diff --git a/.agents/plans/levels-and-editor.md b/.agents/plans/levels-and-editor.md
new file mode 100644
index 0000000..b43fb0a
--- /dev/null
+++ b/.agents/plans/levels-and-editor.md
@@ -0,0 +1,252 @@
+# Levels & the in-game editor — direction note
+
+Status: **direction agreed, not yet built.** 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*.
+
+## The pivot
+
+The game is heading toward a **multiplayer twitch shooter**. Each match loads a
+**fresh, isolated level**. Consequences that shape everything below:
+
+- **Maps are hand-made, not procedural.** Procedural scatter is demoted to a
+  *tool* (a starting-block generator), never the runtime map path. This is the
+  whole reason the editor matters — the editor *is* the map pipeline.
+- **Real authoritative server.** The server bakes the same map the clients do and
+  runs the authoritative sim.
+- **No in-world level switching.** You don't walk through a portal to another
+  world; the match lifecycle loads a level at start. → **portals / transition
+  triggers are explicitly not needed.**
+- **Persistence and player carry-over are YAGNI** for now — but must not be walled
+  off (see hedges).
+
+## Naming: `Level` (data) vs `Scene` (runtime)
+
+Agreed vocabulary — reads as **"bake a `Level` into a `Scene`."** Fits the
+type + namespace convention.
+
+- **`Level`** = the authored, serializable **data document** (what an earlier draft
+  called `LevelSpec`). Pure plain data. The editor's output; the network's payload;
+  the server's and client's input.
+- **`Scene`** = the baked **runtime instance** — the assembled world you render and
+  simulate.
+
+**Repurposing note (so nobody trips):** today the names mean something narrower —
+`Level` (`game/level.ts:69`) is a *bake output* and `Scene` (`renderScene.ts:19`)
+is a *render-only, worker-cloneable subset*. Under the new vocabulary:
+
+- The name **`Level` is freed** for the authored data document.
+- **`Scene` grows** to be the whole runtime instance — it **absorbs** the colliders
+  + live mob array + terrain sampler that currently hang off `Level`. The thing
+  **cloned to workers stays a render-subset projection** of the Scene (no colliders,
+  no live mobs — those are main-thread only), exactly as the current `Scene` already
+  is. This collapses today's incidental `Level`/`Scene` split (main.ts copies
+  fields across) into two clear things.
+
+So the pipeline is:
+
+```
+generator(params) → Level (data)   →   bake(level, textures) → Scene (runtime)
+   (a TOOL: script / editor / never runtime)        (the runtime path)
+```
+
+(`bake` is today's `buildLevel`, renamed and re-typed to take a `Level` document.
+Namespace home — `Scene.from(level)` vs `Level.bake()` — is an open detail.)
+
+## The spine: the `Level` document
+
+One serializable, explicit map document is the center of gravity. Four consumers,
+one artifact:
+
+- **Editor** *writes* it.
+- **Server** *reads* it — bakes headless, runs authoritative collision/sim.
+- **Client** *reads* it — bakes the identical `Scene` to render + predict.
+- **Network** ships it (or its id) at match start.
+
+Because the bake is deterministic, server and every client bake **byte-identical
+geometry and collision** from the same `Level` — so only the document (or its id)
+crosses the wire, never geometry.
+
+### The one real refactor
+
+Today the map *definition* is module-level constants welded **inside**
+`buildLevel()`. Split generation from baking: the generator *produces* an explicit
+`Level`; `bake` consumes it. `bake` should treat the **explicit** document (a list
+of placements) as canonical — the generator emits that form. This one cut serves
+three futures at once: multiplayer sync, the editor, and (later) persistence.
+
+## Build order
+
+1. **`Level` document + `bake(level)` + the gen/bake split.** Pure `game/`,
+   headless, unit-testable, **no UI, no netcode**. The whole foundation — do it
+   first, on its own.
+2. **Then, in parallel — both ride the document, neither blocks the other:**
+   - **Editor** — in-engine, browser, `app/`. Emits a `Level` file.
+   - **Server** — real authoritative, imports `game/`, bakes the `Level` headless.
+
+## The editor shape
+
+- **In-game, single-player, edit↔play toggle.** Same running client: an edit mode
+  to author the `Level` live, and a button that flips to **play mode** and drops you
+  into the environment you're building. "Everything works except multiplayer" —
+  full local sim (player, mobs, collision, later weapons) runs in play mode; no
+  server, no netcode in the editor.
+- The play toggle is a **re-bake + mode switch** — a loading beat, not a hot path.
+  So it may freely re-bake and even reuse the existing worker respawn/`reconfigure`
+  path; there is **no match, so no live-worker-resync problem** (the one genuinely
+  hard sub-problem, thereby dodged).
+- The engine already provides the hard parts: live first-person view, deterministic
+  bake, and `camera` + `Terrain.height` for "where's the ground under the cursor"
+  (raycast/picking). The remaining weight is **UI/interaction**. AGENTS.md notes
+  "no DOM-built UI yet (deliberate)" — the editor is where that ends.
+
+## Editor features (the brainstorm)
+
+Three feature buckets. For each: what's already there, the real new work, the catch.
+
+### 1. Sidebar tree — level config + contents
+
+A **property inspector over the `Level` document.** If the document is clean data,
+the tree is literally a view of it: each node = a field or an instance; edit a
+field = mutate the document + re-bake.
+
+- **World config already exists as data**, just scattered: `SkyConfig`, the
+  `CloudLayer` union (basicCumulus/fancyCumulus + params), `TERRAIN`
+  (amplitude/frequency/peaks/inner/blend), `GROUND_UV`, room dims. Parameterizing =
+  moving these constants into the `Level`.
+- **The tree forces one categorization: world property vs client look-preset.**
+  `RenderConfig` (internalWidth, colorDepth, dither, lodDistance, filters) is a
+  *per-viewer PS1 dial* — stays client-side. Sky/clouds/terrain = per-map, in the
+  document. But **fog + lighting live in `RenderConfig` today**, and in a shooter
+  fog density = sightlines = a *gameplay/map* property → fog probably moves into the
+  `Level`. Decide the world-vs-viewer line once, up front.
+- **Re-bake blast radius varies wildly:** sky color = re-run sky, no chunk touch;
+  one tree = re-bake 1–2 chunks; terrain amplitude = re-bake *every* chunk. For a
+  tool, full re-bake per edit is fine to start; scope to dirty cells only if it janks.
+- **Anti-overengineering line:** "everything parameterized" = *document completeness*
+  (every knob is data — yes). It is **not** a mandate for a generic reflection-UI
+  framework. Hand-wire panels for the handful of config sections; generalize to
+  type-driven widgets only if it hurts.
+
+### 2. Object tools — add / select / move / rotate
+
+- **Add** — palette pick + raycast ground (`camera` + `Terrain.height`) → drop an
+  instance record → re-bake. Easy.
+- **Select / pick** — **no GPU picking needed.** Props bake to anonymous triangles,
+  but the document retains the instance list with positions → **ray-vs-instance-bounds
+  test in JS**, nearest hit wins. (Another reason instances must live on the document.)
+- **Move** — drag → raycast ground → update `position` → re-bake touched cell(s).
+  Crossing a chunk boundary re-bakes 2 (cell membership is by base position).
+- **Rotate — the one real engine gap.** Props have **no orientation today** (Tree/
+  Boulder/Bush/Flower carry position + seed + size, no yaw; only *mobs* have
+  `heading`, applied live via `Mat4.compose`). Fix by **separating the per-instance
+  transform from geometry-gen**: `build` emits the instance's **unique local-space**
+  geometry (keep seed/growth = shape), and the **baker applies position + rotation +
+  scale** when appending to the chunk mesh. This mirrors what mobs already do (TRS
+  via `Mat4.compose`) — props become "unique local mesh × transform," baked-in
+  (static) where mobs are live (dynamic). This is the non-trivial refactor the object
+  tools demand; do it early since it touches every prop builder.
+- **Gizmos** — the rasterizer draws textured tris only, **no line primitive.** A
+  move/rotate gizmo (and selection highlight / wireframe AABB) needs either thin-box
+  tris or a new line-draw path. **Start gizmo-less** (drag on ground = XZ move,
+  scroll/key = yaw; tinted re-draw for selection) and add handles later.
+
+### 3. Terrain brushes — elevation + texture (the biggest new capability)
+
+- **Elevation needs a stored, editable heightfield** — the thing that doesn't exist
+  yet. `Terrain.height` is a **pure analytic function** of noise params; a brush has
+  nowhere to write. So: **the `Level` owns a height grid**; procedural gen
+  *initializes* it; brushes edit it directly; `Terrain.height` bilinear-samples the
+  grid. ("Seeding is a tool," made concrete — noise seeds the grid, then you sculpt.)
+  - **Collision comes free** — player + mobs already sample `Terrain.height`, so once
+    it samples the grid, gameplay collision follows. No separate collision bake.
+  - **Welds still hold** — patches weld by sampling shared height at shared world
+    positions; grid-as-source keeps that. Re-bake only the brushed cells.
+  - Side effect: the room "hole" + flat-inner-clearing special cases **dissolve into
+    authored terrain**. An arena may drop the room concept entirely — the map *is* the
+    sculpted terrain.
+- **Texture brush fits the engine shockingly well** — the chunk baker **already
+  accumulates one mesh per material key** and the renderer draws by DrawGroup list.
+  Ground is one `grass` material today; painting = ground goes to **N materials, each
+  painted tri routed to its material's mesh by a per-vertex/per-cell material id** —
+  the *exact* routing the baker already does for props. **No rasterizer change.** Hard
+  edges between materials (no blend) suit the PS1 look; soft splat-blending would need
+  per-pixel multi-texture rasterizer work — skip it, add later only if missed.
+
+### Threads that cut across
+
+1. **The `Level` document gains three responsibilities:** retain instance lists
+   (pick/move), own an editable **height grid** (elevation), own a **ground-material
+   map** (texture paint). All still pure data — the document grew, the architecture
+   didn't strain.
+2. **One engine refactor unlocks the object tools:** pull per-instance transform
+   (pos/rot/scale) out of prop `build` into the baker — props become "unique local
+   mesh × transform," matching mobs.
+3. **Terrain flips from function to data** — analytic → stored grid. Biggest single
+   change, but it's what "hand-made maps" *means*, and collision + welds fall out free.
+4. **Almost none of this needs new *rendering*** — picking is JS, texture paint
+   reuses per-material DrawGroups, terrain is more patch bake. The only genuinely new
+   render bit is small + optional: **line-draw for gizmos/selection**.
+
+## Why the architecture already fits (the two bets that pre-paid for this)
+
+- **Deterministic bake** — the world is byte-identical from a `Level` every run →
+  multiplayer world-sync is nearly free (ship the document, everyone bakes the same).
+- **DOM-free `engine`/`game`, layering test-enforced** — the authoritative server
+  runs `bake(level)` + sim with no renderer; `app/` is client-only glue. The layering
+  seam already enforced (`tests/layering.test.ts`) *is* the client/server seam. Keep
+  the `Level` document + `bake` in `game/`; editor UI in `app/`; server imports `game/`.
+
+## Cheap hedges (do now, save pain later)
+
+- The `Level` document is **pure serializable data** — no closures, no behavior baked
+  in (behavior stays code, imported per-side, as `Entity` already does it).
+- A `Level` has an **id/name** — "load level X" is a reference; later persistence keys
+  off it for free.
+- **Player state stays out of the `Level`/`Scene`** (already true) — carry-over later
+  touches the player, never the map.
+- `bake` eats the **explicit** document as canonical — keeps the recipe-vs-explicit
+  network choice open.
+- **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
+
+- `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**
+  (chunks/meshes/colliders/mobs) — under the new naming it becomes part of **`Scene`**;
+  the authored **`Level` document** is the missing *input* half. `buildLevel` becomes
+  `bake(level, textures) → Scene`.
+- Placement (`placeTrees/placeBoulders/placeBushes/placeFlowers/placeMobs`,
+  `game/level.ts:359+`) is procedural from fixed seeds + counts, fully deterministic.
+  These become the **generator** (emit a `Level`) rather than running inside the bake.
+- **Prop instances are discarded after bake** — only anonymous triangles survive in
+  per-chunk per-material meshes (`buildChunks`, `game/level.ts:251`). No `level.trees`
+  to iterate. The editor edits the **document**, then re-bakes — never mutates baked
+  meshes in place.
+- **Mobs are the exception** — retained live, simulated each frame, crossing to workers
+  as packed floats. Add/move/delete is cheap, no worker resync (caveat: mob shared
+  buffer sized once to `scene.mobCount` in `app/renderer.ts` — growing past it needs a
+  re-`setup`).
+- Instance shapes are already small plain records (position + seed + kind/size/color/
+  growth) — editor-friendly, directly serializable. See
+  `game/actors/{Tree,Boulder,Bush,Flower,Mob}.ts`.
+- Prop geometry currently bakes **position into world-space verts inside `build`**, with
+  seed/growth driving unique shape — hence the "separate transform from geometry-gen"
+  refactor needed for rotate/scale (see Object tools).
+- `Terrain.height` (`game/Terrain.ts`) is a **pure analytic function**, no stored
+  heightfield — hence the elevation-brush needs a stored grid (see Terrain brushes).
+- The render `Scene` (`renderScene.ts:19`) is the **render-only subset** already; the
+  chunk baker already routes geometry to **one mesh per material key** — the mechanism
+  the texture brush reuses.
+- Workers hold a **one-time structured clone** of the render subset from init
+  (`app/renderer.ts` `setup`); per-frame only camera/matrix/visible/mob buffers cross.
+  Chunk-geometry edits reach workers only via a re-send (`reconfigure`→`setup`, respawns
+  them — the same path keys 1/2/3 use). Fine for a mode-switch re-bake; would be the wall
+  for live in-match editing, which we are **not** doing.
+
+## Explicitly out of scope / dropped
+
+Portals & in-world transitions · persistence · player carry-over · procedural as the
+primary map path · any live-edit-during-a-multiplayer-match capability · GPU picking ·
+soft terrain-texture blending (hard-edged materials first).
diff --git a/AGENTS.md b/AGENTS.md
index 37d075e..ec19f68 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -26,8 +26,14 @@ 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**.
-- **Engine is headless.** `engine/` has no DOM types and could run server-side;
-  all browser glue (canvas, input, image decode) lives in `app/`.
+- **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).
+  Enforced: `engine/` imports nothing from `game`/`app`, `game/` nothing from `app`
+  (`tests/layering.test.ts`). Both `engine` and `game` are DOM-free (tsconfig).
 
 ## Stack & tooling
 
@@ -48,15 +54,16 @@ rules live in `.agents/rules/*.md`.
 - `bun run bench:browser` — Playwright: drive headless Chromium through the
   `?bench=st`/`?bench=mt` flythrough, print single-thread vs worker frame timings
   (median/p95/max). The real-browser profiler; run it on the target machine.
-- `bunx tsc --build tsconfig.app.json` — **typecheck the app+engine graph. Use
+- `bunx tsc --build tsconfig.app.json` — **typecheck the engine+game+app graph. Use
   this**, not `bun run check` (see Caveats).
-- `bunx oxlint engine app` — lint.
-- `bun test` — tests (none yet).
+- `bunx oxlint engine game app` — lint.
+- `bun test` — tests (registry id-order + engine↛game layering guards).
 - `bun run serve` — Bun server (`server/server.ts`, a stub for now).
 
 ## Layout
 
-- `engine/` — headless engine, consumed by `app/` via tsconfig project ref.
+- `engine/` — content-agnostic mechanism (no DOM, no game content); consumed by
+  `game/` then `app/` via tsconfig project refs.
   - `math/` — `Vec2`, `Vec3`, `Mat4` (column-major, OpenGL-style; verified).
   - `render/` — `Color` (packed RGBA, little-endian = canvas ImageData order),
     `Framebuffer` (Uint32 color + Float32 1/w depth; `quantize` = color-depth +
@@ -69,74 +76,70 @@ rules live in `.agents/rules/*.md`.
   - `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), `Terrain` (procedural
-    heightfield around the room: flat clearing in the center, rolling hills, tall
-    edge peaks. `Terrain.patch` builds one ground patch over a rectangle -- called
-    per chunk, aligned so patches weld crack-free, with a hole for the room;
-    `Terrain.height` is the shared ground-height sampler for the player), `Actor`
-    (the `Entity` interface — geometry + behavior + bounds — that each mob kind
-    implements), `Tree` (procedural low-poly oak/spruce/birch, sapling..full via a
-    `growth` knob; each species a `TreeSpecies` in `trees/<Kind>.ts`, assembled by a
-    registry — see the Trees section), `Boulder`
-    (procedural low-poly rock: a squashed, jittered, part-buried sphere;
-    `Boulder.build` appends into a shared mesh), `Bush` (cluster of small leaf
-    blobs, shares the oak leaf texture/mesh), `Flower` (thin stem + colored bloom;
-    samples a 2x2 color-atlas texture, drawn double-sided), `Mob` (a **roaming**
-    creature — `frog` hops the ground, `bee` hovers/darts, `robin` mostly hops but
-    now and then takes a short powered flight — the engine's only moving geometry.
-    Unlike the baked props, a mob's low-poly mesh is built once per kind in **local
-    space**; `Mob.build` bakes the canonical meshes, `Mob.update` steps the wander
-    AI (leashed to a home anchor, deterministic via an evolving per-mob seed) each
-    frame, and the live `position`/`heading`/`scale` become a per-frame model matrix
-    at draw time. New kinds extend the `MobKind` union + `MOB_KINDS` order).
-- `app/` — browser glue.
-  - `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
-    interval, visible chunks / LOD-aware tri count — the real profiler in play).
-    Also owns the **mob sim**: each frame it steps `Mob.update` for every mob,
-    rebuilds the near-player mob colliders into `level.colliders`, and culls the
-    mobs (`visibleMobs`) so only the visible transforms get dispatched.
-  - `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 it renders inline. `dispatch`/`done`
-    are non-blocking so the caller paces on rAF. Per-frame inputs ride shared
-    arrays: camera/matrix/visible-chunk list, plus the visible **mob transforms**
-    (`mobState`, count in the `MOBVIS` control slot). `?bench=st|mt` A/Bs the paths.
-  - `renderScene.ts` — `renderBand(fb, scene, …, mobDraws, …, y0, y1)`: the single
-    source of render truth (sky + room + culled chunks + 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 two canonical mob
-    meshes) so it clones to a worker whole; each mob is drawn double-sided through
-    its own `viewProj × Mat4.compose(...)` model matrix, and `visibleMobs`
-    frustum-culls the moving mobs per frame.
-  - `assets.ts` — load `/assets/*.png` → `Texture` (zero-copy; ImageData bytes
-    are already the `Color` layout).
+    (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
+  (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`
+    (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_COUNT`, `MOB_SEED`, `MOB_REACH` — mobs move,
-    so they carry 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`, where a `DrawGroup` is a baked
-    mesh + its `Material` = texture + cull; the renderer just loops them and knows no
-    content by name) that `main` frustum-culls; bushes fold into the leaf mesh,
-    flowers get their own (double-sided) group. Trees + boulders are baked **twice** —
-    full geometry into `near` and a low-poly impostor into `far` (via the builders'
-    `lod` arg) — so a far chunk swaps to the cheap group set with no per-frame work
-    (see `chunkFar` / `RenderConfig.lodDistance`). `buildLevel(textures)` binds the
-    ground/prop materials once and shares them across chunks. `Aabb` colliders (walls, crate, grown trunks, big
-    boulders), NPC position, `TERRAIN`/`TERRAIN_SUBDIV`/`GROUND_UV`, sky/cloud config. The stone floor is lifted by `FLOOR_LIFT` (a z-bias) so it
-    stays clean over the terrain skirt that laps under the room edges. Room surfaces
-    are single flat quads -- no subdivision needed since texturing is
-    perspective-correct.
-  - `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).
+    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).
+- `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.
+  - `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.
+  - `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
   `#fps` meter div (styled inline).
 - `scripts/gen-assets.ts` — procedurally draws the placeholder textures and
@@ -206,10 +209,10 @@ front-out — a culled mesh that renders inside-out has its index order flipped
   (well inside `fog.far`, so far detail is already fog-dimmed at the switch),
   `Infinity` on `clean` to disable LOD. Lower it for more headroom (more pop),
   raise it for more far detail (more tris).
-- **`app/level.ts` `GROUND_UV`** (0.25) — outdoor ground texture tiles per world
+- **`game/level.ts` `GROUND_UV`** (0.25) — outdoor ground texture tiles per world
   unit. Lower = the stone tiles bigger and less busy = less far-distance moire
   (there are no mipmaps); higher = finer but shimmerier.
-- **`app/level.ts` `CHUNK_GRID`** (12) / `TERRAIN_SUBDIV` (5) — spatial-cull
+- **`game/level.ts` `CHUNK_GRID`** (12) / `TERRAIN_SUBDIV` (5) — spatial-cull
   granularity and terrain resolution. World terrain divisions = `CHUNK_GRID *
   TERRAIN_SUBDIV`. Smaller cells cull tighter (draw less off-screen) but cost more
   per-cell tests/bounds. This is the lever if a dense world still lags.
@@ -272,12 +275,12 @@ by a `CloudLayer` discriminated union `kind`:
 - **`fancyCumulus`** — domain-warped + heightfield-shaded fake volume,
   ~5 lookups/pixel (pricier; watch the FPS meter).
 
-Both are exported presets in `app/level.ts`; the active one is set in
+Both are exported presets in `game/level.ts`; the active one is set in
 `buildLevel`'s `sky.clouds`. Add new cloud types by extending the union and
 branching in the cloud shader. Cost scales with sky resolution — fine at
 `standard`, heavy at `clean` (mitigate: fewer fbm octaves or half-res sky).
 
-## Trees (`engine/scene/Tree.ts` + `engine/scene/trees/`)
+## 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 +
@@ -298,13 +301,13 @@ 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. `app/level.ts`
+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`.
 
-**Boulders** (`engine/scene/Boulder.ts`) work the same way: `Boulder.build`
+**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
 never cracks) into one shared rock mesh, sunk partway into the ground.
 `scatterBoulders` sizes them small→big (biased small) and drops colliders on the
@@ -314,7 +317,7 @@ colliders; add a new prop type by cloning the pattern (generator + scatter).
 
 ## Controls
 
-WASD move · **Shift** run (speed ×`RUN_MULTIPLIER` in `app/player.ts`) · mouse
+WASD move · **Shift** run (speed ×`RUN_MULTIPLIER` 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.
diff --git a/README.md b/README.md
index 88e8e5d..7f80696 100644
--- a/README.md
+++ b/README.md
@@ -7,5 +7,15 @@
 
 Start to make cohesive game:
 
-- Split apart the "engine" and "game"
+- [x] Split apart the "engine" and "game"
+- `Level`
+  - Configurable everything
+  - Terrain
+  - Level editor?
+- Start thinking about MP
+- Fixes
+  - 1, 2, 3 stopped working
+  - "main.ts" is huge - separate it out. most of whats in here should be captured under the domain term "Client". ideally, architecturally aiming for the client consumes the game which consumes the engine.
+- Take HMR seriously, start building it in to the big changes
+
 
diff --git a/app/assets.ts b/app/assets.ts
index 9e67e17..ddf330f 100644
--- a/app/assets.ts
+++ b/app/assets.ts
@@ -1,4 +1,5 @@
 import type { Texture } from "../engine/render/Texture"
+import type { Textures } from "../game/textures"
 import barkUrl from "../assets/bark.png"
 import beeUrl from "../assets/bee.png"
 import birchUrl from "../assets/birch.png"
@@ -12,28 +13,12 @@ import needleUrl from "../assets/needle.png"
 import npcUrl from "../assets/npc.png"
 import robinUrl from "../assets/robin.png"
 import rockUrl from "../assets/rock.png"
+import skyboxUrl from "../assets/rockies.skybox.png"
 import wallUrl from "../assets/wall.png"
 
-export type 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
-}
-
 /** Load every game texture up front. Call once before starting the loop. */
 export async function loadTextures(): Promise<Textures> {
-  const [floor, grass, bark, birch, leaf, needle, rock, flower, wall, crate, npc, frog, bee, robin] = await Promise.all([
+  const [floor, grass, bark, birch, leaf, needle, rock, flower, wall, crate, npc, frog, bee, robin, skybox] = await Promise.all([
     loadTexture(floorUrl),
     loadTexture(grassUrl),
     loadTexture(barkUrl),
@@ -48,8 +33,9 @@ export async function loadTextures(): Promise<Textures> {
     loadTexture(frogUrl),
     loadTexture(beeUrl),
     loadTexture(robinUrl),
+    loadTexture(skyboxUrl),
   ])
-  return { floor, grass, bark, birch, leaf, needle, rock, flower, wall, crate, npc, frog, bee, robin }
+  return { floor, grass, bark, birch, leaf, needle, rock, flower, wall, crate, npc, frog, bee, robin, skybox }
 }
 
 function loadTexture(url: string): Promise<Texture> {
diff --git a/app/main.ts b/app/main.ts
index 0ded1be..2e320e6 100644
--- a/app/main.ts
+++ b/app/main.ts
@@ -1,13 +1,13 @@
 import { RenderConfig } from "../engine/render/RenderConfig"
 import { Camera } from "../engine/scene/Camera"
 import type { Mesh } from "../engine/scene/Mesh"
-import { Mob, MOB_KINDS, type MobKind } from "../engine/scene/Mob"
+import { Mob, MOB_KINDS, type MobKind } from "../game/actors/Mob"
 import type { Vec3 } from "../engine/math/Vec3"
 import { loadTextures } from "./assets"
-import { buildLevel, type Level } from "./level"
-import { EYE_HEIGHT, Player } from "./player"
+import { buildLevel, type Level } from "../game/level"
+import { EYE_HEIGHT, Player } from "../game/player"
 import { createRenderer } from "./renderer"
-import { chunkFar, visibleChunks, visibleMobs, type Scene } from "./renderScene"
+import { chunkFar, visibleChunks, visibleMobs, type Scene } from "../game/renderScene"
 
 const FOV_DEGREES = 75
 const FOV = (FOV_DEGREES * Math.PI) / 180
diff --git a/app/render-worker.ts b/app/render-worker.ts
index 50773c4..51e0575 100644
--- a/app/render-worker.ts
+++ b/app/render-worker.ts
@@ -1,7 +1,7 @@
 import type { Framebuffer } from "../engine/render/Framebuffer"
 import type { RenderConfig } from "../engine/render/RenderConfig"
-import { MOB_KINDS } from "../engine/scene/Mob"
-import { renderBand, MOB_FLOATS, type MobDraw, type Scene } from "./renderScene"
+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. */
diff --git a/app/renderer.ts b/app/renderer.ts
index 08b4af1..254a6f6 100644
--- a/app/renderer.ts
+++ b/app/renderer.ts
@@ -2,10 +2,11 @@ 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 "../engine/scene/Mob"
-import { renderBand, MOB_FLOATS, type MobDraw, type Scene } from "./renderScene"
+import { MOB_KINDS } from "../game/actors/Mob"
+import { renderBand, MOB_FLOATS, type MobDraw, type Scene } from "../game/renderScene"
 
-/** Sky is drawn at 1/SKY_STEP resolution; band splits align to it. */
+/** 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. */
 const SKY_STEP = 2
 /** Use worker threads when the page can share memory (else single-thread). */
 const ENABLE_WORKERS = true
diff --git a/assets/rockies.skybox.png b/assets/rockies.skybox.png
new file mode 100644
index 0000000..6cbadc6
Binary files /dev/null and b/assets/rockies.skybox.png differ
diff --git a/engine/render/RenderConfig.ts b/engine/render/RenderConfig.ts
index 6ae3df4..ed147f9 100644
--- a/engine/render/RenderConfig.ts
+++ b/engine/render/RenderConfig.ts
@@ -57,8 +57,8 @@ export type RenderConfig = {
  *  color depth, dither, vertex snap, and filtering from crunchy PS1 to clean. */
 export namespace RenderConfig {
   export const standard: RenderConfig = {
-    internalWidth: 640,
-    internalHeight: 360,
+    internalWidth: 384,
+    internalHeight: 216,
     upscaleFilter: "nearest",
     colorDepth: 5,
     dither: 1,
diff --git a/engine/render/Sky.ts b/engine/render/Sky.ts
index 58684dd..488b20e 100644
--- a/engine/render/Sky.ts
+++ b/engine/render/Sky.ts
@@ -2,6 +2,7 @@ import { Color } from "./Color"
 import type { Framebuffer } from "./Framebuffer"
 import { Camera } from "../scene/Camera"
 import { Vec3 } from "../math/Vec3"
+import { Texture } from "./Texture"
 
 /** Fields shared by every cumulus style. */
 export type CumulusBase = {
@@ -35,7 +36,18 @@ export type FancyCumulus = CumulusBase & {
  *  branching on `kind` in the cloud shader. */
 export type CloudLayer = BasicCumulus | FancyCumulus
 
-/** Procedural sky: a vertical gradient, a sun disc, and optional moving clouds. */
+/** An equirectangular panorama used as the sky's base color in place of the
+ *  vertical gradient. The sun glow and clouds still layer over it. Set it on
+ *  `SkyConfig.skybox` to switch a level over. */
+export type Skybox = {
+  texture: Texture
+  /** Azimuth offset in turns (0..1) to spin the panorama to taste. Default 0. */
+  yaw?: number
+}
+
+/** Procedural sky: a vertical gradient, a sun disc, and optional moving clouds.
+ *  If `skybox` is set, the panorama replaces the gradient base while the sun and
+ *  clouds still draw over it. */
 export type SkyConfig = {
   zenith: Color
   horizon: Color
@@ -45,9 +57,17 @@ export type SkyConfig = {
   /** Angular radius of the sun's core, in radians. */
   sunSize: number
   clouds: CloudLayer | null
+  /** Optional equirectangular panorama; when present, replaces the gradient
+   *  base color (sun + clouds still layer over it). */
+  skybox?: Skybox
 }
 
 const UP: Vec3 = { x: 0, y: 1, z: 0 }
+const INV_TAU = 1 / (2 * Math.PI)
+const INV_PI = 1 / Math.PI
+/** Keep equirect V a hair off the exact poles: Texture wraps V, so a ray pointing
+ *  straight up/down would otherwise blend the panorama's top row into its bottom. */
+const POLE_EPS = 1e-3
 
 export namespace Sky {
   /**
@@ -55,14 +75,16 @@ export namespace Sky {
    * frame in place of Framebuffer.clear; opaque geometry then overwrites the sky
    * wherever it is nearer. `time` (seconds) drives cloud motion.
    *
-   * Per pixel it reconstructs the view ray from the camera basis, shades a
-   * horizon->zenith gradient by the ray's elevation, brightens toward `sun` near
-   * `sunDir`, then lays crisp-edged cumulus over the top.
+   * Per pixel it reconstructs the view ray from the camera basis, shades the
+   * base (the equirect panorama if `sky.skybox` is set, else a horizon->zenith
+   * gradient), brightens toward `sun` near `sunDir`, then composites cumulus
+   * over the top.
    *
-   * `step` (>= 1) renders the sky at 1/step resolution: the expensive shading
-   * (the per-pixel cloud fbm dominates the frame) runs once per step x step
-   * block and is copied across it. The sky is low-frequency, so 2 is nearly free
-   * visually and quarters the cloud cost; 1 is full resolution.
+   * The base + sun are shaded per pixel so they stay crisp. `step` (>= 1) only
+   * lowers the *cloud* resolution: the cloud fbm dominates the frame, so it is
+   * sampled once per step x step block and composited across it. Clouds are
+   * low-frequency, so 2 is nearly free visually and quarters the cloud cost; 1
+   * is full cloud resolution.
    */
   export function render(fb: Framebuffer, camera: Camera, sky: SkyConfig, time: number, step = 1, y0 = 0, y1 = -1): void {
     const { width, height, color, depth } = fb
@@ -75,48 +97,78 @@ export namespace Sky {
     const sun = Vec3.normalize(sky.sunDir)
     const cosSun = Math.cos(sky.sunSize)
     const clouds = sky.clouds
+    const skybox = sky.skybox ?? null
+    const skyboxYaw = skybox?.yaw ?? 0
     const cloud: CloudSample = { cover: 0, shade: 1 }
     const s = Math.max(1, step | 0)
-    // Band `y0`..`bottom` must be step-aligned (callers ensure it) so the block
-    // grid stays global and neighboring bands don't seam.
+    // The cheap base (skybox/gradient + sun) is shaded per pixel so it stays
+    // crisp; only the pricey cloud fbm is amortized -- sampled once per `s`x`s`
+    // block and composited over every pixel in it. So `step` lowers cloud
+    // resolution, not the whole sky. Bands must be step-aligned (callers ensure
+    // it) so the cloud block grid stays global and neighboring bands don't seam.
     for (let by = y0; by < bottom; by += s) {
-      // Shade at the block center, then flood the whole block with that color.
-      const sampleY = Math.min(height - 1, by + (s >> 1))
-      const ndcY = 1 - ((sampleY + 0.5) / height) * 2
       const yEnd = Math.min(bottom, by + s)
+      // Block-center elevation, used only for the shared cloud sample.
+      const sampleY = Math.min(height - 1, by + (s >> 1))
+      const ndcYc = 1 - ((sampleY + 0.5) / height) * 2
       for (let bx = 0; bx < width; bx += s) {
-        const sampleX = Math.min(width - 1, bx + (s >> 1))
-        const ndcX = ((sampleX + 0.5) / width) * 2 - 1
-        // View ray = forward + right*ndcX*tanX + up*ndcY*tanY, then normalized.
-        let dx = forward.x + right.x * ndcX * tanX + up.x * ndcY * tanY
-        let dy = forward.y + right.y * ndcX * tanX + up.y * ndcY * tanY
-        let dz = forward.z + right.z * ndcX * tanX + up.z * ndcY * tanY
-        const inv = 1 / Math.hypot(dx, dy, dz)
-        dx *= inv
-        dy *= inv
-        dz *= inv
-        // dy is the ray elevation: 0 at the horizon, 1 straight up.
-        const t = Math.max(0, Math.min(1, dy))
-        let c = Color.lerp(sky.horizon, sky.zenith, t)
-        const facing = dx * sun.x + dy * sun.y + dz * sun.z
-        if (facing > cosSun) {
-          const glow = Math.min(1, ((facing - cosSun) / (1 - cosSun)) * 1.5)
-          c = Color.lerp(c, sky.sun, glow)
-        }
-        if (clouds !== null && dy > 0.02) {
-          if (clouds.kind === "fancy") {
-            fancyCumulus(dx, dy, dz, clouds, time, sun, cloud)
-          } else {
-            basicCumulus(dx, dy, dz, clouds, time, cloud)
-          }
-          if (cloud.cover > 0) {
-            c = Color.lerp(c, Color.scale(clouds.color, cloud.shade), cloud.cover)
-          }
-        }
         const xEnd = Math.min(width, bx + s)
+        // Sample the clouds once for the block, from the block-center ray.
+        const sampleX = Math.min(width - 1, bx + (s >> 1))
+        const ndcXc = ((sampleX + 0.5) / width) * 2 - 1
+        let cdx = forward.x + right.x * ndcXc * tanX + up.x * ndcYc * tanY
+        let cdy = forward.y + right.y * ndcXc * tanX + up.y * ndcYc * tanY
+        let cdz = forward.z + right.z * ndcXc * tanX + up.z * ndcYc * tanY
+        const cinv = 1 / Math.hypot(cdx, cdy, cdz)
+        cdx *= cinv
+        cdy *= cinv
+        cdz *= cinv
+        cloud.cover = 0
+        cloud.shade = 1
+        if (clouds !== null && cdy > 0.02) {
+          if (clouds.kind === "fancy") {
+            fancyCumulus(cdx, cdy, cdz, clouds, time, sun, cloud)
+          } else {
+            basicCumulus(cdx, cdy, cdz, clouds, time, cloud)
+          }
+        }
+        const cover = cloud.cover
+        const cloudColor = clouds !== null ? Color.scale(clouds.color, cloud.shade) : 0
+        // Per-pixel base: reconstruct this pixel's ray, shade the panorama (or
+        // gradient) + sun, then composite the block's shared cloud on top.
         for (let y = by; y < yEnd; y++) {
+          const ndcY = 1 - ((y + 0.5) / height) * 2
           const o = y * width
           for (let x = bx; x < xEnd; x++) {
+            const ndcX = ((x + 0.5) / width) * 2 - 1
+            let dx = forward.x + right.x * ndcX * tanX + up.x * ndcY * tanY
+            let dy = forward.y + right.y * ndcX * tanX + up.y * ndcY * tanY
+            let dz = forward.z + right.z * ndcX * tanX + up.z * ndcY * tanY
+            const inv = 1 / Math.hypot(dx, dy, dz)
+            dx *= inv
+            dy *= inv
+            dz *= inv
+            let c: Color
+            if (skybox !== null) {
+              // Equirectangular lookup: azimuth -> u (wraps at the seam, which
+              // Texture.sample handles), elevation -> v, clamped off the poles
+              // (Texture also wraps V, which would smear top into bottom).
+              const u = Math.atan2(dx, -dz) * INV_TAU + 0.5 + skyboxYaw
+              const lat = Math.acos(Math.max(-1, Math.min(1, dy))) * INV_PI
+              const v = Math.min(1 - POLE_EPS, Math.max(POLE_EPS, lat))
+              c = Texture.sample(skybox.texture, u, v, "linear")
+            } else {
+              // dy is the ray elevation: 0 at the horizon, 1 straight up.
+              c = Color.lerp(sky.horizon, sky.zenith, Math.max(0, Math.min(1, dy)))
+            }
+            const facing = dx * sun.x + dy * sun.y + dz * sun.z
+            if (facing > cosSun) {
+              const glow = Math.min(1, ((facing - cosSun) / (1 - cosSun)) * 1.5)
+              c = Color.lerp(c, sky.sun, glow)
+            }
+            if (cover > 0) {
+              c = Color.lerp(c, cloudColor, cover)
+            }
             color[o + x] = c
             depth[o + x] = 0
           }
diff --git a/engine/scene/Terrain.ts b/game/Terrain.ts
similarity index 98%
rename from engine/scene/Terrain.ts
rename to game/Terrain.ts
index d1de1ec..b38e6a9 100644
--- a/engine/scene/Terrain.ts
+++ b/game/Terrain.ts
@@ -1,4 +1,4 @@
-import { STRIDE, type Mesh } from "./Mesh"
+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
diff --git a/engine/scene/Boulder.ts b/game/actors/Boulder.ts
similarity index 96%
rename from engine/scene/Boulder.ts
rename to game/actors/Boulder.ts
index e71c869..7d412f6 100644
--- a/engine/scene/Boulder.ts
+++ b/game/actors/Boulder.ts
@@ -1,5 +1,5 @@
-import type { Vec3 } from "../math/Vec3"
-import { STRIDE, type Mesh } from "./Mesh"
+import type { Vec3 } from "../../engine/math/Vec3"
+import { STRIDE, type Mesh } from "../../engine/scene/Mesh"
 
 const TAU = Math.PI * 2
 
diff --git a/engine/scene/Bush.ts b/game/actors/Bush.ts
similarity index 95%
rename from engine/scene/Bush.ts
rename to game/actors/Bush.ts
index c55442d..c8fd73e 100644
--- a/engine/scene/Bush.ts
+++ b/game/actors/Bush.ts
@@ -1,5 +1,5 @@
-import type { Vec3 } from "../math/Vec3"
-import { STRIDE, type Mesh } from "./Mesh"
+import type { Vec3 } from "../../engine/math/Vec3"
+import { STRIDE, type Mesh } from "../../engine/scene/Mesh"
 
 const TAU = Math.PI * 2
 
diff --git a/engine/scene/Flower.ts b/game/actors/Flower.ts
similarity index 96%
rename from engine/scene/Flower.ts
rename to game/actors/Flower.ts
index e154e8b..6a13cc7 100644
--- a/engine/scene/Flower.ts
+++ b/game/actors/Flower.ts
@@ -1,5 +1,5 @@
-import type { Vec3 } from "../math/Vec3"
-import { Mesh } from "./Mesh"
+import type { Vec3 } from "../../engine/math/Vec3"
+import { Mesh } from "../../engine/scene/Mesh"
 
 const TAU = Math.PI * 2
 
diff --git a/engine/scene/Mob.ts b/game/actors/Mob.ts
similarity index 94%
rename from engine/scene/Mob.ts
rename to game/actors/Mob.ts
index 4b75469..29b3487 100644
--- a/engine/scene/Mob.ts
+++ b/game/actors/Mob.ts
@@ -1,7 +1,7 @@
-import type { Terrain } from "./Terrain"
-import type { Vec3 } from "../math/Vec3"
-import type { Mesh } from "./Mesh"
-import type { Entity } from "./Actor"
+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"
diff --git a/engine/scene/Tree.ts b/game/actors/Tree.ts
similarity index 95%
rename from engine/scene/Tree.ts
rename to game/actors/Tree.ts
index d509d5a..9c6751b 100644
--- a/engine/scene/Tree.ts
+++ b/game/actors/Tree.ts
@@ -1,5 +1,5 @@
-import type { Vec3 } from "../math/Vec3"
-import type { Mesh } from "./Mesh"
+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"
diff --git a/engine/scene/mobs/Bee.ts b/game/actors/mobs/Bee.ts
similarity index 79%
rename from engine/scene/mobs/Bee.ts
rename to game/actors/mobs/Bee.ts
index 0e1f236..82d3e8d 100644
--- a/engine/scene/mobs/Bee.ts
+++ b/game/actors/mobs/Bee.ts
@@ -1,10 +1,16 @@
-import { Terrain } from "../Terrain"
-import type { Mesh } from "../Mesh"
+import { Terrain } from "../../Terrain"
+import type { Mesh } from "../../../engine/scene/Mesh"
 import type { Mob } from "../Mob"
-import type { Entity } from "../Actor"
+import type { Entity } from "../../../engine/scene/Actor"
 import { ellipsoid, nextRand, ovoidZ, wanderHeading, wing } from "./mobkit"
 
-// Everything about the bee: small, hovers and darts through the air, wings out.
+export const bee: Entity<Mob, Terrain> = {
+  name: "bee",
+  build,
+  update,
+  boundingRadius: 0.5,
+  bodyHeight: 0.5,
+}
 
 const LEASH = 6
 const SPEED = 1.7
@@ -36,5 +42,3 @@ function update(mob: Mob, dt: number, terrain: Terrain): void {
   const ground = Terrain.height(terrain, mob.position.x, mob.position.z)
   mob.position.y = ground + HOVER + Math.sin(mob.phase * BOB_FREQ) * BOB_AMP
 }
-
-export const bee: Entity<Mob, Terrain> = { name: "bee", build, update, boundingRadius: 0.5, bodyHeight: 0.5 }
diff --git a/engine/scene/mobs/Frog.ts b/game/actors/mobs/Frog.ts
similarity index 86%
rename from engine/scene/mobs/Frog.ts
rename to game/actors/mobs/Frog.ts
index c144c01..a703fa8 100644
--- a/engine/scene/mobs/Frog.ts
+++ b/game/actors/mobs/Frog.ts
@@ -1,11 +1,19 @@
-import { Terrain } from "../Terrain"
-import type { Mesh } from "../Mesh"
+import { Terrain } from "../../Terrain"
+import type { Mesh } from "../../../engine/scene/Mesh"
 import type { Mob } from "../Mob"
-import type { Entity } from "../Actor"
+import type { Entity } from "../../../engine/scene/Actor"
 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,
+}
+
 const LEASH = 5
 const REST_MIN = 0.7
 const REST_SPAN = 1.8
@@ -53,5 +61,3 @@ function update(mob: Mob, dt: number, terrain: Terrain): void {
     mob.timer = REST_MIN + nextRand(mob) * REST_SPAN
   }
 }
-
-export const frog: Entity<Mob, Terrain> = { name: "frog", build, update, boundingRadius: 0.7, bodyHeight: 0.6 }
diff --git a/engine/scene/mobs/Robin.ts b/game/actors/mobs/Robin.ts
similarity index 91%
rename from engine/scene/mobs/Robin.ts
rename to game/actors/mobs/Robin.ts
index e7e6846..3a01f60 100644
--- a/engine/scene/mobs/Robin.ts
+++ b/game/actors/mobs/Robin.ts
@@ -1,12 +1,20 @@
-import { Terrain } from "../Terrain"
-import type { Mesh } from "../Mesh"
+import { Terrain } from "../../Terrain"
+import type { Mesh } from "../../../engine/scene/Mesh"
 import type { Mob } from "../Mob"
-import type { Entity } from "../Actor"
+import type { Entity } from "../../../engine/scene/Actor"
 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,
+}
+
 const LEASH = 6
 const REST_MIN = 0.5
 const REST_SPAN = 1.3
@@ -74,5 +82,3 @@ function update(mob: Mob, dt: number, terrain: Terrain): void {
     mob.timer = REST_MIN + nextRand(mob) * REST_SPAN
   }
 }
-
-export const robin: Entity<Mob, Terrain> = { name: "robin", build, update, boundingRadius: 0.45, bodyHeight: 0.55 }
diff --git a/engine/scene/mobs/mobkit.ts b/game/actors/mobs/mobkit.ts
similarity index 98%
rename from engine/scene/mobs/mobkit.ts
rename to game/actors/mobs/mobkit.ts
index 6a1deac..3127ebe 100644
--- a/engine/scene/mobs/mobkit.ts
+++ b/game/actors/mobs/mobkit.ts
@@ -1,5 +1,5 @@
 import type { Mob } from "../Mob"
-import { STRIDE, type Mesh } from "../Mesh"
+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
diff --git a/engine/scene/trees/Birch.ts b/game/actors/trees/Birch.ts
similarity index 95%
rename from engine/scene/trees/Birch.ts
rename to game/actors/trees/Birch.ts
index 6032d4e..00eeba3 100644
--- a/engine/scene/trees/Birch.ts
+++ b/game/actors/trees/Birch.ts
@@ -1,5 +1,5 @@
-import { Vec3 } from "../../math/Vec3"
-import type { Mesh } from "../Mesh"
+import { Vec3 } from "../../../engine/math/Vec3"
+import type { Mesh } from "../../../engine/scene/Mesh"
 import type { Tree, TreeSpecies } from "../Tree"
 import { blob, lerp, limb, TAU, rng } from "./treekit"
 
@@ -7,6 +7,8 @@ import { blob, lerp, limb, TAU, rng } from "./treekit"
 // 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 }
+
 function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"): void {
   const base = tree.position
   const g = tree.growth
@@ -48,5 +50,3 @@ function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"):
     }
   }
 }
-
-export const birch: TreeSpecies = { kind: "birch", trunk: "birch", foliage: "leaf", build }
diff --git a/engine/scene/trees/Oak.ts b/game/actors/trees/Oak.ts
similarity index 95%
rename from engine/scene/trees/Oak.ts
rename to game/actors/trees/Oak.ts
index c57fdfd..a6e7888 100644
--- a/engine/scene/trees/Oak.ts
+++ b/game/actors/trees/Oak.ts
@@ -1,11 +1,13 @@
-import { Vec3 } from "../../math/Vec3"
-import type { Mesh } from "../Mesh"
+import { Vec3 } from "../../../engine/math/Vec3"
+import type { Mesh } from "../../../engine/scene/Mesh"
 import type { Tree, TreeSpecies } 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 }
+
 function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"): void {
   const base = tree.position
   const g = tree.growth
@@ -49,5 +51,3 @@ function build(tree: Tree, trunk: Mesh, leaves: Mesh, lod: "full" | "impostor"):
     }
   }
 }
-
-export const oak: TreeSpecies = { kind: "oak", trunk: "bark", foliage: "leaf", build }
diff --git a/engine/scene/trees/Spruce.ts b/game/actors/trees/Spruce.ts
similarity index 95%
rename from engine/scene/trees/Spruce.ts
rename to game/actors/trees/Spruce.ts
index 57fac37..e7a2286 100644
--- a/engine/scene/trees/Spruce.ts
+++ b/game/actors/trees/Spruce.ts
@@ -1,10 +1,12 @@
-import type { Mesh } from "../Mesh"
+import type { Mesh } from "../../../engine/scene/Mesh"
 import type { Tree, TreeSpecies } 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 }
+
 function build(tree: Tree, trunk: Mesh, needles: Mesh, lod: "full" | "impostor"): void {
   const base = tree.position
   const g = tree.growth
@@ -28,5 +30,3 @@ function build(tree: Tree, trunk: Mesh, needles: Mesh, lod: "full" | "impostor")
     cone(needles, { x: base.x, y, z: base.z }, coneH, radius, sides)
   }
 }
-
-export const spruce: TreeSpecies = { kind: "spruce", trunk: "bark", foliage: "needle", build }
diff --git a/engine/scene/trees/treekit.ts b/game/actors/trees/treekit.ts
similarity index 96%
rename from engine/scene/trees/treekit.ts
rename to game/actors/trees/treekit.ts
index 3d62674..27e2e09 100644
--- a/engine/scene/trees/treekit.ts
+++ b/game/actors/trees/treekit.ts
@@ -1,5 +1,5 @@
-import { Vec3 } from "../../math/Vec3"
-import { STRIDE, type Mesh } from "../Mesh"
+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
diff --git a/app/level.ts b/game/level.ts
similarity index 96%
rename from app/level.ts
rename to game/level.ts
index 5092fdb..a4780af 100644
--- a/app/level.ts
+++ b/game/level.ts
@@ -2,13 +2,13 @@ import { Color } from "../engine/render/Color"
 import type { DrawGroup, Material } from "../engine/render/Material"
 import type { CloudLayer, SkyConfig } from "../engine/render/Sky"
 import { STRIDE, type Mesh } from "../engine/scene/Mesh"
-import { Boulder } from "../engine/scene/Boulder"
-import { Bush } from "../engine/scene/Bush"
-import { Flower, type FlowerColor } from "../engine/scene/Flower"
-import type { Mob, MobKind } from "../engine/scene/Mob"
-import { Terrain } from "../engine/scene/Terrain"
-import { Tree } from "../engine/scene/Tree"
-import type { Textures } from "./assets"
+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 type { Textures } from "./textures"
 
 type Corner = [number, number, number]
 
@@ -98,11 +98,11 @@ const FLOOR_LIFT = 0.02
  *  `outer` for a bigger world. */
 const TERRAIN: Terrain = {
   inner: ARENA,
-  outer: ARENA * 20,
+  outer: ARENA * 10,
   blend: 12,
   amplitude: 5,
   frequency: 0.14,
-  peakHeight: 90,
+  peakHeight: 0,
   peakFrequency: 0.05,
   peakStart: 0.45,
 }
@@ -110,22 +110,22 @@ const TERRAIN: Terrain = {
 /** 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 = 500
+const TREE_COUNT = 50
 const TREE_SEED = 0x5EED
-const TREE_REACH = 0.6
+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 = 70
+const BOULDER_COUNT = 50
 const BOULDER_SEED = 0xB0142
-const BOULDER_REACH = 0.7
+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 = 140
+const BUSH_COUNT = 50
 const BUSH_SEED = 0xB554
-const BUSH_REACH = 0.35
-const FLOWER_COUNT = 340
+const BUSH_REACH = 1
+const FLOWER_COUNT = 50
 const FLOWER_SEED = 0xF10E
 const FLOWER_REACH = 0.3
 const FLOWER_COLORS: FlowerColor[] = ["white", "red", "yellow"]
@@ -133,11 +133,11 @@ 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 FROG_COUNT = 40
-const BEE_COUNT = 30
-const ROBIN_COUNT = 30
+const FROG_COUNT = 20
+const BEE_COUNT = 20
+const ROBIN_COUNT = 20
 const MOB_SEED = 0x30B
-const MOB_REACH = 0.5
+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
@@ -214,7 +214,8 @@ export function buildLevel(textures: Textures): Level {
     sun: Color.rgb(255, 246, 214),
     sunDir: { x: 0.3, y: 0.5, z: -0.8 },
     sunSize: 0.04,
-    clouds: basicCumulus,
+    clouds: fancyCumulus,
+    skybox: { texture: textures.skybox },
   }
 
   const npcPosition = { x: 2, y: 0, z: -1 }
diff --git a/app/player.ts b/game/player.ts
similarity index 99%
rename from app/player.ts
rename to game/player.ts
index 32a6130..f45d376 100644
--- a/app/player.ts
+++ b/game/player.ts
@@ -1,4 +1,4 @@
-import { Terrain } from "../engine/scene/Terrain"
+import { Terrain } from "./Terrain"
 import type { Vec3 } from "../engine/math/Vec3"
 import type { Aabb, Level } from "./level"
 
diff --git a/app/renderScene.ts b/game/renderScene.ts
similarity index 98%
rename from app/renderScene.ts
rename to game/renderScene.ts
index e7cde7d..96b0d7e 100644
--- a/app/renderScene.ts
+++ b/game/renderScene.ts
@@ -6,11 +6,11 @@ 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 "../engine/scene/Mob"
+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 "./assets"
+import type { Textures } from "./textures"
 import type { Chunk } from "./level"
 
 /** Everything needed to render the world: the room, the cullable chunks, the NPC
diff --git a/game/textures.ts b/game/textures.ts
new file mode 100644
index 0000000..b970e1e
--- /dev/null
+++ b/game/textures.ts
@@ -0,0 +1,23 @@
+import type { Texture } from "../engine/render/Texture"
+
+/** The game's texture palette -- the named surfaces content refers to (materials,
+ *  mobs, room). `app/assets.ts` loads the actual pixels via the DOM; this is the
+ *  shape both sides agree on, kept in `game/` so content never imports the browser
+ *  loader. Filenames in `/assets` are the contract. */
+export type 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
+}
diff --git a/tests/layering.test.ts b/tests/layering.test.ts
new file mode 100644
index 0000000..b6cefe5
--- /dev/null
+++ b/tests/layering.test.ts
@@ -0,0 +1,32 @@
+import { expect, test } from "bun:test"
+import { readdirSync, readFileSync, statSync } from "node:fs"
+import { join } 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
+// fine; the reverse is the violation. This freezes the Stage-3 seam so a stray import
+// can't quietly re-couple the layers.
+function tsFiles(dir: string): string[] {
+  const out: string[] = []
+  for (const name of readdirSync(dir)) {
+    const p = join(dir, name)
+    if (statSync(p).isDirectory()) {
+      out.push(...tsFiles(p))
+    } else if (p.endsWith(".ts")) {
+      out.push(p)
+    }
+  }
+  return out
+}
+
+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")))
+  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")))
+  expect(offenders).toEqual([])
+})
diff --git a/tests/mobs.test.ts b/tests/mobs.test.ts
index d097a9f..89b5344 100644
--- a/tests/mobs.test.ts
+++ b/tests/mobs.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "bun:test"
-import { MOB_KINDS, Mob } from "../engine/scene/Mob"
+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,
diff --git a/tests/trees.test.ts b/tests/trees.test.ts
index c550675..5056cf8 100644
--- a/tests/trees.test.ts
+++ b/tests/trees.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "bun:test"
-import { Tree, TREE_KINDS } from "../engine/scene/Tree"
+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
diff --git a/tsconfig.app.json b/tsconfig.app.json
index cf173ba..a39dc5c 100644
--- a/tsconfig.app.json
+++ b/tsconfig.app.json
@@ -1,7 +1,8 @@
 {
   "extends": "./tsconfig.base.json",
   "references": [
-    { "path": "./tsconfig.engine.json" }
+    { "path": "./tsconfig.engine.json" },
+    { "path": "./tsconfig.game.json" }
   ],
   "compilerOptions": {
     "composite": true,
diff --git a/tsconfig.game.json b/tsconfig.game.json
new file mode 100644
index 0000000..4577985
--- /dev/null
+++ b/tsconfig.game.json
@@ -0,0 +1,12 @@
+{
+  "extends": "./tsconfig.base.json",
+  "references": [
+    { "path": "./tsconfig.engine.json" }
+  ],
+  "compilerOptions": {
+    "composite": true
+  },
+  "include": [
+    "game"
+  ]
+}
diff --git a/tsconfig.json b/tsconfig.json
index 02330e4..3870bbf 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -10,6 +10,9 @@
     {
       "path": "./tsconfig.engine.json"
     },
+    {
+      "path": "./tsconfig.game.json"
+    },
     {
       "path": "./tsconfig.app.json"
     },