13`, `engine/math/Mat4.ts:37-43`,
-    `engine/render/Sky.ts:62-66`, `app/main.ts:73-79`: camera pitch validity is
-    documented by `Camera` but enforced by one caller through the unexplained
-    literal `1.4`. Both camera and sky basis construction rely on that ritual.
-    Any second camera producer can create a degenerate basis. Smallest fix: own
-    the pitch limit and look-delta/clamp operation in the `Camera` namespace.
-
-14. **Low** `engine/math/Vec3.ts:3-4`, `engine/math/Vec3.ts:34-37`:
-    `Vec3.normalize` violates its namespace-wide fresh-result guarantee only for
-    zero vectors by returning the mutable input alias. Callers can safely mutate
-    ordinary results but unexpectedly mutate source state at one edge. Smallest
-    fix: return a fresh zero vector.
-
-**Scorecard**
-
-- DRY: concern - collision, release, and resource-update policy have split owners.
-- KISS: pass - core engine stays direct, data-oriented, and framework-free.
-- YAGNI: concern - two unused public placeholders remain.
-- SOC: concern - render config application and release artifacts mix concerns.
-- Cohesion: concern - player physics consumes unrelated level rendering data.
-- Coupling: fail - config/resources and projection/clipping rely on hidden cross-module rules.
-- Dependency Direction: pass - browser code points inward and engine remains DOM-free.
-- Law of Demeter: pass - shallow plain-data access; no traversal chains or service locators.
-- Immutability: concern - mutable preset aliases and zero-vector aliasing weaken boundaries.
-- Declarative Shape: concern - option unions and release phases are not exhaustively interpreted.
-- Implicit Contracts: fail - alpha, dimensions, pitch, clipping, checks, and publishing depend on rituals.
-- Abstraction Pressure: concern - important rules are under-centralized while stale exports remain.
-- Naming/API Clarity: fail - `Color.lerp`, `check`, `publish`, and `Sprite.texture` overpromise.
-- Locality: concern - NPC behavior and configuration changes require cross-file coordination.
-- Testability: fail - zero tests, false-green test command, and broad player fixtures.
-- File/API Shape: concern - type/namespace pattern is strong; ignored and stale exports weaken it.
-- Predicate Accuracy: concern - binary fallback dispatch silently accepts future union variants.
-- Construction Phase Separation: concern - level and release construction each hide multiple phases.
-
-**Strengths**
-
-- Engine/browser dependency boundary is clean and enforced by separate TypeScript libraries.
-- Domain types generally own behavior through matching namespaces and matching filenames.
-- Hot-loop mutation is local, explicit, and appropriate for a software rasterizer.
-- Rasterizer, sky, texture loading, and procedural mesh generation remain cohesive despite numeric code.
-- `main.ts` is still a reasonable composition root; splitting presentation or FPS code now would add ceremony.
-- No ECS, service locator, class hierarchy, utility bag, dependency cycle, or speculative plugin system appeared.
-
-**Validation**
-
-- `bun run build`: passed.
-- `bunx tsc --build --dry`: selected engine, app, and config only.
-- `bun run lint`: exited with one `typescript(array-type)` warning at `scripts/gen-assets.ts:162`.
-- `bun run test`: found zero tests and emitted Bun's tsconfig directory-mismatch internal error; `--pass-with-no-tests` kept the command green.
-
-**Verdict**
-
-Refactor soon. Keep the core architecture. Fix lying primitives and quality
-commands first, then centralize configuration, input, and collision contracts.
diff --git a/.agents/plans/gpu.md b/.agents/plans/gpu.md
new file mode 100644
index 0000000..1cc2ec4
--- /dev/null
+++ b/.agents/plans/gpu.md
@@ -0,0 +1,714 @@
+# GPU renderer migration direction note
+
+Status: **options open; migration seam agreed.** This note records the current
+problem, viable approaches, expected scaling, proposed architecture, migration
+order, and decisions still needed. It is not approval to delete the software
+renderer or to commit to WebGL2, WebGPU rasterization, or WebGPU compute.
+
+## Goal
+
+Move triangle transformation and pixel rasterization off the CPU so adding more
+world geometry and moving actors does not collapse frame rate.
+
+The GPU path must preserve the configurable PS1 look rather than replace it with
+a fixed visual preset. `RenderConfig` remains the source of live settings for
+internal resolution, vertex snap, texture filtering, lighting, fog, color depth,
+dither, and LOD distance.
+
+The current software renderer remains playable during migration. A GPU backend
+is added beside it and selected at startup or by a debug option until parity and
+performance are proven.
+
+## Decisions already made
+
+- Build a parallel backend instead of replacing the software renderer in place.
+- Keep engine world/content boundaries unchanged. GPU work must not reintroduce
+  content kinds, registries, or renderer knowledge of frogs, trees, texture names,
+  or other game content.
+- Keep `RenderScene` as the clone-safe, content-agnostic render projection of a
+  live `Level`.
+- Keep main-thread frustum culling and scene-local render prototype indexes at
+  first. GPU culling is not required to obtain the expected performance gain.
+- Optimize for scaling as content grows, not merely for improving the current
+  benchmark by a small constant factor.
+- Preserve low-resolution rendering and the live PS1 controls.
+
+## Decisions not made
+
+- WebGPU versus WebGL2 as the first GPU backend.
+- Fixed-function GPU rasterization versus a custom WebGPU compute rasterizer.
+- Whether WebGL2 and WebGPU should both exist long-term.
+- Whether the software renderer remains a permanent fallback after a GPU backend
+  becomes default.
+- Whether GPU output must be pixel-identical to software output or only visually
+  equivalent under the same `RenderConfig`.
+- Required browser, OS, and device support.
+- Whether GPU timing statistics are required for the first usable backend.
+
+## Current baseline
+
+Current final browser benchmark at 384x216:
+
+| Backend | Work median | Work p95 | Frame p95 |
+| --- | ---: | ---: | ---: |
+| Software, single thread | 30.07 ms | 32.19 ms | 32.60 ms |
+| Software, 3 workers | 11.16 ms | 13.35 ms | 16.88 ms |
+
+These numbers are machine- and scene-specific. They are useful as the baseline
+for this repository, not as universal predictions.
+
+The software cost grows with transformed triangles, covered pixels, and texture
+samples. Workers divide framebuffer rows, but every worker still loops over the
+same visible draw groups and transforms the same triangles for its band. More
+content therefore keeps increasing CPU work even when screen resolution stays
+fixed.
+
+## Remaining implementation options
+
+### Option A: standard WebGPU rasterization
+
+Use WebGPU render pipelines, vertex/index buffers, textures, samplers, a depth
+texture, actor instancing, and WGSL shaders. Recreate PS1 traits in shaders and a
+post-process pass.
+
+Strengths:
+
+- Uses hardware raster units for the work they are designed to perform.
+- Best route to large geometry and actor-count headroom.
+- Explicit resource and command model fits immutable compiled `RenderScene` data.
+- Storage buffers and compute remain available later without changing API.
+- Device-loss handling can fall back to the software backend.
+
+Costs:
+
+- More setup and resource-lifecycle code than WebGL2.
+- Uniform/storage alignment and bind-group layout require care.
+- Texture upload row pitch must satisfy WebGPU alignment requirements.
+- Browser/device support must be checked against actual release targets.
+- GPU work timing needs optional timestamp queries or coarse CPU submission timing.
+
+Expected scaling:
+
+Current geometry should normally fit in low single-digit GPU milliseconds on a
+reasonable desktop GPU. At this low internal resolution, 50k triangles is small
+for fixed-function GPU rasterization. Hundreds of thousands of visible triangles
+should remain practical if draw count, state changes, and overdraw stay controlled.
+These are estimates, not acceptance results.
+
+### Option B: standard WebGL2 rasterization
+
+Use a WebGL2 context, VAOs, vertex/index buffers, textures, samplers, an offscreen
+framebuffer, a depth attachment, GLSL ES 3 shaders, and instanced actor draws.
+
+Strengths:
+
+- Simpler first standard-raster backend.
+- Broad and mature browser implementation history.
+- All current PS1 effects can be implemented without compute shaders.
+- Hardware triangle throughput should be enough for this engine by a wide margin.
+- Easier shader/program debugging in many browser tools.
+
+Costs:
+
+- More implicit global state than WebGPU.
+- Resource binding and synchronization are less explicit.
+- No general compute path if exact software rasterization becomes necessary.
+- Large dynamic instance data is less flexible than WebGPU storage buffers.
+- A later WebGPU backend would duplicate substantial platform code.
+
+Expected scaling:
+
+For this renderer, standard WebGL2 and standard WebGPU should have similar basic
+triangle throughput because both use hardware rasterization. JavaScript draw-call
+overhead, material changes, and actor submission are more likely to distinguish
+them than raw fill rate at 384x216.
+
+### Option C: WebGPU compute software rasterizer
+
+Port the custom rasterizer to WGSL compute rather than using render pipelines.
+This is the path with the best chance of preserving exact custom edge, depth, and
+pixel rules, but it does not automatically scale like hardware rasterization.
+
+A serious implementation needs multiple stages:
+
+1. Transform vertices and clip triangles.
+2. Compute screen bounds and assign triangles to 8x8 or 16x16 pixel tiles.
+3. Store per-tile triangle lists with overflow handling.
+4. Rasterize each tile in a workgroup, using workgroup memory where useful.
+5. Resolve depth, alpha cutout, texture sampling, lighting, and color.
+6. Run color quantization/dither and copy to the canvas.
+
+Expected speed:
+
+A properly tiled compute renderer could plausibly reduce the current scene to
+roughly 1-5 ms on a decent desktop GPU. A naive port can be slower than the current
+worker renderer. Exact performance depends on tile occupancy, atomics, overdraw,
+texture access, and hardware.
+
+Scaling limitations:
+
+- Vertex transformation and binning still grow with triangle count.
+- Dense tiles grow with local triangle count and overdraw.
+- Triangle-parallel writes contend on depth and color.
+- Pixel-parallel loops over every triangle are catastrophically expensive.
+- Correct alpha-cutout depth ordering complicates packed atomic updates.
+- Reproducing deterministic software ordering can serialize work.
+
+Use this option when exact software-raster behavior is more important than maximum
+content headroom. It is not the recommended first answer to the current scaling
+problem, but it remains open.
+
+### Option D: CPU rasterizer with GPU presentation
+
+Keep software rendering and upload the completed CPU framebuffer into a GPU texture
+for presentation.
+
+Strengths:
+
+- Small migration step.
+- Preserves exact current pixels.
+- Can establish canvas, texture-upload, scaling, and backend-selection plumbing.
+- May simplify or replace Canvas2D presentation.
+
+Limitations:
+
+- Does not move triangle or pixel work off the CPU.
+- Does not solve frame-rate collapse as content grows.
+- Adds an upload every frame.
+
+This remains useful as an intermediate bridge or diagnostic backend, not as the
+destination for the stated performance goal.
+
+### Option E: both WebGPU and WebGL2
+
+Implement a common backend contract, then supply WebGPU, WebGL2, and software
+implementations.
+
+Strengths:
+
+- Best runtime coverage while retaining modern WebGPU capabilities.
+- Allows direct performance comparison on the same machine and scene.
+- Software remains the reference renderer.
+
+Costs:
+
+- Three renderers, shader languages, resource systems, and failure paths.
+- PS1 feature fixes must be maintained in multiple implementations.
+- Highest test and debugging burden.
+
+Do not start both GPU backends simultaneously unless supported-browser requirements
+make that necessary. The common seam should permit a second backend without making
+it mandatory.
+
+## Current architecture that should survive
+
+No game-content rewrite is needed.
+
+- `engine/world/Level.ts` owns live actors, collision, terrain, and render projection.
+- `engine/render/RenderScene.ts` owns static groups, chunks, billboards, prototypes,
+  sky configuration, culling, and scene-local instance data.
+- `engine/render/Chunk.ts` owns LOD choice.
+- `Mesh` already provides flat position/UV vertices and indexed triangles.
+- `Material` already binds a concrete `Texture` and cull setting.
+- `ChunkBuilder` already batches static geometry by material object.
+- Actor definitions already expose material-bound render prototypes.
+- Main-thread frustum culling already prevents invisible chunks and actors from
+  reaching the renderer.
+
+GPU compilation should consume those objects directly. Backend-local maps may
+deduplicate resources by `Mesh`, `Texture`, `Material`, or `RenderPrototype` object
+identity. Such maps are compiled-resource caches, not semantic content registries:
+they have no content names, stable IDs, or dispatch behavior.
+
+## Proposed backend seam
+
+Current `app/renderer.ts` exposes software-specific `fb` and `parallel` fields.
+Presentation also lives partly in `app/main.ts`. A GPU backend needs a backend-neutral
+surface.
+
+Candidate frame input:
+
+```ts
+export type RenderFrame = {
+  camera: Camera
+  viewProjection: Mat4
+  visibleChunks: readonly number[]
+  instances: readonly RenderInstance[]
+  time: number
+}
+```
+
+Candidate renderer contract:
+
+```ts
+export type Renderer = {
+  readonly width: number
+  readonly height: number
+  readonly backend: "software" | "webgl2" | "webgpu"
+  reconfigure: (config: RenderConfig) => void
+  dispatch: (frame: RenderFrame) => void
+  done: () => boolean
+  present: () => void
+  workMs: () => number | null
+  dispose: () => void
+}
+```
+
+This is a candidate, not a final API. Important properties:
+
+- Main loop no longer reads a software `Framebuffer` to discover dimensions.
+- Backend owns presentation. Software calls `putImageData`; WebGL/WebGPU finish a
+  pass targeting the canvas.
+- Software `done()` polls workers; standard GPU backends can initially report true
+  after command submission.
+- `workMs()` may be unavailable until GPU timing support exists.
+- Renderer owns teardown for workers, buffers, textures, and device/context loss.
+- Scene replacement or level reload recompiles backend resources explicitly.
+
+## Module ownership options
+
+Core engine must remain DOM-free and usable by the server.
+
+Recommended initial split:
+
+- `engine/render/RenderScene.ts` keeps backend-neutral scene and frame contracts.
+- `app/renderers/SoftwareRenderer.ts` wraps the current worker renderer.
+- `app/renderers/WebGpuRenderer.ts` or `app/renderers/WebGlRenderer.ts` owns browser
+  API calls and canvas contexts.
+- `app/main.ts` selects a backend and uses only the common renderer contract.
+
+If a GPU backend grows too large for `app/`, another viable option is a separate
+platform project such as `renderers/webgpu/` that depends on `engine/` but is not
+part of DOM-free engine core. Do not add DOM/WebGPU globals to `tsconfig.engine.json`
+merely to make placement convenient.
+
+## Standard GPU resource compilation
+
+Compile resources once per `RenderScene` or level load.
+
+### Meshes
+
+- Convert `Mesh.verts` into one `Float32Array` with stride 5: x, y, z, u, v.
+- Convert `Mesh.indices` into `Uint16Array` when safe or `Uint32Array` otherwise.
+- Create one backend mesh resource per distinct `Mesh` object.
+- Preserve separate chunk meshes; merging all chunks would defeat CPU culling.
+- Release resources when replacing the scene.
+
+### Textures
+
+- Upload existing packed RGBA bytes through a `Uint8Array` view.
+- Keep repeat wrapping.
+- Create nearest and linear samplers without mipmaps.
+- Handle WebGPU `bytesPerRow` alignment with padded staging rows when needed.
+- Deduplicate by `Texture` object identity.
+
+### Materials
+
+- Bind texture resources by `Material.texture` object identity.
+- Keep culling as finite renderer capability, not content identity.
+- Standard GPU paths will probably need two world pipeline variants: culled and
+  double-sided.
+- Avoid one shader program or pipeline per game material.
+
+### Prototypes and instances
+
+- Compile each `RenderPrototype` once.
+- Group visible instances by prototype each frame.
+- Upload transform data once per frame.
+- Draw repeated actors with instancing rather than one command per actor.
+- Keep prototype indexes local to the compiled scene.
+
+### Billboards
+
+- Replace per-frame CPU quad construction with one static unit quad.
+- Supply position/size as instance data.
+- Derive camera-right direction in the vertex shader so billboards stay upright.
+
+## Standard GPU frame structure
+
+### Pass 1: scene color and depth
+
+Render at `RenderConfig.internalWidth` x `RenderConfig.internalHeight` into an
+offscreen RGBA color texture plus depth attachment.
+
+Suggested order:
+
+1. Draw full-screen sky with depth writes disabled.
+2. Draw static groups.
+3. Draw visible chunks using CPU-selected near/far groups.
+4. Draw billboards with alpha cutout and no culling.
+5. Draw actor prototype instances.
+
+### Pass 2: quantization and presentation
+
+Sample the offscreen color texture and apply color-depth quantization plus Bayer
+dither in a full-screen pass. Write to the canvas texture. Keep CSS integer scaling
+and `image-rendering` behavior where useful.
+
+This two-pass shape matches current behavior better than quantizing each material
+fragment independently because software quantization runs after the complete frame,
+including sky.
+
+## Mapping current raster features to shaders
+
+| Current feature | Standard GPU implementation | Parity risk |
+| --- | --- | --- |
+| Perspective-correct UV | Native interpolation | Low; this is already desired behavior |
+| Internal low resolution | Offscreen render target at configured size | Low |
+| Nearest/linear texture filter | Select sampler from `RenderConfig` | Low |
+| No mipmaps | Allocate only base level and use non-mipmap sampler | Low |
+| Vertex snap | Snap projected screen coordinates in vertex shader, then rebuild clip xy | Medium; edge rules differ |
+| Flat lighting | Fragment derivatives of world/view position, or baked face normals | Medium |
+| Distance fog | Fragment shader using view-space distance | Low |
+| Alpha cutout | Fragment `discard` below alpha threshold | Low |
+| Backface culling | Culled and double-sided pipeline variants | Low; front-face sign must be checked |
+| Color depth | Full-screen post-process quantization | Low |
+| Bayer dither | Full-screen integer pixel-coordinate lookup | Low |
+| 1/w depth behavior | Native perspective depth or explicit fragment depth | Medium; exact values differ |
+| Near clipping | Native clipping | Low visually, not pixel-identical |
+| Procedural sky | Full-screen sky shader port | Medium; noise parity must be tested |
+| Chunk frustum culling | Keep existing CPU `RenderScene.visibleChunks` | Low |
+| Actor culling | Keep existing `Level.visibleInstances` | Low |
+| Chunk LOD | Keep existing CPU `Chunk.isFar` selection | Low |
+
+Vertex snap sketch:
+
+```text
+clip = projection * view * model * position
+ndc = clip.xy / clip.w
+pixel = (ndc * 0.5 + 0.5) * internalResolution
+pixel = round(pixel / snap) * snap
+clip.xy = ((pixel / internalResolution) * 2.0 - 1.0) * clip.w
+```
+
+Y orientation and half-pixel conventions differ between APIs and need screenshot
+tests. Do not guess front-face or snap signs from the software renderer.
+
+## Flat-lighting options
+
+### Fragment derivatives
+
+Calculate a face normal from `cross(dpdx(position), dpdy(position))` in the fragment
+shader. This preserves flat faceted lighting without changing mesh data.
+
+Pros:
+
+- Smallest geometry change.
+- Naturally one normal per rasterized face.
+- Available in WebGL2 fragment shaders and WGSL fragment shaders.
+
+Cons:
+
+- Exact shade may differ from the CPU cross-product calculation.
+- Orientation and two-sided handling need validation.
+
+### Baked face normals
+
+Duplicate shared vertices per triangle and store one face normal per vertex.
+
+Pros:
+
+- Explicit and predictable.
+- Can reproduce CPU directional-light math closely.
+
+Cons:
+
+- Increases vertex memory.
+- Requires mesh compilation to expand indexed geometry.
+- Changes cache behavior.
+
+Both options remain open. Derivatives are the recommended first implementation.
+
+## WebGPU-specific notes
+
+- Request adapter/device once and handle failed acquisition cleanly.
+- Configure the canvas using the preferred canvas format.
+- Use an offscreen `rgba8unorm` scene texture and `depth24plus` initially.
+- Keep frame uniforms in a uniform buffer.
+- Use dynamic uniform offsets, instance vertex attributes, or storage buffers for
+  model transforms. Do not repeatedly overwrite one model uniform before submit.
+- Respect 256-byte dynamic-uniform alignment.
+- Group actors by prototype and use `instance_index` for transform lookup.
+- Keep bind-group layouts stable across materials.
+- Separate frame data, texture views, and samplers so changing texture filtering
+  does not force rebuilding every texture resource.
+- Listen for device loss and switch to software rather than leaving a dead canvas.
+- Treat timestamp queries as optional capability.
+- Recreate size-dependent color/depth textures after `RenderConfig` resolution
+  changes.
+
+## WebGL2-specific notes
+
+- Request `webgl2` with alpha and antialias settings chosen explicitly.
+- Use one VAO per compiled mesh.
+- Use an FBO with RGBA color texture and depth renderbuffer/texture.
+- Use GLSL ES 3 vertex/fragment programs for world, billboard, sky, and post passes.
+- Use `drawElementsInstanced` and per-instance matrix attributes for actors.
+- Use `dFdx`/`dFdy` fragment derivatives for flat lighting if selected.
+- Use `EXT_disjoint_timer_query_webgl2` only when available.
+- Handle context loss/restoration by releasing and recompiling scene resources.
+- Reset or centralize state changes; implicit stale state is a major WebGL failure
+  mode.
+
+## WebGPU compute-raster details
+
+Avoid these naive designs:
+
+- One compute invocation per pixel looping over every triangle.
+- One invocation per triangle writing non-atomic color and depth.
+- A global atomic lock per pixel around full shading.
+- Unbounded fixed-size tile lists with silent overflow.
+- Recreating CPU row-band splitting on the GPU.
+
+Open design questions for compute:
+
+- Tile size and maximum triangle references per tile.
+- Multi-pass prefix sums versus fixed tile capacity.
+- Depth encoding suitable for atomic comparison.
+- How alpha-cutout fragments update depth and color consistently.
+- Whether exact triangle order is required for equal-depth fragments.
+- Whether perspective-correct UV and texture filtering use native sampling.
+- How clipping-generated triangles enter tile lists.
+- Whether post-process quantization remains a separate render pass.
+
+Do not implement compute first unless pixel parity is declared a hard requirement
+after testing a standard raster prototype.
+
+## Draw-call and batching strategy
+
+Current chunks are already grouped by material, which is suitable for GPU upload.
+Culling should remain more important than globally merging geometry.
+
+Initial strategy:
+
+- Draw each visible chunk group separately.
+- Skip invisible chunks on CPU.
+- Select near/far groups on CPU.
+- Sort or bucket visible groups by cull pipeline and material only if profiling
+  shows draw-call overhead matters.
+- Instance actors by prototype.
+- Use one unit-quad mesh for billboards.
+
+Possible later optimizations:
+
+- Merge neighboring chunk groups only if visibility remains acceptably granular.
+- Multi-draw or indirect draws where API support and complexity justify them.
+- GPU frustum/occlusion culling only after CPU submission becomes measured cost.
+- Texture atlases or arrays only after material binding becomes measured cost.
+
+Do not add batching abstractions before a profile identifies the bottleneck.
+
+## Performance expectations and growth testing
+
+Standard GPU rasterization is recommended for the content-scaling goal because
+hardware raster units remove the CPU per-triangle/per-pixel loop. However, GPU
+rendering can still lose frame rate through excessive draws, overdraw, huge texture
+uploads, per-frame allocation, or synchronization.
+
+Benchmark growth levels, not only the current scene:
+
+| Scenario | Purpose |
+| --- | --- |
+| 1x current content | Parity and baseline |
+| 2x static props | Early scaling slope |
+| 5x static props | Dense-world target |
+| 10x static props | Stress and culling behavior |
+| 2x/5x moving actors | Instance upload and draw scaling |
+| Worst forest camera | Fill, overdraw, and visible draw count |
+| Empty clearing | Fixed per-frame overhead |
+
+Record:
+
+- CPU simulation time.
+- CPU render submission time.
+- GPU time when available.
+- Median, p95, and max frame time.
+- Visible triangles, draw count, and visible actor count.
+- GPU memory and scene compilation time where practical.
+
+Candidate budget, not yet agreed:
+
+- Keep renderer p95 below roughly 10 ms at the chosen content target, leaving
+  room inside a 16.67 ms frame for simulation, input, browser, and presentation.
+- Demonstrate a substantially flatter frame-time slope than software at 2x and 5x
+  content.
+
+## Migration sequence
+
+### Phase 1: isolate backend contract
+
+1. Introduce `RenderFrame` and backend-neutral renderer dimensions/lifecycle.
+2. Wrap current software renderer without changing output.
+3. Move Canvas2D presentation behind the software backend.
+4. Keep `?bench=st|mt` working.
+5. Add explicit backend query selection such as `?renderer=software|webgl2|webgpu`.
+
+Acceptance:
+
+- Software screenshots and benchmark remain unchanged.
+- Preset switching, resize, worker fallback, and presentation still work.
+
+### Phase 2: GPU scene compiler
+
+1. Traverse `RenderScene` once.
+2. Deduplicate meshes, textures, materials, and prototypes by object identity.
+3. Upload immutable resources.
+4. Record compile time and resource counts.
+5. Add disposal and level-reload behavior.
+
+Acceptance:
+
+- Compiling a scene does not mutate engine scene data.
+- No content names or registries enter backend code.
+- Repeated object references produce one GPU resource.
+
+### Phase 3: minimum standard-raster world
+
+1. Render static groups and visible chunk groups.
+2. Add depth testing and material culling.
+3. Add texture sampling.
+4. Keep CPU culling and LOD.
+5. Use a simple clear color before sky parity exists.
+
+Acceptance:
+
+- Geometry, UVs, winding, depth, and near/far LOD are visibly correct.
+- Current scene already shows major software-to-GPU work-time reduction.
+
+### Phase 4: actors and billboards
+
+1. Compile render prototypes.
+2. Group visible actors by prototype.
+3. Upload per-frame transforms.
+4. Draw actors with instancing.
+5. Draw billboards from a shared unit quad.
+6. Add alpha cutout.
+
+Acceptance:
+
+- No actor content dispatch exists in backend.
+- Worker scene-local prototype semantics remain backend-neutral.
+- Dynamic actor count scaling is measured.
+
+### Phase 5: PS1 look parity
+
+1. Implement vertex snap.
+2. Implement nearest/linear sampler selection.
+3. Implement flat lighting.
+4. Implement fog.
+5. Implement color-depth quantization and Bayer dither in post-processing.
+6. Validate `standard`, `soft`, `clean`, and `ps1` presets.
+
+Acceptance:
+
+- Every current `RenderConfig` knob works live.
+- No PS1 trait is silently hardcoded into GPU shaders.
+
+### Phase 6: sky parity
+
+1. Port gradient and sun.
+2. Port skybox sampling.
+3. Port basic cumulus.
+4. Port fancy cumulus.
+5. Preserve reduced cloud sampling where still useful.
+
+Acceptance:
+
+- Sky animation and panorama orientation match visually.
+- Cloud cost is profiled separately at each internal resolution.
+
+### Phase 7: reliability and selection
+
+1. Handle WebGPU device loss or WebGL context loss.
+2. Fall back to software when GPU initialization fails.
+3. Verify preset switching and resize during active rendering.
+4. Add screenshot comparison and growth benchmarks.
+5. Decide default backend only from support and measured results.
+
+## Validation plan
+
+### Visual scenes
+
+Capture stable views that expose different failure modes:
+
+- Room edge crossing near plane.
+- Terrain horizon with fog.
+- Dense trees and boulders at LOD transition.
+- Flowers and sprite alpha cutout.
+- Frog/bee/robin close and far.
+- Skybox poles and seam.
+- Basic and fancy clouds.
+- Backface-culling winding checks.
+
+### Comparison policy
+
+If standard GPU rasterization is selected, require visual equivalence rather than
+bit-identical frames unless exact parity is later declared. Native clipping, depth,
+edge fill, derivatives, and floating-point behavior will differ.
+
+If compute rasterization is selected specifically for exactness, define which
+parts must match bit-for-bit before implementation. "Exact" cannot remain vague.
+
+### Automated checks
+
+- GPU scene compiler imports no game modules.
+- Renderer backends import no concrete game modules.
+- GPU compilation creates no stable content IDs.
+- Software tests continue passing.
+- Shader compilation errors fail backend initialization clearly.
+- Scene replacement releases old resources.
+- Config switch and resize recreate only size/config-dependent resources.
+- Device/context loss reaches a working fallback.
+
+## Backend choice guide
+
+Choose standard WebGPU first when:
+
+- Target browsers/devices support WebGPU adequately.
+- Future compute or storage-buffer work matters.
+- Explicit resource management is worth the larger initial implementation.
+- Software fallback is acceptable where WebGPU is absent.
+
+Choose WebGL2 first when:
+
+- Broad browser/device coverage is the priority.
+- Fastest path to hardware rasterization is the priority.
+- Current feature set is enough and compute is not required.
+- Maintaining software fallback covers correctness/reference needs.
+
+Choose WebGPU compute first only when:
+
+- Exact custom raster behavior is a hard product requirement.
+- Standard GPU raster tests prove shader emulation insufficient.
+- The project accepts a tile-binning/atomic rasterizer as a major subsystem.
+- WebGPU-only support is acceptable.
+
+Choose both standard GPU APIs only when:
+
+- Browser support requirements cannot be met by one GPU API plus software fallback.
+- The maintenance cost is explicitly accepted.
+
+## Current recommendation
+
+Start with the backend seam, then prototype **standard WebGPU rasterization** while
+keeping software fully operational. Standard WebGL2 remains a valid first backend
+if target-browser research favors it. Measure one textured static world pass before
+porting every visual feature.
+
+Do not begin with compute unless exact edge/depth behavior is declared mandatory.
+For the stated problem, standard hardware rasterization offers the strongest chance
+of adding substantially more content without frame time growing like the current
+CPU rasterizer.
+
+## Questions required before implementation
+
+1. Which browsers, OS versions, and device classes must run the GPU path?
+2. Is software-renderer pixel identity required, or is visual equivalence enough?
+3. What content-growth target must hold 60 fps: 2x, 5x, 10x, or a concrete level?
+4. Is the software backend a permanent supported mode or only migration/reference?
+5. Is GPU timing required in the HUD for the first version?
+6. Should backend selection be automatic, query-driven, or user-configurable?
+7. Is WebGPU compute still desired after a standard-raster visual prototype exists?
+
+Until these are answered, keep all options above open and avoid API choices that
+make WebGL2, WebGPU rasterization, or WebGPU compute unnecessarily impossible.
diff --git a/.agents/plans/levels-and-editor.md b/.agents/plans/levels-and-editor.md
index b43fb0a..05acc47 100644
--- a/.agents/plans/levels-and-editor.md
+++ b/.agents/plans/levels-and-editor.md
@@ -1,9 +1,18 @@
 # Levels & the in-game editor — direction note
 
-Status: **direction agreed, not yet built.** Captures a brainstorm so the next
+Status: **historical proposal, partially superseded.** Captures a brainstorm so the next
 session starts from the conclusion, not a cold read. Nothing here is committed
 code; it's the shape we want and *why*.
 
+> **Architecture note (2026-08-20):** Naming and ownership sections below are
+> superseded by `docs/adr/0001-engine-owns-world-concepts.md` and `CONTEXT.md`.
+> Canonical terms are now engine `LevelDefinition` (live-level creation input),
+> engine `Level` (live runtime), and clone-safe engine `RenderScene`; game owns
+> concrete definitions and values. A future serializable editor document needs its
+> own name rather than overloading these runtime terms. References below to game-owned world contracts, content
+> `kind` fields/registries, `game/Terrain.ts`, or `game/renderScene.ts` describe the
+> old code only. Editor goals remain valid but must use the canonical boundary.
+
 ## The pivot
 
 The game is heading toward a **multiplayer twitch shooter**. Each match loads a
@@ -20,7 +29,7 @@ The game is heading toward a **multiplayer twitch shooter**. Each match loads a
 - **Persistence and player carry-over are YAGNI** for now — but must not be walled
   off (see hedges).
 
-## Naming: `Level` (data) vs `Scene` (runtime)
+## Historical naming proposal: `Level` (data) vs `Scene` (runtime)
 
 Agreed vocabulary — reads as **"bake a `Level` into a `Scene`."** Fits the
 type + namespace convention.
@@ -210,7 +219,7 @@ field = mutate the document + re-bake.
 - **No hardcoded buffer sizes** tied to today's world — mob/framebuffer sizing already
   re-runs on `setup`; keep it so odd-shaped match maps just work.
 
-## Current-state facts the next session will need
+## Historical current-state facts (before 2026-08-20)
 
 - `buildLevel(textures): Level` (`game/level.ts:175`) is the single entry, called once
   in `app/main.ts`. Today's `Level` (`game/level.ts:69-81`) is a **bake result**
diff --git a/.agents/rules/forge-sync.md b/.agents/rules/forge-sync.md
deleted file mode 100644
index 6270721..0000000
--- a/.agents/rules/forge-sync.md
+++ /dev/null
@@ -1,29 +0,0 @@
----
-description: Local vs sync mode rules for git and Forgejo — commit, push, and PR policy per workflow.
----
-
-# Forge Sync Rules
-
-When a workflow uses explicit mode:
-
-- `Mode: sync` or `--sync` means sync mode.
-- no sync marker means local mode.
-- Do not ask whether git workflow should be agent-managed.
-
-Local mode:
-- No push.
-- No forge write tools.
-- No PR create/update/comment.
-
-Sync mode:
-- Commit completed workflow units.
-- Push after each unit commit.
-- Create PR after first push if missing.
-- Reuse existing PR on later pushes.
-- Comment/update PR only when workflow asks for it.
-
-Forbidden always:
-- No force push.
-- No branch deletion.
-- No hard reset.
-- No amending unless explicitly requested.
diff --git a/.agents/rules/openspec.md b/.agents/rules/openspec.md
deleted file mode 100644
index b8b8bf1..0000000
--- a/.agents/rules/openspec.md
+++ /dev/null
@@ -1,19 +0,0 @@
----
-description: Rules for OpenSpec propose and archive workflows.
----
-
-# OpenSpec Instructions
-
-## OpenSpec Propose Workflow
-
-When proposing changes via `/opsx-propose`:
-
-- If the change introduces or modifies user-facing behavior (API changes, conventions), include a task section for updating `README.md` in the proposal's impact assessment.
-
-## OpenSpec Archive Workflow
-
-When archiving tasks via `/opsx-archive`:
-
-1. Automatically sync specs, do not ask the user.
-2. If mode is explicit, use `forge-sync` for archive commit, push, PR, and Forgejo behavior.
-3. If no mode is explicit, default to local mode.
diff --git a/.claude/skills b/.claude/skills
deleted file mode 120000
index 2b7a412..0000000
--- a/.claude/skills
+++ /dev/null
@@ -1 +0,0 @@
-../.agents/skills
\ No newline at end of file
diff --git a/AGENTS.md b/AGENTS.md
index ec19f68..fb5325f 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -26,14 +26,19 @@ rules live in `.agents/rules/*.md`.
   frame; on-screen solids also **backface-cull**. This is what keeps a dense world
   (thousands of trees/rocks) affordable — off-screen content costs ~nothing.
 - **2D assets only.** Sprites/billboards (PS1-style), **no 3D model loading**.
-- **Three layers, one-way deps: `engine` ← `game` ← `app`.** `engine/` is the
-  reusable, content-agnostic **mechanism** (rasterizer, framebuffer, culling, the
-  `Actor`/`Material` interfaces) — no DOM, no game content, could run server-side.
-  `game/` is **this game's content** (the creatures/props, terrain, level, scene
-  assembly + render orchestration) built on the engine interfaces. `app/` is
-  **browser glue** (canvas, input, image decode, the worker render driver + loop).
+- **Three layers, one-way deps: `engine` ← `game` ← `app`.** `engine/` owns
+  reusable, content-agnostic **concepts and mechanisms**: levels, terrain, actors,
+  prefabs, collision, render scenes, chunking/LOD, rasterization, and worker render
+  transport. `game/` owns **this game's concrete content**: actual level values,
+  placements, materials, and frog/bee/robin or oak/spruce/birch definitions.
+  `app/` is browser glue (canvas, input mapping, image decode, workers, frame loop).
   Enforced: `engine/` imports nothing from `game`/`app`, `game/` nothing from `app`
   (`tests/layering.test.ts`). Both `engine` and `game` are DOM-free (tsconfig).
+- **No closed game-content kinds or registries.** Instances reference concrete
+  `ActorDefinition`/`Prefab` objects directly. Do not add `MobKind`, `TreeKind`,
+  `*_KINDS`, content dispatch switches, or stable content-order protocols. Numeric
+  prototype indexes are scene-local engine transport details only. Closed unions
+  remain valid for finite engine capabilities such as collider or cloud shape.
 
 ## Stack & tooling
 
@@ -57,7 +62,7 @@ rules live in `.agents/rules/*.md`.
 - `bunx tsc --build tsconfig.app.json` — **typecheck the engine+game+app graph. Use
   this**, not `bun run check` (see Caveats).
 - `bunx oxlint engine game app` — lint.
-- `bun test` — tests (registry id-order + engine↛game layering guards).
+- `bun test` — tests (world compilation, render protocol, boundary guards).
 - `bun run serve` — Bun server (`server/server.ts`, a stub for now).
 
 ## Layout
@@ -71,73 +76,51 @@ rules live in `.agents/rules/*.md`.
     (optional backface cull per draw), `Frustum` (6 planes from the viewProj +
     AABB test, for chunk culling), `Texture` (nearest/bilinear, wrapping, no
     mipmaps), `Material` (texture + cull flag; a `DrawGroup` pairs a mesh with one,
-    so the renderer draws by list, not by named texture), `Sky` (gradient + sun +
-    procedural clouds; renders at 1/`step` res).
+    so the renderer draws by list, not by named texture), `Chunk`/`ChunkBuilder`
+    (spatial batches + two-level LOD), `RenderScene` (clone-safe scene projection,
+    culling + band rendering), `RenderProtocol` (shared worker frame layout), and
+    `Sky` (full-resolution gradient + sun, procedural clouds sampled at 1/`step`).
   - `scene/` — `Camera` (fps yaw/pitch; far plane reaches the outdoor peaks),
     `Mesh` (indexed tris; verts stored flat: `STRIDE` floats x,y,z,u,v per vertex,
     no per-vertex objects — cache-friendly + alloc-free to draw), `Sprite`
-    (Y-axis billboard), `Actor` (the generic `Entity<State, World>` interface —
-    build + update + bounds — that a content kind implements; the engine dispatches
-    through it, never a `kind` switch).
-- `game/` — this game's content + world assembly, on the engine interfaces
+    (Y-axis billboard), `MeshBuilder` (generic quad/slab/box construction), `Actor`
+    (open behavior + render/collider contract), and `Prefab` (open static-content
+    contract + type-erased placed value).
+  - `world/` — `Terrain` (height contract, built-in rolling generator, generic
+    patch meshing), `Collider`/`CollisionWorld`, `CharacterController`, and `Level`
+    (live actor/collision state + clone-safe `RenderScene` projection).
+- `game/` — this game's definitions and level data, on the engine interfaces
   (headless: no DOM, imports nothing from `app`).
   - `actors/` — the placeable things. `Mob` (a **roaming** creature — `frog` hops
     the ground, `bee` hovers/darts, `robin` mostly hops but now and then takes a
-    short powered flight — the only moving geometry; each kind an `Entity` in
-    `mobs/<Kind>.ts` + shared `mobs/mobkit.ts`, assembled by the thin `Mob` registry.
-    Its local-space mesh is built once per kind; `Mob.update` steps the wander AI
-    (leashed to a home anchor, deterministic per evolving `seed`) each frame and the
-    live `position`/`heading`/`scale` become a per-frame model matrix at draw.
-    `MOB_KINDS` is the SAB id order). `Tree` (oak/spruce/birch, each a `TreeSpecies`
-    in `trees/<Kind>.ts` + `trees/treekit.ts` — see the Trees section), `Boulder`
+    short powered flight — the only moving geometry; each module exports an
+    `ActorDefinition` factory and instances hold the resulting object directly.
+    `Tree` is shared placement state; Oak/Spruce/Birch modules export material-bound
+    `Prefab<Tree>` factories with no species registry. `Boulder`
     (squashed jittered part-buried sphere), `Bush` (leaf-blob cluster, shares the
     leaf mesh), `Flower` (stem + colored bloom, 2x2 atlas, double-sided). Baked props
     append into shared per-material meshes; mobs draw live.
-  - `Terrain.ts` — procedural heightfield around the room (flat clearing, rolling
-    hills, tall edge peaks). `Terrain.patch` builds one ground patch over a rectangle
-    (per chunk, welds crack-free, hole for the room); `Terrain.height` is the shared
-    ground sampler for the player + mobs.
-  - `level.ts` — builds the playground: a flat stone-floored room (three thick
-    walls via `slab`, north side open) always drawn, in the center of a big grassy
-    `Terrain` world (~20x across). Props are placed first (`placeTrees` /
-    `placeBoulders` / `placeBushes` / `placeFlowers` → instance lists + colliders;
-    `TREE_/BOULDER_/BUSH_/FLOWER_COUNT`/`_SEED`/`_REACH`) and the roaming mobs
-    scattered (`placeMobs`; `FROG_/BEE_/ROBIN_COUNT`, `MOB_SEED`, `MOB_REACH` — mobs
-    move, so no baked colliders), then `buildChunks` bakes terrain + props into a
-    `CHUNK_GRID` x `CHUNK_GRID` grid of `Chunk`s (each = a tight AABB + two
-    `DrawGroup[]` lists `near`/`far`; the baker accumulates one mesh per **material
-    key** (`MAT_ORDER`) and routes each prop by its declared material, so it names no
-    texture) that `main` frustum-culls. Trees + boulders bake **twice** — full into
-    `near`, a low-poly impostor into `far` — so a far chunk swaps to the cheap set
-    with no per-frame work (`chunkFar` / `RenderConfig.lodDistance`).
-    `buildLevel(textures)` binds the ground/prop `Material`s once + shares them.
-    Also: `Aabb` colliders, NPC position, `TERRAIN`/`TERRAIN_SUBDIV`/`GROUND_UV`,
-    sky/cloud config, `FLOOR_LIFT` (a z-bias lifting the stone floor over the terrain
-    skirt). Room surfaces are single flat quads (texturing is perspective-correct).
-  - `renderScene.ts` — `renderBand(fb, scene, …, mobDraws, …, y0, y1)`: the single
-    source of render truth (sky + room + culled chunk draw-groups + sprite + roaming
-    mobs + quantize for a row band). Used full-height by the inline path, per-band by
-    each worker. `Scene` bundles the static meshes/textures (incl. the canonical mob
-    meshes) so it clones to a worker whole; each mob draws double-sided through its
-    own `viewProj × Mat4.compose(...)` model matrix, and `visibleChunks`/`visibleMobs`
-    frustum-cull per frame. `textures.ts` holds the `Textures` palette type.
-  - `player.ts` — feet-cylinder player: gravity/jump + Shift-run (`RUN_MULTIPLIER`)
-    + circle-vs-AABB/-circle collision, substepped so fast running can't tunnel
-    walls; ground height from `Terrain.height` (plus standable AABBs).
+  - `level.ts` — concrete playground values and placement policy: room dimensions,
+    rolling-terrain parameters, counts/seeds/reach, material bindings, sky, and
+    spawn definition lists. It places direct `Prefab` objects, submits the resulting
+    values to engine `ChunkBuilder`, then creates engine `Level`; no game renderer or material-key
+    registry exists. Trees + boulders bake full and far-impostor geometry; bushes
+    and flowers provide near geometry only.
+  - `player.ts` — concrete player tuning only; movement and collision live in
+    engine `CharacterController`.
 - `app/` — browser glue only (top layer; depends on `game` + `engine`).
   - `main.ts` — game loop: input, sim, preset switching, per-frame culling, then
     the non-blocking pump (`renderer.dispatch`/`done`) + `present` (GPU/CSS upscale)
     + a multi-line frame HUD (`work + present` critical-path ms, vsync, visible
-    chunks / LOD-aware tris). Owns the **mob sim**: steps `Mob.update` for every mob,
-    rebuilds near-player mob colliders into `level.colliders`, culls mobs
-    (`visibleMobs`) so only visible transforms dispatch.
+    chunks / LOD-aware tris). Calls engine `Level` simulation/collider extraction,
+    maps browser keys into `CharacterInput`, and dispatches visible render instances.
   - `renderer.ts` — the render driver. When the page is cross-origin-isolated it runs
     a pool of `render-worker.ts` threads (`MAX_WORKERS`) over a `SharedArrayBuffer`
     framebuffer, each owning a disjoint row band, synced by a lock-free `Atomics`
     barrier; otherwise inline. `dispatch`/`done` are non-blocking so the caller paces
     on rAF. Per-frame inputs ride shared arrays: camera/matrix/visible-chunk list +
-    visible **mob transforms** (`mobState`, count in `MOBVIS`). `?bench=st|mt` A/Bs
-    the paths.
+    visible engine instance prototype indexes + transforms. `?bench=st|mt` A/Bs
+    the paths. Renderer and worker import no game modules.
   - `assets.ts` — load `/assets/*.png` → `Texture` (zero-copy; ImageData bytes are
     already the `Color` layout); returns the `game` `Textures` palette.
 - `index.html` — Vite entry at repo root; holds the `#screen` canvas and the
@@ -155,9 +138,10 @@ rules live in `.agents/rules/*.md`.
 
 ## Frame pipeline (`app/main.ts` `tick`)
 
-`Mob.update` (all mobs) + rebuild near-player mob colliders → `Player.update` →
-build `Camera` → `Camera.viewProjection` → `visibleChunks` + `visibleMobs`
-(frustum-cull, once on the main thread) → `renderer.dispatch` (non-blocking) →
+`Level.update` (all actors) + `Level.refreshActorColliders` →
+`CharacterController.update` → build `Camera` → `Camera.viewProjection` →
+`RenderScene.visibleChunks` + `Level.visibleInstances` (frustum-cull, once on the
+main thread) → `renderer.dispatch` (non-blocking) →
 next rAF: `renderer.done()` ? `present` : skip this vsync. Frame N is presented
 while N+1 is dispatched; the pump never blocks or async-awaits, so it can't
 desync from rAF.
@@ -171,16 +155,15 @@ an integer multiple (crisp letterbox, centered) once per resize/config, and
 `linear`). This replaced a per-frame main-thread `drawImage` that scaled to the
 whole window (cost grew with window size); present is now ~0.2ms.
 
-`renderBand` runs `renderScene.renderBand` for rows [y0,y1): `Sky.render` at
-1/`SKY_STEP` res (fills color + resets depth, replaces a clear) → `Rasterizer.draw`
+`renderBand` runs `RenderScene.renderBand` for rows [y0,y1): `Sky.render` with
+clouds sampled at 1/`SKY_STEP` res (fills color + resets depth, replaces a clear) → `Rasterizer.draw`
 floor/walls/crate (room, always) → for each visible `Chunk`, loop its draw-groups —
-`near` or `far` chosen by the pure `chunkFar` test (dist² from camera to the chunk
+`near` or `far` chosen by the pure `Chunk.isFar` test (dist² from camera to the chunk
 AABB vs `lodDistance²`): `near` is grass + full trees/rocks + flowers, `far` is grass
 + the cheap impostors (foliage/flowers dropped). Each group draws with its own
 `Material` (cull per-material, so solids backface-cull and flowers stay double-sided)
-→ `Sprite.billboard(npc)` →
-the roaming mobs (each: shared local mesh × its `Mat4.compose` model matrix,
-double-sided) → `Framebuffer.quantize`. `chunkFar` is pure (camera + baked bounds + config
+→ each billboard → each visible actor prototype instance (shared local draw groups ×
+its `Mat4.compose` model matrix) → `Framebuffer.quantize`. `Chunk.isFar` is pure (camera + baked bounds + config
 only), so every worker band picks the same LOD for a chunk → no horizontal seam.
 Multi-threaded: N workers each run `renderBand` over
 their band of the shared framebuffer in parallel; single-threaded: one call over
@@ -225,9 +208,9 @@ off-screen or fogged each frame, so several things keep it cheap:
   chunks that fall outside the view. Behind you + off to the sides = free.
 - **Backface culling** (`draw(..., true)`) — ~halves fill on solid geometry
   (terrain, foliage, rock). See the Rasterizer note re winding.
-- **Half-res sky** (`SKY_STEP` in `main`, default 2) — the cloud fbm runs per
+- **Half-res clouds** (`SKY_STEP` in `app/renderer.ts`, default 2) — cloud fbm runs per
   pixel and dominated the frame; sampling once per 2×2 block quarters it.
-- **Distance LOD** (`RenderConfig.lodDistance`, `chunkFar` in `renderScene`) —
+- **Distance LOD** (`RenderConfig.lodDistance`, `Chunk.isFar`) —
   past `lodDistance` a chunk's trees + boulders swap to pre-baked low-poly
   impostors and its bushes/flowers drop; both meshes are baked once at load, and
   the near/far pick is a pure function of camera + chunk bounds, so it costs
@@ -282,11 +265,10 @@ branching in the cloud shader. Cost scales with sky resolution — fine at
 
 ## Trees (`game/actors/Tree.ts` + `game/actors/trees/`)
 
-Procedural low-poly geometry, faceted flat-shaded like everything else. Each species
-is a `TreeSpecies` definition in its own `trees/<Kind>.ts` module (geometry +
-which chunk materials its trunk/foliage bake into); `Tree.ts` just assembles them
-into a registry (`Tree.species(kind)`, `TREE_KINDS`) and shared primitives live in
-`trees/treekit.ts`. Three `kind`s carry the species read purely by silhouette:
+Procedural low-poly geometry, faceted flat-shaded like everything else. `Tree.ts`
+contains only shared placement state. Oak, Spruce, and Birch each expose a concrete
+`Prefab<Tree>` factory from their own module; level data references those definition
+objects directly, and shared geometry primitives live in `trees/treekit.ts`.
 - **`oak`** — short tapered trunk, a couple of branches, a broad cluster of
   lumpy canopy `blob`s (wider than tall, bushy).
 - **`spruce`** — tall thin trunk under stacked narrowing `cone` tiers pointing
@@ -298,14 +280,11 @@ into a registry (`Tree.species(kind)`, `TREE_KINDS`) and shared primitives live
 
 `growth` (0..1) runs **sapling → full grown**: it scales height/girth and adds
 canopy blobs (oak/birch) / tiers (spruce); `seed` gives each tree its own wobble.
-A species declares its `trunk`/`foliage` **material keys** (e.g. birch → white
-`birch` trunk, oak `leaf` foliage); the chunk baker (`level.ts`) accumulates one
-mesh per material key and routes each tree via `Tree.species(kind)` — so a forest
-still batches into a few draw calls and the baker names no texture. `game/level.ts`
-`placeTrees` seeds the forest and rolls the species. **Add a species** = add a
-`trees/<Kind>.ts` module (its geometry + material keys) + one entry in the `Tree`
-registry; only a genuinely new material also needs a `Material` in `buildLevel` +
-its key in `MAT_ORDER`.
+Each factory receives concrete trunk/foliage `Material` objects and closes over
+them. `ChunkBuilder` accumulates meshes by material object, so a forest still
+batches into a few draw groups without string keys or a registry. `game/level.ts`
+`placeTrees` selects from a weighted list of prefab objects. **Add a species** =
+add one concrete prefab module and include its object in level data.
 
 **Boulders** (`game/actors/Boulder.ts`) work the same way: `Boulder.build`
 appends a squashed, per-vertex-jittered low-poly sphere (seam/pole-safe so it
@@ -317,7 +296,7 @@ colliders; add a new prop type by cloning the pattern (generator + scatter).
 
 ## Controls
 
-WASD move · **Shift** run (speed ×`RUN_MULTIPLIER` in `game/player.ts`) · mouse
+WASD move · **Shift** run (speed from `Player.config` in `game/player.ts`) · mouse
 look (click canvas to pointer-lock) · **Space** jump · **1/2/3** switch look
 presets. FPS shown bottom-right. The room's north wall is open — walk out onto
 the terrain and toward the peaks.
@@ -349,7 +328,7 @@ job tmp dir, not the repo.
 ## Roadmap / not yet built
 
 In-browser RenderConfig slider panel; mipmaps; `painter` depth mode; gouraud
-lighting; more cloud types; more props / a weapon; more mob kinds + smarter mob
+lighting; more cloud types; more props / a weapon; more mob definitions + smarter mob
 behavior (they wander + block/stand-on today, but don't yet react to the player). `shared/`
 is nearly empty. The FPS meter is static HTML + `textContent` writes only — no
 DOM-built UI yet (deliberate).
diff --git a/CLAUDE.md b/CLAUDE.md
deleted file mode 100644
index bd3438f..0000000
--- a/CLAUDE.md
+++ /dev/null
@@ -1,10 +0,0 @@
-@AGENTS.md
-@.agents/rules/big-red-dog.md
-@.agents/rules/caveman.md
-@.agents/rules/commits.md
-@.agents/rules/forge-sync.md
-@.agents/rules/openspec.md
-@.agents/rules/quality.md
-
-Don't nudge the user towards branching or commiting. User is perfectly capable of handling this.
-
diff --git a/CONTEXT.md b/CONTEXT.md
new file mode 100644
index 0000000..6091c46
--- /dev/null
+++ b/CONTEXT.md
@@ -0,0 +1,29 @@
+# Meat Engine
+
+Meat separates reusable first-person game capabilities from one game's concrete world and creatures.
+
+## Language
+
+**Level Definition**:
+A complete engine-shaped input for creating one live Level. Game code produces it from concrete values and definitions; it is not the worker rendering payload.
+_Avoid_: Scene assembly
+
+**Level**:
+A live playable world created from a Level Definition, including terrain, actors, collision, and rendering state.
+_Avoid_: Map, scene
+
+**Terrain**:
+A bounded ground surface that can report height at any horizontal world position.
+_Avoid_: Ground mesh
+
+**Actor Definition**:
+A concrete reusable definition of one moving thing's behavior, representation, transform, and physical presence. Actor instances reference definitions directly.
+_Avoid_: Mob kind, actor kind, type registry
+
+**Prefab**:
+A concrete reusable definition for static level content, including its geometry and optional physical presence. Placed prefabs reference definitions directly.
+_Avoid_: Prop kind, tree kind, species registry
+
+**Render Scene**:
+The behavior-free rendering projection of a Level.
+_Avoid_: Level
diff --git a/app/main.ts b/app/main.ts
index 2e320e6..9a360e7 100644
--- a/app/main.ts
+++ b/app/main.ts
@@ -1,20 +1,18 @@
 import { RenderConfig } from "../engine/render/RenderConfig"
+import { RenderScene, type RenderInstance } from "../engine/render/RenderScene"
 import { Camera } from "../engine/scene/Camera"
-import type { Mesh } from "../engine/scene/Mesh"
-import { Mob, MOB_KINDS, type MobKind } from "../game/actors/Mob"
-import type { Vec3 } from "../engine/math/Vec3"
+import {
+  CharacterController,
+  type CharacterInput,
+} from "../engine/world/CharacterController"
+import { Level } from "../engine/world/Level"
 import { loadTextures } from "./assets"
-import { buildLevel, type Level } from "../game/level"
-import { EYE_HEIGHT, Player } from "../game/player"
+import { buildLevel } from "../game/level"
+import { Player, type Player as PlayerState } from "../game/player"
 import { createRenderer } from "./renderer"
-import { chunkFar, visibleChunks, visibleMobs, type Scene } from "../game/renderScene"
 
 const FOV_DEGREES = 75
 const FOV = (FOV_DEGREES * Math.PI) / 180
-/** How close (world units) a mob must be to the player to get a live collider.
- *  Mobs farther than this can't be touched this frame, so skip them -- keeps the
- *  per-frame collider list (and the player's collision loop) short. */
-const MOB_COLLIDE_RANGE = 3
 
 const screen = document.querySelector<HTMLCanvasElement>("#screen")!
 const ctx = screen.getContext("2d")!
@@ -28,7 +26,11 @@ function benchCamera(tv: number): Camera {
   const drift = tv * 0.12
   const radius = 65 + 30 * Math.sin(tv * 0.25)
   return {
-    position: { x: Math.cos(drift) * radius, y: 3, z: Math.sin(drift) * radius },
+    position: {
+      x: Math.cos(drift) * radius,
+      y: 3,
+      z: Math.sin(drift) * radius,
+    },
     yaw: tv * 0.7,
     pitch: 0.05 * Math.sin(tv * 0.5),
     fov: FOV,
@@ -39,41 +41,34 @@ function round2(n: number): number {
   return Math.round(n * 100) / 100
 }
 
-function benchStats(a: number[]): { median: number; p95: number; max: number; mean: number } {
+function benchStats(a: number[]): {
+  median: number
+  p95: number
+  max: number
+  mean: number
+} {
   const s = a.toSorted((x, y) => x - y)
-  const q = (p: number): number => s[Math.min(s.length - 1, Math.floor(p * s.length))]
-  return { median: round2(q(0.5)), p95: round2(q(0.95)), max: round2(s[s.length - 1]), mean: round2(a.reduce((x, y) => x + y, 0) / a.length) }
+  const q = (p: number): number =>
+    s[Math.min(s.length - 1, Math.floor(p * s.length))]
+  return {
+    median: round2(q(0.5)),
+    p95: round2(q(0.95)),
+    max: round2(s[s.length - 1]),
+    mean: round2(a.reduce((x, y) => x + y, 0) / a.length),
+  }
 }
 
 async function main(): Promise<void> {
   const textures = await loadTextures()
   const level = buildLevel(textures)
-  // Build each kind's canonical mesh once, shared by every instance (the sim
-  // supplies each mob's per-frame transform). Registry-driven -- a new kind needs
-  // no change here.
-  const mobMesh = {} as Record<MobKind, Mesh>
-  for (const kind of MOB_KINDS) {
-    const m: Mesh = { verts: [], indices: [] }
-    Mob.build(kind, m)
-    mobMesh[kind] = m
-  }
-  const scene: Scene = {
-    chunks: level.chunks,
-    floor: level.floor,
-    walls: level.walls,
-    crate: level.crate,
-    npc: { position: level.npcPosition, size: { x: 1.1, y: 1.5 } },
-    mobMesh,
-    mobCount: level.mobs.length,
-    sky: level.sky,
-    textures,
-  }
   // `?bench=st` / `?bench=mt` runs a scripted flythrough and reports timings.
   const benchMode = new URLSearchParams(globalThis.location.search).get("bench")
-  const forceWorkers = benchMode === "mt" ? true : benchMode === "st" ? false : undefined
+  const forceWorkers =
+    benchMode === "mt" ? true : benchMode === "st" ? false : undefined
 
   let config: RenderConfig = RenderConfig.standard
-  const renderer = createRenderer(scene, config, forceWorkers)
+  const renderer = createRenderer(level.render, config, forceWorkers)
+  let inFlight = false
   let image = new ImageData(renderer.fb.width, renderer.fb.height)
   let colorBytes = new Uint8ClampedArray(renderer.fb.color.buffer)
 
@@ -93,20 +88,30 @@ async function main(): Promise<void> {
   // letterboxed upscale, done by the GPU). Recomputed only on resize/config.
   function layout(): void {
     const fb = renderer.fb
-    const scale = Math.max(1, Math.floor(Math.min(globalThis.innerWidth / fb.width, globalThis.innerHeight / fb.height)))
+    const scale = Math.max(
+      1,
+      Math.floor(
+        Math.min(
+          globalThis.innerWidth / fb.width,
+          globalThis.innerHeight / fb.height,
+        ),
+      ),
+    )
     const w = fb.width * scale
     const h = fb.height * scale
     screen.style.width = `${w}px`
     screen.style.height = `${h}px`
     screen.style.left = `${(globalThis.innerWidth - w) >> 1}px`
     screen.style.top = `${(globalThis.innerHeight - h) >> 1}px`
-    screen.style.imageRendering = config.upscaleFilter === "linear" ? "auto" : "pixelated"
+    screen.style.imageRendering =
+      config.upscaleFilter === "linear" ? "auto" : "pixelated"
   }
   retarget()
 
   function useConfig(next: RenderConfig): void {
     config = next
     renderer.reconfigure(next)
+    inFlight = false
     retarget()
   }
 
@@ -122,9 +127,7 @@ async function main(): Promise<void> {
     return
   }
 
-  const player: Player = { position: { x: 0, y: 0, z: 8 }, yaw: 0, pitch: 0, velocityY: 0, onGround: true }
-  // Colliders past this index are the dynamic mob ones, rebuilt every frame.
-  const staticColliderCount = level.colliders.length
+  const player: PlayerState = Player.create()
   const keys = new Set<string>()
   globalThis.addEventListener("keydown", (e) => {
     keys.add(e.code)
@@ -154,26 +157,30 @@ async function main(): Promise<void> {
       return
     }
     player.yaw += e.movementX * 0.0025
-    player.pitch = Math.max(-1.4, Math.min(1.4, player.pitch - e.movementY * 0.0025))
+    player.pitch = Math.max(
+      -1.4,
+      Math.min(1.4, player.pitch - e.movementY * 0.0025),
+    )
   })
 
   // Triangles drawn this frame (room + each visible chunk, LOD-aware) for the HUD.
-  function frameTris(visible: number[], cam: Camera): number {
-    let t = level.floor.indices.length + level.walls.indices.length + level.crate.indices.length
-    for (const i of visible) {
-      const c = level.chunks[i]
-      const groups = chunkFar(c, cam.position, config.lodDistance) ? c.far : c.near
-      for (const g of groups) {
-        t += g.mesh.indices.length
-      }
-    }
-    return (t / 3) | 0
+  function frameTris(
+    visible: number[],
+    instances: RenderInstance[],
+    camera: Camera,
+  ): number {
+    return RenderScene.triangleCount(
+      level.render,
+      visible,
+      instances,
+      camera.position,
+      config.lodDistance,
+    )
   }
 
   // Poll-based pump: present the finished frame, dispatch the next; if workers
   // aren't done we skip this vsync (no async/rAF desync). The HUD reports the
   // critical-path budget (work + present) so the real bottleneck is visible.
-  let inFlight = false
   let last = performance.now()
   let fpsLast = last
   let fpsFrames = 0
@@ -182,7 +189,13 @@ async function main(): Promise<void> {
   let vsyncMax = 0
   let lastPresent = performance.now()
   let lastVisible: number[] = []
-  let lastCamera: Camera = { position: { x: 0, y: 0, z: 0 }, yaw: 0, pitch: 0, fov: FOV }
+  let lastInstances: RenderInstance[] = []
+  let lastCamera: Camera = {
+    position: { x: 0, y: 0, z: 0 },
+    yaw: 0,
+    pitch: 0,
+    fov: FOV,
+  }
 
   function show(): void {
     const p0 = performance.now()
@@ -213,30 +226,42 @@ async function main(): Promise<void> {
       fpsEl.textContent =
         `${fps} fps${tag}\n` +
         `work ${round2(workMax)} + present ${round2(presentMax)} = ${round2(workMax + presentMax)}ms\n` +
-        `vsync ${round2(vsyncMax)}ms · ${lastVisible.length} ch · ${frameTris(lastVisible, lastCamera)} tris`
+        `vsync ${round2(vsyncMax)}ms · ${lastVisible.length} ch · ${frameTris(lastVisible, lastInstances, lastCamera)} tris`
       fpsLast = now
       fpsFrames = 0
       workMax = 0
       presentMax = 0
       vsyncMax = 0
     }
-    for (const m of level.mobs) {
-      Mob.update(m, dt, level.terrain)
-    }
-    rebuildMobColliders(level, player.position, staticColliderCount)
-    Player.update(player, keys, dt, level)
+    Level.update(level, dt)
+    Level.refreshActorColliders(level, player.position, Player.actorCollisionRange)
+    CharacterController.update(
+      player,
+      readPlayerInput(keys),
+      dt,
+      level.collision,
+      Player.config,
+    )
     const camera: Camera = {
-      position: { x: player.position.x, y: player.position.y + EYE_HEIGHT, z: player.position.z },
+      position: {
+        x: player.position.x,
+        y: player.position.y + Player.config.eyeHeight,
+        z: player.position.z,
+      },
       yaw: player.yaw,
       pitch: player.pitch,
       fov: FOV,
     }
-    const viewProj = Camera.viewProjection(camera, renderer.fb.width / renderer.fb.height)
-    const visible = visibleChunks(level.chunks, viewProj)
-    const mobDraws = visibleMobs(level.mobs, viewProj)
+    const viewProj = Camera.viewProjection(
+      camera,
+      renderer.fb.width / renderer.fb.height,
+    )
+    const visible = RenderScene.visibleChunks(level.render, viewProj)
+    const instances = Level.visibleInstances(level, viewProj)
     lastVisible = visible
+    lastInstances = instances
     lastCamera = camera
-    renderer.dispatch(camera, viewProj, visible, now / 1000, mobDraws)
+    renderer.dispatch(camera, viewProj, visible, now / 1000, instances)
     inFlight = true
     if (renderer.done()) {
       show()
@@ -250,7 +275,7 @@ async function main(): Promise<void> {
  *  interval, then reports the distributions (exposed on `window.__BENCH__`). */
 function runBench(
   renderer: ReturnType<typeof createRenderer>,
-  level: Level,
+  level: ReturnType<typeof buildLevel>,
   present: () => void,
   mode: string,
 ): void {
@@ -282,7 +307,9 @@ function runBench(
       mode,
       parallel: renderer.parallel,
       cores: (globalThis.navigator as Navigator).hardwareConcurrency,
-      coi: (globalThis as { crossOriginIsolated?: boolean }).crossOriginIsolated === true,
+      coi:
+        (globalThis as { crossOriginIsolated?: boolean })
+          .crossOriginIsolated === true,
       res: `${renderer.fb.width}x${renderer.fb.height}`,
       workMs: benchStats(work),
       frameMs: benchStats(frame),
@@ -306,14 +333,15 @@ function runBench(
         return
       }
     }
-    for (const m of level.mobs) {
-      Mob.update(m, 1 / 60, level.terrain)
-    }
+    Level.update(level, 1 / 60)
     const camera = benchCamera(i / 60)
-    const viewProj = Camera.viewProjection(camera, renderer.fb.width / renderer.fb.height)
-    const visible = visibleChunks(level.chunks, viewProj)
-    const mobDraws = visibleMobs(level.mobs, viewProj)
-    renderer.dispatch(camera, viewProj, visible, i / 60, mobDraws)
+    const viewProj = Camera.viewProjection(
+      camera,
+      renderer.fb.width / renderer.fb.height,
+    )
+    const visible = RenderScene.visibleChunks(level.render, viewProj)
+    const instances = Level.visibleInstances(level, viewProj)
+    renderer.dispatch(camera, viewProj, visible, i / 60, instances)
     inFlight = true
     if (renderer.done() && record()) {
       report()
@@ -322,29 +350,12 @@ function runBench(
   requestAnimationFrame(tick)
 }
 
-/** Rebuild the dynamic tail of `level.colliders`: keep the static prefix, then add
- *  a block/stand-on AABB for each mob near the player. Mobs move, so these can't be
- *  baked. Only mobs on the ground are `standable` (hop onto a resting frog/perched
- *  robin); bees and airborne birds still block but never make a mid-air platform.
- *  Only mobs within `MOB_COLLIDE_RANGE` are added -- the rest can't be reached this
- *  frame anyway. */
-function rebuildMobColliders(level: Level, playerPos: Vec3, staticCount: number): void {
-  level.colliders.length = staticCount
-  for (const m of level.mobs) {
-    const dx = m.position.x - playerPos.x
-    const dz = m.position.z - playerPos.z
-    if (dx * dx + dz * dz > MOB_COLLIDE_RANGE * MOB_COLLIDE_RANGE) {
-      continue
-    }
-    const half = Mob.boundingRadius(m.kind) * m.scale * 0.7
-    level.colliders.push({
-      minX: m.position.x - half,
-      maxX: m.position.x + half,
-      minZ: m.position.z - half,
-      maxZ: m.position.z + half,
-      top: m.position.y + Mob.bodyHeight(m.kind) * m.scale,
-      standable: m.kind !== "bee" && m.grounded,
-    })
+function readPlayerInput(keys: Set<string>): CharacterInput {
+  return {
+    forward: (keys.has("KeyW") ? 1 : 0) - (keys.has("KeyS") ? 1 : 0),
+    right: (keys.has("KeyD") ? 1 : 0) - (keys.has("KeyA") ? 1 : 0),
+    jump: keys.has("Space"),
+    run: keys.has("ShiftLeft") || keys.has("ShiftRight"),
   }
 }
 
diff --git a/app/render-worker.ts b/app/render-worker.ts
index 51e0575..7610fb9 100644
--- a/app/render-worker.ts
+++ b/app/render-worker.ts
@@ -1,35 +1,12 @@
 import type { Framebuffer } from "../engine/render/Framebuffer"
-import type { RenderConfig } from "../engine/render/RenderConfig"
-import { MOB_KINDS } from "../game/actors/Mob"
-import { renderBand, MOB_FLOATS, type MobDraw, type Scene } from "../game/renderScene"
-
-/** One-time setup: shared framebuffer + control/param buffers, the (cloned)
- *  scene, this worker's row band, and its index into the per-worker times array. */
-type Init = {
-  colorSAB: SharedArrayBuffer
-  depthSAB: SharedArrayBuffer
-  width: number
-  height: number
-  scene: Scene
-  band: [number, number]
-  config: RenderConfig
-  skyStep: number
-  ctrlSAB: SharedArrayBuffer
-  camSAB: SharedArrayBuffer
-  vpSAB: SharedArrayBuffer
-  visSAB: SharedArrayBuffer
-  mobSAB: SharedArrayBuffer
-  timesSAB: SharedArrayBuffer
-  index: number
-}
-
-const FRAME = 0
-const DONE = 1
-const VIS = 2
-const MOBVIS = 3
+import { RenderProtocol, type RenderWorkerInit } from "../engine/render/RenderProtocol"
+import { RenderScene, type RenderInstance } from "../engine/render/RenderScene"
 
 const ctx = globalThis as unknown as {
-  addEventListener: (type: "message", handler: (e: { data: Init }) => void) => void
+  addEventListener: (
+    type: "message",
+    handler: (e: { data: RenderWorkerInit }) => void,
+  ) => void
 }
 
 ctx.addEventListener("message", (e) => {
@@ -41,31 +18,46 @@ ctx.addEventListener("message", (e) => {
     depth: new Float32Array(m.depthSAB),
   }
   const ctrl = new Int32Array(m.ctrlSAB)
-  const cam = new Float64Array(m.camSAB)
-  const vp = new Float32Array(m.vpSAB)
-  const vis = new Int32Array(m.visSAB)
-  const mob = new Float32Array(m.mobSAB)
+  const cameraData = new Float64Array(m.cameraSAB)
+  const viewProjection = new Float32Array(m.viewProjectionSAB)
+  const visibleChunks = new Int32Array(m.visibleChunkSAB)
+  const instanceIds = new Int32Array(m.instanceIdSAB)
+  const instanceTransforms = new Float32Array(m.instanceTransformSAB)
   const times = new Float64Array(m.timesSAB)
-  const { scene, band, config, skyStep, index } = m
+  const { scene, band, config, skyStep, workerIndex } = m
+  const instances: RenderInstance[] = []
 
   // Lock-free frame loop: block until main bumps the frame counter, render this
   // band, record the band time, and signal done. No messages per frame.
   let last = 0
   for (;;) {
-    Atomics.wait(ctrl, FRAME, last)
-    last = Atomics.load(ctrl, FRAME)
+    Atomics.wait(ctrl, RenderProtocol.FRAME, last)
+    last = Atomics.load(ctrl, RenderProtocol.FRAME)
     const t0 = performance.now()
-    const camera = { position: { x: cam[0], y: cam[1], z: cam[2] }, yaw: cam[3], pitch: cam[4], fov: cam[5] }
-    const count = Atomics.load(ctrl, VIS)
-    const visible = [...vis.subarray(0, count)]
-    const mobCount = Atomics.load(ctrl, MOBVIS)
-    const mobDraws: MobDraw[] = []
-    for (let i = 0; i < mobCount; i++) {
-      const o = i * MOB_FLOATS
-      mobDraws.push({ kind: MOB_KINDS[mob[o]] ?? "frog", x: mob[o + 1], y: mob[o + 2], z: mob[o + 3], heading: mob[o + 4], scale: mob[o + 5] })
-    }
-    renderBand(fb, scene, camera, vp, visible, mobDraws, config, skyStep, cam[6], band[0], band[1])
-    times[index] = performance.now() - t0
-    Atomics.add(ctrl, DONE, 1)
+    const frameCamera = RenderProtocol.readCamera(cameraData)
+    const count = Atomics.load(ctrl, RenderProtocol.VISIBLE_CHUNKS)
+    const visible = [...visibleChunks.subarray(0, count)]
+    const instanceCount = Atomics.load(ctrl, RenderProtocol.VISIBLE_INSTANCES)
+    RenderProtocol.readInstances(
+      instanceIds,
+      instanceTransforms,
+      instanceCount,
+      instances,
+    )
+    RenderScene.renderBand(
+      fb,
+      scene,
+      frameCamera.camera,
+      viewProjection,
+      visible,
+      instances,
+      config,
+      skyStep,
+      frameCamera.time,
+      band[0],
+      band[1],
+    )
+    times[workerIndex] = performance.now() - t0
+    Atomics.add(ctrl, RenderProtocol.DONE, 1)
   }
 })
diff --git a/app/renderer.ts b/app/renderer.ts
index 254a6f6..3fca7f2 100644
--- a/app/renderer.ts
+++ b/app/renderer.ts
@@ -2,8 +2,8 @@ import { Framebuffer } from "../engine/render/Framebuffer"
 import type { RenderConfig } from "../engine/render/RenderConfig"
 import type { Mat4 } from "../engine/math/Mat4"
 import type { Camera } from "../engine/scene/Camera"
-import { MOB_KINDS } from "../game/actors/Mob"
-import { renderBand, MOB_FLOATS, type MobDraw, type Scene } from "../game/renderScene"
+import { RenderProtocol, type RenderWorkerInit } from "../engine/render/RenderProtocol"
+import { RenderScene, type RenderInstance } from "../engine/render/RenderScene"
 
 /** Clouds are drawn at 1/SKY_STEP resolution (the sky base + sun stay per-pixel);
  *  band splits align to it so the cloud block grid stays seamless across workers. */
@@ -19,12 +19,6 @@ const ENABLE_WORKERS = true
  *  bench. */
 const MAX_WORKERS = 3
 
-// Indices into the shared control Int32Array.
-const FRAME = 0 // bumped by main to dispatch a frame
-const DONE = 1 // workers add 1 when their band is finished
-const VIS = 2 // number of visible chunk indices this frame
-const MOBVIS = 3 // number of visible mobs this frame
-
 /**
  * Render driver. When the page is cross-origin-isolated it runs a pool of worker
  * threads, each owning a disjoint row band of a `SharedArrayBuffer` framebuffer;
@@ -41,18 +35,37 @@ export type Renderer = {
   readonly parallel: boolean
   reconfigure: (config: RenderConfig) => void
   /** Start rendering one frame (non-blocking in the worker path). */
-  dispatch: (camera: Camera, viewProj: Mat4, visible: number[], time: number, mobDraws: MobDraw[]) => void
+  dispatch: (
+    camera: Camera,
+    viewProj: Mat4,
+    visible: number[],
+    time: number,
+    instances: RenderInstance[],
+  ) => void
   /** Has the dispatched frame finished? (always true single-threaded.) */
   done: () => boolean
   /** Critical-path render time of the last frame, ms (max band time / inline time). */
   workMs: () => number
 }
 
-export function createRenderer(scene: Scene, initial: RenderConfig, forceWorkers?: boolean): Renderer {
-  const hw = (globalThis.navigator as Navigator | undefined)?.hardwareConcurrency ?? 4
+type PendingFrame = {
+  camera: Camera
+  viewProjection: Mat4
+  visibleChunks: number[]
+  instances: RenderInstance[]
+  time: number
+}
+
+export function createRenderer(
+  scene: RenderScene,
+  initial: RenderConfig,
+  forceWorkers?: boolean,
+): Renderer {
+  const hw =
+    (globalThis.navigator as Navigator | undefined)?.hardwareConcurrency ?? 4
   const workerCount = Math.max(1, Math.min(MAX_WORKERS, hw - 1))
   const maxVis = Math.max(1, scene.chunks.length)
-  const maxMobs = Math.max(1, scene.mobCount)
+  const maxInstances = Math.max(1, scene.maxInstances)
   let config = initial
   const want = forceWorkers ?? ENABLE_WORKERS
   let parallel = want && canShare()
@@ -63,58 +76,116 @@ export function createRenderer(scene: Scene, initial: RenderConfig, forceWorkers
   let cam: Float64Array<ArrayBufferLike> = new Float64Array(0) // pos x/y/z, yaw, pitch, fov, time
   let vp: Float32Array<ArrayBufferLike> = new Float32Array(0) // the view-projection matrix
   let vis: Int32Array<ArrayBufferLike> = new Int32Array(0) // visible chunk indices
-  let mob: Float32Array<ArrayBufferLike> = new Float32Array(0) // visible mob transforms (MOB_FLOATS each)
+  let instanceIds: Int32Array<ArrayBufferLike> = new Int32Array(0)
+  let instanceTransforms: Float32Array<ArrayBufferLike> = new Float32Array(0)
   let times: Float64Array<ArrayBufferLike> = new Float64Array(0) // per-worker band render ms
   let lastWork = 0
+  let generation = 0
+  let pending: PendingFrame | null = null
 
-  function setup(): void {
-    for (const w of workers) {
-      w.terminate()
+  function stopWorkers(): void {
+    for (const worker of workers) {
+      worker.terminate()
     }
     workers = []
+  }
+
+  function renderInline(frame: PendingFrame): void {
+    const t0 = performance.now()
+    RenderScene.renderBand(
+      fb,
+      scene,
+      frame.camera,
+      frame.viewProjection,
+      frame.visibleChunks,
+      frame.instances,
+      config,
+      SKY_STEP,
+      frame.time,
+      0,
+      fb.height,
+    )
+    lastWork = performance.now() - t0
+  }
+
+  function disableParallel(currentGeneration: number): void {
+    if (!parallel || currentGeneration !== generation) {
+      return
+    }
+    const frame = pending
+    parallel = false
+    stopWorkers()
+    if (frame !== null) {
+      renderInline(frame)
+      pending = null
+    }
+  }
+
+  function setup(): void {
+    generation++
+    const currentGeneration = generation
+    pending = null
+    stopWorkers()
     const width = config.internalWidth
     const height = config.internalHeight
     if (parallel) {
       const n = width * height
-      fb = { width, height, color: new Uint32Array(new SharedArrayBuffer(n * 4)), depth: new Float32Array(new SharedArrayBuffer(n * 4)) }
+      fb = {
+        width,
+        height,
+        color: new Uint32Array(new SharedArrayBuffer(n * 4)),
+        depth: new Float32Array(new SharedArrayBuffer(n * 4)),
+      }
       const bands = splitBands(height, workerCount, SKY_STEP)
-      ctrl = new Int32Array(new SharedArrayBuffer(4 * 4))
-      cam = new Float64Array(new SharedArrayBuffer(7 * 8))
-      vp = new Float32Array(new SharedArrayBuffer(16 * 4))
+      ctrl = new Int32Array(
+        new SharedArrayBuffer(RenderProtocol.CONTROL_LENGTH * 4),
+      )
+      cam = new Float64Array(
+        new SharedArrayBuffer(RenderProtocol.CAMERA_LENGTH * 8),
+      )
+      vp = new Float32Array(
+        new SharedArrayBuffer(RenderProtocol.VIEW_PROJECTION_LENGTH * 4),
+      )
       vis = new Int32Array(new SharedArrayBuffer(maxVis * 4))
-      mob = new Float32Array(new SharedArrayBuffer(maxMobs * MOB_FLOATS * 4))
+      instanceIds = new Int32Array(new SharedArrayBuffer(maxInstances * 4))
+      instanceTransforms = new Float32Array(
+        new SharedArrayBuffer(
+          maxInstances * RenderProtocol.TRANSFORM_FLOATS * 4,
+        ),
+      )
       times = new Float64Array(new SharedArrayBuffer(bands.length * 8))
       try {
         bands.forEach((band, index) => {
-          const worker = new Worker(new URL("./render-worker.ts", import.meta.url), { type: "module" })
-          worker.addEventListener("error", () => {
-            parallel = false
-          })
-          worker.postMessage({
-            colorSAB: fb.color.buffer,
-            depthSAB: fb.depth.buffer,
+          const worker = new Worker(
+            new URL("./render-worker.ts", import.meta.url),
+            { type: "module" },
+          )
+          worker.addEventListener("error", () => disableParallel(currentGeneration))
+          const init: RenderWorkerInit = {
+            colorSAB: shared(fb.color.buffer),
+            depthSAB: shared(fb.depth.buffer),
             width,
             height,
             scene,
             band,
             config,
             skyStep: SKY_STEP,
-            ctrlSAB: ctrl.buffer,
-            camSAB: cam.buffer,
-            vpSAB: vp.buffer,
-            visSAB: vis.buffer,
-            mobSAB: mob.buffer,
-            timesSAB: times.buffer,
-            index,
-          })
+            ctrlSAB: shared(ctrl.buffer),
+            cameraSAB: shared(cam.buffer),
+            viewProjectionSAB: shared(vp.buffer),
+            visibleChunkSAB: shared(vis.buffer),
+            instanceIdSAB: shared(instanceIds.buffer),
+            instanceTransformSAB: shared(instanceTransforms.buffer),
+            timesSAB: shared(times.buffer),
+            workerIndex: index,
+          }
+          worker.postMessage(init)
           workers.push(worker)
         })
+        Atomics.store(ctrl, RenderProtocol.DONE, workers.length)
       } catch {
         parallel = false
-        for (const w of workers) {
-          w.terminate()
-        }
-        workers = []
+        stopWorkers()
       }
     }
     if (!parallel || workers.length === 0) {
@@ -134,44 +205,44 @@ export function createRenderer(scene: Scene, initial: RenderConfig, forceWorkers
       config = next
       setup()
     },
-    dispatch(camera, viewProj, visible, time, mobDraws) {
+    dispatch(camera, viewProj, visible, time, instances) {
+      pending = {
+        camera,
+        viewProjection: viewProj,
+        visibleChunks: visible,
+        instances,
+        time,
+      }
       if (parallel && workers.length > 0) {
-        cam[0] = camera.position.x
-        cam[1] = camera.position.y
-        cam[2] = camera.position.z
-        cam[3] = camera.yaw
-        cam[4] = camera.pitch
-        cam[5] = camera.fov
-        cam[6] = time
-        vp.set(viewProj)
+        RenderProtocol.writeCamera(cam, camera, time)
+        RenderProtocol.writeViewProjection(vp, viewProj)
         const count = Math.min(visible.length, vis.length)
         for (let i = 0; i < count; i++) {
           vis[i] = visible[i]
         }
-        const mobCount = Math.min(mobDraws.length, maxMobs)
-        for (let i = 0; i < mobCount; i++) {
-          const d = mobDraws[i]
-          const o = i * MOB_FLOATS
-          mob[o] = MOB_KINDS.indexOf(d.kind)
-          mob[o + 1] = d.x
-          mob[o + 2] = d.y
-          mob[o + 3] = d.z
-          mob[o + 4] = d.heading
-          mob[o + 5] = d.scale
-        }
-        Atomics.store(ctrl, VIS, count)
-        Atomics.store(ctrl, MOBVIS, mobCount)
-        Atomics.store(ctrl, DONE, 0)
-        Atomics.add(ctrl, FRAME, 1)
-        Atomics.notify(ctrl, FRAME, workers.length)
+        const instanceCount = RenderProtocol.writeInstances(
+          instanceIds,
+          instanceTransforms,
+          instances,
+        )
+        Atomics.store(ctrl, RenderProtocol.VISIBLE_CHUNKS, count)
+        Atomics.store(ctrl, RenderProtocol.VISIBLE_INSTANCES, instanceCount)
+        Atomics.store(ctrl, RenderProtocol.DONE, 0)
+        Atomics.add(ctrl, RenderProtocol.FRAME, 1)
+        Atomics.notify(ctrl, RenderProtocol.FRAME, workers.length)
         return
       }
-      const t0 = performance.now()
-      renderBand(fb, scene, camera, viewProj, visible, mobDraws, config, SKY_STEP, time, 0, fb.height)
-      lastWork = performance.now() - t0
+      renderInline(pending)
+      pending = null
     },
     done() {
-      return !(parallel && workers.length > 0) || Atomics.load(ctrl, DONE) >= workers.length
+      const complete =
+        !(parallel && workers.length > 0) ||
+        Atomics.load(ctrl, RenderProtocol.DONE) >= workers.length
+      if (complete) {
+        pending = null
+      }
+      return complete
     },
     workMs() {
       if (parallel && workers.length > 0) {
@@ -194,20 +265,33 @@ function canShare(): boolean {
   return (
     typeof SharedArrayBuffer !== "undefined" &&
     typeof Worker !== "undefined" &&
-    (globalThis as { crossOriginIsolated?: boolean }).crossOriginIsolated === true
+    (globalThis as { crossOriginIsolated?: boolean }).crossOriginIsolated ===
+      true
   )
 }
 
+function shared(buffer: ArrayBufferLike): SharedArrayBuffer {
+  if (!(buffer instanceof SharedArrayBuffer)) {
+    throw new Error("render worker buffer is not shared")
+  }
+  return buffer
+}
+
 /** Split `height` rows into ~`count` bands. Interior boundaries snap up to a
  *  multiple of `step` so the sky's block grid stays aligned (no seam), while the
  *  bands stay disjoint so no two workers write the same pixel. */
-function splitBands(height: number, count: number, step: number): [number, number][] {
+function splitBands(
+  height: number,
+  count: number,
+  step: number,
+): [number, number][] {
   const bands: [number, number][] = []
   const per = Math.ceil(height / count)
   let y = 0
   while (y < height) {
     const raw = y + per
-    const y1 = raw >= height ? height : Math.min(height, Math.ceil(raw / step) * step)
+    const y1 =
+      raw >= height ? height : Math.min(height, Math.ceil(raw / step) * step)
     bands.push([y, y1])
     y = y1
   }
diff --git a/docs/adr/0001-engine-owns-world-concepts.md b/docs/adr/0001-engine-owns-world-concepts.md
new file mode 100644
index 0000000..bcda3b7
--- /dev/null
+++ b/docs/adr/0001-engine-owns-world-concepts.md
@@ -0,0 +1,3 @@
+# Engine owns world concepts
+
+Engine owns contracts and reusable mechanisms for levels, terrain, actors, prefabs, collision, scene rendering, chunking, LOD, and render transport; game owns concrete level values and concrete actor or prefab definitions. Game content is referenced through definition objects, never closed `MobKind`, `TreeKind`, or equivalent content registries; finite engine capability unions remain allowed. A live `Level` may contain behavior, while its `RenderScene` projection contains only clone-safe data for workers, with numeric prototype indexes confined to engine transport.
diff --git a/engine/math/Mat4.ts b/engine/math/Mat4.ts
index 7848e3c..9686715 100644
--- a/engine/math/Mat4.ts
+++ b/engine/math/Mat4.ts
@@ -22,7 +22,7 @@ export namespace Mat4 {
 
   /** Model transform T * Ry * S: uniform `scale`, then a yaw rotation about Y,
    *  then a translation. Built directly in column-major storage (no intermediate
-   *  matmuls) since it runs per mob per frame. A vertex at local +Z ends up
+   *  matmuls) since it runs per instance per frame. A vertex at local +Z ends up
    *  pointing along world (sin yaw, 0, cos yaw), i.e. the object faces `yaw`. */
   export function compose(tx: number, ty: number, tz: number, yaw: number, scale: number): Mat4 {
     const c = Math.cos(yaw)
diff --git a/engine/render/Chunk.ts b/engine/render/Chunk.ts
new file mode 100644
index 0000000..b2b9f2d
--- /dev/null
+++ b/engine/render/Chunk.ts
@@ -0,0 +1,29 @@
+import type { DrawGroup } from "./Material"
+import type { Vec3 } from "../math/Vec3"
+
+export type Bounds3 = {
+  minX: number
+  minY: number
+  minZ: number
+  maxX: number
+  maxY: number
+  maxZ: number
+}
+
+/** One cullable section of static world geometry with two engine-supported LODs. */
+export type Chunk = Bounds3 & {
+  readonly near: readonly DrawGroup[]
+  readonly far: readonly DrawGroup[]
+}
+
+export namespace Chunk {
+  export function isFar(chunk: Chunk, eye: Vec3, lodDistance: number): boolean {
+    if (!(lodDistance < Infinity)) {
+      return false
+    }
+    const dx = eye.x - Math.max(chunk.minX, Math.min(chunk.maxX, eye.x))
+    const dy = eye.y - Math.max(chunk.minY, Math.min(chunk.maxY, eye.y))
+    const dz = eye.z - Math.max(chunk.minZ, Math.min(chunk.maxZ, eye.z))
+    return dx * dx + dy * dy + dz * dz > lodDistance * lodDistance
+  }
+}
diff --git a/engine/render/ChunkBuilder.ts b/engine/render/ChunkBuilder.ts
new file mode 100644
index 0000000..6bf1486
--- /dev/null
+++ b/engine/render/ChunkBuilder.ts
@@ -0,0 +1,123 @@
+import { STRIDE, type Mesh } from "../scene/Mesh"
+import type { Chunk, Bounds3 } from "./Chunk"
+import type { DrawGroup, Material } from "./Material"
+
+export type MeshBatch = {
+  mesh: (material: Material) => Mesh
+  use: (material: Material, mesh: Mesh) => void
+}
+
+export type ChunkItem = {
+  position: { x: number; z: number }
+  bakeNear: (batch: MeshBatch) => void
+  bakeFar?: (batch: MeshBatch) => void
+}
+
+export type ChunkCell = {
+  x0: number
+  z0: number
+  x1: number
+  z1: number
+}
+
+export type ChunkBuilder = {
+  minX: number
+  minZ: number
+  maxX: number
+  maxZ: number
+  columns: number
+  rows: number
+  bakeCell: (near: MeshBatch, far: MeshBatch, cell: ChunkCell) => void
+}
+
+export namespace ChunkBuilder {
+  export function build(config: ChunkBuilder, items: ChunkItem[]): Chunk[] {
+    const width = (config.maxX - config.minX) / config.columns
+    const depth = (config.maxZ - config.minZ) / config.rows
+    const chunks: Chunk[] = []
+    for (let column = 0; column < config.columns; column++) {
+      const x0 = config.minX + column * width
+      const x1 = x0 + width
+      for (let row = 0; row < config.rows; row++) {
+        const z0 = config.minZ + row * depth
+        const z1 = z0 + depth
+        const nearMeshes = new Map<Material, Mesh>()
+        const farMeshes = new Map<Material, Mesh>()
+        const near = batch(nearMeshes)
+        const far = batch(farMeshes)
+        config.bakeCell(near, far, { x0, z0, x1, z1 })
+        for (const item of items) {
+          if (inCell(item.position, x0, z0, x1, z1)) {
+            item.bakeNear(near)
+            item.bakeFar?.(far)
+          }
+        }
+        const nearGroups = groups(nearMeshes)
+        const farGroups = groups(farMeshes)
+        const box = bounds([...nearMeshes.values(), ...farMeshes.values()])
+        if (box !== null) {
+          chunks.push({ ...box, near: nearGroups, far: farGroups })
+        }
+      }
+    }
+    return chunks
+  }
+
+  function batch(meshes: Map<Material, Mesh>): MeshBatch {
+    return {
+      mesh(material) {
+        let mesh = meshes.get(material)
+        if (mesh === undefined) {
+          mesh = { verts: [], indices: [] }
+          meshes.set(material, mesh)
+        }
+        return mesh
+      },
+      use(material, mesh) {
+        meshes.set(material, mesh)
+      },
+    }
+  }
+
+  function groups(meshes: Map<Material, Mesh>): DrawGroup[] {
+    const result: DrawGroup[] = []
+    for (const [material, mesh] of meshes) {
+      if (mesh.indices.length > 0) {
+        result.push({ mesh, material })
+      }
+    }
+    return result
+  }
+
+  function inCell(
+    position: { x: number; z: number },
+    x0: number,
+    z0: number,
+    x1: number,
+    z1: number,
+  ): boolean {
+    return (
+      position.x >= x0 && position.x < x1 && position.z >= z0 && position.z < z1
+    )
+  }
+
+  function bounds(meshes: Mesh[]): Bounds3 | null {
+    let minX = Infinity
+    let minY = Infinity
+    let minZ = Infinity
+    let maxX = -Infinity
+    let maxY = -Infinity
+    let maxZ = -Infinity
+    for (const mesh of meshes) {
+      for (let i = 0; i < mesh.verts.length; i += STRIDE) {
+        minX = Math.min(minX, mesh.verts[i])
+        minY = Math.min(minY, mesh.verts[i + 1])
+        minZ = Math.min(minZ, mesh.verts[i + 2])
+        maxX = Math.max(maxX, mesh.verts[i])
+        maxY = Math.max(maxY, mesh.verts[i + 1])
+        maxZ = Math.max(maxZ, mesh.verts[i + 2])
+      }
+    }
+    return maxX < minX ? null : { minX, minY, minZ, maxX, maxY, maxZ }
+  }
+}
diff --git a/engine/render/Rasterizer.ts b/engine/render/Rasterizer.ts
index 68da0b3..edbf202 100644
--- a/engine/render/Rasterizer.ts
+++ b/engine/render/Rasterizer.ts
@@ -115,8 +115,8 @@ export namespace Rasterizer {
    * NEAR_W) with a single Sutherland-Hodgman pass, writing the result (0, 3, or
    * 4 verts) to `dst` and returning its vertex count.
    *
-   * This matters even when standing inside the room: a wall to your side has
-   * vertices both in front of and behind the eye. Without clipping, the behind
+   * Geometry intersecting the camera plane has vertices both in front of and
+   * behind the eye. Without clipping, the behind
    * vertices have w <= 0 and invert under the perspective divide, smearing the
    * triangle across the whole screen (and risking divide-by-zero).
    */
@@ -201,7 +201,7 @@ export namespace Rasterizer {
       return
     }
     // Backface cull: a back-facing triangle has positive area here. Only for
-    // solid, consistently-wound meshes; sprites/room stay double-sided.
+    // solid, consistently-wound meshes; other materials may stay double-sided.
     if (cull && area > 0) {
       return
     }
diff --git a/engine/render/RenderConfig.ts b/engine/render/RenderConfig.ts
index ed147f9..1379544 100644
--- a/engine/render/RenderConfig.ts
+++ b/engine/render/RenderConfig.ts
@@ -46,10 +46,8 @@ export type RenderConfig = {
    *  short draw distance and the shimmer of far geometry. It also colors pixels
    *  no triangle covers, so the frame's clear color should match `fog.color`. */
   fog: Fog | null
-  /** Beyond this distance (world units) trees + boulders draw as cheap low-poly
-   *  impostors instead of full geometry, cutting per-triangle work in dense
-   *  views. Kept inside `fog.far` so far detail is already fog-dimmed at the
-   *  switch; `Infinity` disables LOD. */
+  /** Beyond this distance (world units), chunks draw their cheaper far groups
+   *  instead of near geometry. `Infinity` disables LOD. */
   lodDistance: number
 }
 
diff --git a/engine/render/RenderProtocol.ts b/engine/render/RenderProtocol.ts
new file mode 100644
index 0000000..f497c14
--- /dev/null
+++ b/engine/render/RenderProtocol.ts
@@ -0,0 +1,123 @@
+import type { Mat4 } from "../math/Mat4"
+import type { Camera } from "../scene/Camera"
+import type { RenderConfig } from "./RenderConfig"
+import type { RenderInstance, RenderScene } from "./RenderScene"
+
+export type RenderWorkerInit = {
+  colorSAB: SharedArrayBuffer
+  depthSAB: SharedArrayBuffer
+  width: number
+  height: number
+  scene: RenderScene
+  band: [number, number]
+  config: RenderConfig
+  skyStep: number
+  ctrlSAB: SharedArrayBuffer
+  cameraSAB: SharedArrayBuffer
+  viewProjectionSAB: SharedArrayBuffer
+  visibleChunkSAB: SharedArrayBuffer
+  instanceIdSAB: SharedArrayBuffer
+  instanceTransformSAB: SharedArrayBuffer
+  timesSAB: SharedArrayBuffer
+  workerIndex: number
+}
+
+export type RenderFrameCamera = {
+  camera: Camera
+  time: number
+}
+
+/** Shared frame-buffer layout used by browser driver and render workers. */
+export namespace RenderProtocol {
+  export const FRAME = 0
+  export const DONE = 1
+  export const VISIBLE_CHUNKS = 2
+  export const VISIBLE_INSTANCES = 3
+  export const CONTROL_LENGTH = 4
+  export const CAMERA_X = 0
+  export const CAMERA_Y = 1
+  export const CAMERA_Z = 2
+  export const CAMERA_YAW = 3
+  export const CAMERA_PITCH = 4
+  export const CAMERA_FOV = 5
+  export const CAMERA_TIME = 6
+  export const CAMERA_LENGTH = 7
+  export const VIEW_PROJECTION_LENGTH = 16
+  export const TRANSFORM_FLOATS = 5
+
+  export function writeCamera(
+    output: Float64Array<ArrayBufferLike>,
+    camera: Camera,
+    time: number,
+  ): void {
+    output[CAMERA_X] = camera.position.x
+    output[CAMERA_Y] = camera.position.y
+    output[CAMERA_Z] = camera.position.z
+    output[CAMERA_YAW] = camera.yaw
+    output[CAMERA_PITCH] = camera.pitch
+    output[CAMERA_FOV] = camera.fov
+    output[CAMERA_TIME] = time
+  }
+
+  export function readCamera(input: Float64Array<ArrayBufferLike>): RenderFrameCamera {
+    return {
+      camera: {
+        position: {
+          x: input[CAMERA_X],
+          y: input[CAMERA_Y],
+          z: input[CAMERA_Z],
+        },
+        yaw: input[CAMERA_YAW],
+        pitch: input[CAMERA_PITCH],
+        fov: input[CAMERA_FOV],
+      },
+      time: input[CAMERA_TIME],
+    }
+  }
+
+  export function writeViewProjection(
+    output: Float32Array<ArrayBufferLike>,
+    viewProjection: Mat4,
+  ): void {
+    output.set(viewProjection)
+  }
+
+  export function writeInstances(
+    ids: Int32Array<ArrayBufferLike>,
+    transforms: Float32Array<ArrayBufferLike>,
+    instances: RenderInstance[],
+  ): number {
+    const count = Math.min(instances.length, ids.length)
+    for (let i = 0; i < count; i++) {
+      const instance = instances[i]
+      const offset = i * TRANSFORM_FLOATS
+      ids[i] = instance.prototype
+      transforms[offset] = instance.x
+      transforms[offset + 1] = instance.y
+      transforms[offset + 2] = instance.z
+      transforms[offset + 3] = instance.heading
+      transforms[offset + 4] = instance.scale
+    }
+    return count
+  }
+
+  export function readInstances(
+    ids: Int32Array<ArrayBufferLike>,
+    transforms: Float32Array<ArrayBufferLike>,
+    count: number,
+    output: RenderInstance[],
+  ): void {
+    output.length = 0
+    for (let i = 0; i < count; i++) {
+      const offset = i * TRANSFORM_FLOATS
+      output.push({
+        prototype: ids[i],
+        x: transforms[offset],
+        y: transforms[offset + 1],
+        z: transforms[offset + 2],
+        heading: transforms[offset + 3],
+        scale: transforms[offset + 4],
+      })
+    }
+  }
+}
diff --git a/engine/render/RenderScene.ts b/engine/render/RenderScene.ts
new file mode 100644
index 0000000..225567f
--- /dev/null
+++ b/engine/render/RenderScene.ts
@@ -0,0 +1,224 @@
+import { Mat4 as Matrix, type Mat4 } from "../math/Mat4"
+import type { Vec2 } from "../math/Vec2"
+import type { Vec3 } from "../math/Vec3"
+import type { Camera } from "../scene/Camera"
+import { Sprite } from "../scene/Sprite"
+import { Framebuffer, type Framebuffer as Frame } from "./Framebuffer"
+import { Frustum } from "./Frustum"
+import type { DrawGroup, Material } from "./Material"
+import { Rasterizer } from "./Rasterizer"
+import type { RenderConfig } from "./RenderConfig"
+import { Sky, type SkyConfig } from "./Sky"
+import { Chunk, type Chunk as RenderChunk } from "./Chunk"
+
+export type Billboard = {
+  position: Vec3
+  size: Vec2
+  material: Material
+}
+
+export type RenderPrototype = {
+  readonly groups: readonly DrawGroup[]
+  readonly radius: number
+  readonly minY: number
+  readonly maxY: number
+}
+
+export type RenderTransform = {
+  x: number
+  y: number
+  z: number
+  heading: number
+  scale: number
+}
+
+export type RenderInstance = RenderTransform & {
+  prototype: number
+}
+
+/** Clone-safe render projection of a live level. Contains no behavior callbacks or
+ * game-content registries, so workers need only engine code. */
+export type RenderScene = {
+  readonly chunks: readonly RenderChunk[]
+  readonly staticGroups: readonly DrawGroup[]
+  readonly billboards: readonly Billboard[]
+  readonly prototypes: readonly RenderPrototype[]
+  readonly maxInstances: number
+  readonly sky: SkyConfig
+}
+
+export namespace RenderScene {
+  export function visibleChunks(
+    scene: RenderScene,
+    viewProjection: Mat4,
+  ): number[] {
+    const frustum = Frustum.fromViewProj(viewProjection)
+    const visible: number[] = []
+    for (let i = 0; i < scene.chunks.length; i++) {
+      const chunk = scene.chunks[i]
+      if (
+        Frustum.intersectsAabb(
+          frustum,
+          chunk.minX,
+          chunk.minY,
+          chunk.minZ,
+          chunk.maxX,
+          chunk.maxY,
+          chunk.maxZ,
+        )
+      ) {
+        visible.push(i)
+      }
+    }
+    return visible
+  }
+
+  export function visibleInstances(
+    scene: RenderScene,
+    instances: RenderInstance[],
+    viewProjection: Mat4,
+  ): RenderInstance[] {
+    const frustum = Frustum.fromViewProj(viewProjection)
+    const visible: RenderInstance[] = []
+    for (const instance of instances) {
+      const prototype = scene.prototypes[instance.prototype]
+      if (prototype === undefined) {
+        continue
+      }
+      const radius = prototype.radius * instance.scale
+      if (
+        Frustum.intersectsAabb(
+          frustum,
+          instance.x - radius,
+          instance.y + prototype.minY * instance.scale,
+          instance.z - radius,
+          instance.x + radius,
+          instance.y + prototype.maxY * instance.scale,
+          instance.z + radius,
+        )
+      ) {
+        visible.push(instance)
+      }
+    }
+    return visible
+  }
+
+  export function renderBand(
+    framebuffer: Frame,
+    scene: RenderScene,
+    camera: Camera,
+    viewProjection: Mat4,
+    visible: number[],
+    instances: RenderInstance[],
+    config: RenderConfig,
+    skyStep: number,
+    time: number,
+    y0: number,
+    y1: number,
+  ): void {
+    Sky.render(framebuffer, camera, scene.sky, time, skyStep, y0, y1)
+    drawGroups(framebuffer, scene.staticGroups, viewProjection, config, y0, y1)
+    for (const index of visible) {
+      const chunk = scene.chunks[index]
+      const groups = Chunk.isFar(chunk, camera.position, config.lodDistance)
+        ? chunk.far
+        : chunk.near
+      drawGroups(framebuffer, groups, viewProjection, config, y0, y1)
+    }
+    for (const billboard of scene.billboards) {
+      const sprite = {
+        position: billboard.position,
+        size: billboard.size,
+        texture: billboard.material.texture,
+      }
+      Rasterizer.draw(
+        framebuffer,
+        Sprite.billboard(sprite, camera),
+        billboard.material.texture,
+        viewProjection,
+        config,
+        billboard.material.cull,
+        y0,
+        y1,
+      )
+    }
+    for (const instance of instances) {
+      const prototype = scene.prototypes[instance.prototype]
+      if (prototype === undefined) {
+        continue
+      }
+      const modelViewProjection = Matrix.multiply(
+        viewProjection,
+        Matrix.compose(
+          instance.x,
+          instance.y,
+          instance.z,
+          instance.heading,
+          instance.scale,
+        ),
+      )
+      drawGroups(
+        framebuffer,
+        prototype.groups,
+        modelViewProjection,
+        config,
+        y0,
+        y1,
+      )
+    }
+    Framebuffer.quantize(framebuffer, config, y0, y1)
+  }
+
+  export function triangleCount(
+    scene: RenderScene,
+    visible: number[],
+    instances: RenderInstance[],
+    eye: Vec3,
+    lodDistance: number,
+  ): number {
+    let indices = groupIndices(scene.staticGroups) + scene.billboards.length * 6
+    for (const index of visible) {
+      const chunk = scene.chunks[index]
+      indices += groupIndices(
+        Chunk.isFar(chunk, eye, lodDistance) ? chunk.far : chunk.near,
+      )
+    }
+    for (const instance of instances) {
+      const prototype = scene.prototypes[instance.prototype]
+      if (prototype !== undefined) {
+        indices += groupIndices(prototype.groups)
+      }
+    }
+    return (indices / 3) | 0
+  }
+
+  function drawGroups(
+    framebuffer: Frame,
+    groups: readonly DrawGroup[],
+    matrix: Mat4,
+    config: RenderConfig,
+    y0: number,
+    y1: number,
+  ): void {
+    for (const group of groups) {
+      Rasterizer.draw(
+        framebuffer,
+        group.mesh,
+        group.material.texture,
+        matrix,
+        config,
+        group.material.cull,
+        y0,
+        y1,
+      )
+    }
+  }
+
+  function groupIndices(groups: readonly DrawGroup[]): number {
+    let count = 0
+    for (const group of groups) {
+      count += group.mesh.indices.length
+    }
+    return count
+  }
+}
diff --git a/engine/scene/Actor.ts b/engine/scene/Actor.ts
index 3318786..4e2729c 100644
--- a/engine/scene/Actor.ts
+++ b/engine/scene/Actor.ts
@@ -1,26 +1,48 @@
-import type { Mesh } from "./Mesh"
+import type { RenderPrototype, RenderTransform } from "../render/RenderScene"
+import type { Collider } from "../world/Collider"
 
-/** Definition of an **Entity** actor kind: something that lives in the world with
- *  its own behavior and a live transform (mobs, and later the npc / powerups) -- as
- *  opposed to a baked, static `Prop`. `State` is the per-instance runtime record the
- *  behavior mutates; `World` is whatever that behavior reads (e.g. `Terrain`).
- *
- *  Every field is plain data or a module function, so a definition is **imported
- *  into each context** (main thread + each render worker) rather than structured-
- *  cloned across the wire -- the per-kind polymorphism is code, not serialized
- *  state. That's what lets a registry of these stay compatible with the worker
- *  renderer (only plain instance data ever crosses; behavior is loaded per side). */
-export type Entity<State, World> = {
-  /** Stable tag for the kind (also the texture key today). The registry's order,
-   *  not this string, is what becomes the id packed into the mob SAB. */
-  name: string
-  /** Build the canonical local-space mesh once; every instance shares it, differing
-   *  only by its per-frame model matrix. */
-  build: (mesh: Mesh) => void
-  /** Advance one instance by `dt` seconds. */
+/** Open actor behavior and representation. Concrete definitions are ordinary game
+ * objects referenced directly by instances. */
+export type ActorDefinition<State, World> = {
+  prototype: RenderPrototype
   update: (state: State, dt: number, world: World) => void
-  /** Local bounding radius (pre-scale) for the per-frame cull AABB. */
-  boundingRadius: number
-  /** Local body height (pre-scale) for the top of the stand-on collider. */
-  bodyHeight: number
+  transform: (state: State) => RenderTransform
+  collider?: (state: State, world: World) => Collider | null
+}
+
+/** Type-erased live actor. `create` captures concrete state safely, allowing one
+ * level to hold unrelated actor state types without a content union. */
+export type Actor<World> = {
+  readonly definition: object
+  readonly prototype: RenderPrototype
+  readonly updateState: (dt: number, world: World) => void
+  readonly readTransform: () => RenderTransform
+  readonly readCollider: (world: World) => Collider | null
+}
+
+export namespace Actor {
+  export function create<State, World>(
+    definition: ActorDefinition<State, World>,
+    state: State,
+  ): Actor<World> {
+    return {
+      definition,
+      prototype: definition.prototype,
+      updateState: (dt, world) => definition.update(state, dt, world),
+      readTransform: () => definition.transform(state),
+      readCollider: (world) => definition.collider?.(state, world) ?? null,
+    }
+  }
+
+  export function update<World>(actor: Actor<World>, dt: number, world: World): void {
+    actor.updateState(dt, world)
+  }
+
+  export function transform<World>(actor: Actor<World>): RenderTransform {
+    return actor.readTransform()
+  }
+
+  export function collider<World>(actor: Actor<World>, world: World): Collider | null {
+    return actor.readCollider(world)
+  }
 }
diff --git a/engine/scene/MeshBuilder.ts b/engine/scene/MeshBuilder.ts
new file mode 100644
index 0000000..66b5249
--- /dev/null
+++ b/engine/scene/MeshBuilder.ts
@@ -0,0 +1,80 @@
+import { STRIDE, type Mesh } from "./Mesh"
+
+type Corner = [number, number, number]
+
+export namespace MeshBuilder {
+  export function quad(
+    mesh: Mesh,
+    a: Corner,
+    b: Corner,
+    c: Corner,
+    d: Corner,
+    uScale: number,
+    vScale: number,
+  ): void {
+    const base = mesh.verts.length / STRIDE
+    mesh.verts.push(
+      a[0],
+      a[1],
+      a[2],
+      0,
+      0,
+      b[0],
+      b[1],
+      b[2],
+      uScale,
+      0,
+      c[0],
+      c[1],
+      c[2],
+      uScale,
+      vScale,
+      d[0],
+      d[1],
+      d[2],
+      0,
+      vScale,
+    )
+    mesh.indices.push(base, base + 1, base + 2, base, base + 2, base + 3)
+  }
+
+  export function slab(
+    mesh: Mesh,
+    x0: number,
+    x1: number,
+    z0: number,
+    z1: number,
+    y0: number,
+    y1: number,
+    tilesPerUnit: number,
+  ): void {
+    const dx = (x1 - x0) * tilesPerUnit
+    const dz = (z1 - z0) * tilesPerUnit
+    const dy = (y1 - y0) * tilesPerUnit
+    quad(mesh, [x0, y1, z0], [x1, y1, z0], [x1, y1, z1], [x0, y1, z1], dx, dz)
+    quad(mesh, [x0, y0, z0], [x1, y0, z0], [x1, y1, z0], [x0, y1, z0], dx, dy)
+    quad(mesh, [x1, y0, z1], [x0, y0, z1], [x0, y1, z1], [x1, y1, z1], dx, dy)
+    quad(mesh, [x0, y0, z1], [x0, y0, z0], [x0, y1, z0], [x0, y1, z1], dz, dy)
+    quad(mesh, [x1, y0, z0], [x1, y0, z1], [x1, y1, z1], [x1, y1, z0], dz, dy)
+  }
+
+  export function box(
+    mesh: Mesh,
+    centerX: number,
+    centerZ: number,
+    half: number,
+    base: number,
+    height: number,
+  ): void {
+    const x0 = centerX - half
+    const x1 = centerX + half
+    const z0 = centerZ - half
+    const z1 = centerZ + half
+    const y1 = base + height
+    quad(mesh, [x0, y1, z0], [x1, y1, z0], [x1, y1, z1], [x0, y1, z1], 1, 1)
+    quad(mesh, [x0, base, z0], [x1, base, z0], [x1, y1, z0], [x0, y1, z0], 1, 1)
+    quad(mesh, [x1, base, z1], [x0, base, z1], [x0, y1, z1], [x1, y1, z1], 1, 1)
+    quad(mesh, [x1, base, z0], [x1, base, z1], [x1, y1, z1], [x1, y1, z0], 1, 1)
+    quad(mesh, [x0, base, z1], [x0, base, z0], [x0, y1, z0], [x0, y1, z1], 1, 1)
+  }
+}
diff --git a/engine/scene/Prefab.ts b/engine/scene/Prefab.ts
new file mode 100644
index 0000000..74674b3
--- /dev/null
+++ b/engine/scene/Prefab.ts
@@ -0,0 +1,38 @@
+import type { Vec3 } from "../math/Vec3"
+import type { MeshBatch } from "../render/ChunkBuilder"
+import type { Collider } from "../world/Collider"
+
+/** Static content recipe. Concrete game prefabs implement this engine contract and
+ * are referenced as objects, never through a closed content-kind registry. */
+export type Prefab<State> = {
+  position: (state: State) => Vec3
+  bakeNear: (state: State, batch: MeshBatch) => void
+  bakeFar?: (state: State, batch: MeshBatch) => void
+  collider?: (state: State) => Collider | null
+}
+
+/** Type-erased placed prefab consumed during level compilation only. */
+export type PlacedPrefab = {
+  position: Vec3
+  bakeNear: (batch: MeshBatch) => void
+  bakeFar?: (batch: MeshBatch) => void
+  collider: Collider | null
+}
+
+export namespace Prefab {
+  export function place<State>(
+    definition: Prefab<State>,
+    state: State,
+  ): PlacedPrefab {
+    const bakeFar = definition.bakeFar
+    return {
+      position: definition.position(state),
+      bakeNear: (batch) => definition.bakeNear(state, batch),
+      bakeFar:
+        bakeFar === undefined
+          ? undefined
+          : (batch) => bakeFar(state, batch),
+      collider: definition.collider?.(state) ?? null,
+    }
+  }
+}
diff --git a/engine/world/CharacterController.ts b/engine/world/CharacterController.ts
new file mode 100644
index 0000000..a45e593
--- /dev/null
+++ b/engine/world/CharacterController.ts
@@ -0,0 +1,89 @@
+import type { Vec3 } from "../math/Vec3"
+import { CollisionWorld, type CollisionWorld as World } from "./CollisionWorld"
+
+export type Character = {
+  position: Vec3
+  yaw: number
+  velocityY: number
+  onGround: boolean
+}
+
+export type CharacterInput = {
+  forward: number
+  right: number
+  jump: boolean
+  run: boolean
+}
+
+export type CharacterConfig = {
+  radius: number
+  speed: number
+  runMultiplier: number
+  gravity: number
+  jumpSpeed: number
+  eyeHeight: number
+}
+
+export namespace CharacterController {
+  export function update(
+    character: Character,
+    input: CharacterInput,
+    dt: number,
+    world: World,
+    config: CharacterConfig,
+  ): void {
+    if (input.jump && character.onGround) {
+      character.velocityY = config.jumpSpeed
+      character.onGround = false
+    }
+    const steps = moveSubsteps(input, dt, config)
+    for (let i = 0; i < steps; i++) {
+      moveHorizontal(character, input, dt / steps, config)
+      CollisionWorld.pushOut(world, character.position, config.radius)
+    }
+    character.velocityY -= config.gravity * dt
+    character.position.y += character.velocityY * dt
+    const ground = CollisionWorld.groundHeight(world, character.position)
+    if (character.position.y <= ground) {
+      character.position.y = ground
+      character.velocityY = 0
+      character.onGround = true
+    } else {
+      character.onGround = false
+    }
+  }
+
+  function moveSubsteps(
+    input: CharacterInput,
+    dt: number,
+    config: CharacterConfig,
+  ): number {
+    const distance =
+      config.speed *
+      runFactor(input, config) *
+      dt *
+      Math.hypot(input.forward, input.right)
+    return Math.max(1, Math.ceil(distance / config.radius))
+  }
+
+  function moveHorizontal(
+    character: Character,
+    input: CharacterInput,
+    dt: number,
+    config: CharacterConfig,
+  ): void {
+    const speed = config.speed * runFactor(input, config) * dt
+    const forwardX = Math.sin(character.yaw)
+    const forwardZ = -Math.cos(character.yaw)
+    const rightX = Math.cos(character.yaw)
+    const rightZ = Math.sin(character.yaw)
+    character.position.x +=
+      (forwardX * input.forward + rightX * input.right) * speed
+    character.position.z +=
+      (forwardZ * input.forward + rightZ * input.right) * speed
+  }
+
+  function runFactor(input: CharacterInput, config: CharacterConfig): number {
+    return input.run ? config.runMultiplier : 1
+  }
+}
diff --git a/engine/world/Collider.ts b/engine/world/Collider.ts
new file mode 100644
index 0000000..926916f
--- /dev/null
+++ b/engine/world/Collider.ts
@@ -0,0 +1,116 @@
+import type { Vec3 } from "../math/Vec3"
+
+/** A 2.5D box: horizontal footprint plus top height. */
+export type BoxCollider = {
+  shape: "box"
+  minX: number
+  maxX: number
+  minZ: number
+  maxZ: number
+  top: number
+  standable: boolean
+}
+
+/** A 2.5D circle: horizontal footprint plus top height. */
+export type CircleCollider = {
+  shape: "circle"
+  x: number
+  z: number
+  radius: number
+  top: number
+  standable: boolean
+}
+
+/** Finite engine collision capabilities, not game-content identity. */
+export type Collider = BoxCollider | CircleCollider
+
+export namespace Collider {
+  export function centerX(collider: Collider): number {
+    return collider.shape === "circle"
+      ? collider.x
+      : (collider.minX + collider.maxX) * 0.5
+  }
+
+  export function centerZ(collider: Collider): number {
+    return collider.shape === "circle"
+      ? collider.z
+      : (collider.minZ + collider.maxZ) * 0.5
+  }
+
+  export function contains(collider: Collider, x: number, z: number): boolean {
+    if (collider.shape === "circle") {
+      const dx = x - collider.x
+      const dz = z - collider.z
+      return dx * dx + dz * dz <= collider.radius * collider.radius
+    }
+    return (
+      x >= collider.minX &&
+      x <= collider.maxX &&
+      z >= collider.minZ &&
+      z <= collider.maxZ
+    )
+  }
+
+  /** Push a horizontal player circle out of one collider. */
+  export function pushOut(
+    collider: Collider,
+    position: Vec3,
+    radius: number,
+  ): void {
+    if (collider.shape === "circle") {
+      pushFromCircle(position, radius, collider)
+      return
+    }
+    pushFromBox(position, radius, collider)
+  }
+
+  function pushFromBox(position: Vec3, radius: number, box: BoxCollider): void {
+    const cx = Math.max(box.minX, Math.min(box.maxX, position.x))
+    const cz = Math.max(box.minZ, Math.min(box.maxZ, position.z))
+    const dx = position.x - cx
+    const dz = position.z - cz
+    const distanceSquared = dx * dx + dz * dz
+    if (distanceSquared >= radius * radius) {
+      return
+    }
+    if (distanceSquared > 1e-6) {
+      const distance = Math.sqrt(distanceSquared)
+      const push = (radius - distance) / distance
+      position.x += dx * push
+      position.z += dz * push
+      return
+    }
+    const left = position.x - box.minX
+    const right = box.maxX - position.x
+    const near = position.z - box.minZ
+    const far = box.maxZ - position.z
+    const nearest = Math.min(left, right, near, far)
+    if (nearest === left) {
+      position.x = box.minX - radius
+    } else if (nearest === right) {
+      position.x = box.maxX + radius
+    } else if (nearest === near) {
+      position.z = box.minZ - radius
+    } else {
+      position.z = box.maxZ + radius
+    }
+  }
+
+  function pushFromCircle(
+    position: Vec3,
+    radius: number,
+    circle: CircleCollider,
+  ): void {
+    const dx = position.x - circle.x
+    const dz = position.z - circle.z
+    const reach = radius + circle.radius
+    const distanceSquared = dx * dx + dz * dz
+    if (distanceSquared >= reach * reach || distanceSquared < 1e-6) {
+      return
+    }
+    const distance = Math.sqrt(distanceSquared)
+    const push = (reach - distance) / distance
+    position.x += dx * push
+    position.z += dz * push
+  }
+}
diff --git a/engine/world/CollisionWorld.ts b/engine/world/CollisionWorld.ts
new file mode 100644
index 0000000..2f2e945
--- /dev/null
+++ b/engine/world/CollisionWorld.ts
@@ -0,0 +1,62 @@
+import type { Vec3 } from "../math/Vec3"
+import { Collider, type Collider as ColliderShape } from "./Collider"
+import type { Terrain } from "./Terrain"
+
+export type CollisionWorld = {
+  terrain: Terrain
+  staticColliders: ColliderShape[]
+  dynamicColliders: ColliderShape[]
+}
+
+export namespace CollisionWorld {
+  export function create(
+    terrain: Terrain,
+    staticColliders: ColliderShape[],
+  ): CollisionWorld {
+    return { terrain, staticColliders, dynamicColliders: [] }
+  }
+
+  export function pushOut(
+    world: CollisionWorld,
+    position: Vec3,
+    radius: number,
+  ): void {
+    pushFrom(world.staticColliders, position, radius)
+    pushFrom(world.dynamicColliders, position, radius)
+  }
+
+  export function groundHeight(world: CollisionWorld, position: Vec3): number {
+    let ground = world.terrain.heightAt(position.x, position.z)
+    ground = standingHeight(world.staticColliders, position, ground)
+    return standingHeight(world.dynamicColliders, position, ground)
+  }
+
+  function pushFrom(
+    colliders: ColliderShape[],
+    position: Vec3,
+    radius: number,
+  ): void {
+    for (const collider of colliders) {
+      if (position.y < collider.top - 0.01) {
+        Collider.pushOut(collider, position, radius)
+      }
+    }
+  }
+
+  function standingHeight(
+    colliders: ColliderShape[],
+    position: Vec3,
+    initial: number,
+  ): number {
+    let ground = initial
+    for (const collider of colliders) {
+      if (
+        collider.standable &&
+        Collider.contains(collider, position.x, position.z)
+      ) {
+        ground = Math.max(ground, collider.top)
+      }
+    }
+    return ground
+  }
+}
diff --git a/engine/world/Level.ts b/engine/world/Level.ts
new file mode 100644
index 0000000..e608940
--- /dev/null
+++ b/engine/world/Level.ts
@@ -0,0 +1,123 @@
+import {
+  Actor,
+  type Actor as RuntimeActor,
+} from "../scene/Actor"
+import { Collider, type Collider as CollisionShape } from "./Collider"
+import {
+  CollisionWorld,
+  type CollisionWorld as Collision,
+} from "./CollisionWorld"
+import type { Terrain } from "./Terrain"
+import {
+  RenderScene,
+  type Billboard,
+  type RenderInstance,
+  type RenderPrototype,
+  type RenderScene as Scene,
+} from "../render/RenderScene"
+import type { Chunk } from "../render/Chunk"
+import type { DrawGroup } from "../render/Material"
+import type { SkyConfig } from "../render/Sky"
+import type { Mat4 } from "../math/Mat4"
+import type { Vec3 } from "../math/Vec3"
+
+export type LevelDefinition<World> = {
+  terrain: Terrain
+  actorWorld: World
+  actors: readonly RuntimeActor<World>[]
+  staticColliders: CollisionShape[]
+  staticGroups: DrawGroup[]
+  chunks: Chunk[]
+  billboards: Billboard[]
+  sky: SkyConfig
+}
+
+/** Live engine world. Behavior-bearing actors stay here on the main thread; only
+ * `render` is clone-safe and sent to workers. */
+export type Level<World> = {
+  readonly terrain: Terrain
+  readonly actorWorld: World
+  readonly actors: readonly RuntimeActor<World>[]
+  readonly collision: Collision
+  readonly render: Scene
+}
+
+const prototypeIndexes = new WeakMap<object, ReadonlyMap<object, number>>()
+
+export namespace Level {
+  export function create<World>(definition: LevelDefinition<World>): Level<World> {
+    const actors = Object.freeze([...definition.actors])
+    const prototypes: RenderPrototype[] = []
+    const prototypeIndex = new Map<object, number>()
+    for (const actor of actors) {
+      if (!prototypeIndex.has(actor.definition)) {
+        prototypeIndex.set(actor.definition, prototypes.length)
+        prototypes.push(actor.prototype)
+      }
+    }
+    const level: Level<World> = {
+      terrain: definition.terrain,
+      actorWorld: definition.actorWorld,
+      actors,
+      collision: CollisionWorld.create(
+        definition.terrain,
+        definition.staticColliders,
+      ),
+      render: Object.freeze({
+        chunks: Object.freeze([...definition.chunks]),
+        staticGroups: Object.freeze([...definition.staticGroups]),
+        billboards: Object.freeze([...definition.billboards]),
+        prototypes: Object.freeze(prototypes),
+        maxInstances: actors.length,
+        sky: definition.sky,
+      }),
+    }
+    prototypeIndexes.set(level, prototypeIndex)
+    return level
+  }
+
+  export function update<World>(level: Level<World>, dt: number): void {
+    for (const actor of level.actors) {
+      Actor.update(actor, dt, level.actorWorld)
+    }
+  }
+
+  export function visibleInstances<World>(
+    level: Level<World>,
+    viewProjection: Mat4,
+  ): RenderInstance[] {
+    const prototypeIndex = prototypeIndexes.get(level)
+    if (prototypeIndex === undefined) {
+      throw new Error("level was not created by Level.create")
+    }
+    const instances: RenderInstance[] = []
+    for (const actor of level.actors) {
+      const prototype = prototypeIndex.get(actor.definition)
+      if (prototype !== undefined) {
+        instances.push({ prototype, ...Actor.transform(actor) })
+      }
+    }
+    return RenderScene.visibleInstances(level.render, instances, viewProjection)
+  }
+
+  export function refreshActorColliders<World>(
+    level: Level<World>,
+    focus: Vec3,
+    range: number,
+  ): void {
+    const dynamic = level.collision.dynamicColliders
+    dynamic.length = 0
+    const rangeSquared = range * range
+    for (const actor of level.actors) {
+      const collider = Actor.collider(actor, level.actorWorld)
+      if (collider === null) {
+        continue
+      }
+      const dx = Collider.centerX(collider) - focus.x
+      const dz = Collider.centerZ(collider) - focus.z
+      if (dx * dx + dz * dz <= rangeSquared) {
+        dynamic.push(collider)
+      }
+    }
+  }
+}
diff --git a/engine/world/Terrain.ts b/engine/world/Terrain.ts
new file mode 100644
index 0000000..e015a0f
--- /dev/null
+++ b/engine/world/Terrain.ts
@@ -0,0 +1,121 @@
+import { STRIDE, type Mesh } from "../scene/Mesh"
+
+/** A bounded ground surface. Implementations may be procedural, sampled, or
+ * loaded; callers only depend on world-space height sampling. */
+export type Terrain = {
+  minX: number
+  minZ: number
+  maxX: number
+  maxZ: number
+  heightAt: (x: number, z: number) => number
+}
+
+/** Parameters for the built-in rolling terrain generator. Values describe the
+ * surface only; level-specific holes and materials belong to level data. */
+export type RollingTerrainConfig = {
+  inner: number
+  outer: number
+  blend: number
+  amplitude: number
+  frequency: number
+  peakHeight: number
+  peakFrequency: number
+  peakStart: number
+}
+
+export namespace Terrain {
+  /** Built-in square world with a flat center, rolling hills, and edge ridges. */
+  export function rolling(config: RollingTerrainConfig): Terrain {
+    return {
+      minX: -config.outer,
+      minZ: -config.outer,
+      maxX: config.outer,
+      maxZ: config.outer,
+      heightAt(x, z) {
+        const r = Math.max(Math.abs(x), Math.abs(z))
+        if (r <= config.inner) {
+          return 0
+        }
+        const rise = smoothstep(config.inner, config.inner + config.blend, r)
+        const hills = config.amplitude * bumps(x, z, config.frequency)
+        const k = Math.min(
+          1,
+          (r - config.inner) / (config.outer - config.inner),
+        )
+        const peaks =
+          config.peakHeight *
+          ridges(x, z, config.peakFrequency) *
+          smoothstep(config.peakStart, 1, k)
+        return rise * (hills + peaks)
+      },
+    }
+  }
+
+  export function height(terrain: Terrain, x: number, z: number): number {
+    return terrain.heightAt(x, z)
+  }
+
+  /** Append one sampled heightfield patch. `include` is level policy evaluated at
+   * each quad center, allowing arbitrary holes without teaching terrain what
+   * occupies them. */
+  export function patch(
+    terrain: Terrain,
+    mesh: Mesh,
+    x0: number,
+    z0: number,
+    x1: number,
+    z1: number,
+    cols: number,
+    rows: number,
+    uvScale: number,
+    include?: (x: number, z: number) => boolean,
+  ): void {
+    const base = mesh.verts.length / STRIDE
+    const dx = (x1 - x0) / cols
+    const dz = (z1 - z0) / rows
+    const rowLength = cols + 1
+    for (let row = 0; row <= rows; row++) {
+      const z = z0 + row * dz
+      for (let col = 0; col <= cols; col++) {
+        const x = x0 + col * dx
+        mesh.verts.push(x, terrain.heightAt(x, z), z, x * uvScale, z * uvScale)
+      }
+    }
+    for (let row = 0; row < rows; row++) {
+      for (let col = 0; col < cols; col++) {
+        const cx = x0 + (col + 0.5) * dx
+        const cz = z0 + (row + 0.5) * dz
+        if (include !== undefined && !include(cx, cz)) {
+          continue
+        }
+        const p = base + row * rowLength + col
+        mesh.indices.push(
+          p,
+          p + rowLength + 1,
+          p + 1,
+          p,
+          p + rowLength,
+          p + rowLength + 1,
+        )
+      }
+    }
+  }
+
+  function bumps(x: number, z: number, frequency: number): number {
+    const a = Math.sin(x * frequency) * Math.cos(z * frequency)
+    const b = Math.sin((x + z) * frequency * 0.5 + 1.7) * 0.5
+    return (a + b + 1.5) / 3
+  }
+
+  function ridges(x: number, z: number, frequency: number): number {
+    const n =
+      Math.sin(x * frequency + 1.3) * Math.cos(z * frequency - 0.7) * 0.7 +
+      Math.sin((x + z) * frequency * 0.6 + 2.5) * 0.3
+    return 1 - Math.abs(n)
+  }
+
+  function smoothstep(a: number, b: number, x: number): number {
+    const t = Math.max(0, Math.min(1, (x - a) / (b - a || 1e-4)))
+    return t * t * (3 - 2 * t)
+  }
+}
diff --git a/game/Terrain.ts b/game/Terrain.ts
deleted file mode 100644
index b38e6a9..0000000
--- a/game/Terrain.ts
+++ /dev/null
@@ -1,106 +0,0 @@
-import { STRIDE, type Mesh } from "../engine/scene/Mesh"
-
-/** A procedural heightfield surrounding the room. It is the single source of
- *  ground height: the outdoor mesh is built from it and the player stands on the
- *  same `height` samples, so what you see and what you collide with agree. The
- *  center (out to `inner`) is a flat clearing where the room sits; from there the
- *  land rolls outward and ramps up into tall peaks at the far edge. Every field
- *  is a live knob -- edit them in the level to reshape the world. */
-export type Terrain = {
-  /** Half-extent of the flat central clearing (the room lives here); height 0. */
-  inner: number
-  /** World half-extent. Peaks ramp up toward this outer rim. */
-  outer: number
-  /** Ease-up distance just outside `inner`, so the clearing meets the hills with
-   *  a slope instead of a wall. */
-  blend: number
-  /** Rolling-hill height across the open ground. */
-  amplitude: number
-  /** Rolling-hill frequency (low = broad hills over the big world). */
-  frequency: number
-  /** Extra height of the mountains near the edge -- make this big for peaks. */
-  peakHeight: number
-  /** Mountain frequency (low = few, massive ridges). */
-  peakFrequency: number
-  /** Fraction of the way out (0..1) where the peaks begin rising. */
-  peakStart: number
-}
-
-export namespace Terrain {
-  /** Ground height at world (x, z). 0 inside the clearing, rolling hills beyond,
-   *  ramping into peaks toward the edge. Uses a square (Chebyshev) radius so the
-   *  clearing is a square that lines up with the square room. */
-  export function height(t: Terrain, x: number, z: number): number {
-    const r = Math.max(Math.abs(x), Math.abs(z))
-    if (r <= t.inner) {
-      return 0
-    }
-    const rise = smoothstep(t.inner, t.inner + t.blend, r)
-    const hills = t.amplitude * bumps(x, z, t.frequency)
-    const k = Math.min(1, (r - t.inner) / (t.outer - t.inner))
-    const peaks = t.peakHeight * ridges(x, z, t.peakFrequency) * smoothstep(t.peakStart, 1, k)
-    return rise * (hills + peaks)
-  }
-
-  /** Append one ground patch: a `cols`x`rows` heightfield grid over the rectangle
-   *  [x0,x1] x [z0,z1], each vertex lifted onto the heightfield. Quads whose
-   *  center is inside the clearing are skipped (the room floor's hole). UVs use
-   *  world position * `uvScale`, so neighboring patches tile seamlessly. Callers
-   *  keep the spacing uniform and cell edges aligned, so shared edges weld with
-   *  no cracks. Used to build the terrain per spatial chunk. */
-  export function patch(
-    t: Terrain,
-    mesh: Mesh,
-    x0: number,
-    z0: number,
-    x1: number,
-    z1: number,
-    cols: number,
-    rows: number,
-    uvScale: number,
-  ): void {
-    const base = mesh.verts.length / STRIDE
-    const dx = (x1 - x0) / cols
-    const dz = (z1 - z0) / rows
-    const rowLen = cols + 1
-    for (let i = 0; i <= rows; i++) {
-      const z = z0 + i * dz
-      for (let j = 0; j <= cols; j++) {
-        const x = x0 + j * dx
-        mesh.verts.push(x, height(t, x, z), z, x * uvScale, z * uvScale)
-      }
-    }
-    for (let i = 0; i < rows; i++) {
-      for (let j = 0; j < cols; j++) {
-        const cx = x0 + (j + 0.5) * dx
-        const cz = z0 + (i + 0.5) * dz
-        if (Math.max(Math.abs(cx), Math.abs(cz)) < t.inner) {
-          continue
-        }
-        const p = base + i * rowLen + j
-        // Wound so the surface faces up/out, matching the backface-cull sign.
-        mesh.indices.push(p, p + rowLen + 1, p + 1, p, p + rowLen, p + rowLen + 1)
-      }
-    }
-  }
-
-  /** Rolling hills in 0..1, always non-negative so the ground never dips below
-   *  the clearing. */
-  function bumps(x: number, z: number, f: number): number {
-    const a = Math.sin(x * f) * Math.cos(z * f)
-    const b = Math.sin((x + z) * f * 0.5 + 1.7) * 0.5
-    return (a + b + 1.5) / 3
-  }
-
-  /** Ridged noise in 0..1: crests where the field crosses zero give sharp
-   *  mountain ridgelines rather than round blobs. */
-  function ridges(x: number, z: number, f: number): number {
-    const n = Math.sin(x * f + 1.3) * Math.cos(z * f - 0.7) * 0.7 + Math.sin((x + z) * f * 0.6 + 2.5) * 0.3
-    return 1 - Math.abs(n)
-  }
-
-  function smoothstep(a: number, b: number, x: number): number {
-    const t = Math.max(0, Math.min(1, (x - a) / (b - a || 1e-4)))
-    return t * t * (3 - 2 * t)
-  }
-}
diff --git a/game/actors/Boulder.ts b/game/actors/Boulder.ts
index 7d412f6..3c76819 100644
--- a/game/actors/Boulder.ts
+++ b/game/actors/Boulder.ts
@@ -1,5 +1,7 @@
 import type { Vec3 } from "../../engine/math/Vec3"
 import { STRIDE, type Mesh } from "../../engine/scene/Mesh"
+import type { Material } from "../../engine/render/Material"
+import type { Prefab } from "../../engine/scene/Prefab"
 
 const TAU = Math.PI * 2
 
@@ -22,8 +24,35 @@ export type Boulder = {
  * field of boulders batches into a single draw call.
  */
 export namespace Boulder {
+  export function create(material: Material): Prefab<Boulder> {
+    return {
+      position: (boulder) => boulder.position,
+      bakeNear: (boulder, batch) => build(boulder, batch.mesh(material)),
+      bakeFar: (boulder, batch) =>
+        build(boulder, batch.mesh(material), "impostor"),
+      collider(boulder) {
+        if (boulder.radius <= 0.7) {
+          return null
+        }
+        return {
+          shape: "box",
+          minX: boulder.position.x - boulder.radius,
+          maxX: boulder.position.x + boulder.radius,
+          minZ: boulder.position.z - boulder.radius,
+          maxZ: boulder.position.z + boulder.radius,
+          top: boulder.position.y + boulder.radius * 0.7,
+          standable: false,
+        }
+      },
+    }
+  }
+
   /** `lod` "impostor" bakes a coarser rock (fewer facets) for far chunks. */
-  export function build(boulder: Boulder, mesh: Mesh, lod: "full" | "impostor" = "full"): void {
+  export function build(
+    boulder: Boulder,
+    mesh: Mesh,
+    lod: "full" | "impostor" = "full",
+  ): void {
     const rand = rng(boulder.seed)
     const seg = lod === "impostor" ? 4 : 5
     const rings = lod === "impostor" ? 2 : 4
@@ -67,7 +96,11 @@ export namespace Boulder {
   /** Per-vertex radial scale in ~0.72..1.14 for a chunky, angular surface. The
    *  longitude seam (last column == first) and each pole row (one shared value)
    *  match so the mesh stays closed. */
-  function jitterGrid(seg: number, rings: number, rand: () => number): number[][] {
+  function jitterGrid(
+    seg: number,
+    rings: number,
+    rand: () => number,
+  ): number[][] {
     const grid: number[][] = []
     for (let ir = 0; ir <= rings; ir++) {
       const pole = ir === 0 || ir === rings
diff --git a/game/actors/Bush.ts b/game/actors/Bush.ts
index c8fd73e..1c6b47d 100644
--- a/game/actors/Bush.ts
+++ b/game/actors/Bush.ts
@@ -1,5 +1,7 @@
 import type { Vec3 } from "../../engine/math/Vec3"
 import { STRIDE, type Mesh } from "../../engine/scene/Mesh"
+import type { Material } from "../../engine/render/Material"
+import type { Prefab } from "../../engine/scene/Prefab"
 
 const TAU = Math.PI * 2
 
@@ -17,6 +19,13 @@ export type Bush = {
  *  wound outward, so backface culling is safe. `build` appends into a shared
  *  (leaf-textured) mesh. */
 export namespace Bush {
+  export function create(material: Material): Prefab<Bush> {
+    return {
+      position: (bush) => bush.position,
+      bakeNear: (bush, batch) => build(bush, batch.mesh(material)),
+    }
+  }
+
   export function build(bush: Bush, mesh: Mesh): void {
     const rand = rng(bush.seed)
     // A handful of smaller overlapping lumps reads as a soft shrub; one big
@@ -34,7 +43,14 @@ export namespace Bush {
   }
 
   /** A small lumpy low-poly sphere, wound outward (matches the oak canopy blob). */
-  function blob(mesh: Mesh, cx: number, cy: number, cz: number, radius: number, rand: () => number): void {
+  function blob(
+    mesh: Mesh,
+    cx: number,
+    cy: number,
+    cz: number,
+    radius: number,
+    rand: () => number,
+  ): void {
     const seg = 6
     const rings = 4
     const start = mesh.verts.length / STRIDE
diff --git a/game/actors/Flower.ts b/game/actors/Flower.ts
index 6a13cc7..5bcf167 100644
--- a/game/actors/Flower.ts
+++ b/game/actors/Flower.ts
@@ -1,17 +1,19 @@
 import type { Vec3 } from "../../engine/math/Vec3"
 import { Mesh } from "../../engine/scene/Mesh"
+import type { Material } from "../../engine/render/Material"
+import type { Prefab } from "../../engine/scene/Prefab"
 
 const TAU = Math.PI * 2
 
-/** Flower bloom color, indexing a region of the `flower` texture atlas. */
-export type FlowerColor = "white" | "red" | "yellow"
+/** Concrete atlas style referenced directly by flower instances. */
+export type FlowerStyle = { bloomUv: [number, number] }
 
 /** A single small flower: a thin crossed-quad stem plus a shallow fan of petals.
  *  Tiny, so it is drawn double-sided (no backface cull) and carries no collider.
  *  `size` is roughly its height; `seed` jitters the petals. */
 export type Flower = {
   position: Vec3
-  color: FlowerColor
+  style: FlowerStyle
   size: number
   seed: number
 }
@@ -23,16 +25,21 @@ export type Flower = {
  * or draw call. `build` appends into one shared flower mesh.
  */
 export namespace Flower {
-  /** uv center of each bloom color's atlas region (tile units). */
-  const BLOOM_UV: Record<FlowerColor, [number, number]> = {
-    white: [0.75, 0.25],
-    red: [0.25, 0.75],
-    yellow: [0.75, 0.75],
-  }
+  export const white: FlowerStyle = { bloomUv: [0.75, 0.25] }
+  export const red: FlowerStyle = { bloomUv: [0.25, 0.75] }
+  export const yellow: FlowerStyle = { bloomUv: [0.75, 0.75] }
+
   /** uv center of the green stem region. */
   const STEM_U = 0.25
   const STEM_V = 0.25
 
+  export function create(material: Material): Prefab<Flower> {
+    return {
+      position: (flower) => flower.position,
+      bakeNear: (flower, batch) => build(flower, batch.mesh(material)),
+    }
+  }
+
   export function build(flower: Flower, mesh: Mesh): void {
     const rand = rng(flower.seed)
     const p = flower.position
@@ -43,14 +50,21 @@ export namespace Flower {
     stem(mesh, p.x, p.y, p.z, bloomY, w, 0)
     stem(mesh, p.x, p.y, p.z, bloomY, 0, w)
     // Bloom: a shallow fan of petals, center raised a touch so it domes.
-    const [bu, bv] = BLOOM_UV[flower.color]
+    const [bu, bv] = flower.style.bloomUv
     const rad = flower.size * 0.38
     const center = Mesh.push(mesh, p.x, bloomY + rad * 0.3, p.z, bu, bv)
     const ring = center + 1
     const petals = 5
     for (let i = 0; i <= petals; i++) {
       const angle = (i / petals) * TAU + rand() * 0.4
-      Mesh.push(mesh, p.x + Math.cos(angle) * rad, bloomY, p.z + Math.sin(angle) * rad, bu, bv)
+      Mesh.push(
+        mesh,
+        p.x + Math.cos(angle) * rad,
+        bloomY,
+        p.z + Math.sin(angle) * rad,
+        bu,
+        bv,
+      )
     }
     for (let i = 0; i < petals; i++) {
       mesh.indices.push(center, ring + i, ring + i + 1)
@@ -58,7 +72,15 @@ export namespace Flower {
   }
 
   /** A thin vertical quad from the ground to `y1`, width along (dx, dz). */
-  function stem(mesh: Mesh, x: number, y0: number, z: number, y1: number, dx: number, dz: number): void {
+  function stem(
+    mesh: Mesh,
+    x: number,
+    y0: number,
+    z: number,
+    y1: number,
+    dx: number,
+    dz: number,
+  ): void {
     const a = Mesh.push(mesh, x - dx, y0, z - dz, STEM_U, STEM_V)
     const b = Mesh.push(mesh, x + dx, y0, z + dz, STEM_U, STEM_V)
     const c = Mesh.push(mesh, x + dx, y1, z + dz, STEM_U, STEM_V)
diff --git a/game/actors/Mob.ts b/game/actors/Mob.ts
index 29b3487..ff64bb5 100644
--- a/game/actors/Mob.ts
+++ b/game/actors/Mob.ts
@@ -1,27 +1,14 @@
-import type { Terrain } from "../Terrain"
 import type { Vec3 } from "../../engine/math/Vec3"
-import type { Mesh } from "../../engine/scene/Mesh"
-import type { Entity } from "../../engine/scene/Actor"
-import { frog } from "./mobs/Frog"
-import { bee } from "./mobs/Bee"
-import { robin } from "./mobs/Robin"
+import type { Actor } from "../../engine/scene/Actor"
+import type { RenderTransform } from "../../engine/render/RenderScene"
+import type { BoxCollider } from "../../engine/world/Collider"
+import type { Terrain } from "../../engine/world/Terrain"
 
-/** A roaming creature drawn as a moving low-poly mesh (unlike the static baked
- *  world). Each kind is an `Entity` definition (geometry + behavior + bounds) living
- *  in its own module under `mobs/`; this file just assembles them into a registry
- *  and exposes a thin per-kind dispatch. Adding a kind = add a `mobs/<Kind>.ts` +
- *  one entry in `MOB_KINDS`/`DEFS`.
- *
- *  A mob's geometry is a **canonical local-space mesh** built once per kind (front =
- *  +Z, frog/robin feet / bee body at the origin); the live `position`/`heading`/
- *  `scale` are turned into a per-frame model matrix by the renderer. All wander
- *  state lives on the instance so `update` is a pure stepping function of the mob +
- *  dt (deterministic via the evolving `seed`), which keeps the sim on the main
- *  thread and cloneable-free. */
-export type MobKind = "frog" | "bee" | "robin"
+/** Runtime actor using shared roaming-creature state. Concrete definitions are
+ * direct object references supplied by Frog, Bee, Robin, or future content. */
+export type Mob = Actor<Terrain>
 
-export type Mob = {
-  kind: MobKind
+export type MobState = {
   /** Leash anchor (where it was scattered); wandering is pulled back toward it. */
   home: Vec3
   /** Live feet-center (frog/robin) / body-center (bee), advanced each frame. */
@@ -39,46 +26,39 @@ export type Mob = {
   vy: number
   /** Countdown to the next decision (frog/robin: next hop; bee: next heading change). */
   timer: number
-  /** Per-kind scratch clock: the bee's hover-bob phase; the robin's remaining
+  /** Behavior scratch clock: the bee's hover-bob phase; the robin's remaining
    *  powered-flight cruise time (>0 while gliding between perches). */
   phase: number
   /** Frog/robin: resting on the ground vs airborne (a hop or a flight). */
   grounded: boolean
 }
 
-/** Canonical kind order. **The index is the id packed into the mob SAB** (see
- *  renderer/worker), so this order must be identical in every context and must not
- *  change under existing kinds -- `mobs.test.ts` guards it. Append new kinds. */
-export const MOB_KINDS: MobKind[] = ["frog", "bee", "robin"]
-
-/** The per-kind `Entity` definitions, one module each. Imported (not cloned) into
- *  whatever context uses it, so it works the same on the main thread and in workers. */
-const DEFS: Record<MobKind, Entity<Mob, Terrain>> = { frog, bee, robin }
-
 export namespace Mob {
-  /** The definition for a kind (geometry, behavior, bounds). */
-  export function def(kind: MobKind): Entity<Mob, Terrain> {
-    return DEFS[kind]
+  export function transform(state: MobState): RenderTransform {
+    return {
+      x: state.position.x,
+      y: state.position.y,
+      z: state.position.z,
+      heading: state.heading,
+      scale: state.scale,
+    }
   }
 
-  /** Advance one mob by `dt` seconds, sampling `terrain` for ground height. */
-  export function update(mob: Mob, dt: number, terrain: Terrain): void {
-    DEFS[mob.kind].update(mob, dt, terrain)
-  }
-
-  /** Append the canonical local-space mesh for `kind` into `mesh` (once per kind at
-   *  load; every instance shares it, differing only by transform). */
-  export function build(kind: MobKind, mesh: Mesh): void {
-    DEFS[kind].build(mesh)
-  }
-
-  /** Local bounding radius (pre-scale), for building the per-frame cull AABB. */
-  export function boundingRadius(kind: MobKind): number {
-    return DEFS[kind].boundingRadius
-  }
-
-  /** Local body height (pre-scale), for the top of the stand-on collider. */
-  export function bodyHeight(kind: MobKind): number {
-    return DEFS[kind].bodyHeight
+  export function collider(
+    state: MobState,
+    radius: number,
+    height: number,
+    standable: boolean,
+  ): BoxCollider {
+    const half = radius * state.scale * 0.7
+    return {
+      shape: "box",
+      minX: state.position.x - half,
+      maxX: state.position.x + half,
+      minZ: state.position.z - half,
+      maxZ: state.position.z + half,
+      top: state.position.y + height * state.scale,
+      standable,
+    }
   }
 }
diff --git a/game/actors/Tree.ts b/game/actors/Tree.ts
index 9c6751b..0356872 100644
--- a/game/actors/Tree.ts
+++ b/game/actors/Tree.ts
@@ -1,54 +1,11 @@
 import type { Vec3 } from "../../engine/math/Vec3"
-import type { Mesh } from "../../engine/scene/Mesh"
-import { oak } from "./trees/Oak"
-import { spruce } from "./trees/Spruce"
-import { birch } from "./trees/Birch"
-
-export type TreeKind = "oak" | "spruce" | "birch"
 
 /** One procedural tree instance. `growth` 0..1 runs sapling -> full grown: it scales
  *  height and girth and adds canopy blobs / tiers. `seed` drives the per-tree random
  *  wobble so a forest doesn't look cloned. */
 export type Tree = {
-  kind: TreeKind
   /** Trunk base, sitting on the ground. */
   position: Vec3
   growth: number
   seed: number
 }
-
-/** Definition of a tree species: which chunk materials its trunk + foliage bake
- *  into, plus how to append its geometry. Each lives in its own `trees/<Kind>.ts`
- *  module (silhouette carries the species read); this file just assembles them.
- *  `trunk`/`foliage` are chunk-material keys (see `level.ts` `ChunkMaterials`):
- *  oak/spruce use the brown `bark`, birch the white `birch`; foliage is the oak
- *  `leaf` or spruce `needle`. */
-export type TreeSpecies = {
-  kind: TreeKind
-  trunk: string
-  foliage: string
-  build: (tree: Tree, trunk: Mesh, foliage: Mesh, lod: "full" | "impostor") => void
-}
-
-/** All tree species (also the placement roll's palette). Trees are baked at load,
- *  not shipped per frame, so this order isn't an id contract like `MOB_KINDS` -- but
- *  keeping it lets placement + tests stay registry-driven. */
-export const TREE_KINDS: TreeKind[] = ["oak", "spruce", "birch"]
-
-/** The per-species definitions, one module each. Imported (not cloned) wherever
- *  used, so it works the same on the main thread and in workers. */
-const SPECIES: Record<TreeKind, TreeSpecies> = { oak, spruce, birch }
-
-export namespace Tree {
-  /** The species definition for a kind (its trunk/foliage materials + geometry). */
-  export function species(kind: TreeKind): TreeSpecies {
-    return SPECIES[kind]
-  }
-
-  /** Append one tree into the caller-provided `trunk` + `foliage` meshes (which the
-   *  caller selects from the species' `trunk`/`foliage` material keys). `lod`
-   *  "impostor" bakes a much cheaper stand-in for far chunks; "full" is up close. */
-  export function build(tree: Tree, trunk: Mesh, foliage: Mesh, lod: "full" | "impostor" = "full"): void {
-    SPECIES[tree.kind].build(tree, trunk, foliage, lod)
-  }
-}
diff --git a/game/actors/mobs/Bee.ts b/game/actors/mobs/Bee.ts
index 82d3e8d..9befcbe 100644
--- a/game/actors/mobs/Bee.ts
+++ b/game/actors/mobs/Bee.ts
@@ -1,15 +1,28 @@
-import { Terrain } from "../../Terrain"
-import type { Mesh } from "../../../engine/scene/Mesh"
-import type { Mob } from "../Mob"
-import type { Entity } from "../../../engine/scene/Actor"
+import { Terrain, type Terrain as Ground } from "../../../engine/world/Terrain"
+import { Mesh, type Mesh as Geometry } from "../../../engine/scene/Mesh"
+import type { Material } from "../../../engine/render/Material"
+import type { ActorDefinition } from "../../../engine/scene/Actor"
+import { Mob, type MobState } from "../Mob"
 import { ellipsoid, nextRand, ovoidZ, wanderHeading, wing } from "./mobkit"
 
-export const bee: Entity<Mob, Terrain> = {
-  name: "bee",
-  build,
-  update,
-  boundingRadius: 0.5,
-  bodyHeight: 0.5,
+export type Bee = ActorDefinition<MobState, Ground>
+
+export namespace Bee {
+  export function create(material: Material): Bee {
+    const mesh = Mesh.create()
+    build(mesh)
+    return {
+      prototype: {
+        groups: [{ mesh, material }],
+        radius: 0.6,
+        minY: -0.5,
+        maxY: 1,
+      },
+      update,
+      transform: Mob.transform,
+      collider: (state) => Mob.collider(state, 0.5, 0.5, false),
+    }
+  }
 }
 
 const LEASH = 6
@@ -20,7 +33,7 @@ const HOVER = 1.1
 const BOB_AMP = 0.18
 const BOB_FREQ = 3
 
-function build(mesh: Mesh): void {
+function build(mesh: Geometry): void {
   // Fore-aft ovoid body striped along its length, a dark head at the front, two
   // pale wings. UVs: bee texture is stripe bands (left), head-dark (mid), wing-pale
   // (right); the body maps v along z so the stripes band across it.
@@ -30,7 +43,7 @@ function build(mesh: Mesh): void {
   wing(mesh, -1, 0.83, 0.99, 0, 1)
 }
 
-function update(mob: Mob, dt: number, terrain: Terrain): void {
+function update(mob: MobState, dt: number, terrain: Ground): void {
   mob.phase += dt
   mob.timer -= dt
   if (mob.timer <= 0) {
diff --git a/game/actors/mobs/Frog.ts b/game/actors/mobs/Frog.ts
index a703fa8..4bdafd4 100644
--- a/game/actors/mobs/Frog.ts
+++ b/game/actors/mobs/Frog.ts
@@ -1,17 +1,30 @@
-import { Terrain } from "../../Terrain"
-import type { Mesh } from "../../../engine/scene/Mesh"
-import type { Mob } from "../Mob"
-import type { Entity } from "../../../engine/scene/Actor"
+import { Terrain, type Terrain as Ground } from "../../../engine/world/Terrain"
+import { Mesh, type Mesh as Geometry } from "../../../engine/scene/Mesh"
+import type { Material } from "../../../engine/render/Material"
+import type { ActorDefinition } from "../../../engine/scene/Actor"
+import { Mob, type MobState } from "../Mob"
 import { ellipsoid, nextRand, wanderHeading } from "./mobkit"
 
 // Everything about the frog: squat, ground-bound, sits then springs a ballistic hop.
 
-export const frog: Entity<Mob, Terrain> = {
-  name: "frog",
-  build,
-  update,
-  boundingRadius: 0.7,
-  bodyHeight: 0.6,
+export type Frog = ActorDefinition<MobState, Ground>
+
+export namespace Frog {
+  export function create(material: Material): Frog {
+    const mesh = Mesh.create()
+    build(mesh)
+    return {
+      prototype: {
+        groups: [{ mesh, material }],
+        radius: 0.7,
+        minY: -0.7,
+        maxY: 1.3,
+      },
+      update,
+      transform: Mob.transform,
+      collider: (state) => Mob.collider(state, 0.7, 0.6, state.grounded),
+    }
+  }
 }
 
 const LEASH = 5
@@ -21,7 +34,7 @@ const HOP_SPEED = 1.6
 const HOP_IMPULSE = 3.2
 const GRAVITY = 14
 
-function build(mesh: Mesh): void {
+function build(mesh: Geometry): void {
   // Wide squat body, two eye bumps on the top-front, two hind haunches. UVs:
   // the frog texture is green skin on the left, a dark eye tone on the right.
   ellipsoid(mesh, 0, 0.26, 0, 0.5, 0.28, 0.52, 6, 4, 0, 0.68, 0, 1)
@@ -31,7 +44,7 @@ function build(mesh: Mesh): void {
   ellipsoid(mesh, -0.3, 0.2, -0.26, 0.2, 0.2, 0.26, 4, 3, 0, 0.68, 0, 1)
 }
 
-function update(mob: Mob, dt: number, terrain: Terrain): void {
+function update(mob: MobState, dt: number, terrain: Ground): void {
   if (mob.grounded) {
     mob.timer -= dt
     mob.position.y = Terrain.height(terrain, mob.position.x, mob.position.z)
diff --git a/game/actors/mobs/Robin.ts b/game/actors/mobs/Robin.ts
index 3a01f60..7473620 100644
--- a/game/actors/mobs/Robin.ts
+++ b/game/actors/mobs/Robin.ts
@@ -1,18 +1,31 @@
-import { Terrain } from "../../Terrain"
-import type { Mesh } from "../../../engine/scene/Mesh"
-import type { Mob } from "../Mob"
-import type { Entity } from "../../../engine/scene/Actor"
+import { Terrain, type Terrain as Ground } from "../../../engine/world/Terrain"
+import { Mesh, type Mesh as Geometry } from "../../../engine/scene/Mesh"
+import type { Material } from "../../../engine/render/Material"
+import type { ActorDefinition } from "../../../engine/scene/Actor"
+import { Mob, type MobState } from "../Mob"
 import { ellipsoid, nextRand, wanderHeading } from "./mobkit"
 
 // Everything about the robin: round red-breasted bird that mostly hops like a frog
 // but now and then takes a short powered flight to a new perch.
 
-export const robin: Entity<Mob, Terrain> = {
-  name: "robin",
-  build,
-  update,
-  boundingRadius: 0.45,
-  bodyHeight: 0.55,
+export type Robin = ActorDefinition<MobState, Ground>
+
+export namespace Robin {
+  export function create(material: Material): Robin {
+    const mesh = Mesh.create()
+    build(mesh)
+    return {
+      prototype: {
+        groups: [{ mesh, material }],
+        radius: 0.5,
+        minY: -0.5,
+        maxY: 1,
+      },
+      update,
+      transform: Mob.transform,
+      collider: (state) => Mob.collider(state, 0.45, 0.55, state.grounded),
+    }
+  }
 }
 
 const LEASH = 6
@@ -27,7 +40,7 @@ const FLY_IMPULSE = 3.5
 const CRUISE = 0.8
 const GRAVITY = 14
 
-function build(mesh: Mesh): void {
+function build(mesh: Geometry): void {
   // Round European robin: plump brown body, an orange-red breast bulging on the
   // front, a round brown head with two dark eyes + a small dark beak, short tail.
   // UVs: robin texture is brown (left), orange breast (mid), dark eye/beak (right).
@@ -40,7 +53,7 @@ function build(mesh: Mesh): void {
   ellipsoid(mesh, 0, 0.26, -0.32, 0.09, 0.05, 0.16, 4, 2, 0, 0.38, 0, 1) // tail (brown)
 }
 
-function update(mob: Mob, dt: number, terrain: Terrain): void {
+function update(mob: MobState, dt: number, terrain: Ground): void {
   if (mob.grounded) {
     mob.timer -= dt
     mob.position.y = Terrain.height(terrain, mob.position.x, mob.position.z)
diff --git a/game/actors/mobs/mobkit.ts b/game/actors/mobs/mobkit.ts
index 3127ebe..630f940 100644
--- a/game/actors/mobs/mobkit.ts
+++ b/game/actors/mobs/mobkit.ts
@@ -1,10 +1,8 @@
-import type { Mob } from "../Mob"
+import type { MobState } from "../Mob"
 import { STRIDE, type Mesh } from "../../../engine/scene/Mesh"
 
-// Shared building blocks for the per-kind mob definitions (Frog/Bee/Robin): the
-// faceted geometry primitives and the deterministic wander helpers. Kept in its own
-// module (no runtime import of `Mob`, only its type) so the per-kind files and the
-// `Mob` registry don't form an import cycle.
+// Shared building blocks for concrete mob definitions: faceted geometry primitives
+// and deterministic wander helpers.
 
 export const TAU = Math.PI * 2
 
@@ -13,7 +11,11 @@ export const TAU = Math.PI * 2
 /** A new heading: free wander when inside the leash, else biased back toward home
  *  so the mob never drifts off into the peaks (`jitter` = the random cone half-width
  *  in radians layered on top of the homeward bearing). */
-export function wanderHeading(mob: Mob, leash: number, jitter: number): number {
+export function wanderHeading(
+  mob: MobState,
+  leash: number,
+  jitter: number,
+): number {
   const dx = mob.home.x - mob.position.x
   const dz = mob.home.z - mob.position.z
   if (dx * dx + dz * dz > leash * leash) {
@@ -24,7 +26,7 @@ export function wanderHeading(mob: Mob, leash: number, jitter: number): number {
 
 /** mulberry32 step over the mob's own `seed` (mutated), so a mob's motion is
  *  deterministic and needs no external RNG object to clone. */
-export function nextRand(mob: Mob): number {
+export function nextRand(mob: MobState): number {
   const a = (mob.seed + 0x6D2B79F5) | 0
   mob.seed = a
   let t = Math.imul(a ^ (a >>> 15), 1 | a)
@@ -33,7 +35,7 @@ export function nextRand(mob: Mob): number {
 }
 
 // --- Geometry primitives --------------------------------------------------
-// Mobs are drawn double-sided (see renderScene), so winding is not load-bearing --
+// Mobs are drawn double-sided, so winding is not load-bearing --
 // these only need to place faceted, flat-shaded surfaces.
 
 /** A UV-rected ellipsoid (pole on Y), faceted like the boulders. */
@@ -61,7 +63,13 @@ export function ellipsoid(
     for (let is = 0; is <= seg; is++) {
       const theta = (is / seg) * TAU
       const u = u0 + (u1 - u0) * (is / seg)
-      mesh.verts.push(cx + crv * Math.cos(theta) * rx, cy + cyv * ry, cz + crv * Math.sin(theta) * rz, u, v)
+      mesh.verts.push(
+        cx + crv * Math.cos(theta) * rx,
+        cy + cyv * ry,
+        cz + crv * Math.sin(theta) * rz,
+        u,
+        v,
+      )
     }
   }
   quadGrid(mesh, start, seg, rings)
@@ -97,13 +105,36 @@ export function ovoidZ(
 }
 
 /** One flat wing quad on `side` (+1 right / -1 left), swept up and out. */
-export function wing(mesh: Mesh, side: number, u0: number, u1: number, v0: number, v1: number): void {
+export function wing(
+  mesh: Mesh,
+  side: number,
+  u0: number,
+  u1: number,
+  v0: number,
+  v1: number,
+): void {
   const base = mesh.verts.length / STRIDE
   mesh.verts.push(
-    side * 0.06, 0.12, 0.14, u0, v0,
-    side * 0.42, 0.24, 0.1, u1, v0,
-    side * 0.42, 0.24, -0.12, u1, v1,
-    side * 0.06, 0.12, -0.1, u0, v1,
+    side * 0.06,
+    0.12,
+    0.14,
+    u0,
+    v0,
+    side * 0.42,
+    0.24,
+    0.1,
+    u1,
+    v0,
+    side * 0.42,
+    0.24,
+    -0.12,
+    u1,
+    v1,
+    side * 0.06,
+    0.12,
+    -0.1,
+    u0,
+    v1,
   )
   mesh.indices.push(base, base + 1, base + 2, base, base + 2, base + 3)
 }
diff --git a/game/actors/trees/Birch.ts b/game/actors/trees/Birch.ts
index 00eeba3..01a8c97 100644
--- a/game/actors/trees/Birch.ts
+++ b/game/actors/trees/Birch.ts
@@ -1,15 +1,51 @@
 import { Vec3 } from "../../../engine/math/Vec3"
 import type { Mesh } from "../../../engine/scene/Mesh"
-import type { Tree, TreeSpecies } from "../Tree"
+import type { Material } from "../../../engine/render/Material"
+import type { Prefab } from "../../../engine/scene/Prefab"
+import type { Tree } from "../Tree"
 import { blob, lerp, limb, TAU, rng } from "./treekit"
 
 // Silver birch: tall, slender, near-straight trunk under an airy, high, slightly
 // drooping canopy -- a lean silhouette between the broad oak and conical spruce.
 // Trunk = white birch bark, foliage = oak leaf (the white trunk carries the read).
 
-export const birch: TreeSpecies = { kind: "birch", trunk: "birch", foliage: "leaf", build }
+export type Birch = Prefab<Tree>
 
-function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"): void {
+export namespace Birch {
+  export function create(trunk: Material, foliage: Material): Birch {
+    return {
+      position: (tree) => tree.position,
+      bakeNear: (tree, batch) =>
+        build(tree, batch.mesh(trunk), batch.mesh(foliage), "full"),
+      bakeFar: (tree, batch) =>
+        build(tree, batch.mesh(trunk), batch.mesh(foliage), "impostor"),
+      collider: treeCollider,
+    }
+  }
+
+  function treeCollider(tree: Tree) {
+    if (tree.growth <= 0.35) {
+      return null
+    }
+    const radius = tree.growth * 0.2 + 0.15
+    return {
+      shape: "box" as const,
+      minX: tree.position.x - radius,
+      maxX: tree.position.x + radius,
+      minZ: tree.position.z - radius,
+      maxZ: tree.position.z + radius,
+      top: tree.position.y + 3,
+      standable: false,
+    }
+  }
+}
+
+function build(
+  tree: Tree,
+  trunk: Mesh,
+  leaves: Mesh,
+  lod: "full" | "impostor",
+): void {
   const base = tree.position
   const g = tree.growth
   const rand = rng(tree.seed)
@@ -18,11 +54,25 @@ function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"):
   const canopyY = base.y + h * 0.75
   const blobR = h * 0.22
   if (lod === "impostor") {
-    limb(trunk, base, { x: base.x, y: base.y + h * 0.9, z: base.z }, rTrunk, rTrunk * 0.5, 3)
+    limb(
+      trunk,
+      base,
+      { x: base.x, y: base.y + h * 0.9, z: base.z },
+      rTrunk,
+      rTrunk * 0.5,
+      3,
+    )
     blob(leaves, { x: base.x, y: canopyY, z: base.z }, blobR * 1.1, rand, 4, 2)
     return
   }
-  limb(trunk, base, { x: base.x, y: base.y + h * 0.88, z: base.z }, rTrunk, rTrunk * 0.35, 5)
+  limb(
+    trunk,
+    base,
+    { x: base.x, y: base.y + h * 0.88, z: base.z },
+    rTrunk,
+    rTrunk * 0.35,
+    5,
+  )
 
   const spread = h * 0.22
   // Sparse small blobs clustered high, biased downward so the crown droops.
@@ -42,7 +92,11 @@ function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"):
     const branches = 2 + Math.round(rand())
     for (let i = 0; i < branches; i++) {
       const angle = rand() * TAU
-      const dir = Vec3.normalize({ x: Math.cos(angle), y: 0.6, z: Math.sin(angle) })
+      const dir = Vec3.normalize({
+        x: Math.cos(angle),
+        y: 0.6,
+        z: Math.sin(angle),
+      })
       const start = { x: base.x, y: base.y + h * 0.7, z: base.z }
       const end = Vec3.add(start, Vec3.scale(dir, h * 0.22))
       limb(trunk, start, end, rTrunk * 0.4, rTrunk * 0.15, 4)
diff --git a/game/actors/trees/Oak.ts b/game/actors/trees/Oak.ts
index a6e7888..30c37e9 100644
--- a/game/actors/trees/Oak.ts
+++ b/game/actors/trees/Oak.ts
@@ -1,14 +1,48 @@
 import { Vec3 } from "../../../engine/math/Vec3"
 import type { Mesh } from "../../../engine/scene/Mesh"
-import type { Tree, TreeSpecies } from "../Tree"
+import type { Material } from "../../../engine/render/Material"
+import type { Prefab } from "../../../engine/scene/Prefab"
+import type { Tree } from "../Tree"
 import { blob, lerp, limb, TAU, rng } from "./treekit"
 
 // Oak: short tapered trunk, a couple of branches, a broad cluster of rounded canopy
 // blobs (bushy, wider than tall). Trunk = brown bark, foliage = oak leaf.
 
-export const oak: TreeSpecies = { kind: "oak", trunk: "bark", foliage: "leaf", build }
+export type Oak = Prefab<Tree>
 
-function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"): void {
+export namespace Oak {
+  export function create(trunk: Material, foliage: Material): Oak {
+    return {
+      position: (tree) => tree.position,
+      bakeNear: (tree, batch) =>
+        build(tree, batch.mesh(trunk), batch.mesh(foliage), "full"),
+      bakeFar: (tree, batch) =>
+        build(tree, batch.mesh(trunk), batch.mesh(foliage), "impostor"),
+      collider(tree) {
+        if (tree.growth <= 0.35) {
+          return null
+        }
+        const radius = tree.growth * 0.3 + 0.15
+        return {
+          shape: "box",
+          minX: tree.position.x - radius,
+          maxX: tree.position.x + radius,
+          minZ: tree.position.z - radius,
+          maxZ: tree.position.z + radius,
+          top: tree.position.y + 3,
+          standable: false,
+        }
+      },
+    }
+  }
+}
+
+function build(
+  tree: Tree,
+  trunk: Mesh,
+  leaves: Mesh,
+  lod: "full" | "impostor",
+): void {
   const base = tree.position
   const g = tree.growth
   const rand = rng(tree.seed)
@@ -19,7 +53,14 @@ function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"):
   const blobR = h * 0.3
   if (lod === "impostor") {
     // One low-poly blob on a stubby trunk -- reads as an oak at distance.
-    limb(trunk, base, { x: base.x, y: forkY, z: base.z }, rTrunk, rTrunk * 0.6, 3)
+    limb(
+      trunk,
+      base,
+      { x: base.x, y: forkY, z: base.z },
+      rTrunk,
+      rTrunk * 0.6,
+      3,
+    )
     blob(leaves, { x: base.x, y: canopyY, z: base.z }, blobR * 1.15, rand, 4, 2)
     return
   }
@@ -43,7 +84,11 @@ function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"):
     const branches = 2 + Math.round(rand())
     for (let i = 0; i < branches; i++) {
       const angle = rand() * TAU
-      const dir = Vec3.normalize({ x: Math.cos(angle), y: 1.2, z: Math.sin(angle) })
+      const dir = Vec3.normalize({
+        x: Math.cos(angle),
+        y: 1.2,
+        z: Math.sin(angle),
+      })
       const start = { x: base.x, y: base.y + h * 0.42, z: base.z }
       const end = Vec3.add(start, Vec3.scale(dir, h * 0.3))
       limb(trunk, start, end, rTrunk * 0.4, rTrunk * 0.2, 4)
diff --git a/game/actors/trees/Spruce.ts b/game/actors/trees/Spruce.ts
index e7a2286..b168f65 100644
--- a/game/actors/trees/Spruce.ts
+++ b/game/actors/trees/Spruce.ts
@@ -1,20 +1,63 @@
 import type { Mesh } from "../../../engine/scene/Mesh"
-import type { Tree, TreeSpecies } from "../Tree"
+import type { Material } from "../../../engine/render/Material"
+import type { Prefab } from "../../../engine/scene/Prefab"
+import type { Tree } from "../Tree"
 import { cone, lerp, limb, rng } from "./treekit"
 
 // Spruce: tall thin trunk under stacked cones that narrow to a point (tiered, taller
 // than wide). Trunk = brown bark, foliage = spruce needle.
 
-export const spruce: TreeSpecies = { kind: "spruce", trunk: "bark", foliage: "needle", build }
+export type Spruce = Prefab<Tree>
 
-function build(tree: Tree, trunk: Mesh, needles: Mesh, lod: "full" | "impostor"): void {
+export namespace Spruce {
+  export function create(trunk: Material, foliage: Material): Spruce {
+    return {
+      position: (tree) => tree.position,
+      bakeNear: (tree, batch) =>
+        build(tree, batch.mesh(trunk), batch.mesh(foliage), "full"),
+      bakeFar: (tree, batch) =>
+        build(tree, batch.mesh(trunk), batch.mesh(foliage), "impostor"),
+      collider: treeCollider,
+    }
+  }
+
+  function treeCollider(tree: Tree) {
+    if (tree.growth <= 0.35) {
+      return null
+    }
+    const radius = tree.growth * 0.2 + 0.15
+    return {
+      shape: "box" as const,
+      minX: tree.position.x - radius,
+      maxX: tree.position.x + radius,
+      minZ: tree.position.z - radius,
+      maxZ: tree.position.z + radius,
+      top: tree.position.y + 3,
+      standable: false,
+    }
+  }
+}
+
+function build(
+  tree: Tree,
+  trunk: Mesh,
+  needles: Mesh,
+  lod: "full" | "impostor",
+): void {
   const base = tree.position
   const g = tree.growth
   const rand = rng(tree.seed)
   const h = lerp(0.6, 9, g)
   const rTrunk = lerp(0.03, 0.2, g)
   const impostor = lod === "impostor"
-  limb(trunk, base, { x: base.x, y: base.y + h, z: base.z }, rTrunk, rTrunk * 0.25, impostor ? 3 : 5)
+  limb(
+    trunk,
+    base,
+    { x: base.x, y: base.y + h, z: base.z },
+    rTrunk,
+    rTrunk * 0.25,
+    impostor ? 3 : 5,
+  )
 
   // Stacked cones: widest low, shrinking to a point up top -> conical tiers. The
   // impostor keeps the first two tiers at low sides (same seed => aligned).
diff --git a/game/actors/trees/treekit.ts b/game/actors/trees/treekit.ts
index 27e2e09..dd9b833 100644
--- a/game/actors/trees/treekit.ts
+++ b/game/actors/trees/treekit.ts
@@ -1,9 +1,8 @@
 import { Vec3 } from "../../../engine/math/Vec3"
 import { STRIDE, type Mesh } from "../../../engine/scene/Mesh"
 
-// Shared faceted-geometry primitives + the per-tree RNG, used by the species
-// modules (Oak/Spruce/Birch). Kept separate so a species and the `Tree` registry
-// don't form an import cycle.
+// Shared faceted-geometry primitives + the per-tree RNG used by concrete tree
+// prefab modules.
 
 export const TAU = Math.PI * 2
 
diff --git a/game/level.ts b/game/level.ts
index a4780af..8244a78 100644
--- a/game/level.ts
+++ b/game/level.ts
@@ -1,51 +1,37 @@
 import { Color } from "../engine/render/Color"
-import type { DrawGroup, Material } from "../engine/render/Material"
+import type { Material } from "../engine/render/Material"
 import type { CloudLayer, SkyConfig } from "../engine/render/Sky"
-import { STRIDE, type Mesh } from "../engine/scene/Mesh"
+import { ChunkBuilder } from "../engine/render/ChunkBuilder"
+import { Actor, type ActorDefinition } from "../engine/scene/Actor"
+import { Mesh } from "../engine/scene/Mesh"
+import { MeshBuilder } from "../engine/scene/MeshBuilder"
+import {
+  Prefab,
+  type PlacedPrefab,
+  type Prefab as PrefabDefinition,
+} from "../engine/scene/Prefab"
+import type { BoxCollider, Collider } from "../engine/world/Collider"
+import { Level, type Level as RuntimeLevel } from "../engine/world/Level"
+import {
+  Terrain,
+  type RollingTerrainConfig,
+  type Terrain as Ground,
+} from "../engine/world/Terrain"
 import { Boulder } from "./actors/Boulder"
 import { Bush } from "./actors/Bush"
-import { Flower, type FlowerColor } from "./actors/Flower"
-import type { Mob, MobKind } from "./actors/Mob"
-import { Terrain } from "./Terrain"
-import { Tree } from "./actors/Tree"
+import { Flower, type FlowerStyle } from "./actors/Flower"
+import type { Mob, MobState } from "./actors/Mob"
+import type { Tree } from "./actors/Tree"
+import { Bee } from "./actors/mobs/Bee"
+import { Frog } from "./actors/mobs/Frog"
+import { Robin } from "./actors/mobs/Robin"
+import { Birch } from "./actors/trees/Birch"
+import { Oak } from "./actors/trees/Oak"
+import { Spruce } from "./actors/trees/Spruce"
 import type { Textures } from "./textures"
 
-type Corner = [number, number, number]
-
-/** Axis-aligned solid. Blocks the player horizontally while their feet are
- *  below `top`; if `standable`, its `top` also counts as ground to land on. */
-export type Aabb = {
-  minX: number
-  maxX: number
-  minZ: number
-  maxZ: number
-  top: number
-  standable: boolean
-}
-
-/** One spatial cell of the outdoor world: its terrain patch + the trees/boulders
- *  standing in it, baked into `DrawGroup`s (mesh + material), plus an axis-aligned
- *  bounding box (tight to the actual geometry, so overhanging canopies aren't
- *  clipped). The renderer frustum-tests the box and skips the whole cell when it
- *  is off-screen -- this is what keeps a big, dense world affordable. Empty cells
- *  are never created; empty groups are pruned at bake time. */
-export type Chunk = {
-  minX: number
-  minY: number
-  minZ: number
-  maxX: number
-  maxY: number
-  maxZ: number
-  /** Full-detail draw groups (grass + full trees/boulders), used up close. */
-  near: DrawGroup[]
-  /** LOD draw groups (grass + cheap tree/boulder impostors, no bushes/flowers),
-   *  used once the chunk is past `config.lodDistance` (see `chunkFar`). */
-  far: DrawGroup[]
-}
-
-/** The materials the chunk baker binds its meshes to -- one per ground/prop
- *  texture. Built once from the loaded `Textures`, shared across every chunk. */
-type ChunkMaterials = {
+type Materials = {
+  floor: Material
   grass: Material
   bark: Material
   birch: Material
@@ -53,50 +39,35 @@ type ChunkMaterials = {
   needle: Material
   rock: Material
   flower: Material
+  wall: Material
+  crate: Material
+  npc: Material
+  frog: Material
+  bee: Material
+  robin: Material
 }
 
-/** A chunk-material key (also the tag props reference, e.g. a tree's `trunk`). */
-type MatKey = keyof ChunkMaterials
+type WeightedTree = {
+  definition: PrefabDefinition<Tree>
+  weight: number
+}
 
-/** The fixed order draw groups are emitted in (grass first, flowers -- double-sided
- *  -- last), so the per-chunk draw sequence is deterministic and matches the pre-
- *  registry order. Every material key must appear here. */
-const MAT_ORDER: MatKey[] = ["grass", "rock", "bark", "birch", "leaf", "needle", "flower"]
-
-/** The playground: a flat-floored room dropped into the center of a big open
- *  landscape. The room (floor/walls/crate) is small and always drawn; the
- *  outdoor world is split into `chunks` that are frustum-culled per frame. */
-export type Level = {
-  floor: Mesh
-  walls: Mesh
-  crate: Mesh
-  chunks: Chunk[]
-  colliders: Aabb[]
-  npcPosition: { x: number; y: number; z: number }
-  /** Roaming mobs -- simulated on the main thread each frame (see main.ts), not
-   *  baked into the static culled chunks. */
-  mobs: Mob[]
-  terrain: Terrain
-  sky: SkyConfig
+type MobSpawn = {
+  definition: ActorDefinition<MobState, Ground>
+  count: number
+  minScale: number
+  maxScale: number
+  grounded: boolean
+  phase: (random: () => number) => number
 }
 
 const ARENA = 12
 const WALL_HEIGHT = 4
-/** How deep the perimeter walls are. Thick enough to read as solid walls (and to
- *  give the doorway real jambs); their outer faces sit flush with the room edge,
- *  so they eat into the interior, not the terrain. */
 const WALL_THICKNESS = 1.5
 const CRATE = { x: -2, z: -2, half: 1, height: 1 }
-/** Z-bias lifting the stone floor above the terrain skirt that laps under the
- *  room edge (see `buildLevel`). Big enough to beat depth precision, too small
- *  to see. */
 const FLOOR_LIFT = 0.02
 
-/** The world around the room: a flat clearing the size of the room (`inner`),
- *  rolling hills beyond, ramping into very high peaks at the `outer` rim ~20x
- *  the room across. Tune freely -- crank `peakHeight` for taller mountains,
- *  `outer` for a bigger world. */
-const TERRAIN: Terrain = {
+const TERRAIN_CONFIG: RollingTerrainConfig = {
   inner: ARENA,
   outer: ARENA * 10,
   blend: 12,
@@ -106,52 +77,30 @@ const TERRAIN: Terrain = {
   peakFrequency: 0.05,
   peakStart: 0.45,
 }
+const TERRAIN = Terrain.rolling(TERRAIN_CONFIG)
 
-/** Forest: how many trees to scatter on the grass, and the seed for their
- *  placement/kind/growth. Trees ring the room out to `TREE_REACH` of the world;
- *  each rolls oak-or-spruce and a growth 0..1 (sapling .. full grown). */
 const TREE_COUNT = 50
 const TREE_SEED = 0x5EED
 const TREE_REACH = 1
-
-/** Boulders: how many to scatter, their seed, and how far out they reach
- *  (fraction of the world). Sizes range small pebble .. big boulder. */
 const BOULDER_COUNT = 50
 const BOULDER_SEED = 0xB0142
 const BOULDER_REACH = 1
-
-/** Bushes + flowers: ground detail, kept to the nearer band since they're small
- *  and fog/size hides them far out. Flowers roll white/red/yellow. */
 const BUSH_COUNT = 50
 const BUSH_SEED = 0xB554
 const BUSH_REACH = 1
 const FLOWER_COUNT = 50
 const FLOWER_SEED = 0xF10E
 const FLOWER_REACH = 0.3
-const FLOWER_COLORS: FlowerColor[] = ["white", "red", "yellow"]
-
-/** Roaming mobs: how many frogs/bees to scatter, their seed, and how far out they
- *  reach (fraction of the world). Kept modest -- roaming meshes are drawn every
- *  frame (frustum-culled), not baked into the static chunks. */
+const FLOWER_STYLES: FlowerStyle[] = [Flower.white, Flower.red, Flower.yellow]
 const FROG_COUNT = 20
 const BEE_COUNT = 20
 const ROBIN_COUNT = 20
 const MOB_SEED = 0x30B
 const MOB_REACH = 1
-
-/** Spatial partition of the world for frustum culling: `CHUNK_GRID` x
- *  `CHUNK_GRID` square cells over [-outer, outer]. Smaller cells cull tighter
- *  (less drawn off-screen) but cost more per-cell tests + bounds; this is the
- *  granularity knob. `TERRAIN_SUBDIV` is the terrain quads per cell edge, so the
- *  world's terrain resolution is `CHUNK_GRID * TERRAIN_SUBDIV`. `GROUND_UV` sets
- *  texture tiles/unit. */
 const CHUNK_GRID = 12
 const TERRAIN_SUBDIV = 5
 const GROUND_UV = 0.25
 
-/** The two cloud styles; swap which one the sky uses in `buildLevel`.
- *  `basicCumulus` is cheap flat puffs; `fancyCumulus` is the pricier
- *  heightfield-shaded, domain-warped version with faked volume. */
 export const basicCumulus: CloudLayer = {
   kind: "basic",
   color: Color.rgb(248, 250, 255),
@@ -172,33 +121,63 @@ export const fancyCumulus: CloudLayer = {
   relief: 7,
 }
 
-export function buildLevel(textures: Textures): Level {
-  // Flat room floor, lifted a hair above the terrain's clearing (y 0). The
-  // outdoor grid's cells straddle the room boundary and lap under the floor's
-  // edges; this small z-bias keeps the flat stone floor winning the depth test
-  // there instead of z-fighting the grass. The step is invisible at the doorway.
-  const floor = mesh()
-  const fy = FLOOR_LIFT
-  quad(floor, [-ARENA, fy, -ARENA], [ARENA, fy, -ARENA], [ARENA, fy, ARENA], [-ARENA, fy, ARENA], 12, 12)
+/** Concrete playground data assembled through engine-owned level mechanisms. */
+export function buildLevel(textures: Textures): RuntimeLevel<Ground> {
+  const materials = createMaterials(textures)
+  const floor = Mesh.create()
+  MeshBuilder.quad(
+    floor,
+    [-ARENA, FLOOR_LIFT, -ARENA],
+    [ARENA, FLOOR_LIFT, -ARENA],
+    [ARENA, FLOOR_LIFT, ARENA],
+    [-ARENA, FLOOR_LIFT, ARENA],
+    12,
+    12,
+  )
 
-  const walls = mesh()
-  const h = WALL_HEIGHT
-  const t = WALL_THICKNESS
-  // Three thick perimeter walls, outer faces flush with the room edge; the north
-  // (-Z) side is left open onto the world. No ceiling, so the sky shows above.
-  slab(walls, -ARENA, ARENA, ARENA - t, ARENA, 0, h, 0.5) // south (+Z)
-  slab(walls, ARENA - t, ARENA, -ARENA, ARENA - t, 0, h, 0.5) // east (+X)
-  slab(walls, -ARENA, -ARENA + t, -ARENA, ARENA - t, 0, h, 0.5) // west (-X)
+  const walls = Mesh.create()
+  const thickness = WALL_THICKNESS
+  MeshBuilder.slab(
+    walls,
+    -ARENA,
+    ARENA,
+    ARENA - thickness,
+    ARENA,
+    0,
+    WALL_HEIGHT,
+    0.5,
+  )
+  MeshBuilder.slab(
+    walls,
+    ARENA - thickness,
+    ARENA,
+    -ARENA,
+    ARENA - thickness,
+    0,
+    WALL_HEIGHT,
+    0.5,
+  )
+  MeshBuilder.slab(
+    walls,
+    -ARENA,
+    -ARENA + thickness,
+    -ARENA,
+    ARENA - thickness,
+    0,
+    WALL_HEIGHT,
+    0.5,
+  )
 
-  // Crate on the flat room floor.
-  const crate = mesh()
-  box(crate, CRATE.x, CRATE.z, CRATE.half, 0, CRATE.height)
+  const crate = Mesh.create()
+  MeshBuilder.box(crate, CRATE.x, CRATE.z, CRATE.half, 0, CRATE.height)
 
-  const colliders: Aabb[] = [
-    wall(-ARENA, ARENA, ARENA - t, ARENA),
-    wall(ARENA - t, ARENA, -ARENA, ARENA - t),
-    wall(-ARENA, -ARENA + t, -ARENA, ARENA - t),
+  const npcPosition = { x: 2, y: 0, z: -1 }
+  const staticColliders: Collider[] = [
+    wall(-ARENA, ARENA, ARENA - thickness, ARENA),
+    wall(ARENA - thickness, ARENA, -ARENA, ARENA - thickness),
+    wall(-ARENA, -ARENA + thickness, -ARENA, ARENA - thickness),
     {
+      shape: "box",
       minX: CRATE.x - CRATE.half,
       maxX: CRATE.x + CRATE.half,
       minZ: CRATE.z - CRATE.half,
@@ -206,8 +185,94 @@ export function buildLevel(textures: Textures): Level {
       top: CRATE.height,
       standable: true,
     },
+    {
+      shape: "circle",
+      x: npcPosition.x,
+      z: npcPosition.z,
+      radius: 0.5,
+      top: Infinity,
+      standable: false,
+    },
   ]
 
+  const treeDefinitions: WeightedTree[] = [
+    { definition: Oak.create(materials.bark, materials.leaf), weight: 0.4 },
+    {
+      definition: Spruce.create(materials.bark, materials.needle),
+      weight: 0.32,
+    },
+    { definition: Birch.create(materials.birch, materials.leaf), weight: 0.28 },
+  ]
+  const props = [
+    ...placeTrees(treeDefinitions),
+    ...placeBoulders(Boulder.create(materials.rock)),
+    ...placeBushes(Bush.create(materials.leaf)),
+    ...placeFlowers(Flower.create(materials.flower)),
+  ]
+  for (const prop of props) {
+    if (prop.collider !== null) {
+      staticColliders.push(prop.collider)
+    }
+  }
+
+  const chunks = ChunkBuilder.build(
+    {
+      minX: TERRAIN.minX,
+      minZ: TERRAIN.minZ,
+      maxX: TERRAIN.maxX,
+      maxZ: TERRAIN.maxZ,
+      columns: CHUNK_GRID,
+      rows: CHUNK_GRID,
+      bakeCell(near, far, cell) {
+        const ground = near.mesh(materials.grass)
+        far.use(materials.grass, ground)
+        Terrain.patch(
+          TERRAIN,
+          ground,
+          cell.x0,
+          cell.z0,
+          cell.x1,
+          cell.z1,
+          TERRAIN_SUBDIV,
+          TERRAIN_SUBDIV,
+          GROUND_UV,
+          (x, z) => Math.max(Math.abs(x), Math.abs(z)) >= ARENA,
+        )
+      },
+    },
+    props,
+  )
+
+  const frog = Frog.create(materials.frog)
+  const bee = Bee.create(materials.bee)
+  const robin = Robin.create(materials.robin)
+  const actors = placeMobs([
+    {
+      definition: frog,
+      count: FROG_COUNT,
+      minScale: 0.5,
+      maxScale: 0.85,
+      grounded: true,
+      phase: () => 0,
+    },
+    {
+      definition: bee,
+      count: BEE_COUNT,
+      minScale: 0.5,
+      maxScale: 0.8,
+      grounded: false,
+      phase: (random) => random() * 10,
+    },
+    {
+      definition: robin,
+      count: ROBIN_COUNT,
+      minScale: 0.4,
+      maxScale: 0.65,
+      grounded: true,
+      phase: () => 0,
+    },
+  ])
+
   const sky: SkyConfig = {
     zenith: Color.rgb(58, 108, 196),
     horizon: Color.rgb(178, 198, 226),
@@ -218,12 +283,31 @@ export function buildLevel(textures: Textures): Level {
     skybox: { texture: textures.skybox },
   }
 
-  const npcPosition = { x: 2, y: 0, z: -1 }
+  return Level.create({
+    terrain: TERRAIN,
+    actorWorld: TERRAIN,
+    actors,
+    staticColliders,
+    staticGroups: [
+      { mesh: floor, material: materials.floor },
+      { mesh: walls, material: materials.wall },
+      { mesh: crate, material: materials.crate },
+    ],
+    chunks,
+    billboards: [
+      {
+        position: npcPosition,
+        size: { x: 1.1, y: 1.5 },
+        material: materials.npc,
+      },
+    ],
+    sky,
+  })
+}
 
-  // The ground/prop materials the chunk baker draws with (grass + trees + rocks +
-  // flowers). Solid surfaces backface-cull; flowers are double-sided. Shared by
-  // every chunk, so cloning to a worker dedups them.
-  const materials: ChunkMaterials = {
+function createMaterials(textures: Textures): Materials {
+  return {
+    floor: { texture: textures.floor, cull: false },
     grass: { texture: textures.grass, cull: true },
     bark: { texture: textures.bark, cull: true },
     birch: { texture: textures.birch, cull: true },
@@ -231,319 +315,219 @@ export function buildLevel(textures: Textures): Level {
     needle: { texture: textures.needle, cull: true },
     rock: { texture: textures.rock, cull: true },
     flower: { texture: textures.flower, cull: false },
+    wall: { texture: textures.wall, cull: false },
+    crate: { texture: textures.crate, cull: false },
+    npc: { texture: textures.npc, cull: false },
+    frog: { texture: textures.frog, cull: false },
+    bee: { texture: textures.bee, cull: false },
+    robin: { texture: textures.robin, cull: false },
   }
-
-  // Place the props (also pushes their colliders), then bake everything into
-  // frustum-cullable spatial chunks.
-  const trees = placeTrees(colliders)
-  const boulders = placeBoulders(colliders)
-  const bushes = placeBushes()
-  const flowers = placeFlowers()
-  const chunks = buildChunks(materials, trees, boulders, bushes, flowers)
-  const mobs = placeMobs()
-
-  return { floor, walls, crate, chunks, colliders, npcPosition, mobs, terrain: TERRAIN, sky }
 }
 
-/** Bake the terrain + props into a `CHUNK_GRID` x `CHUNK_GRID` set of spatial
- *  chunks. Each prop lands in the cell holding its base; the cell's bounds are
- *  grown to the real geometry so overhanging canopies never get culled early.
- *  Bushes share the oak leaf mesh; flowers get their own (double-sided) mesh. */
-function buildChunks(m: ChunkMaterials, trees: Tree[], boulders: Boulder[], bushes: Bush[], flowers: Flower[]): Chunk[] {
-  const cell = (TERRAIN.outer * 2) / CHUNK_GRID
-  const chunks: Chunk[] = []
-  for (let ci = 0; ci < CHUNK_GRID; ci++) {
-    const x0 = -TERRAIN.outer + ci * cell
-    const x1 = x0 + cell
-    for (let cj = 0; cj < CHUNK_GRID; cj++) {
-      const z0 = -TERRAIN.outer + cj * cell
-      const z1 = z0 + cell
-      // Accumulate geometry into one mesh per material key, for the near (full) and
-      // far (impostor) LOD sets. Props declare which material(s) they write, so the
-      // baker never names a texture -- adding a species/material touches no code here.
-      const near = new Map<string, Mesh>()
-      const far = new Map<string, Mesh>()
-      const grass = matMesh(near, "grass")
-      far.set("grass", grass) // the ground is drawn in both LOD sets
-      Terrain.patch(TERRAIN, grass, x0, z0, x1, z1, TERRAIN_SUBDIV, TERRAIN_SUBDIV, GROUND_UV)
-      for (const tree of trees) {
-        if (inCell(tree.position, x0, z0, x1, z1)) {
-          const s = Tree.species(tree.kind)
-          Tree.build(tree, matMesh(near, s.trunk), matMesh(near, s.foliage))
-          Tree.build(tree, matMesh(far, s.trunk), matMesh(far, s.foliage), "impostor")
-        }
-      }
-      for (const boulder of boulders) {
-        if (inCell(boulder.position, x0, z0, x1, z1)) {
-          Boulder.build(boulder, matMesh(near, "rock"))
-          Boulder.build(boulder, matMesh(far, "rock"), "impostor")
-        }
-      }
-      // Bushes fold into the near leaf mesh; they just drop out past lodDistance.
-      for (const bush of bushes) {
-        if (inCell(bush.position, x0, z0, x1, z1)) {
-          Bush.build(bush, matMesh(near, "leaf"))
-        }
-      }
-      for (const flower of flowers) {
-        if (inCell(flower.position, x0, z0, x1, z1)) {
-          Flower.build(flower, matMesh(near, "flower"))
-        }
-      }
-      const b = bounds([...near.values()])
-      if (b === null) {
-        continue
-      }
-      chunks.push({ ...b, near: toGroups(near, m), far: toGroups(far, m) })
-    }
-  }
-  return chunks
-}
-
-function inCell(p: { x: number; z: number }, x0: number, z0: number, x1: number, z1: number): boolean {
-  return p.x >= x0 && p.x < x1 && p.z >= z0 && p.z < z1
-}
-
-/** Lazily get (creating on first use) the accumulation mesh for a material key in a
- *  chunk's near/far map. Props write into these by key, so the baker stays generic. */
-function matMesh(map: Map<string, Mesh>, key: string): Mesh {
-  let m = map.get(key)
-  if (m === undefined) {
-    m = mesh()
-    map.set(key, m)
-  }
-  return m
-}
-
-/** Turn a chunk's per-material meshes into a draw-group list, in a fixed material
- *  order (so the draw sequence is deterministic across bakes) and dropping any that
- *  ended up empty (a cell rarely holds every prop kind). */
-function toGroups(map: Map<string, Mesh>, materials: ChunkMaterials): DrawGroup[] {
-  const out: DrawGroup[] = []
-  for (const key of MAT_ORDER) {
-    const m = map.get(key)
-    if (m !== undefined && m.indices.length > 0) {
-      out.push({ mesh: m, material: materials[key] })
-    }
-  }
-  return out
-}
-
-/** Tight AABB over several meshes' vertices, or null if they are all empty. */
-function bounds(meshes: Mesh[]): Pick<Chunk, "minX" | "minY" | "minZ" | "maxX" | "maxY" | "maxZ"> | null {
-  let minX = Infinity
-  let minY = Infinity
-  let minZ = Infinity
-  let maxX = -Infinity
-  let maxY = -Infinity
-  let maxZ = -Infinity
-  for (const m of meshes) {
-    const verts = m.verts
-    for (let i = 0; i < verts.length; i += STRIDE) {
-      const x = verts[i]
-      const y = verts[i + 1]
-      const z = verts[i + 2]
-      minX = Math.min(minX, x)
-      minY = Math.min(minY, y)
-      minZ = Math.min(minZ, z)
-      maxX = Math.max(maxX, x)
-      maxY = Math.max(maxY, y)
-      maxZ = Math.max(maxZ, z)
-    }
-  }
-  return maxX < minX ? null : { minX, minY, minZ, maxX, maxY, maxZ }
-}
-
-/** Place `TREE_COUNT` trees around the room on walkable grass: each sits on the
- *  terrain, rolls oak/spruce and a growth stage, and (once past sapling size)
- *  drops a trunk collider so you can't walk through it. */
-function placeTrees(colliders: Aabb[]): Tree[] {
-  const rand = mulberry(TREE_SEED)
-  const maxDist = TERRAIN.outer * TREE_REACH
-  const trees: Tree[] = []
-  for (let guard = 0; trees.length < TREE_COUNT && guard < TREE_COUNT * 20; guard++) {
-    const angle = rand() * Math.PI * 2
-    const dist = ARENA + 5 + rand() * (maxDist - ARENA - 5)
-    const x = Math.cos(angle) * dist
-    const z = Math.sin(angle) * dist
-    // Stay out of the room clearing and its flat rim.
-    if (Math.max(Math.abs(x), Math.abs(z)) < TERRAIN.inner + 3) {
+function placeTrees(definitions: WeightedTree[]): PlacedPrefab[] {
+  const random = mulberry(TREE_SEED)
+  const maxDistance = TERRAIN_CONFIG.outer * TREE_REACH
+  const trees: PlacedPrefab[] = []
+  for (
+    let guard = 0;
+    trees.length < TREE_COUNT && guard < TREE_COUNT * 20;
+    guard++
+  ) {
+    const point = scatterPoint(random, maxDistance, 5, 3)
+    if (point === null) {
       continue
     }
-    const roll = rand()
-    const kind = roll < 0.4 ? "oak" : roll < 0.72 ? "spruce" : "birch"
-    const growth = 0.08 + rand() * 0.92
-    const position = { x, y: Terrain.height(TERRAIN, x, z), z }
-    trees.push({ kind, position, growth, seed: (rand() * 0xFFFFFFFF) | 0 })
-    // Saplings are passable; grown trunks block. Square footprint, non-standable.
-    if (growth > 0.35) {
-      const r = growth * (kind === "oak" ? 0.3 : 0.2) + 0.15
-      colliders.push({ minX: x - r, maxX: x + r, minZ: z - r, maxZ: z + r, top: position.y + 3, standable: false })
+    const definition = weightedTree(definitions, random())
+    const tree: Tree = {
+      position: {
+        x: point.x,
+        y: TERRAIN.heightAt(point.x, point.z),
+        z: point.z,
+      },
+      growth: 0.08 + random() * 0.92,
+      seed: (random() * 0xFFFFFFFF) | 0,
     }
+    trees.push(Prefab.place(definition, tree))
   }
   return trees
 }
 
-/** Scatter `BOULDER_COUNT` boulders across the terrain, sizes biased toward
- *  small. Each sits on the ground; big ones drop a blocking collider so you
- *  can't walk through them (little rocks stay passable). */
-function placeBoulders(colliders: Aabb[]): Boulder[] {
-  const rand = mulberry(BOULDER_SEED)
-  const maxDist = TERRAIN.outer * BOULDER_REACH
-  const boulders: Boulder[] = []
-  for (let guard = 0; boulders.length < BOULDER_COUNT && guard < BOULDER_COUNT * 20; guard++) {
-    const angle = rand() * Math.PI * 2
-    const dist = ARENA + 4 + rand() * (maxDist - ARENA - 4)
-    const x = Math.cos(angle) * dist
-    const z = Math.sin(angle) * dist
-    if (Math.max(Math.abs(x), Math.abs(z)) < TERRAIN.inner + 2) {
+function placeBoulders(definition: PrefabDefinition<Boulder>): PlacedPrefab[] {
+  const random = mulberry(BOULDER_SEED)
+  const maxDistance = TERRAIN_CONFIG.outer * BOULDER_REACH
+  const boulders: PlacedPrefab[] = []
+  for (
+    let guard = 0;
+    boulders.length < BOULDER_COUNT && guard < BOULDER_COUNT * 20;
+    guard++
+  ) {
+    const point = scatterPoint(random, maxDistance, 4, 2)
+    if (point === null) {
       continue
     }
-    // Square the roll so most rocks are small, a few are big.
-    const radius = 0.35 + rand() * rand() * 2.2
-    const position = { x, y: Terrain.height(TERRAIN, x, z), z }
-    boulders.push({ position, radius, seed: (rand() * 0xFFFFFFFF) | 0 })
-    if (radius > 0.7) {
-      colliders.push({ minX: x - radius, maxX: x + radius, minZ: z - radius, maxZ: z + radius, top: position.y + radius * 0.7, standable: false })
-    }
+    boulders.push(
+      Prefab.place(definition, {
+        position: {
+          x: point.x,
+          y: TERRAIN.heightAt(point.x, point.z),
+          z: point.z,
+        },
+        radius: 0.35 + random() * random() * 2.2,
+        seed: (random() * 0xFFFFFFFF) | 0,
+      }),
+    )
   }
   return boulders
 }
 
-/** Scatter bushes on the grass near the play area (no colliders -- walk through). */
-function placeBushes(): Bush[] {
-  const rand = mulberry(BUSH_SEED)
-  const maxDist = TERRAIN.outer * BUSH_REACH
-  const bushes: Bush[] = []
-  for (let guard = 0; bushes.length < BUSH_COUNT && guard < BUSH_COUNT * 20; guard++) {
-    const angle = rand() * Math.PI * 2
-    const dist = ARENA + 3 + rand() * (maxDist - ARENA - 3)
-    const x = Math.cos(angle) * dist
-    const z = Math.sin(angle) * dist
-    if (Math.max(Math.abs(x), Math.abs(z)) < TERRAIN.inner + 2) {
+function placeBushes(definition: PrefabDefinition<Bush>): PlacedPrefab[] {
+  const random = mulberry(BUSH_SEED)
+  const maxDistance = TERRAIN_CONFIG.outer * BUSH_REACH
+  const bushes: PlacedPrefab[] = []
+  for (
+    let guard = 0;
+    bushes.length < BUSH_COUNT && guard < BUSH_COUNT * 20;
+    guard++
+  ) {
+    const point = scatterPoint(random, maxDistance, 3, 2)
+    if (point === null) {
       continue
     }
-    bushes.push({ position: { x, y: Terrain.height(TERRAIN, x, z), z }, size: 0.8 + rand() * 1, seed: (rand() * 0xFFFFFFFF) | 0 })
+    bushes.push(
+      Prefab.place(definition, {
+        position: {
+          x: point.x,
+          y: TERRAIN.heightAt(point.x, point.z),
+          z: point.z,
+        },
+        size: 0.8 + random(),
+        seed: (random() * 0xFFFFFFFF) | 0,
+      }),
+    )
   }
   return bushes
 }
 
-/** Scatter small flowers on the grass near the play area, colors rolled. */
-function placeFlowers(): Flower[] {
-  const rand = mulberry(FLOWER_SEED)
-  const maxDist = TERRAIN.outer * FLOWER_REACH
-  const flowers: Flower[] = []
-  for (let guard = 0; flowers.length < FLOWER_COUNT && guard < FLOWER_COUNT * 20; guard++) {
-    const angle = rand() * Math.PI * 2
-    const dist = ARENA + 2 + rand() * (maxDist - ARENA - 2)
-    const x = Math.cos(angle) * dist
-    const z = Math.sin(angle) * dist
-    if (Math.max(Math.abs(x), Math.abs(z)) < TERRAIN.inner + 1) {
+function placeFlowers(definition: PrefabDefinition<Flower>): PlacedPrefab[] {
+  const random = mulberry(FLOWER_SEED)
+  const maxDistance = TERRAIN_CONFIG.outer * FLOWER_REACH
+  const flowers: PlacedPrefab[] = []
+  for (
+    let guard = 0;
+    flowers.length < FLOWER_COUNT && guard < FLOWER_COUNT * 20;
+    guard++
+  ) {
+    const point = scatterPoint(random, maxDistance, 2, 1)
+    if (point === null) {
       continue
     }
-    const color = FLOWER_COLORS[(rand() * FLOWER_COLORS.length) | 0]
-    flowers.push({ position: { x, y: Terrain.height(TERRAIN, x, z), z }, color, size: 0.28 + rand() * 0.22, seed: (rand() * 0xFFFFFFFF) | 0 })
+    flowers.push(
+      Prefab.place(definition, {
+        position: {
+          x: point.x,
+          y: TERRAIN.heightAt(point.x, point.z),
+          z: point.z,
+        },
+        style: FLOWER_STYLES[(random() * FLOWER_STYLES.length) | 0],
+        size: 0.28 + random() * 0.22,
+        seed: (random() * 0xFFFFFFFF) | 0,
+      }),
+    )
   }
   return flowers
 }
 
-/** Scatter frogs, bees + robins across the grass (like the boulders), each at its
- *  home anchor with a random heading and size. No colliders here -- mobs move, so
- *  their block/stand-on AABBs are rebuilt per frame in `main`. */
-function placeMobs(): Mob[] {
-  const rand = mulberry(MOB_SEED)
-  const maxDist = TERRAIN.outer * MOB_REACH
+function placeMobs(spawns: MobSpawn[]): Mob[] {
+  const random = mulberry(MOB_SEED)
+  const maxDistance = TERRAIN_CONFIG.outer * MOB_REACH
   const mobs: Mob[] = []
-  const total = FROG_COUNT + BEE_COUNT + ROBIN_COUNT
-  for (let guard = 0; mobs.length < total && guard < total * 20; guard++) {
-    const angle = rand() * Math.PI * 2
-    const dist = ARENA + 3 + rand() * (maxDist - ARENA - 3)
-    const x = Math.cos(angle) * dist
-    const z = Math.sin(angle) * dist
-    if (Math.max(Math.abs(x), Math.abs(z)) < TERRAIN.inner + 2) {
-      continue
+  for (const spawn of spawns) {
+    let placed = 0
+    for (
+      let guard = 0;
+      placed < spawn.count && guard < spawn.count * 20;
+      guard++
+    ) {
+      const point = scatterPoint(random, maxDistance, 3, 2)
+      if (point === null) {
+        continue
+      }
+      const y = TERRAIN.heightAt(point.x, point.z)
+      const scale = spawn.minScale + random() * (spawn.maxScale - spawn.minScale)
+      const heading = random() * Math.PI * 2
+      const state: MobState = {
+        home: { x: point.x, y, z: point.z },
+        position: { x: point.x, y, z: point.z },
+        heading,
+        scale,
+        seed: (random() * 0xFFFFFFFF) | 0,
+        vx: 0,
+        vz: 0,
+        vy: 0,
+        timer: random() * 1.5,
+        phase: spawn.phase(random),
+        grounded: spawn.grounded,
+      }
+      mobs.push(Actor.create(spawn.definition, state))
+      placed++
     }
-    const n = mobs.length
-    const kind: MobKind = n < FROG_COUNT ? "frog" : n < FROG_COUNT + BEE_COUNT ? "bee" : "robin"
-    const y = Terrain.height(TERRAIN, x, z)
-    const scale = kind === "frog" ? 0.5 + rand() * 0.35 : kind === "robin" ? 0.4 + rand() * 0.25 : 0.5 + rand() * 0.3
-    mobs.push({
-      kind,
-      home: { x, y, z },
-      position: { x, y, z },
-      heading: rand() * Math.PI * 2,
-      scale,
-      seed: (rand() * 0xFFFFFFFF) | 0,
-      vx: 0,
-      vz: 0,
-      vy: 0,
-      timer: rand() * 1.5,
-      // Bees hover (never grounded) and use phase for the bob; frogs/robins start
-      // resting on the ground.
-      phase: kind === "bee" ? rand() * 10 : 0,
-      grounded: kind !== "bee",
-    })
   }
   return mobs
 }
 
-/** Deterministic 0..1 generator (mulberry32) for tree placement. */
-function mulberry(seed: number): () => number {
-  let a = seed >>> 0
-  return () => {
-    a = (a + 0x6D2B79F5) | 0
-    let t = Math.imul(a ^ (a >>> 15), 1 | a)
-    t ^= t + Math.imul(t ^ (t >>> 7), 61 | t)
-    return ((t ^ (t >>> 14)) >>> 0) / 4294967296
+function scatterPoint(
+  random: () => number,
+  maxDistance: number,
+  clearance: number,
+  flatMargin: number,
+): { x: number; z: number } | null {
+  const angle = random() * Math.PI * 2
+  const distance =
+    ARENA + clearance + random() * (maxDistance - ARENA - clearance)
+  const x = Math.cos(angle) * distance
+  const z = Math.sin(angle) * distance
+  return Math.max(Math.abs(x), Math.abs(z)) < TERRAIN_CONFIG.inner + flatMargin
+    ? null
+    : { x, z }
+}
+
+function weightedTree(
+  definitions: WeightedTree[],
+  roll: number,
+): PrefabDefinition<Tree> {
+  let cumulative = 0
+  for (const entry of definitions) {
+    cumulative += entry.weight
+    if (roll < cumulative) {
+      return entry.definition
+    }
+  }
+  return definitions[definitions.length - 1].definition
+}
+
+function wall(
+  minX: number,
+  maxX: number,
+  minZ: number,
+  maxZ: number,
+): BoxCollider {
+  return {
+    shape: "box",
+    minX,
+    maxX,
+    minZ,
+    maxZ,
+    top: WALL_HEIGHT,
+    standable: true,
   }
 }
 
-function mesh(): Mesh {
-  return { verts: [], indices: [] }
-}
-
-/** A perimeter wall collider: blocks from the sides, and `standable` so you can
- *  jump up and land on its top (given enough JUMP_SPEED to clear WALL_HEIGHT). */
-function wall(minX: number, maxX: number, minZ: number, maxZ: number): Aabb {
-  return { minX, maxX, minZ, maxZ, top: WALL_HEIGHT, standable: true }
-}
-
-/** One flat quad (two tris). Corners run a (uv 0,0) -> b (us,0) -> c (us,vs) ->
- *  d (0,vs); `us`/`vs` set how many texture tiles span it. No subdivision is
- *  needed -- texturing is perspective-correct, so a single quad looks right at
- *  any size. */
-function quad(m: Mesh, a: Corner, b: Corner, c: Corner, d: Corner, us: number, vs: number): void {
-  const base = m.verts.length / STRIDE
-  m.verts.push(a[0], a[1], a[2], 0, 0, b[0], b[1], b[2], us, 0, c[0], c[1], c[2], us, vs, d[0], d[1], d[2], 0, vs)
-  m.indices.push(base, base + 1, base + 2, base, base + 2, base + 3)
-}
-
-/** An axis-aligned box from (x0,z0)-(x1,z1), y0..y1: four sides + top, no bottom
- *  (never seen from below). `tpu` = texture tiles per world unit, so every face
- *  tiles at the same density whatever its size. Used for the thick walls. */
-function slab(m: Mesh, x0: number, x1: number, z0: number, z1: number, y0: number, y1: number, tpu: number): void {
-  const dx = (x1 - x0) * tpu
-  const dz = (z1 - z0) * tpu
-  const dy = (y1 - y0) * tpu
-  quad(m, [x0, y1, z0], [x1, y1, z0], [x1, y1, z1], [x0, y1, z1], dx, dz)
-  quad(m, [x0, y0, z0], [x1, y0, z0], [x1, y1, z0], [x0, y1, z0], dx, dy)
-  quad(m, [x1, y0, z1], [x0, y0, z1], [x0, y1, z1], [x1, y1, z1], dx, dy)
-  quad(m, [x0, y0, z1], [x0, y0, z0], [x0, y1, z0], [x0, y1, z1], dz, dy)
-  quad(m, [x1, y0, z0], [x1, y0, z1], [x1, y1, z1], [x1, y1, z0], dz, dy)
-}
-
-/** A box centered at (cx, cz), rising `height` units from `base`: top face plus
- *  four sides, one uv tile per face. No bottom (never seen). */
-function box(m: Mesh, cx: number, cz: number, half: number, base: number, height: number): void {
-  const x0 = cx - half
-  const x1 = cx + half
-  const z0 = cz - half
-  const z1 = cz + half
-  const y0 = base
-  const y1 = base + height
-  quad(m, [x0, y1, z0], [x1, y1, z0], [x1, y1, z1], [x0, y1, z1], 1, 1)
-  quad(m, [x0, y0, z0], [x1, y0, z0], [x1, y1, z0], [x0, y1, z0], 1, 1)
-  quad(m, [x1, y0, z1], [x0, y0, z1], [x0, y1, z1], [x1, y1, z1], 1, 1)
-  quad(m, [x1, y0, z0], [x1, y0, z1], [x1, y1, z1], [x1, y1, z0], 1, 1)
-  quad(m, [x0, y0, z1], [x0, y0, z0], [x0, y1, z0], [x0, y1, z1], 1, 1)
+function mulberry(seed: number): () => number {
+  let state = seed >>> 0
+  return () => {
+    state = (state + 0x6D2B79F5) | 0
+    let value = Math.imul(state ^ (state >>> 15), 1 | state)
+    value ^= value + Math.imul(value ^ (value >>> 7), 61 | value)
+    return ((value ^ (value >>> 14)) >>> 0) / 4294967296
+  }
 }
diff --git a/game/player.ts b/game/player.ts
index f45d376..6fba438 100644
--- a/game/player.ts
+++ b/game/player.ts
@@ -1,169 +1,32 @@
-import { Terrain } from "./Terrain"
-import type { Vec3 } from "../engine/math/Vec3"
-import type { Aabb, Level } from "./level"
+import type {
+  Character,
+  CharacterConfig,
+} from "../engine/world/CharacterController"
 
-/** The player as a vertical cylinder. `position` is at the feet; the camera
- *  eye sits EYE_HEIGHT above it. */
-export type Player = {
-  position: Vec3
-  yaw: number
+export type Player = Character & {
   pitch: number
-  velocityY: number
-  onGround: boolean
 }
 
-export const EYE_HEIGHT = 1.6
-const RADIUS = 0.35
-const SPEED = 6
-/** Speed multiplier while a Run key (Shift) is held. Tweak to taste; set high to
- *  blast across the big terrain -- move+collision is substepped, so walls stay
- *  solid even at big multipliers. */
-const RUN_MULTIPLIER = 2
-const GRAVITY = 22
-const JUMP_SPEED = 14
-const NPC_RADIUS = 0.5
-
+/** Concrete player tuning. Movement and collision behavior live in engine. */
 export namespace Player {
-  /** Advance the player one frame: jump, horizontal move + collision, gravity. */
-  export function update(player: Player, keys: Set<string>, dt: number, level: Level): void {
-    if (keys.has("Space") && player.onGround) {
-      player.velocityY = JUMP_SPEED
-      player.onGround = false
-    }
-    // Move + collide in small substeps: collision is discrete (move, then push
-    // out), so a single big running step could otherwise skip clean through a
-    // wall. Substepping keeps each advance short enough to always hit it.
-    const steps = moveSubsteps(keys, dt)
-    for (let i = 0; i < steps; i++) {
-      moveHorizontal(player, keys, dt / steps)
-      collide(player, level)
-    }
-    fall(player, dt, level)
+  export const actorCollisionRange = 3
+
+  export const config: CharacterConfig = {
+    radius: 0.35,
+    speed: 6,
+    runMultiplier: 2,
+    gravity: 22,
+    jumpSpeed: 14,
+    eyeHeight: 1.6,
   }
 
-  /** Run-speed factor for the frame: RUN_MULTIPLIER while Shift is held, else 1. */
-  function runFactor(keys: Set<string>): number {
-    return keys.has("ShiftLeft") || keys.has("ShiftRight") ? RUN_MULTIPLIER : 1
-  }
-
-  /** Number of move+collide substeps so each advances at most ~RADIUS, keeping
-   *  the player from tunneling walls however fast they run. */
-  function moveSubsteps(keys: Set<string>, dt: number): number {
-    const perFrame = SPEED * runFactor(keys) * dt * Math.SQRT2
-    return Math.max(1, Math.ceil(perFrame / RADIUS))
-  }
-
-  function moveHorizontal(player: Player, keys: Set<string>, dt: number): void {
-    const speed = SPEED * runFactor(keys) * dt
-    const fx = Math.sin(player.yaw)
-    const fz = -Math.cos(player.yaw)
-    const rx = Math.cos(player.yaw)
-    const rz = Math.sin(player.yaw)
-    const p = player.position
-    if (keys.has("KeyW")) {
-      p.x += fx * speed
-      p.z += fz * speed
+  export function create(): Player {
+    return {
+      position: { x: 0, y: 0, z: 8 },
+      yaw: 0,
+      pitch: 0,
+      velocityY: 0,
+      onGround: true,
     }
-    if (keys.has("KeyS")) {
-      p.x -= fx * speed
-      p.z -= fz * speed
-    }
-    if (keys.has("KeyD")) {
-      p.x += rx * speed
-      p.z += rz * speed
-    }
-    if (keys.has("KeyA")) {
-      p.x -= rx * speed
-      p.z -= rz * speed
-    }
-  }
-
-  /** Push the player's circle out of any solid it overlaps: level colliders it
-   *  is not standing above, and the NPC. This is what makes walls and the NPC
-   *  impassable while still letting you stand on the crate. */
-  function collide(player: Player, level: Level): void {
-    for (const aabb of level.colliders) {
-      if (player.position.y < aabb.top - 0.01) {
-        pushFromAabb(player.position, aabb)
-      }
-    }
-    pushFromCircle(player.position, level.npcPosition.x, level.npcPosition.z, NPC_RADIUS)
-  }
-
-  /** Apply gravity and land on the highest ground under the player. */
-  function fall(player: Player, dt: number, level: Level): void {
-    player.velocityY -= GRAVITY * dt
-    player.position.y += player.velocityY * dt
-    const ground = groundHeight(player.position, level)
-    if (player.position.y <= ground) {
-      player.position.y = ground
-      player.velocityY = 0
-      player.onGround = true
-    } else {
-      player.onGround = false
-    }
-  }
-
-  function groundHeight(position: Vec3, level: Level): number {
-    let ground = Terrain.height(level.terrain, position.x, position.z)
-    for (const aabb of level.colliders) {
-      if (
-        aabb.standable &&
-        position.x >= aabb.minX &&
-        position.x <= aabb.maxX &&
-        position.z >= aabb.minZ &&
-        position.z <= aabb.maxZ
-      ) {
-        ground = Math.max(ground, aabb.top)
-      }
-    }
-    return ground
-  }
-
-  function pushFromAabb(position: Vec3, aabb: Aabb): void {
-    const cx = Math.max(aabb.minX, Math.min(aabb.maxX, position.x))
-    const cz = Math.max(aabb.minZ, Math.min(aabb.maxZ, position.z))
-    const dx = position.x - cx
-    const dz = position.z - cz
-    const d2 = dx * dx + dz * dz
-    if (d2 >= RADIUS * RADIUS) {
-      return
-    }
-    if (d2 > 1e-6) {
-      const d = Math.sqrt(d2)
-      const push = (RADIUS - d) / d
-      position.x += dx * push
-      position.z += dz * push
-      return
-    }
-    // Center is inside the box: eject through the nearest face.
-    const left = position.x - aabb.minX
-    const rightSide = aabb.maxX - position.x
-    const near = position.z - aabb.minZ
-    const far = aabb.maxZ - position.z
-    const m = Math.min(left, rightSide, near, far)
-    if (m === left) {
-      position.x = aabb.minX - RADIUS
-    } else if (m === rightSide) {
-      position.x = aabb.maxX + RADIUS
-    } else if (m === near) {
-      position.z = aabb.minZ - RADIUS
-    } else {
-      position.z = aabb.maxZ + RADIUS
-    }
-  }
-
-  function pushFromCircle(position: Vec3, cx: number, cz: number, otherRadius: number): void {
-    const dx = position.x - cx
-    const dz = position.z - cz
-    const reach = RADIUS + otherRadius
-    const d2 = dx * dx + dz * dz
-    if (d2 >= reach * reach || d2 < 1e-6) {
-      return
-    }
-    const d = Math.sqrt(d2)
-    const push = (reach - d) / d
-    position.x += dx * push
-    position.z += dz * push
   }
 }
diff --git a/game/renderScene.ts b/game/renderScene.ts
deleted file mode 100644
index 96b0d7e..0000000
--- a/game/renderScene.ts
+++ /dev/null
@@ -1,133 +0,0 @@
-import { Framebuffer } from "../engine/render/Framebuffer"
-import { Frustum } from "../engine/render/Frustum"
-import { Rasterizer } from "../engine/render/Rasterizer"
-import type { RenderConfig } from "../engine/render/RenderConfig"
-import { Sky, type SkyConfig } from "../engine/render/Sky"
-import type { Camera } from "../engine/scene/Camera"
-import { Mat4 } from "../engine/math/Mat4"
-import type { Mesh } from "../engine/scene/Mesh"
-import { Mob, type MobKind } from "./actors/Mob"
-import { Sprite } from "../engine/scene/Sprite"
-import type { Vec2 } from "../engine/math/Vec2"
-import type { Vec3 } from "../engine/math/Vec3"
-import type { Textures } from "./textures"
-import type { Chunk } from "./level"
-
-/** Everything needed to render the world: the room, the cullable chunks, the NPC
- *  billboard source, sky, and textures. Bundled so it can be handed to a worker
- *  whole (it is plain data + typed arrays, structured-clone friendly). */
-export type Scene = {
-  chunks: Chunk[]
-  floor: Mesh
-  walls: Mesh
-  crate: Mesh
-  npc: { position: Vec3; size: Vec2 }
-  /** Canonical local-space mob meshes, one per kind, built once + shared by every
-   *  instance (each instance differs only by its per-frame model matrix). */
-  mobMesh: Record<MobKind, Mesh>
-  /** How many mobs the sim has -- sizes the worker's shared transform buffer. */
-  mobCount: number
-  sky: SkyConfig
-  textures: Textures
-}
-
-/** One mob's live transform for a frame: which mesh + where/how to place it.
- *  Produced by `visibleMobs` on the main thread, then either passed straight to
- *  `renderBand` (single-thread) or packed into the shared `mobState` buffer and
- *  rebuilt in each worker. `MOB_FLOATS` is that packed layout's stride. */
-export type MobDraw = { kind: MobKind; x: number; y: number; z: number; heading: number; scale: number }
-export const MOB_FLOATS = 6 // kind index (into MOB_KINDS), x, y, z, heading, scale
-
-/** Chunk indices whose bounding box is inside the view frustum. Computed once on
- *  the main thread and shared with every worker (so they don't each re-cull). */
-export function visibleChunks(chunks: Chunk[], viewProj: Mat4): number[] {
-  const frustum = Frustum.fromViewProj(viewProj)
-  const out: number[] = []
-  for (let i = 0; i < chunks.length; i++) {
-    const c = chunks[i]
-    if (Frustum.intersectsAabb(frustum, c.minX, c.minY, c.minZ, c.maxX, c.maxY, c.maxZ)) {
-      out.push(i)
-    }
-  }
-  return out
-}
-
-/** The `MobDraw`s for mobs whose world AABB is inside the view frustum. Mobs move,
- *  so (unlike chunks) they can't be baked into the culled world -- they're culled
- *  here per frame instead. Computed once on the main thread; the visible set is
- *  what gets shipped to the workers. */
-export function visibleMobs(mobs: Mob[], viewProj: Mat4): MobDraw[] {
-  const frustum = Frustum.fromViewProj(viewProj)
-  const out: MobDraw[] = []
-  for (const m of mobs) {
-    const r = Mob.boundingRadius(m.kind) * m.scale
-    const h = Mob.bodyHeight(m.kind) * m.scale
-    const p = m.position
-    if (Frustum.intersectsAabb(frustum, p.x - r, p.y - r, p.z - r, p.x + r, p.y + h + r, p.z + r)) {
-      out.push({ kind: m.kind, x: p.x, y: p.y, z: p.z, heading: m.heading, scale: m.scale })
-    }
-  }
-  return out
-}
-
-/**
- * Render rows [y0, y1) of one frame into `fb`. This is the single source of
- * render truth: the single-thread path calls it with the full height, and each
- * worker calls it with its own disjoint band -- same output either way, and no
- * two bands touch the same pixel (so the shared framebuffer needs no locking).
- */
-export function renderBand(
-  fb: Framebuffer,
-  scene: Scene,
-  camera: Camera,
-  viewProj: Mat4,
-  visible: number[],
-  mobDraws: MobDraw[],
-  config: RenderConfig,
-  skyStep: number,
-  time: number,
-  y0: number,
-  y1: number,
-): void {
-  const tx = scene.textures
-  Sky.render(fb, camera, scene.sky, time, skyStep, y0, y1)
-  // Room: small and always near, drawn unconditionally (double-sided).
-  Rasterizer.draw(fb, scene.floor, tx.floor, viewProj, config, false, y0, y1)
-  Rasterizer.draw(fb, scene.walls, tx.wall, viewProj, config, false, y0, y1)
-  Rasterizer.draw(fb, scene.crate, tx.crate, viewProj, config, false, y0, y1)
-  for (const i of visible) {
-    const c = scene.chunks[i]
-    // Past lodDistance, draw the cheap impostor group set instead of full detail.
-    // `chunkFar` is pure (camera + chunk bounds + config), so every worker band
-    // makes the identical choice -- no full/impostor seam across bands. The loop
-    // is content-agnostic: each group carries its own mesh + material.
-    const groups = chunkFar(c, camera.position, config.lodDistance) ? c.far : c.near
-    for (const g of groups) {
-      Rasterizer.draw(fb, g.mesh, g.material.texture, viewProj, config, g.material.cull, y0, y1)
-    }
-  }
-  const sprite: Sprite = { position: scene.npc.position, size: scene.npc.size, texture: tx.npc }
-  Rasterizer.draw(fb, Sprite.billboard(sprite, camera), tx.npc, viewProj, config, false, y0, y1)
-  // Roaming mobs: each is the shared local-space mesh for its kind, placed by its
-  // own model matrix (viewProj x model). Drawn double-sided (cull off) -- they're
-  // small and few, so the winding-correct backface cull isn't worth the fuss.
-  for (const m of mobDraws) {
-    const mvp = Mat4.multiply(viewProj, Mat4.compose(m.x, m.y, m.z, m.heading, m.scale))
-    Rasterizer.draw(fb, scene.mobMesh[m.kind], tx[m.kind], mvp, config, false, y0, y1)
-  }
-  Framebuffer.quantize(fb, config, y0, y1)
-}
-
-/** Whether a chunk is far enough to draw its impostor meshes: squared distance
- *  from the camera to the chunk's AABB vs `lodDistance²`. Pure -- depends only on
- *  camera, the chunk's baked bounds, and the config constant, all of which every
- *  worker already holds, so the choice is identical across bands. */
-export function chunkFar(chunk: Chunk, eye: Vec3, lodDistance: number): boolean {
-  if (!(lodDistance < Infinity)) {
-    return false
-  }
-  const dx = eye.x - Math.max(chunk.minX, Math.min(chunk.maxX, eye.x))
-  const dy = eye.y - Math.max(chunk.minY, Math.min(chunk.maxY, eye.y))
-  const dz = eye.z - Math.max(chunk.minZ, Math.min(chunk.maxZ, eye.z))
-  return dx * dx + dy * dy + dz * dz > lodDistance * lodDistance
-}
diff --git a/meat.code-workspace b/meat.code-workspace
index 7db0cb1..019843d 100644
--- a/meat.code-workspace
+++ b/meat.code-workspace
@@ -2,8 +2,11 @@
 	"folders": [
 		{
 			"name": "meat",
-			"path": ".",
+			"path": "."
 		},
+		{
+			"path": "../meat.project"
+		}
 	],
 	"settings": {
 		"oxc.path.oxfmt": "node_modules/.bin/oxfmt",
diff --git a/tests/actors.test.ts b/tests/actors.test.ts
new file mode 100644
index 0000000..2f317ee
--- /dev/null
+++ b/tests/actors.test.ts
@@ -0,0 +1,38 @@
+import { expect, test } from "bun:test"
+import { Actor, type Actor as RuntimeActor, type ActorDefinition } from "../engine/scene/Actor"
+
+type World = { updates: string[] }
+
+const numberDefinition: ActorDefinition<{ value: number }, World> = {
+  prototype: { groups: [], radius: 1, minY: 0, maxY: 1 },
+  update: (state, _dt, world) => {
+    state.value++
+    world.updates.push(String(state.value))
+  },
+  transform: (state) => ({ x: state.value, y: 0, z: 0, heading: 0, scale: 1 }),
+}
+
+const textDefinition: ActorDefinition<{ value: string }, World> = {
+  prototype: { groups: [], radius: 1, minY: 0, maxY: 1 },
+  update: (state, _dt, world) => {
+    state.value += "!"
+    world.updates.push(state.value)
+  },
+  transform: (state) => ({ x: state.value.length, y: 0, z: 0, heading: 0, scale: 1 }),
+}
+
+test("one actor collection safely erases unrelated state types", () => {
+  const actors: RuntimeActor<World>[] = [
+    Actor.create(numberDefinition, { value: 1 }),
+    Actor.create(textDefinition, { value: "a" }),
+  ]
+  const world: World = { updates: [] }
+
+  for (const actor of actors) {
+    Actor.update(actor, 1, world)
+  }
+
+  expect(world.updates).toEqual(["2", "a!"])
+  expect(Actor.transform(actors[0]).x).toBe(2)
+  expect(Actor.transform(actors[1]).x).toBe(2)
+})
diff --git a/tests/layering.test.ts b/tests/layering.test.ts
index b6cefe5..3d1fcb6 100644
--- a/tests/layering.test.ts
+++ b/tests/layering.test.ts
@@ -1,6 +1,6 @@
 import { expect, test } from "bun:test"
-import { readdirSync, readFileSync, statSync } from "node:fs"
-import { join } from "node:path"
+import { existsSync, readdirSync, readFileSync, statSync } from "node:fs"
+import path from "node:path"
 
 // The engine is the reusable, content-agnostic layer: it must import nothing from
 // game (content) or app (browser glue). game -> engine and app -> game -> engine are
@@ -9,7 +9,7 @@ import { join } from "node:path"
 function tsFiles(dir: string): string[] {
   const out: string[] = []
   for (const name of readdirSync(dir)) {
-    const p = join(dir, name)
+    const p = path.join(dir, name)
     if (statSync(p).isDirectory()) {
       out.push(...tsFiles(p))
     } else if (p.endsWith(".ts")) {
@@ -19,14 +19,42 @@ function tsFiles(dir: string): string[] {
   return out
 }
 
+function repositoryRoot(): string {
+  const parent = new URL("..", import.meta.url).pathname
+  return existsSync(path.join(parent, "app/renderer.ts")) ? parent : path.join(parent, "..")
+}
+
+function importsLayer(source: string, layers: string): boolean {
+  return new RegExp(`(?:from\\s+|import\\s*(?:\\(\\s*)?)["'][^"']*/(?:${layers})/`).test(source)
+}
+
 test("engine imports nothing from game or app", () => {
-  const engineDir = new URL("../engine", import.meta.url).pathname
-  const offenders = tsFiles(engineDir).filter((f) => /from\s+["'][^"']*\/(?:game|app)\//.test(readFileSync(f, "utf8")))
+  const engineDir = path.join(repositoryRoot(), "engine")
+  const offenders = tsFiles(engineDir).filter((file) => importsLayer(readFileSync(file, "utf8"), "game|app"))
   expect(offenders).toEqual([])
 })
 
 test("game imports nothing from app", () => {
-  const gameDir = new URL("../game", import.meta.url).pathname
-  const offenders = tsFiles(gameDir).filter((f) => /from\s+["'][^"']*\/app\//.test(readFileSync(f, "utf8")))
+  const gameDir = path.join(repositoryRoot(), "game")
+  const offenders = tsFiles(gameDir).filter((file) => importsLayer(readFileSync(file, "utf8"), "app"))
+  expect(offenders).toEqual([])
+})
+
+test("render driver and worker know no game content", () => {
+  const root = repositoryRoot()
+  const files = [path.join(root, "app/renderer.ts"), path.join(root, "app/render-worker.ts")]
+  const offenders = files.filter((file) => importsLayer(readFileSync(file, "utf8"), "game"))
+  expect(offenders).toEqual([])
+})
+
+test("game exports no closed content-kind registries", () => {
+  const gameDir = path.join(repositoryRoot(), "game")
+  const offenders = tsFiles(gameDir).filter((file) => {
+    const source = readFileSync(file, "utf8")
+    return (
+      /\b(?:export\s+)?(?:type|enum)\s+\w+Kind\b/.test(source) ||
+      /\b(?:const|let|var)\s+\w*_(?:KINDS|REGISTRY)\b/.test(source)
+    )
+  })
   expect(offenders).toEqual([])
 })
diff --git a/tests/level.test.ts b/tests/level.test.ts
new file mode 100644
index 0000000..d101283
--- /dev/null
+++ b/tests/level.test.ts
@@ -0,0 +1,72 @@
+import { expect, test } from "bun:test"
+import type { Texture } from "../engine/render/Texture"
+import { buildLevel } from "../game/level"
+import type { Textures } from "../game/textures"
+
+const texture: Texture = { width: 1, height: 1, data: new Uint32Array([0xFFFFFFFF]) }
+const textures: Textures = {
+  floor: texture,
+  grass: texture,
+  bark: texture,
+  birch: texture,
+  leaf: texture,
+  needle: texture,
+  rock: texture,
+  flower: texture,
+  wall: texture,
+  crate: texture,
+  npc: texture,
+  frog: texture,
+  bee: texture,
+  robin: texture,
+  skybox: texture,
+}
+
+test("game data compiles into a clone-safe engine render scene", () => {
+  const level = buildLevel(textures)
+  expect(level.actors).toHaveLength(60)
+  expect(Object.isFrozen(level.actors)).toBe(true)
+  expect(Object.isFrozen(level.render)).toBe(true)
+  expect(Object.isFrozen(level.render.prototypes)).toBe(true)
+  expect(level.render.prototypes).toHaveLength(3)
+  expect(level.render.maxInstances).toBe(level.actors.length)
+  expect(() => structuredClone(level.render)).not.toThrow()
+})
+
+test("actor prototype bounds cover local geometry", () => {
+  const level = buildLevel(textures)
+  for (const prototype of level.render.prototypes) {
+    let covered = true
+    for (const group of prototype.groups) {
+      const vertices = group.mesh.verts
+      for (let i = 0; i < vertices.length; i += 5) {
+        covered &&=
+          Math.abs(vertices[i]) <= prototype.radius + 1e-6 &&
+          vertices[i + 1] >= prototype.minY - 1e-6 &&
+          vertices[i + 1] <= prototype.maxY + 1e-6 &&
+          Math.abs(vertices[i + 2]) <= prototype.radius + 1e-6
+      }
+    }
+    expect(covered).toBe(true)
+  }
+})
+
+test("chunk bounds cover geometry in every LOD", () => {
+  const level = buildLevel(textures)
+  for (const chunk of level.render.chunks) {
+    let covered = true
+    for (const group of [...chunk.near, ...chunk.far]) {
+      const vertices = group.mesh.verts
+      for (let i = 0; i < vertices.length; i += 5) {
+        covered &&=
+          vertices[i] >= chunk.minX &&
+          vertices[i] <= chunk.maxX &&
+          vertices[i + 1] >= chunk.minY &&
+          vertices[i + 1] <= chunk.maxY &&
+          vertices[i + 2] >= chunk.minZ &&
+          vertices[i + 2] <= chunk.maxZ
+      }
+    }
+    expect(covered).toBe(true)
+  }
+})
diff --git a/tests/mobs.test.ts b/tests/mobs.test.ts
deleted file mode 100644
index 89b5344..0000000
--- a/tests/mobs.test.ts
+++ /dev/null
@@ -1,21 +0,0 @@
-import { expect, test } from "bun:test"
-import { MOB_KINDS, Mob } from "../game/actors/Mob"
-
-// The mob SAB packs a kind as its index in MOB_KINDS; the main thread and every
-// render worker must agree on that order. Freeze it here: appending a kind is fine,
-// but reordering or removing an existing one silently corrupts which mesh/texture a
-// worker draws.
-test("MOB_KINDS order is frozen (mob SAB ids)", () => {
-  expect(MOB_KINDS).toEqual(["frog", "bee", "robin"])
-})
-
-test("every kind resolves to a complete definition", () => {
-  for (const kind of MOB_KINDS) {
-    const d = Mob.def(kind)
-    expect(d.name).toBe(kind)
-    expect(typeof d.build).toBe("function")
-    expect(typeof d.update).toBe("function")
-    expect(d.boundingRadius).toBeGreaterThan(0)
-    expect(d.bodyHeight).toBeGreaterThan(0)
-  }
-})
diff --git a/tests/render-protocol.test.ts b/tests/render-protocol.test.ts
new file mode 100644
index 0000000..be64148
--- /dev/null
+++ b/tests/render-protocol.test.ts
@@ -0,0 +1,38 @@
+import { expect, test } from "bun:test"
+import { RenderProtocol } from "../engine/render/RenderProtocol"
+import type { RenderInstance } from "../engine/render/RenderScene"
+import type { Camera } from "../engine/scene/Camera"
+
+test("render camera protocol owns its complete shared layout", () => {
+  const input: Camera = { position: { x: 1, y: 2, z: 3 }, yaw: 4, pitch: 5, fov: 6 }
+  const data = new Float64Array(RenderProtocol.CAMERA_LENGTH)
+
+  RenderProtocol.writeCamera(data, input, 7)
+  const output = RenderProtocol.readCamera(data)
+
+  expect(output).toEqual({ camera: input, time: 7 })
+  expect(RenderProtocol.VIEW_PROJECTION_LENGTH).toBe(16)
+})
+
+test("render instance protocol round-trips scene-local prototype indexes", () => {
+  const input: RenderInstance[] = [
+    { prototype: 2, x: 1.25, y: -2, z: 3.5, heading: 0.75, scale: 1.5 },
+    { prototype: 0, x: -4, y: 5.25, z: 6, heading: -0.5, scale: 0.625 },
+  ]
+  const ids = new Int32Array(2)
+  const transforms = new Float32Array(2 * RenderProtocol.TRANSFORM_FLOATS)
+  const output: RenderInstance[] = []
+
+  const count = RenderProtocol.writeInstances(ids, transforms, input)
+  RenderProtocol.readInstances(ids, transforms, count, output)
+
+  expect(output).toHaveLength(input.length)
+  for (let i = 0; i < input.length; i++) {
+    expect(output[i].prototype).toBe(input[i].prototype)
+    expect(output[i].x).toBeCloseTo(input[i].x)
+    expect(output[i].y).toBeCloseTo(input[i].y)
+    expect(output[i].z).toBeCloseTo(input[i].z)
+    expect(output[i].heading).toBeCloseTo(input[i].heading)
+    expect(output[i].scale).toBeCloseTo(input[i].scale)
+  }
+})
diff --git a/tests/trees.test.ts b/tests/trees.test.ts
deleted file mode 100644
index 5056cf8..0000000
--- a/tests/trees.test.ts
+++ /dev/null
@@ -1,18 +0,0 @@
-import { expect, test } from "bun:test"
-import { Tree, TREE_KINDS } from "../game/actors/Tree"
-
-// The chunk baker (level.ts) accumulates geometry into a mesh per material key and
-// only draws keys listed in MAT_ORDER. A tree species that declares a trunk/foliage
-// material outside that palette would bake geometry that is silently never drawn.
-// Freeze the palette here so a typo'd or unregistered material key fails a test.
-const MATERIAL_KEYS = new Set(["grass", "rock", "bark", "birch", "leaf", "needle", "flower"])
-
-test("every tree species maps to known chunk materials", () => {
-  for (const kind of TREE_KINDS) {
-    const s = Tree.species(kind)
-    expect(s.kind).toBe(kind)
-    expect(typeof s.build).toBe("function")
-    expect(MATERIAL_KEYS.has(s.trunk)).toBe(true)
-    expect(MATERIAL_KEYS.has(s.foliage)).toBe(true)
-  }
-})