Capability ceiling what the agent cannot author and the in-envelope fallback

When to use

Read this before promising anything that sounds like arbitrary-code rendering (voxels, custom shaders, hand-built meshes, rigged animation). The typed surface takes the agent FARTHER than raw code for game systems (netcode, physics, persistence, mobs, UI, audio) but LESS far for a few raw content primitives. Those few are listed here with the substitute that IS expressible. Each is a redirect, not a dead end: design to the fallback and the request ships.

The five ceilings and what to use instead

1. Per-voxel / blocky mineable terrain at scale is not authorable. Use instead: procedural HEIGHTFIELD terrain (terrain.patch.apply generate, biome, erosion, scatter, then terrain.artifacts.build; see terrain-and-heightmaps). For a truly blocky world the only path is instantiating the voxel_frontier template WHOLE at project creation (project_create_game creationIntent { mode:"template", templateId:"voxel_frontier" }); it cannot be edited as typed capabilities afterward and per-block entities breach the 1000-entity/collider runtime cap (runtimePolicies maxEntitiesPerTick). Do not attempt per-block set/place ops or spawn thousands of block entities; both fail-closed or stall physics.

2. Raw vertex/index buffers and marching-cubes meshes are not authorable. Use instead: parametric primitives plus CSG booleans through model_save (box/sphere/cylinder/capsule/cone/torus/plane, union/subtract/intersect; see model-authoring-parametric-csg), OR import a gltf/glb/obj asset (primitiveType: "imported"), OR take a fitting mesh from the catalog. There is no vertex-array field anywhere; RenderableComponent.shape is a fixed enum (box, sphere, disc, capsule, billboard, mesh, plane).

3. Custom shader code (WGSL/GLSL) is rejected by design. Use instead: the twelve ai_safe PBR ops (base color, metallic, roughness, emissive, alpha, double-sided, texture slots; see materials-and-looks). Any key like shaderSource, wgsl, glsl, rawShader, fragmentShader, vertexShader triggers raw_shader_source_forbidden. Never emit shader strings.

4. Procedural material networks beyond the small node catalog are not expressible. The graph ops themselves (addCatalogNode, connectSockets, disconnectEdge, setNodeParameter and friends) ARE ai_safe, the same alphabet the visual editor gets (authoring symmetry); only replaceGraph stays import-only, and trustedOnly nodes (trusted.shader.plugin) are rejected for every normal source. The ceiling is the CATALOG: an OpenPBR surface, output, color and float constants, texture sample, water depth, scalar math, color mix, and procedural noise. A look those nodes cannot express (custom lighting response, stylized ramps) is out of reach; for most looks the twelve PBR ops stay the shorter path (see materials-and-looks).

5. Skeletal animation authoring beyond clip playback is not expressible. Use instead: AnimationStateComponent to PLAY a named clip off a rigged imported model (clipKey, playMode loop/once/ping-pong, speed, startTime), plus transform animation authored as a TimerComponent firing a handler that patches a TransformComponent (bob, spin, scale). You cannot author or blend new skeletal clips; a walk cycle needs an imported rigged asset that already carries the clip.

Related runtime ceilings

• Runtime block place/mine works only at SMALL N: ctx.world.spawn/despawn of entities under the 1000-entity/collider cap. A dozen placeable blocks is fine; a mineable voxel field is not.
• Instanced rendering is not a direct AI authoring primitive EXCEPT terrain scatter foliage, which bakes a foliage_instance_buffer the renderer instances. Scatter renders real geometry ONLY for the grass/tall_grass (blade tufts) and rock/boulder (deformed stone) keys; every other foliageKey, tree and flower keys included, renders as a small placeholder cone today (the terrainDetailGeometry fallback), and there is no mesh-backed scatter. Use scatter for grass and rock ground cover; a tree line is a modest number of placed model entities under the entity/collider cap, and do not spawn thousands of entities to fake instancing.
• Water is planar only (WaterComponent); there is no volumetric fluid or lava component. Approximate lava with a recolored water surface plus an emissive PBR material and a damage script.

How to respond when a request exceeds the ceiling

Name the limit in one sentence, propose the in-envelope design, and build that. Do not loop retrying a rejected op, and do not invent a tool name (there is no set_voxel, no create_shader, no author_animation). A first-person survival world with procedural terrain, mobs, inventory, health, day-night, server-authoritative multiplayer, persistence, sound, and particles is fully expressible; lead with that.

Verify

• If unsure whether a capability exists, engine_list_component_types and engine_get_component_schema show the real component surface, and the action catalog shows the real tools. Absence there is the ceiling; trust it.