feat: boulders

AGENTS.md

@@ -58,7 +58,9 @@ rules live in `.agents/rules/*.md`.
     edge peaks. `Terrain.ground` builds the outdoor mesh with a hole for the room;
     `Terrain.height` is the shared ground-height sampler for the player), `Tree`
     (procedural low-poly oak/spruce geometry, sapling..full via a `growth` knob;
-    `Tree.build` appends into shared trunk + foliage meshes).
+    `Tree.build` appends into shared trunk + foliage meshes), `Boulder`
+    (procedural low-poly rock: a squashed, jittered, part-buried sphere;
+    `Boulder.build` appends into a shared mesh).
 - `app/` — browser glue.
   - `main.ts` — game loop, input, preset switching, canvas blit, FPS meter.
   - `assets.ts` — load `/assets/*.png` → `Texture` (zero-copy; ImageData bytes
@@ -66,10 +68,11 @@ rules live in `.agents/rules/*.md`.
   - `level.ts` — builds the playground: a flat stone-floored room (three thick
     walls via `slab`, north side open) in the center of a big grassy `Terrain`
     world (~20x across).
-    Per-texture meshes incl. the outdoor grass `ground` and a scattered forest
+    Per-texture meshes incl. the outdoor grass `ground`, a scattered forest
     (`scatterTrees` → `trunks`/`oakFoliage`/`spruceFoliage`, `TREE_COUNT`/`_SEED`/
-    `_REACH`), `Aabb` colliders (incl. grown-tree trunks), NPC position, `Terrain`
-    config + `GROUND_DIVISIONS`/`GROUND_UV`, sky/cloud config.
+    `_REACH`) and `boulders` (`scatterBoulders`, `BOULDER_COUNT`/`_SEED`/`_REACH`),
+    `Aabb` colliders (incl. grown-tree trunks + big boulders), NPC position,
+    `Terrain` config + `GROUND_DIVISIONS`/`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; ground
@@ -83,9 +86,9 @@ rules live in `.agents/rules/*.md`.
   `#fps` meter div (styled inline).
 - `scripts/gen-assets.ts` — procedurally draws the placeholder textures and
   writes PNGs (hand-rolled encoder via `node:zlib`). Run via `bun run assets`.
-- `assets/` — generated `floor/grass/bark/leaf/needle/wall/crate/npc` PNGs
+- `assets/` — generated `floor/grass/bark/leaf/needle/rock/wall/crate/npc` PNGs
   (`floor` = room stone, `grass` = outdoor ground, `bark`/`leaf`/`needle` = tree
-  trunk/oak/spruce). Swap for real art anytime;
+  trunk/oak/spruce, `rock` = boulders). Swap for real art anytime;
   filenames are the contract.
 - `server/` — Bun server stub. `shared/` — isomorphic slot.
 
@@ -93,8 +96,8 @@ rules live in `.agents/rules/*.md`.
 
 `Player.update` → build `Camera` → `Camera.viewProjection` →
 `Sky.render` (fills color + resets depth, replaces a clear) →
-`Rasterizer.draw` ground, floor, walls, crate, tree trunks, oak foliage, spruce
-foliage (one call per texture) →
+`Rasterizer.draw` ground, floor, walls, crate, boulders, tree trunks, oak
+foliage, spruce foliage (one call per texture) →
 `Sprite.billboard(npc)` drawn via `Rasterizer.draw` →
 `Framebuffer.quantize` → `present` (integer-scale, letterboxed blit;
 `imageSmoothingEnabled` follows `upscaleFilter`).
@@ -152,6 +155,12 @@ canopy blobs (oak) / tiers (spruce); `seed` gives each tree its own wobble.
 (one bark trunk mesh, oak-leaf and spruce-needle foliage meshes). `app/level.ts`
 `scatterTrees` seeds the forest; add a species by extending the union + a builder.
 
+**Boulders** (`engine/scene/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
+big ones.
+
 ## Controls
 
 WASD move · **Shift** run (speed ×`RUN_MULTIPLIER` in `app/player.ts`) · mouse