# asset_change_dispatch (module) Installs `_G.__zero_dispatch_asset_change`, the Luau half of the asset-type **change-callback** system. The engine calls it once per VFS source write (via `zero_scripting::ffi_callbacks::fire_asset_change_dispatch`, queued as `VfsMutation::AssetSourceWritten`). ## What it does 1. Receives the written VFS path. 2. Walks up the path to the enclosing `<name>.<type>/` typed-asset folder (deepest registered-type suffix wins, so the direct owner of the write is chosen for nested typed assets). 3. Loads that type's `<type>.assetType/behavior.luau` via `@builtin::assetTypes.assetType.shared.ref.loadTypeModule`. 4. If the module exports an `onChange` function, calls `onChange(ref, change)` where `ref` is the typed `AssetRef` for the changed asset and `change = { path, asset, type }`. The engine runs each dispatch as its own yieldable task, so a hook can wait on what it reads: a `vfs.read` of bytes only the blob store holds (a binary file on the web build) fetches them. A hook that reads only what is resident finishes inside the dispatch that started it. The writes routed to one asset react in the order they were routed: a write routed while that asset's hook is waiting queues behind it and reacts once the hook has finished. This is the type-level analogue of the component-centric `onAssetReload(field)` fan-out: components react to assets they *reference*; an asset *type* reacts to writes inside its own *instances*. ## The source-write seam A write inside a typed asset is also offered to the importer type's shared layer (`onAssetWrite(assetPath, path, origin)`), the way a write with no enclosing asset is offered to `onLooseWrite`. The asset's `import` record names the file it was imported from (by guid and path); a write to that file re-runs the importers on it, in place; the write that arrived is the only input. A type whose own `onChange` already keeps its retained source current (a texture re-encoding its image, a sound clip its audio) sets `reencodesRetainedSource = true` on its module, and the seam leaves that edit to it. ## Re-entrancy While an asset's `onChange` runs, a dispatch for that same asset made from the hook's own coroutine is suppressed, so a handler that routes a write back into its own folder inline doesn't recurse. A write the hook makes is routed on a later frame like any other and reaches `onChange` again once the hook has finished. `onChange` handlers must therefore be **convergent**: diff the meaningful state before acting and short-circuit when there's nothing to do (the `dynamicAsset` example only regenerates when the prompt actually changed and bails while a generation is in flight). Idempotency is the contract, exactly as it is for services' `start`/`stop`. ## Related - `@builtin::assetTypes.assetType.shared.ref` — owns `loadTypeModule` + the per-type `ref` method dispatch. - `assetTypes/assetType.assetType/template/behavior.luau` — the documented template that shows how to author `ref`, `global`, and `onChange`. - `assetTypes/dynamicAsset.assetType` — the reference type that uses `onChange` for prompt-driven regeneration with version control.

# asset_create `asset.create` — the single, generic "instance a new asset of an existing type" API. The same entry point scripts and agents use; there is deliberately no tool wrapper, because agents author in Luau and call `asset.create(...)` directly. ```lua local inst = asset.create("material", "my_metal", { base_color = { 0.8, 0.7, 0.2 } }) -- → AssetRef: inst.path == "/zero/source/my_metal.material", inst.guid, plus the -- material type's ref methods. ``` `asset.create` makes a new *instance of an already-registered type* by running that type's `onCreate(name, opts)` behaviour hook (declared in its `behavior.luau`) and writing the produced files to `/zero/source/<name>.<typeName>/` — the one authored location, in every mode. While play runs, the play-mode write lock takes that write onto the **play shadow**: live in the session, listed by `vfs.playShadowPaths()`, and promoted or discarded on a guarded play-exit. The asset created in play therefore carries the same identity, path and `require` spelling it has in edit, and the session decides whether it stays. A create whose output the world **reproduces** on every load — one made from a component or a scene entrypoint — writes to the copy-on-write runtime store at `/zero/runtime/assets/<identity>.<typeName>/` instead, so the code that rebuilds it each load is its only source and the saved manifest never carries a second copy. ## Placement Four `opts` keys are consumed by the framework before the type's `onCreate` hook runs, and steer where the instance lands: | Key | Effect | |-----|--------| | `folder` | A relative subfolder under the source root: `/zero/source/<folder>/<name>.<typeName>/`. Groups a generator's output instead of accumulating it at the source root. | | `into` | A resolved container ref (`.toolbox` / `.package`) to author INSIDE — lands at `<container>/<name>.<typeName>/` and registers as a member. Edit-mode only. | | `dest` | An absolute destination path, owned by the caller (an importer building a `<name>.bundle/`). | | `overwrite` | Re-author an existing destination in place, keeping its `.meta` guid so every reference stays valid. | The `name` is always the asset's bare identity — the path goes in `folder`: ```lua local rock = asset.create("mesh", "rock", { positions = p, indices = i, folder = "terrain/props" }) -- → rock.path == "/zero/source/terrain/props/rock.mesh" ``` `dest` and `into` both take precedence over `folder`. `folder` decides the asset's identity, so it applies in every context: the runtime store is flat and spells that identity in one folder name. ```lua -- the same call from a component's awake() -- → rock.path == "/zero/runtime/assets/terrain.props.rock.mesh" -- → rock.identity == "terrain.props.rock", as it is from an execute ``` Types without an `onCreate` hook fall back to cloning their verbatim `template/` skeleton to the same destination, so `create` works for every type. Returns the created asset's `AssetRef` (`.path` / `.guid` plus the type's ref methods — the same interned instance `asset.resolve` returns) on success and raises (via `error`) on bad arguments or a failing `onCreate`. Installed onto the FFI `asset` namespace by the prelude (`M.installInto(asset)`). See `docs/specs/runtime-asset-copying.md`.

# declaration (module) A type's `type.yaml`, decoded and held: the one reader behind every question about a type as a whole — its files, whether it broadcasts its subassets, how its instances are pictured. ## Exports - `M.of(typeName) -> table?` — the decoded declaration, or nil when no type answers to the name, it has no `type.yaml`, or the file does not decode (the last with a warning naming the type). Shared: read it, do not write to it. - `M.forget()` — drop every held declaration. The change dispatcher calls it for every write inside an `.assetType` folder and for every removed type.

# asset_events Per-asset runtime for declared asset events. An assetType's `behavior.luau` declares an `events` schema the same way a component declares one; this module turns that schema into the live objects an asset's ref fires and listens on. ## Three faces, one Signal — keyed by the asset The construction is `component_events`': one `Signal` per declared event, reachable through a private fire-capable table, an owner-side emitter the type's own behavior fires with, and a subscribe-only facade every other holder of the ref sees. The facade exposes `connect` / `once` / `wait` and has no `fire` at any key, so firing authority stays with the type. What differs is the owner. A component event belongs to one instance on one entity; an asset event belongs to the **asset**, so the runtime is keyed by the asset's stable guid. Every resolver of that guid subscribes to the same Signals, and a ref that is reclaimed and re-resolved re-attaches to the subscriptions already there — the same reason `asset_ref`'s `runtime` table is guid-keyed rather than stored on the envelope. Both tables reject an undeclared event name: the private table's metatable raises on a bad key and the facade raises on a bad key, so a typo surfaces at the subscribe call instead of returning nil. ## Declaring events on a type ```lua -- <name>.assetType/behavior.luau local M = {} M.events = { changed = { payload = { value = Field.number(0, NoSync) } }, } M.ref = { poke = function(self) local emitter = require("@builtin::assetTypes.assetType.shared.events").emitter(self.guid) if emitter ~= nil then emitter.changed:fire({ value = 1 }) end end, } return M ``` ```lua -- any holder of the ref local ref = asset.resolve("@builtin::…") ref.events.changed:connect(function(p) print(p.value) end) ``` ## Exports - `M.forAsset(guid, eventSchema)` — the runtime for one guid, built on first use and reused after. A later call with a different schema reconciles: surviving events keep their Signal and their subscribers, new events get a fresh one, removed events are disconnected and dropped. - `M.facade(guid)` — the subscribe-only view, or nil before a runtime exists. - `M.emitter(guid)` — the owner-side `:fire` view, or nil before a runtime exists. - `M.has(guid)` — whether a guid holds a live runtime. - `M.teardown(guid)` — drop one asset's runtime, disconnecting subscribers. - `M.teardownAll()` — drop every runtime. Called on an engine mode flip so a play-mode subscription does not survive into edit. - `M.liveGuids()` — every guid holding a runtime, sorted. ## Notes - Subscriptions made through the facade are ordinary `signal.module` connections and disconnect the same way any other does. - The runtimes table is held strongly, and its lifetime is bounded by the mode flip that clears it.

# assetType.shared.inspector Which inspector a type declares for its assets, and the declaration that file returns. The editor's Inspector (`edui.inspector`) reads it to add, replace and order the sections an asset shows. ## The block A type names its inspectors in `type.yaml`, with either key or both: ```yaml # the Inspector for every asset of the type, a file in the type's own folder inspector: { type: "inspector.luau" } # a file each asset may ship in its own folder, for what that asset declares inspector: { instance: "inspector.luau" } # both inspector: { type: "inspector.luau", instance: "inspector.luau" } ``` `type:` is what selecting an asset of the type shows. `instance:` applies to the things an asset declares, never to the asset's own view: a component names `instance: "inspector.luau"`, and a component that ships that file shapes its card on every entity it is on. Each value is a `.luau` file name. A block that is not a map, names another key, names neither key or names a file that is not `.luau` is malformed; the assetType validator reports it as `assetType.inspector_block`, and a `type:` file missing from the type folder as `assetType.inspector_file_missing`. ## The declaration The file returns a table: ```luau return { -- sections this inspector adds (before Operations) sections = { { id = "summary", title = "Summary", build = function(ctx) return { ctx.widgets.text{ text = "mode is " .. tostring(ctx.settings.mode) } } end }, }, -- a generic section id -> the section shown in its place replace = { tags = { id = "tags", title = "Labels", build = function(ctx) return {} end } }, -- section ids, first to last; ids it does not name follow in default order order = { "summary", "identity" }, } ``` A section is `{ id, title, icon?, open?, build(ctx) }`; `build` returns the section's body as a list of edui nodes. Any member of the declaration other than `sections`, `replace` and `order` must be a function (a helper the file exports). `material.assetType/inspector.luau` is a full example. The Inspector rebuilds an asset's sections when the asset's files change. A section that shows state held outside those files names it with a `signature(ref)` member: text that moves when that state moves, read every time the Inspector checks for a rebuild, so it has to be cheap. `renderFeature.assetType/inspector.luau` folds in whether the feature runs and its live settings, so a feature enabled or reconfigured from a script shows in the Inspector as it happens. ## API ```luau local InspectorDecl = require("@builtin::assetTypes.assetType.shared.inspector") InspectorDecl.blockFor("material") -- { type = "inspector.luau" } InspectorDecl.blockProblem({ other = "x.luau" }) -- why a block is malformed, or nil InspectorDecl.declaresTypeInspector("material") -- true: the asset view reads one local decl, problem, file = InspectorDecl.declarationFor(matRef) local cdecl = InspectorDecl.instanceDeclarationFor(compRef) InspectorDecl.shapeProblem(decl) -- nil when well-formed ``` `declarationFor(ref)` (and `typeDeclaration(typeName)`) read the `type:` file: - `(nil, nil, nil)` when the type names no `type:` inspector; - `(nil, problem, file?)` when the block is malformed, or the file is missing, raises while loading, or returns the wrong shape — the problem names the file and what is wrong with it; - `(declaration, nil, file)` otherwise. `instanceDeclarationFor(declarerRef)` reads the `instance:` file in the declaring asset's own folder, and answers `(nil, nil, file)` when that asset ships none.

# scene_instantiable (module) The instantiation contract's shared implementation. An asset type opts into scene instantiation by defining `instantiate(self, target?, opts?)` on its behaviour `ref` table; this module carries the parts that mean the same thing for every type, so a caller writes ONE piece of code against all of them. ```lua local root, idMap = ref:instantiate(target?, opts?) ``` ## The contract **IN — the base opts.** `target` is an owning entity ref: the instance lands under (or, for a hierarchy type like a bundle, onto) that owner. With no target the type spawns a fresh root. `position`, `rotation`, `scale`, `name` and `temporary` place that root and mean the same for every type. `rotation` takes three numbers as pitch/yaw/roll in DEGREES, or four as a quaternion. A type may honour more opts of its own — `params` for a type built from declared inputs, `idMap` / `diff` / `sourceTag` for the bundle override contract — and says so in its own `instantiate` docs. **OUT — the two returned values.** Every type returns the same pair: - **`root`** — the composed root, as an `EntityRef`. Composition is **synchronous**: the root and everything the type built under it are live the moment the call returns, so a caller can parent to it, read its components and hand it on in the same statement. There is no frame to wait for and no callback. - **`idMap`** — the `originalId -> runtimeId` map naming what the composition spawned, `{}` for a type with no addressable children. **Never nil.** A component that re-composes the asset on every load (`Asset`) keeps this map and passes it back in, which is how a cross-entity reference into the composition — `SkinnedModel.skeletonRoot` pointing at a bone — survives a reload. The return is enforced, not merely described: `AssetRef` dispatches every `ref:instantiate(...)` through `result` on the way out, whether or not the type called it. A type that returns something else fails at its own call rather than handing its caller a nil root or a map that is sometimes absent. ## Exports - `M.root(self, target?, opts?) -> root` — stand the root entity for a type that spawns one: parented to `target`, born temporary when `opts.temporary`, named `opts.name` else the asset's own name, placed. - `M.place(root, opts?) -> root` — apply the placement opts to a root the type already has (the adopt path: a bundle exploding onto its target, a sceneModule reconciling under one). - `M.result(self, root, idMap?) -> (root, idMap)` — return through the contract. Checks `root` is a live entity ref, normalises a missing map to `{}`, and errors naming the asset type when either is something else. - `M.isOwned(opts?) -> boolean` — whether a component drives this call. The `Asset` / `SceneModule` components tag their own calls with `sourceTag`; they hold the reference and re-compose on every load. An untagged call came straight from `ref:instantiate(...)` and has no such owner. - `M.own(root, self, idMap?) -> root` — hand an already-composed root to an `Asset` component pointing at `self`, so the reference and its map persist and the composition is rebuilt on the next load. The component adopts the live composition rather than building a second one. - `M.check(value, constraint) -> ok, reason?` — the `sceneInstantiable` field-constraint validator, also registered under that kind on load. ## The field constraint `Field.instantiableRef` emits `constraint = { kind = "sceneInstantiable" }`, and this module registers the validator for it on load. Given a written value: 1. `nil` passes — the field is optional (no asset assigned). 2. Reads the value's identity — a bare string, or a table's `__ref` / `guid` / `identity` / `name`. 3. Resolves it (`asset.resolve(identity)` — any category) and asks the resolved ref `ref:canInstantiate()`: true iff the asset's type defines an `instantiate` method. This is what lets `Field.instantiableRef` accept by CAPABILITY rather than a hardcoded type list — a new scene-instantiable asset type is accepted the moment it defines the hook, with no edit to the field or its consumers.

# asset_on_register Drives the optional `onRegister(self)` assetType lifecycle hook — the surface that lets an asset instance run code exactly once when it first registers, operating on the per-instance ref (`self`). This is what makes "write an asset into the world → it takes effect live, no restart" work for content that registers into a runtime registry (editor panels, and anything else that opts in). A type opts in by exporting `onRegister` from its `behavior.luau`. The hook fires exactly once per instance: - On `engine.onWorldLoaded` — a batched sweep over every world instance of every type that implements `onRegister`, yielding every 32 instances so a large instance count never stalls a frame. The @builtin library (`/zero/source/libs/`) is excluded. - On live `asset.create` — the create path calls `M.fireFor(ref)` on the freshly-created instance. A per-VM once-guard keyed by the instance's VFS path ensures the two triggers can't double-register the same instance. ## Exports - `M.fireFor(ref, onRegisterFn?) -> boolean` — fire one instance's `onRegister(self)` hook exactly once. Resolves the type's hook from `ref.type` when `onRegisterFn` isn't supplied. Idempotent: a second call on the same instance is a no-op. Returns true if the hook fired this call. - `M.sweep()` — batched sweep: fire `onRegister` once for every world instance of every registered type that implements it. Yields, so it must run inside a task. Safe to call repeatedly. - `M.install()` — install the world-loaded sweep. Idempotent. Runs the sweep on a system task so it ticks through pause and never blocks the caller.

# previewRecipe (module) How a type makes its instances' pictures. A type declares it in its `type.yaml`, under `preview:`, and every instance's `preview.png` is produced by the recipe named there. ```yaml preview: kind: surface # instantiate | image | surface | custom mesh: sphere # surface: the builtin mesh the asset is painted on ``` | `kind` | The picture is | Needs | |---|---|---| | `instantiate` | the asset stood in the studio through its own `instantiate` | — | | `image` | a file the instance already holds, fitted to the frame | `source.file` or `source.files` | | `surface` | the asset painted on a builtin mesh | `mesh` | | `custom` | whatever the type's `behavior.luau` `ref.preview` returns | — | `angle: [yaw, pitch]` (degrees) states the bearing the camera looks from, for any kind that renders. The `preview:` block says how the picture is PRODUCED. Whether search embeds that picture is a separate declaration — an `image` chunk under `indexing.content` naming `preview.png` — so a type states both, and a type that states one without the other gets exactly what it stated. ## Exports - `M.of(typeName) -> PreviewRecipe?` — the recipe `typeName` declares, or nil when it declares none or no type answers to that name. Read once and held; a block naming an unknown `kind`, or missing what its kind needs, is refused with a warning naming the type. - `M.forget()` — drop every held recipe. The change dispatcher calls it, with `declaration.forget()`, for every write inside an `.assetType` folder and for every removed type, so an edited `type.yaml` is read again.

# assetType.shared.ref Builds the metatable every `AssetRef` (the `{ __ref, type, name, guid, identity, path }` envelope returned by `asset.resolve` / `asset.ref`) carries. Replaces the per-call C metatable that used to live in `crates/zero_scripting/src/ffi/bindings/asset.rs::attach_asset_ref_metatable`. ## Public API ```lua local assetRef = require("@builtin::assetTypes.assetType.shared.ref") -- Called by the Rust factory (push_asset_ref_handle) via -- _G.__build_asset_ref_proxy after the envelope fields are set. assetRef.build(envelope) -- attaches AssetRefMT, returns the table ``` The module exposes no invalidation surface — discovery is registry-driven and hot-reload is transparent (see "Discovery and hot-reload" below). ## Method dispatch order `ref.foo` is resolved in this order: 1. **Default methods** — `getSource` / `getBytes` / `getText` / `exists` / `inspect` and the lazy `meta` property. Per-type definitions cannot override these (engine contract from gh#1889). 2. **Per-type `ref` table** — discovered through `asset.resolve(<typename>, "assetType")` + `require(<identity>.behavior)`. The lookup resolves to whichever `<typename>.assetType/` folder is currently registered for the typename (built-in, user, or library-vendored) and pulls its `ref` methods. 3. **Nil** — unknown key, same shape as the original C metatable. ## Adding methods for a new asset type Drop a `behavior.luau` into the type folder: ``` src/lua/lib/assetTypes/<typename>.assetType/ ├── type.yaml -- structural spec (existing) ├── behavior.luau -- ref + global behaviour (new) └── template/ -- placeholder body (existing) ``` `behavior.luau` returns: ```lua return { ref = { --!desc Per-instance method on every `<typename>` AssetRef. myMethod = function(self, ...) ... end, }, global = { -- Reserved for the asset.<typename>.* surface — not consumed -- yet; included so the contract from gh#1889 lands cleanly. }, } ``` Within `ref` methods, `self` is the AssetRef envelope: `self.path`, `self.identity`, `self.guid`, `self.type`, `self.name` are available. Engine-required fields (`guid`, `path`, `identity`, `type`) must not be redefined. ## Discovery and hot-reload Type discovery uses the asset registry, so it doesn't matter where a `<typename>.assetType/` folder lives — engine built-ins under `@builtin::assetTypes.<X>`, user types dropped under `/zero/source/<X>.assetType/`, or types vendored inside an imported library all resolve identically. The dispatcher walks `asset.resolve(<typename>, "assetType")` → canonical identity → `require <identity>.behavior` on every miss; the asset registry is the cache for the resolve half and Luau's `_LOADED` is the cache for the require half. Hot-reload is transparent. When a `<typename>.assetType/behavior.luau` is rewritten through VFS, the engine's `invalidate_require_cache_for_state` re-runs the module and mutates the cached `_LOADED[<identity>.behavior]` table in place. Dispatch reads `mod.ref` on every access (rather than caching a sub-pointer), so existing AssetRefs see the new methods on the very next access — no Rust-side hook into this module is needed, and no invalidation API is exposed for callers to call. The same registry-driven path also handles type **registration** correctness: dropping a new `<typename>.assetType/behavior.luau` updates the asset registry, the next `asset.resolve(<typename>, "assetType")` returns the new ref, and AssetRefs of that type immediately gain the new methods. ## Why Luau, not Rust The asset surface needed per-category behaviour (`material:getProperties()`, `bundle:instantiate(entityId)`, `tool:run(args)`) and the old shape couldn't grow without an FFI change per method. Owning the proxy in Luau means: - Type-specific methods ship as content (the `<typename>.assetType/` folder), not engine code. - Adding a new asset type drops in a new folder; no Rust rebuild. - Methods can call any other Luau global (`vfs`, `asset`, `Material`, `entity`, etc.) directly, instead of going through narrow FFI primitives. ## Consumers - `crates/zero_scripting/src/ffi/bindings/asset.rs::attach_asset_ref_metatable` — the Rust factory that pushes envelopes invokes `_G.__build_asset_ref_proxy` once per push. - Every Luau call site of `asset.resolve` / `asset.ref` / `entity(id).component.X.material` / any binding declared `AssetRef<...>` — they all receive envelopes built through this module.

# asset_ref_shapes Publishes what every `AssetRef<category>` answers to, so a member read on an asset-typed value is checked against the category's own surface. An asset category's per-instance surface is authored: a `<name>.assetType/behavior.luau` declares `M.ref = { ... }`, and each category declares its own. The members an `AssetRef<inputMap>` carries are therefore knowable only to `inputMap` itself — no fixed set of types covers the ones a world defines, and the checker has no way to guess them. This module reads each registered category's `M.ref` table from its source (never executing it), renders it as a Luau table type, and hands the set to the engine. From there a `ref:method(...)` on an asset-typed value resolves against the category's real surface: a name it does not carry is reported along with the ones it does. ## Results shaped by the asset Some results are shaped by the asset rather than by its category — `inputMapRef:activate()` answers one handle per binding THAT map declares, a set that is authored and differs per map. A category states those by declaring `refShapes`, and this module asks it once per instance and publishes the answers keyed by asset identity. `types/assetType` documents the authoring side. ## When it publishes Publishing is driven by use: every entry point that produces diagnostics calls `ensure`, which is a no-op once the set is current. A world load, a write inside a type definition, and a write inside any asset whose container computes shapes each mark it stale, so the cost lands on the next check and only if one comes. The sweep is complete and replaces what was published before, so a category whose type is removed stops being published. ## Reading what the checker believes From a call site, a type that is correct and one that was never published are the same absence of a diagnostic. `published()` tells them apart: ```lua local shapes = require("@builtin::assetTypes.assetType.shared.refShapes").published() shapes.categories.inputMap --> "{ activate: () -> any, controls: () -> { any }, ... }" shapes.returns["@builtin::inputMaps.default"].activate --> "{ crouch: Handle, interact: Handle, jump: Handle, ... }" ```

# assetType.shared.settings Resolves four questions about an asset's typed settings, all answered from its type's `type.yaml` — nothing here is found by convention. ```lua local Settings = require("@builtin::assetTypes.assetType.shared.settings") -- or, from inside the assetType runtime: local Settings = require("@builtin::assetTypes.assetType.shared").settings ``` ## Where does a type's schema live? `type.yaml` names it in a `settings:` block: ```yaml settings: values: "settings.yaml" # where an instance's own values live schema: { type: "settings.luau" } # one schema for every asset of this type ``` or, for a type whose settings differ per instance (an importer): ```yaml settings: values: "settings.yaml" schema: { instance: "settings.luau" } ``` or, for a type whose schema is a table its instance's own source declares and whose values live elsewhere (a component: its `public` fields, valued on each entity it is on): ```yaml settings: schema: { instance: "init.luau", export: "public" } ``` Whether an instance may lack its schema file is what the type's `files:` block says of that file. Listed under `files.optional`, it may be absent, and an instance without it declares no settings — the importer type lists it there, since most importers take none. Listed under `files.required`, or not listed at all, it must load, and an instance missing it is a broken declaration and is logged. `schema.type` is required at the folder relative to the TYPE's own `.assetType/` directory (one schema shared by every instance). `schema.instance` is required relative to each INSTANCE's own folder (`init` resolves the instance's own identity; anything else is a sibling module under it). Without `schema.export`, the file is required as a module and its return value IS the schema. With `schema.export`, the file is run in an environment of its own and `export` is read from a returned table carrying it, or else from the globals the file assigned — a component's `public` is such a global. That environment reads through to `_G` and takes every write itself; its own `_G` is itself, its `declare` and `computed` record into it, and its `task` records spawned, deferred and delayed work instead of starting it. Every other global is the real one, so a call the file makes through one runs as it does anywhere. The schema is the declared table's Field descriptors. A schema that resolves to nothing says why through `Settings.schemaProblemOf(ref)`: the file could not be read, compiled or run, or declared no such table. An instance schema is read again when its file, its type's `type.yaml`, or the entry file of any module the asset `require`s changes. `Settings.blockFor(typeName)` returns the raw block; `Settings.schemaForType(typeName)` and `Settings.schemaOfInstance(ref)` resolve the two schema shapes respectively; `Settings.schemaFor(ref)` tries the type-level schema first, falling back to the instance-level one. `ref` naming an assetType asset itself — e.g. `asset.resolve("texture", "assetType")`, rather than an instance of it — reports that type's own declared schema, the same one every instance of it reports. ## Where do an asset's values live? `settings.values` names a file living beside the asset's own content — `Settings.valuesPathOf(ref)` joins it onto the asset's path. `Settings.valuesOf(ref)` / `Settings.writeValues(ref, values)` read and write it; this module only names where it is. A type that declares its schema with no `settings.values` keeps no values in the asset — a component's live on each entity it is on — so `valuesOf` answers nil for it, `asset.create` refuses a `settings` table for it, and `asset.setSettings` refuses a write. `Settings.recordedWrite(path, text)` writes a file the way every values file is written, and an editor uses it for any other file it writes. It writes the whole contents, records the write into the open undo operation when one is open (so undoing it restores what the file held), and raises when the write does not land. ## In what order are a schema's fields declared? Every `Field.*` constructor stamps its descriptor with `declaredOrder`, one more than the last. Luau evaluates a table constructor's entries in the order they are written, so `Settings.orderedNames(schema)` lists a schema's fields — and a struct's subfields — in the order the source writes them. A values file, or a legacy `.metadata` settings block, may hold an older spelling — a renamed field, an older enum member. Every read passes what is stored through the type's `normalizeSettings` (`Settings.normalizeFor`), so it answers in the fields the schema declares today, and writes nothing. The next local edit of that asset rewrites the file in the declared spelling (`Settings.healLegacyIfNeeded`). `asset.setSettings(ref, patch)` writes a partial patch: `Settings.resolvePatch(ref, patch)` normalises it, merges it over the current values and applies the type's derived defaults for the fields it changed, and `Settings.writeValues(ref, values, patch)` applies the corrections, checks the schema and writes the file. ## How is a new asset's settings resolved at creation? `asset.create` calls `Settings.resolveForCreate(typeName, name, destPath, creationOpts, callerSettings, importerSettings)` before running the type's `onCreate`, checks the result against the schema, writes it to the values file, and hands `onCreate` a COPY of it as `opts.settings` (`Settings. cloneValues`) — never the same table the values file gets, so nothing `onCreate` does to its own copy can reach what was stamped. `onCreate` reads settings from `opts.settings` and never writes to it. `asset.create` also seeds the change baseline with the stamped values (`Settings.seedChangeBaseline`), so the values file's own first dispatch reports nothing changed and the payload `onCreate` encoded is the only encode a create runs. The layers, lowest priority first, each overriding the ones before it field by field: 1. The schema's own declared defaults (`Settings.defaultsOf`). 2. The type's own `settingsDefaults(name, opts, asked)` hook, when its `behavior.luau` exports one. `asked` holds what layers 3 to 5 name, so a default can follow a field one of them sets. 3. The Preset Manager's matching row (`Settings.presetLayerFor`). 4. The creating importer's settings for this type. 5. The `settings` table the caller passed to `asset.create`. 6. The type's own `settingsDerivedDefaults(values, explicit, changed)` hook, when its `behavior.luau` exports one — a field whose default follows another field, set only when no layer from 2 to 5 named it. 7. The type's own `settingsCorrections(values, name, opts)` hook, when its `behavior.luau` exports one — applied last, once every other layer has merged. Layers 2 to 5 are each read through the type's `normalizeSettings`, so a layer naming a field in an older spelling sets the field it names today. `asset.create`'s top-level settings alias accepts those older names too (`Settings.acceptedFieldNames`). Layer 7 is `Settings.applyCorrections(typeName, values, explicit, context)`, the one corrections path every settings write takes — this create chain, and `Settings.writeValues` for every later write (`asset.setSettings`, a type's first-encode seed, the legacy heal). `explicit` names the fields the writer asked for: the caller's `settings` table here, the patch for `asset.setSettings`. A correction lands SILENTLY on a field the writer did not name — nobody asked for that value, so overriding it just states a fact. A correction that contradicts a field the writer named REFUSES the write, naming the field, the value asked for, and why it cannot hold — the same as every other place this codebase refuses an explicit request it cannot satisfy (a `Field.checkSchema` violation, a BC7 alignment error) rather than silently rewriting it into something else. So `asset.setSettings(tex, { compression = "rgba16" })` on a mipped texture stores `generateMipmaps = false` beside it, while `asset.setSettings(tex, { compression = "rgba16", generateMipmaps = true })` is refused. `Field.checkSchema` runs once, over the result AFTER the corrections hook has applied — a bad value nothing corrects refuses the creation. ### Four hooks, four different jobs Every hook is an optional export on a type's `behavior.luau`, alongside `onCreate` / `onChange`. **None is ever handed a table to mutate** — each reads what it's given and RETURNS a table of what it wants changed (or nil); `resolveForCreate`, `resolvePatch`, `applyDerivedDefaults` and `applyCorrections` are the only places that write to the values, by merging what a hook returns the same way every other layer merges. - **`normalizeSettings(values) -> values`** maps every older spelling a stored file or a write may carry to the field and member the schema declares now, returning a new table; a table naming both an older field and its replacement keeps the replacement. The companion export **`normalizedSettingNames = { ... }`** lists the older field names it accepts beyond the schema, so a write naming one is not refused as an undeclared field. `texture.assetType`'s maps the fields its earlier schema stored to `colorSpace` + `compression`, and the older `filter` keywords to `linear` / `nearest`. - **`settingsDerivedDefaults(values, explicit, changed) -> partial?`** answers the values of fields whose default follows another field. At creation `changed` holds every field; on a write it holds the fields the write moved. A returned field applies only where `explicit` — the fields the writer named — does not name it. - **`settingsDefaults(name, opts, asked) -> partial?`** supplies a DEFAULT the schema itself has no syntax for — something only knowable at creation time, like a naming convention, a fact read off a payload the caller handed in, or a value that follows a field a higher layer sets (`asked` holds what the Preset Manager, the importer and the caller name, the higher one's value where two name a field). It runs early (layer 2 above), so any later layer — Preset Manager, importer, caller — freely overrides it. `texture.assetType`'s returns the `textureType` the name suggests (a `_normal`-suffixed name is a `normalMap`), `compression = "uastc"` and `maxDimension = 4096`, with `rgba8` for a `textureType` of `sprite` that a higher layer names; for a pre-encoded ZTEX payload it returns the colour space, compression and sampler the payload's own header carries. Either way, an explicit `settings = { ... }` from the caller still wins. - **`settingsCorrections(values, name, opts) -> (partial?, reasons?)`** enforces a CROSS-FIELD CONSTRAINT the schema itself has no syntax for — a fact about one field that depends on another field's resolved value, true regardless of which layer produced that value. It runs last (layer 7 above), over the fully merged `values`, and again on every later write of the values file. Nothing is left unmet in what gets validated and stamped — but a value the caller explicitly asked for is never silently rewritten to satisfy it; `applyCorrections` refuses instead (see above). The optional second return, `{ [field]: reason }`, supplies the "why" for that refusal message; a field with no reason falls back to a generic one. `texture.assetType`'s returns `{ generateMipmaps = false, maxDimension = 8192, colorSpace = "linear" }` whenever the RESOLVED `compression` is high-precision (the encoder stores one verbatim, linear, and refuses a mip chain or a downsample for it outright), paired with a reason naming the compression, and `nil` otherwise. ## What does a declarer declare? `Field.settingsOf(identity, mode)` embeds another declarer's schema as a struct field without restating it. The identity names one of two kinds of declarer, and `Settings.schemaOfDeclarer(identity)` tells them apart by what `identity` resolves to: - **An assetType** (e.g. `"@builtin::assetTypes.texture"`) — embeds the schema every instance of that type carries, resolved via `schemaForType`. This is the type-level shared schema from the section above, not a per-instance one — an assetType has no settings of its own to declare per instance. - **Anything else** (an importer, or any other asset that declares settings of its own) — embeds that asset's own schema, resolved via `schemaOfInstance`. Every schema this module serves has already run its `Field.settingsOf` fields through this resolution — a caller reading `schema.someField.fields` never sees an unresolved `declarer` with no `fields`. Resolution descends into an already-literal struct's `fields` and a list's `element` the same way, so a declarer embedded several fields deep is still reached. A declarer that embeds itself, directly or through another declarer, stops one level short of the loop instead of recursing forever. ## What are the defaults? `Settings.defaultsOf(schema)` reads every field's declared `default` into a plain table — a field declared without one is absent from the result rather than holding a `nil` value.

# assetType.shared.typeYaml A type's `type.yaml`, parsed. Every block a type declares in its `type.yaml` (`settings:`, `inspector:`) is read through this module, so one file read and one YAML decode serve all of them. ```lua local TypeYaml = require("@builtin::assetTypes.assetType.shared.typeYaml") local folder, identity = TypeYaml.folder("material") -- "/zero/source/libs/@builtin/assetTypes/material.assetType", "@builtin::assetTypes.material" local doc = TypeYaml.of("material") print(doc.suffix) -- ".material" print(doc.inspector.type) -- "inspector.luau" ``` - `TypeYaml.folder(typeName)` resolves the assetType and answers its folder path and identity, or `(nil, nil)` when no such type resolves. - `TypeYaml.of(typeName)` answers the decoded document, or nil when the type does not resolve or its `type.yaml` does not decode to a table. The decode is cached per type and read again whenever the file's content version moves, or the type resolves to a different folder. - `TypeYaml.described(typeName)` lists the files a type's assets must describe: each file its `type.yaml` declares with a `described` content check, with the keys and headings the check names and each key's byte limit. `TypeYaml.PLACEHOLDER` is the marker a template puts where a description is yet to be written. - `TypeYaml.describeBlock(typeName)` answers the `describe:` block of the `type.yaml`: the type's own `guidance` on what a description covers and the identities of `examples` whose descriptions show the shape.

# Module (asset type) A module is a reusable, stateless (or globally-stateful) Luau library that other code pulls in with `require()`. Modules are the unit of factored-out logic in a world: helpers, math libraries, format parsers, registries, shared algorithms. ## When to use one - You have logic you want to share across multiple components, services, scenes, or tools. - You have a registry, lookup table, or shared cache that callers all read from / write to. - You want a stable API surface (`M.fn`) other code can depend on. If the logic is bound to one entity, use a `.component`. If you want a named UI of fields rather than functions, use a `.preset`. ## Where it lives - Source: `/zero/source/.../<name>.module/` - Identity: the source path with `/` written as `.` and each segment's type suffix dropped — `/zero/source/demo/beats.module` is `demo.beats`, and `/zero/source/kit.package/beats.module` is `kit.beats`, the container's name kept and its `.package` suffix gone. `asset.create` returns this string, `asset.resolve(...).identity` reads it back, and the `require` forms below write it as `<identity>`. - Folder shape: - `init.luau` (or `init.lua`) — module body. **Required.** Returns a table (conventionally named `M`). - `README.md` — instance-level documentation. **Required.** - `.metadata` — agent-editable tags + free-form fields. **Required.** ## How to create one ```luau asset.create("module", "<name>") -- Creates: /zero/source/<name>.module/ -- init.luau (canonical `local M = {} … return M`) -- README.md (instance README template) -- `folder` places it in a subfolder of /source, and that subfolder -- leads the identity: `{ folder = "lib" }` produces `lib.<name>`. -- `into` authors it inside a resolved container (a package, a toolbox), -- whose own identity leads the same way: asset.create("module", "<name>", { folder = "lib" }) asset.create("module", "<name>", { into = asset.resolve("myPkg.package") }) ``` ## How it operates 1. **Registration.** Writing `init.luau` into a `.module/` folder indexes the asset and registers the module path with the resolver. 2. **Loading.** The first `require("<identity>")` runs the file's body and caches the returned table. Subsequent requires from anywhere return the **same table** — this is the shared-state lever for "module-local" registries. The body runs in an environment of the module's own: a name it declares without `local` is readable by the module's own functions and by no other script, so an export reaches its callers through the returned table and nothing else. Requiring a component's folder runs its chunk the same way, once, and its `update`, `start` and `public` stay in that environment; a component runs on an entity through `entity(id).component.add(name)`. 3. **Hot reload.** Editing the file re-runs the module body and folds what it returns into the table already loaded, so that table keeps its identity: a caller that captured it with `require` reads the new source's functions and values through the reference it already holds, and a later `require` returns that same table. A key the new source drops goes away; a key something set at runtime stays. The body's own `local`s start again from their initial values, so state that must outlive an edit lives in `modules.state()` (`guides { path: "core/scripting-and-tasks" }`). 4. **Identity resolution.** A module is reached by its `<identity>`, and where the caller lives decides which spelling of it resolves. For a module in a **world**, from a caller in that same world — another module, a component, a scene entrypoint, or an `execute` chunk: - `require("<identity>")` — the identity on its own, resolved against the caller's own root. It carries every folder segment, so a module created with `{ folder = "demo" }` is `require("demo.beats")`. - `require("@root::<identity>")` — the same root-relative resolution, written out. - `require(".sibling")` — a module in the same folder, by its bare name; `..name` steps up one folder, `...name` two. Logs, stack traces and hot-reload notices name that same module `@local.source.<identity>` — its key under the world source root. The `<identity>` tail of that key is the form above, so a trace reading `@local.source.demo.beats` is `require("demo.beats")`. For a module in a **library** — content under `/zero/source/libs/@<lib>/` — `@<lib>::` addresses that library's root from anywhere: `require("@builtin::modules.transform")`. Mounting a world as a library moves its files under such a root and flips the caller root to `@<lib>::`, which is what keeps the root-relative forms above resolving across the move. ## Discovery - `asset.list("module")` — every registered module. - `asset.inspect("<name>")` — public functions, source path, this type README. - `ls /zero/source/<name>.module` lists the files the folder holds. ## Authoring conventions - Return a single `M` table from `init.luau`. Top-level statements with side effects run on first require — useful for one-time initialization, dangerous if they touch the engine before it's ready. - Write exported functions as `typed function`, not `function`: the argument types are enforced at the call and the checker knows the signature, so a caller's mistake is reported where they made it. - Annotate exported functions with `--!desc` / `--!arg` / `--!return` / `--!example` so the LSP, `tools.list`, and `asset.inspect` surface them. A function with no `--!desc` is reachable only by someone already reading this file. - Declare a VALUE with `Field.<kind>(default, mode, description)`, and a table whose members are reached through a metatable with `--!members <TypeName>` — the latter gives the surface its accepted member set, its type, and its documentation from one table. See `guides { path: "core/authoring" }` for all four rules and `modules/api/engine/entity.module/members.module` for a worked member table. - Keep module state in module-local upvalues or in `modules.state()`. A name the body declares without `local` lives in the module's environment, which every run of the module shares: a function the previous run left in place reads what the reload assigned. Module-locals start again from their initial values with each hot reload; the table `modules.state()` returns is the same table on both sides of every reload. - Prefer focused modules over kitchen-sink modules. If two halves of a module have no shared state, split them. ## Common pitfalls - **Cyclic requires.** A `require` chain that loops will return the partial table (the half built before the cycle was detected). Design for one-way dependencies. - **Engine-time side effects.** Don't `entity.spawn` at module top-level — the engine may not be ready. Expose an `M.init` and call it from a scene entrypoint. - **Hot-reload + module-local cache.** A module that caches expensive computation in upvalues loses that cache on reload — fine for dev, but be aware in performance work. - **`init.lua` vs `init.luau`.** Either works, `.luau` is canonical. - **Writing one while play runs.** A `/source` write made while play is running lands on the play shadow, and a guarded play-exit discards it unless it is kept. One `.module` write shadows `init.luau`, the `README.md` and the `.metadata` together. `vfs.write(path, bytes, { durable = true })` skips the shadow, and `vfs.promotePlayShadow` keeps what is already on it — the `core/vfs` guide has the model and what each route costs. ## Related types - `.component` — for entity-bound state + lifecycle hooks. - `.service` — generates content you don't have yet (a mesh, sound, texture, …) via a metered provider. - `.tool` — for a single agent-callable function with a YAML schema. - `.package` — to group several modules + components + scenes into one shippable folder. ## In the Inspector Exports: what the module exports (name, kind, signature), parsed from its source without running it, with **Check** (the LSP's diagnostics for its entry file) and **Open**.

# validate Pure validator for `asset.create` opts — checks a creation `opts` table against the schema produced by `asset.createSchema(typeName)`. Schema in, validated opts (or a teaching error string) out. Consumed by `asset.create`, which calls `M.validate` before forwarding opts to the type's `onCreate`. No FFI, no VFS. Errors are teaching errors: they state what was wrong at which path (`opts.cfg.size`), what was expected, and then render the full creation-parameter contract so the caller can fix the call without reading the type's `behavior.luau`. Unknown parameter names get an edit-distance "did you mean" suggestion. ## Types - `ValidatorShape` — `{ kind, literals?, item?, members?, fields?, indexer? }`, the recursive shape encoding. - `ValidatorParam` — `{ name, shape?, optional?, default?, desc? }`. - `ValidatorSchema` — `{ kind, desc?, example?, open?, error?, params?, indexer? }`. ## Exports - `M.validate(schema, opts?) -> (validatedOpts?, err?)` — validate and default-fill an `opts` table against an `asset.createSchema` result. Returns `(validatedOpts, nil)` on success (a new table for `schema`-kind schemas) or `(nil, err)` where `err` is a bare teaching error string. The caller owns presentation. Handles the `legacy`, `error`, `none`, and `schema` schema kinds. - `M.shapeName(shape) -> string` — render a single parameter shape (literal unions as `"png" | "jpg"`, arrays as `{ T }`, tables as `table`, primitives as their kind, nil/malformed as `any`). Used by `asset.describe`. - `M.renderContract(schema) -> string` — render a schema's creation-parameter contract as one aligned line per parameter, with an `[extra keys]` line for open schemas. ## Usage ```luau local V = require("@builtin::assetTypes.assetType.shared.create.validate") local out, err = V.validate(schema, { bytes = png }) if err then error("asset.create: " .. err) end ```

# assetType (asset type) An asset type says what a kind of asset is: the files an asset of the kind is made of, the code that gives it behaviour, the interface a person uses to work with it, and how it is found, pictured and checked. A `<typename>.assetType/` folder declares a type called `<typename>`, and every `<name>.<typename>/` folder is an asset of it. `assetType` is itself a type, so a type is an asset like any other: it is created, versioned, installed and contributed the same way. ## Making a type `asset.create("assetType", "<typename>")` scaffolds a type. The type registers the moment its folder is written, anywhere under `/zero/source/`, and from then on `<name>.<typename>/` folders are its assets. An asset of a type that is not registered yet is not an asset, so make the type first. A type folder is a root: `~.x` in any file inside it names the type's own `x`, wherever the type is installed. Keep the type's whole implementation inside its folder and reach it that way. What a type folder must hold is set by this type's own `type.yaml`, the same way every type's `type.yaml` sets what its assets hold. `asset.validate` on a type reports anything missing, and the scaffold produces a folder that passes. ## What sets your type's schema (`type.yaml`) `type.yaml` is the structural contract every asset of the type is checked against. The keys below are the ones the engine reads; a key not listed here is ignored. | Key | What it controls | |---|---| | `suffix` | The folder suffix of the type's assets. Defaults to `.<typename>`. | | `primary` | The file or files that are the asset's content: what the asset resolves to when it is used. | | `entry_files`, `primary_aliases` | Further files that load as the asset or share its identity. | | `is_container` | Whether the suffix stays in the identities of what the asset holds. | | `is_opaque_walker` | Whether a walk of the tree stops at the asset and registers only its primary. | | `plural_dir`, `classify_exts` | Loose files in a folder of this name, or with these extensions, are assets of the type. | | `is_text_default` | Whether the asset's files are text unless stated otherwise. | | `broadcasts_subassets` | Whether assets nested inside an asset of the type are found by their own short name. | | `root` | `true` makes every asset of the type a root, so `~.x` inside one names that asset's own `x`. | | `contract_ref: { field, category }` | A key of the primary file that names another asset the asset is built on. | | `files: { required, optional }` | The files an asset holds (below). | | `allow_unlisted` | `false` reports every file the type does not declare. | | `aliases_from: [{ file, key }]` | Further names an asset answers to, read from its own files. | | `settings:` | Typed per-asset settings (below). | | `inspector:` | The interface people use for the type and its assets (below). | | `preview:` | How an asset is pictured (below). | | `references:` | Names of other assets the type's files carry (below). | | `indexing:` | What search reads for each asset (below). | | `describe:` | How a missing description is generated (below). | ### The files an asset holds Each entry under `files.required` or `files.optional` is `{ path, kind: file | folder, one_of_group?, content? }`. `*` in a path matches within one segment. Entries that share a `one_of_group` are satisfied by any one of them. `content` lists checks on the file's bytes: | Check | Passes when | |---|---| | `non_empty` | the file has content | | `json_field { key, type?, non_empty?, accept? }` | the JSON holds the key (a dotted path) with that shape | | `yaml_field { key, type?, non_empty?, accept? }` | the same for YAML | | `described { keys?, headings?, message? }` | the file says what the asset is (see "Ask your assets to say what they are") | Each check takes a `message`, which is what the author is told when it fails. ### Settings `settings: { values, schema: { type | instance, export? } }` gives every asset typed settings. `values` names the file an asset's values live in; `schema.type` declares one schema for the whole type, and `schema.instance` names a file each asset declares its own in. `asset.create` writes the resolved values, and a write to the values file reaches `onChange` with what changed. ## The human side (`inspector.luau`) A type is used by people through its Inspector, and without one the type is usable only from code. The Inspector is the type's interface for a person: for a procedural graph it is the graph editor, for a kit it is the tracking view of what the kit holds and what is still missing. Writing it is part of writing the type. `inspector: { type, instance? }` in `type.yaml` names the files. `type` is the interface for the type itself and for its assets; `instance` names a file an asset may ship to add its own. Each returns: ```luau return { sections = { { id = "graph", title = "Graph", build = function(ctx) ... end } }, replace = { contents = { ... } }, -- replace a default section by id order = { "graph", "contents" }, -- section order } ``` `build(ctx)` receives the asset and builds the section. A section's `title`, and the text its rows carry, is a string or an `i18n.text` value read from a catalog (`i18n.text("inspectors.mesh.title")`), which follows the editor's language. `asset.create("assetType", ...)` scaffolds a working `inspector.luau` to start from. `asset.validate` on a type that names no inspector, or names one that does not load, reports it. ## Say what your type is for (`about.yaml`) Every type carries an `about.yaml` that says what the type is for, in three plain-language texts: ```yaml intent: "Sets the typeface of the text in your game: UI, labels, signs and 3D lettering." function: "A font, from a TTF, OTF or WOFF file, made available to all of Zero's text, including 3D text." usage: "You choose it by name for your UI or your text, and the text appears in that typeface." ``` - **`intent`** is what the type is for in someone's game, in the words a game maker uses. Up to 800 bytes. - **`function`** is how it works today: what an asset of it is made of and what the engine does with it. Up to 1500 bytes. - **`usage`** is what a person or an agent does with one. Up to 1200 bytes. Write about the type as a whole, not one asset of it, and say what it does now. Agents read these texts to learn when to reach for the type and how; people searching find the type by them. The scaffold starts each text with `[[describe]]` and a note on what to write; a text that still starts that way counts as not written. `services describe` can write them. They show up in `asset.inspect` as `detail.about`, in `assetTypeRef:getAbout()`, at the end of the type's `types/<typename>` guide, and at the top of the type's Inspector. ## Ask your assets to say what they are A type can require each asset to carry a description: a file, written by the author or generated, saying what the asset is and what it is for. Declare it with a `described` check: ```yaml files: required: - path: "README.md" kind: "file" content: - { check: "described", message: "Say what this widget is for and where it goes." } ``` A file that is missing, empty or still has a line starting with `[[describe]]` fails the check, and so does a YAML file whose named `keys` are missing or over their `max_bytes`, or a Markdown file missing a named heading. `asset.validate` names the asset, and a push that carries it is refused with `message`. `services describe` finds such assets and writes their descriptions. `describe:` steers what is generated: ```yaml describe: guidance: "Say what the widget shows, what input it reacts to, and where it fits in a UI." examples: - "<identity of an asset of this type whose description reads well>" ``` An example is an asset of your type whose description is a true, written one, never a placeholder and never the asset being described; with none, leave `examples` empty. A type whose assets the model cannot perceive (a sound, a motion) says so in `guidance`, and the description is drawn only from what the asset's own files state. Start the file unwritten in your `template/`: a heading and one line starting with `[[describe]]`, never example content, which every new asset would carry verbatim. A type whose assets say what they are through their own content (a mesh, a texture) declares no check. ## The type's code (`behavior.luau`) `behavior.luau` returns one table. These are the keys the engine reads from it; anything else on the table is the type's own. ### What the type's assets can do | Key | Shape | What the engine does with it | |---|---|---| | `ref` | `{ [name] = function(self, ...) }` | Every function becomes a method on every asset of the type: `ref:name(...)`. | | `modules` | `{ [name] = require(".x") }` | Code the type's assets reach with `asset.containing(__FILE__).modules.<name>`. | | `events` | an events schema | Events an asset fires. Readers subscribe through `ref.events.<name>:connect(...)`; the type fires them. | | `refShapes` | `{ [method] = function(self) -> (typeExpr, source?) }` | The result type of a `ref` method for one particular asset (below). | | `namePattern` | a Lua pattern | The names `asset.create` accepts for the type's assets. Default `^[A-Za-z][A-Za-z0-9_]*$`. | | `derive` | `{ output, module, compute, fingerprint, matches?, required?, timeout? }` | A file computed from the asset when it is committed; a `required` one holds the commit until it lands. | Some `ref` names mean the same for every type, and the engine calls them: - **`instantiate(self, target?, opts?) -> (root, idMap)`**: puts the asset in a scene. Defining it is what makes the type scene-instantiable. Its return is a contract (below). - **`inspect(self) -> detail`**: what `asset.inspect` reports for the asset beyond the common record (below). - **`preview(self, opts)`**: renders the asset's picture; it wins over the type's `preview:` recipe. - **`previewMaterial(self) -> { material }`**: the material a `surface` preview paints. - **`saveDefinition(self)`**: writes the asset's in-memory edits back to its files in edit mode. Some names are answered for every asset before the type is asked, so a `ref` entry of the same name is never reached: `getSource`, `getBytes`, `getText`, `exists`, `deps`, `canInstantiate`, `canPreview`, `preview` (which calls yours when you define one), `meta`, `runtime`, `events`, `typeRef`, `modules`, and the residency flags `has_backing_asset`, `has_runtime_changes`, `cpu_resident`, `gpu_resident`. ### When the engine calls the type | Hook | Signature | When it runs | |---|---|---| | `onCreate` | `(name, opts) -> { [path] = contents }` | On `asset.create`. Returns the files of the new asset, laid over the type's `template/`. Annotate `opts`: its type is the schema `asset.create` checks the caller's arguments against. A `""` key writes a single loose file. | | `onReplace` | `(dest, files) -> files` | On an `asset.create` over an asset already at `dest`, after `onCreate`, so what the author added can be carried into the replacement. | | `onRegister` | `(self)` | Once per asset, when it first registers: when the world loads, on a live `asset.create`, and when an asset arrives later (installed, pulled, synced). This is what makes an asset take effect the moment it is written. | | `onChange` | `(ref, change)` | On every write to a file inside an asset of the type. `change` is `{ path, asset, type, kind, origin }`, plus `settings` and `settingsChanged` for a write to the settings values file; `kind` is `edited` or `seeded`, `origin` is `local` or `remote`. Filter on `change.path`. Writes to one asset arrive in order, each after the hook for the one before has finished, and the hook may wait on what it reads. A write the hook makes inside its own asset arrives later like any other, so keep the hook convergent. | | `onDependencyChange` | `(ref, change)` | When a module the asset's code requires is re-run, or a name the asset carries starts resolving. `change.kind` is `dependency`. | | `onDelete` | `(ref)` | When an asset of the type leaves the world: deleted, or the world it is in is swapped away. | | `validate` | `(ref) -> { { code, message, severity?, path? } }` | On `asset.validate`, after the `type.yaml` checks, for the type's own rules. `severity` defaults to `error`. Runs on every push, so a type's rules hold at publish. A hook that fails reports `validate.hook_failed`. | ### Settings hooks | Hook | When it runs | |---|---| | `settingsDefaults(name, opts, asked) -> table` | Once per `asset.create`, for values the schema's defaults do not give. | | `settingsCorrections(values, name, opts) -> (corrections?, reasons?)` | On every settings write. A correction to a field the writer named refuses the write, giving the reason. | | `settingsDerivedDefaults(values, explicit, changed)` | On a settings write, for fields derived from others. | | `normalizeSettings(values, stored?)` | On every read and write, to map an earlier spelling of a field to the current one. | | `settingsHealed(values, stored)` | On a read, to repair stored values. | | `settingsSchemaProblem(schema, ref) -> string?` | When an asset's own schema is read; a returned string refuses the schema. | `creationInputs` (`{ [opt] = true | selectorOpt }`) names `asset.create` options that are inputs to the type rather than settings. ### Reloading An edit to `behavior.luau` reaches existing assets with no restart. ## How an asset is pictured (`preview:`) | `kind` | The picture is | The type provides | |---|---|---| | `instantiate` | the asset placed in the preview studio through its `instantiate` | `ref.instantiate` | | `image` | a file the asset holds, fitted to the frame | `source: { files }`, the candidate files in order | | `surface` | the asset painted on a mesh | `mesh`, and `ref.previewMaterial` | | `custom` | whatever `ref.preview` returns | `ref.preview` | ```yaml preview: kind: surface mesh: sphere ``` `angle: [yaw, pitch]` turns the camera. The studio owns the light, the backdrop and the framing, so an asset pictures the same in every world. A type with no `preview:` that defines `instantiate` still answers `ref:preview()`. A picture is rendered when something asks to view it (the editor showing the asset, `ref:preview()`), when previews are generated on request (`assets.generatePreviews`), and when the asset is staged. An edit alone renders nothing. The picture records what it was made from, so a stale one is told from a current one. ## The names your type's assets hold (`references:`) Where your type's own format or API carries the name of another asset, declare it here: ```yaml references: keys: # a top-level key of the type's files that holds a name, or a table of them - { key: "shader", type: "shader" } args: # an argument of a call, counting from 1 - { call: "g:node", position: 2, type: "procNode" } fields: # a field of the options table a call takes - { call: "fx.beam", field: "material", type: "material" } ``` `type` is the category the name resolves in. `asset.declareReferenceKey`, `asset.declareReferenceArg` and `asset.declareReferenceField` declare the same from a script. ## What search reads (`indexing:`) `indexing:` is how assets are found. Search reaches an asset only through what its type's `indexing:` names, and adds nothing of its own. That includes you: an asset indexed badly is one you cannot find later, when you are making something else and need it. A type whose assets are never looked for says `indexing: none`. ```yaml indexing: data: # text, read from the asset's files - role: identity extractor: verbatim source: { file: "README.md" } - role: interface extractor: symbols source: { files: ["init.luau"] } - role: implementation extractor: verbatim source: { files: ["init.luau"] } content: # the picture - role: identity modality: image source: { file: "preview.png" } facets: # what a query filters and re-ranks by file: ".metadata" rigged: { type: bool, from: { components: { contains: SkinnedModel } } } roughness: { type: number, filter: range, from: { file: "mat.yaml", field: "floats.roughness" } } ``` **Roles.** Each `data` and `content` entry has a `role`, and a query matches in two slots: - **`identity`**: what an asset is. For anything you look at, the picture; for anything else, the text that says what it is. - **`capability`**: what it does and how it is made. `interface` (the signatures or shape a caller uses) and `implementation` (the body) both count as capability, and a type with code usually declares both. Ask what a person would recognise an asset of the type by, and what it does, and point each role at the file that says it. For text, that is the asset's description: the file your template starts with a `[[describe]]` block, which the author writes or `services describe` fills in (see "Ask your assets to say what they are"). **`data`.** `extractor: verbatim` embeds a file's text as it is; `symbols` embeds the declared signatures of code. `source` is `{ file }` or `{ files: [...] }`. Never index a file name (`source: { field: name }`): one or two words carry nothing to match. **`content`.** `modality: image` embeds the picture itself, so a text query matches what the asset looks like. A type whose assets are looked at makes the picture its identity. **`facets`.** What a query narrows and re-ranks the matches by. `file` is embedded whole, so keys nobody declared in it are still found. Each further key is computed for every asset and states a value for every one, including `false`: a file can imply "not rigged" but never say it, and a query separates rigged from unrigged only because the unrigged ones say `rigged: false`. A key is `{ type: bool | number | enum, filter?: range, from }`, where `from` is `{ file, field }` (a field of one of the asset's files, dotted for nesting), `{ metadata: key }`, or `{ components: { contains | any_outside } }` (what the asset's entities carry). ## What blocks a push A push checks every asset it carries against its type. These refuse it: - a required file that is missing, a `content` check that fails, a `described` file not written yet; - an error from the type's `validate`. Unlisted files and warnings do not. A `described` file blocks only a push that changes the asset. When a push is refused, the message names each asset and what it lacks. `world.publishBlockers()` and `zm status` read the same list without pushing. ## Typing a result from the asset (`refShapes`) A `ref` method whose result depends on the asset (one entry per child folder, per row of a config, per control a map declares) can only be annotated as `{ [string]: Thing }`, which accepts any key. `refShapes` states the result for each asset instead: a function returning a Luau type expression for that asset, and the module whose types the expression uses. Read the asset; never run it. ```lua -- inputMap.assetType/behavior.luau M.refShapes = { activate = function(self): (string, string) local names = {} for _, control in ipairs(M.ref.controls(self)) do table.insert(names, control.name .. ": Handle") end if #names == 0 then return "", "" end return "{ " .. table.concat(names, ", ") .. " }", "@builtin::modules.zinput.scheme" end, } ``` With it, `map.jump:onPressed(fn)` is checked and `map.noexisting` is reported. A per-asset type applies where the call site names which asset: a component field whose default names it, or an annotation `AssetRef<"inputMap", "<identity>">`. `asset.resolve(name, category)` carries only the category, and a name computed at runtime carries nothing, so calls on those keep the declared return. The type belongs to the call's result: index it there, or bind what you need from it there, and the names stay checked. `require("@builtin::assetTypes.assetType.shared.refShapes").published()` shows what was published: `categories` (each type's method surface) and `returns` (per-asset results by identity, then method). An identity missing from `returns` was never published. Results are recomputed when an asset is written; at most 64 assets of one type are read. ## Putting an asset in a scene (`ref.instantiate`) A caller writes one piece of code against every instantiable type, so what `instantiate` returns is fixed: ```lua local Instantiable = require("@builtin::assetTypes.assetType.shared.instantiable") M.ref = { instantiate = function(self, target, opts) local root = Instantiable.root(self, target, opts) -- compose the asset under `root`, now return Instantiable.result(self, root, idMap) end, } ``` **In.** `target` is the entity the asset lands under, or onto for a hierarchy type; with none, the type spawns a new root. `position`, `rotation` (three numbers in degrees, or a quaternion), `scale`, `name` and `temporary` mean the same for every type: `Instantiable.root` applies them to a root you make, `Instantiable.place` to one you adopt. Document any options of your own in the hook's `--!arg` docs. **Out.** `(root, idMap)`. `root` is the composed root, live when you return: build synchronously, never defer to a component's `awake`. `idMap` maps each original id to the spawned one, so a component that composes the asset again on every load can pass it back in and keep references into the composition. Every call goes through `Instantiable.result`, which refuses a root that is not live and turns a missing `idMap` into `{}`. ## Inspecting an asset (`ref.inspect`) `asset.inspect(ref)` builds a record every asset shares (`identity`, `name`, `guid`, `source`, `typeName`, `typeDefinitionPath`, `scope`, `origin`, `description`, `tags`), then calls `ref.inspect(self)` for the type's own `detail`: ```lua M.ref = { inspect = function(self) -- read the asset's own files, never runtime state: inspect works on an asset -- that has not been compiled, uploaded or registered return { --[[ what makes this asset what it is ]] } end, } ``` Without it, the record is the shared part alone, and an agent inspecting the asset learns nothing of what it is. A hook that raises leaves `detail` empty and sets `record.warning`. ## Discovery - `asset.list("assetType")`: every registered type. - `asset.inspect("<typename>")`: the type, its README and its `about.yaml` texts. - `asset.resolve("<typename>", "assetType")`: the type itself.

# shared A module script.

# content_version Per-path content-version counters — a cheap, synchronous "has this file changed?" token. An assetType behavior memoizes its parse in the ref's `runtime` keyed by the counter `get(path)` returned when it parsed, then serves every later read as an integer compare instead of re-reading and re-parsing the file. ## Why it exists A `.data()` behavior that re-reads and re-parses its source on every call is pure overhead when the file hasn't changed. This module gives it a version token to gate the rebuild on: - `get(path)` when the parse ran, stored alongside the parsed value. - On every later call, compare `get(path)` to the stored value — equal means the cache is still valid (no `vfs.read`, no parse); a bump means rebuild. ## Exports - `M.get(path: string) -> number` — the path's current version counter (`0` if never written this VM). - `M.bump(path: string)` — bump `path`'s counter, invalidating every reader memoized against its previous value. Content code rarely calls this directly. ## What bumps a counter Two write surfaces feed it, so the token reflects a change no matter where it originated: - `vfs.write` / `vfs.move` / `vfs.remove` bump **synchronously**, in the same call — so a script that writes a file and reads it back in the same tick sees the new content immediately (the asset-change `onChange` dispatch fires a frame later, too late for a same-tick read). - the generic asset-change dispatcher bumps on every source write it routes, including peer-synced and engine-originated writes that never pass through the Luau `vfs.*` surface — with the engine's normalized path, the canonical form a reader keys on. ## Per-path, not a global epoch Counters are per **path**, not one global epoch. The per-frame dirty-entity writer churns scene-dirty paths every frame during play; a global epoch would let that churn invalidate every unrelated cache. Per-path isolation means only a change to the file a reader depends on rebuilds it. The counters are held once for the process (`__contentVersion`), so a single store is shared across every VM and every copy of this module that a require-cache reset (`vfs.reload`) might create. A bumper and a reader that landed on different VMs or module copies read the same number: a write made in a worker VM, the engine thread's dispatch of it, and a write made on the engine thread advance one counter.

# yaml.module YAML decode + encode for authored engine content. Pure Luau, no engine dependencies — a general parsing library, not data-system plumbing. ```luau local Yaml = require("@builtin::modules.yaml") local doc = Yaml.decode(vfs.read(path)) vfs.write(path, Yaml.encode(doc)) ``` ## Supported subset - Block mappings (`key: value`) and block sequences (`- item`), nested to any depth. - Compact sequence-of-mapping entries (`- path: x` / ` kind: y`). - Flow collections — `{ a: 1, b: 2 }` and `[1, 2, 3]` — single line. - Plain scalars with type inference: `~` / `null` → nil, `true` / `false` → boolean, numeric literals → number, everything else → string. - Single- and double-quoted strings (`''` escapes a literal quote inside a single-quoted string; `\n` `\t` `\r` `\\` `\"` inside a double-quoted one). A quote opens a quoted scalar where a scalar begins — after `key:`, after a `- ` entry marker, or inside a flow collection — so a plain scalar carries an apostrophe as data (`note: the world's rules`). Quoted keys are read in flow mappings. - `#` comments — honored outside quotes, so a `#` inside a quoted string is kept as data. - Literal (`|`) and folded (`>`) block scalars, with a chomping indicator (`-` strips the final newline, `+` keeps every trailing blank line, none keeps one newline) and an indentation indicator (`1`-`9`: the content's indent past the parent's), in either order (`|-`, `>+`, `|2`, `>1-`). A block scalar's content is literal text: quotes (balanced or not), `#`, `key: value` and `---` inside it are data. - An optional leading `---` document marker. ## Loud-error contract Constructs outside the subset above raise instead of misparsing: anchors/aliases (`&`, `*`), tags (`!`), directives (`%`), multi-document streams (a second `---`), a block-scalar header it cannot read (`|x`, `|-+`, `|0`), tab indentation, and inconsistent indentation (both block structure and block-scalar bodies). Every error carries the offending line number (`yaml: line N: ...`), so a bad config points straight at the line to fix. Tab indentation is rejected everywhere — including block-scalar body lines whose leading whitespace contains a tab. A tab after the first non-space character of a line is content and passes through. ## API - `Yaml.decode(text: string): any` — decode a YAML document into a Luau value (table, scalar, or nil for an empty document). Raises on malformed input or an unsupported construct. - `Yaml.decodeWithComments(text: string): (any, boolean)` — decode as `decode` does, and report whether the text carries a comment by the decoder's own rule: a `#` at a line's start or after whitespace, outside a quoted scalar and outside a block scalar. Re-encoding the value drops such comments, so an editor that writes a document back reads this first. - `Yaml.encode(value: table): string` — encode a Luau table as YAML (block style, two-space indent, alphabetically sorted keys). Raises on values YAML can't represent (functions, userdata, non-string mapping keys). A top-level empty table encodes to an empty document, which decodes back to `nil` (the YAML empty-document ambiguity).

# engine_records The engine's own records: the tables a subsystem keeps as its account of what stands in the running engine, and the classes whose every instance is one. The input maps activated, a signal's handlers and connections, the entity and asset event registries and the renderer's registry of live features are records; each follows whoever holds the thing it records. `declare(t)` makes a table a record, `declareClass(mt)` makes every table carrying that metatable one, and `holds(v)` answers whether a value is a record. `engine.snapshotModuleState` carries a record by reference without walking it, and `engine.restoreModuleState` leaves it as it stands, so what went away since a reading stays away and what arrived stays in place. A leaf with no requires, so a module that loads before the `engine` global exists declares its records as it loads.

# component_events Per-instance runtime for declared component events. A component's `events` block (built with `Event(...)`, see `event.module`) is a schema: a map of event name to descriptor. This module turns that schema into the live objects an instance actually fires and listens on. ## Three faces, one Signal Each declared event resolves to one `signal.module` `Signal`, reachable through three tables that share it: - `buildSignals(schema)` returns the private, fire-capable table (`:Fire`, the raw Signal method). Engine-internal — never handed to user code directly. - `buildEmitter(signals, schema)` returns the owner-side emitter, bound into the declaring component's own env as `events`. Each entry has `:fire(payload)` only — lowercase, symmetric with the facade — and validates the payload against the event's declared members before dispatch. The component's own code fires with `events.onHit:fire({ dmg = 10 })`. - `buildFacade(signals)` returns a subscribe-only view over the same table, exposed to outside callers through the ComponentProxy's `.events` key. Each entry has `:connect(fn)` / `:once(fn)` / `:wait()` — no `:fire`. `setup(schema)` builds all three in one call and returns `{ signals, emitter, facade }`; the engine calls it once per instance. ```lua local schema = { onHit = { payload = { dmg = Field.number(0, NoSync) }, sync = false } } local runtime = component_events.setup(schema) -- inside the component's own code (env global `events` is runtime.emitter): events.onHit:fire({ dmg = 10 }) -- outside code, through the proxy (proxy.events is runtime.facade): proxy.events.onHit:connect(function(p) print("hit for", p.dmg) end) ``` ## Fire authority by construction `buildFacade` never returns the underlying `Signal` object, only a fresh table exposing `connect` / `once` / `wait`. There is no `fire` method to find on the facade at any key, so outside code cannot fire a component's events no matter what it holds a reference to. Firing authority lives only with the owner, through the emitter's env `events` global. Both tables reject access to an undeclared event name: the private table's metatable raises on a bad key, and the facade raises on a bad key too, so a typo surfaces immediately instead of silently returning nil. ## Cleanup Connections made through the facade are ordinary `signal.module` connections, tracked and torn down the same way as any other signal connection: `entity_signals.module` disconnects everything sourced from an entity when that entity is destroyed. Component events carry no separate cleanup path.

# field_constraints (module) Generic field-constraint dispatch. Installs `_G.__zero_check_field_constraint(value, constraint)`, the Luau half of the opaque field-constraint primitive: a component field descriptor may carry a `constraint` value (an arbitrary table with a `kind` string), and the engine calls this hook whenever a constrained field's default resolves or a write lands. The engine copies `constraint` verbatim — it never reads inside it — and treats the hook's first return as accept/reject, the second as the rejection reason. ## What it does 1. Reads `constraint.kind` and looks up a registered validator for that kind. 2. Built-in kinds (currently `dataContract`) resolve their validator module lazily on first use, so component registration never depends on load order. 3. Calls the validator with `(value, constraint)` and returns its `(ok, reason?)` result. The registry is held in the module's durable state (`modules.state`), so every run of this module, and the engine hook the first run installed, read and write the one registry. A malformed constraint (not a table, or missing `kind`) and a missing validator both reject — the primitive fails closed rather than silently accepting an unconstrained value. ## Exports - `M.register(kind, fn)` — register the validator for a constraint kind. `fn(value, constraint) -> ok, reason?`. A kind belongs to the chunk its validator is defined in: registering it again from that chunk (its module running again, on a hot reload or after its require cache entry was dropped) replaces the validator, and registering it with a validator defined in another chunk errors, naming both. - `M.check(value, constraint) -> ok, reason?` — run the check directly (same function installed as the engine hook). ## Consumers `Field.dataRef` (`field.module`) emits `constraint = { kind = "dataContract", contract = ... }`; `data_contract.module` registers the `dataContract` validator against this registry.

# Asset Promote the bundle's spawned children from temporary to permanent scene state and remove the Asset component, "baking" the bundle's contents directly into the owning scene. Subsequent saves persist the baked entities verbatim and stop replaying the bundle template. Location: `src/lua/lib/components/Asset.component`

# modules.api.engine.engine The `engine` global's Luau implementation. Exposes `engine.mode` (edit vs play), `engine.onModeChange(callback)` subscription registry, and the mode-flip orchestration that fires the canonical onModeChange dispatch through `ENGINE_MODE_WATCHERS`.

# frame_budget The share of a frame that cooperative engine work spends before it hands the frame back. Some engine work is one long sequence of small units run on a task: a scene load applies one record after another, and the world-load `onRegister` sweep fires one instance's hook after another. Run back to back in one frame, a long sequence holds that frame for its whole length, and nothing else the engine does (answering a call, drawing, input) happens until it is through. Asking `due()` before each unit and yielding when it answers true runs the same work across as many frames as it needs, a slice of each. ```luau local FrameBudget = require("@builtin::modules.frame_budget") for _, item in ipairs(items) do FrameBudget.yield() process(item) end ``` - **One slice per frame, shared.** Each caller is charged the time it runs between its readings of the slice in a frame (`task.runTime`), whoever runs it, and the charges of every caller add up to the frame's slice. What the rest of the frame runs (systems, components, other tasks) is not charged, so a busy frame still gives the slice to the work. Two long pieces of work running at once share a frame's slice rather than taking one each. - **A unit is never split.** The first unit of a frame always runs, so a frame holds at most the slice plus the one unit that crossed it. A unit that is itself long stays one piece of work. - **Code that cannot yield runs in its frame.** `due()` answers false outside a coroutine that can yield, so a caller called from such code does all its units in the frame it was called in, as it would without the budget. A caller that does work of its own around the yield asks `due()` and calls `wait()`, which yields to the next frame and opens that frame's slice as the caller resumes; `yield()` is the two together. Work whose unit is a native call that bounds itself by time is told how long it may run: `remainingMs()` answers what is left of the current frame's slice, or nil for code that cannot yield, which then runs the whole of its work in the frame it was called in. The publish gate's script check runs this way: ```luau local block, checking = __spacetime_vcs.scriptPublishBlock(FrameBudget.remainingMs()) while checking do FrameBudget.wait() block, checking = __spacetime_vcs.scriptPublishBlock(FrameBudget.remainingMs()) end ``` `FrameBudget.DEFAULT_MS` is the slice a call that names none spends. `spent()` answers how much of the current frame's slice is gone. A caller with a budget of its own reads `mark()` where its work starts. `ranMs(mark)` answers how long it has run since, none of the time it spent suspended; `cpuMs(mark)` answers the CPU time of its work since: those stretches and the stretches of every coroutine it resumes, and every one they resume, while it waits on them, which a machine whose cores are taken by other work does not stretch. A bound that refuses work for running too long (procgen's `cpu.call` ceiling) reads `cpuMs`, so it refuses the same work on a loaded machine as on an idle one, and work handed to a coroutine as work run in place.

# preview Render an asset's preview in the preview studio: an isolated camera, lit only by its own three-point rig, over a neutral backdrop, that nothing in the scene reaches. `ref:preview()` renders any asset by the recipe its type declares under `preview:` in its `type.yaml`, and these are the primitives it calls: they spawn temporary entities, frame an offscreen camera over them, render one frame, read it back as a PNG, and tear the entities down. ## Surface - `preview.fromEntities(makeFn, opts?) -> PreviewResult` — run `makeFn` to instantiate entities, frame a camera to their bounds, render one offscreen frame, and return the still PNG. - `preview.fromRecipe(ref, recipe, opts?) -> PreviewResult` — render `ref` by a declared recipe: `instantiate` stands it through its own `instantiate`, `surface` paints the material its type's `ref.previewMaterial` returns on the recipe's mesh, and `image` fits a file the asset holds to the frame on the studio backdrop without rendering anything. - `preview.backdrop() -> { r, g, b }` — the studio backdrop's colour in a finished preview, 0-255. `PreviewResult` is `{ available, imageBase64?, rendered?, width?, height?, bounds?, stats?, reason? }` — `imageBase64` is the rendered PNG when `available` is true, and `reason` explains why when it is false. `opts` is `{ size? = { width, height }, angle? = { yaw, pitch } }`. ## Example local result = asset.resolve("gold", "material"):preview({ size = { width = 512, height = 512 } }) -- result.imageBase64 holds the rendered PNG (base64)

# asset_residency Compute backends for the **lazy** residency properties on every `AssetRef` (`has_backing_asset`, `has_runtime_changes`, `cpu_resident`, `gpu_resident`). The AssetRef metatable's `__index` dispatcher (`assetType.shared.ref`) calls these only when a caller actually reads a flag — nothing is computed at resolve time, so an asset costs nothing for residency until it is observed. The three backing/runtime states: | `has_backing_asset` | `has_runtime_changes` | Meaning | |---|---|---| | true | false | USED, UNMODIFIED | | true | true | USED, MODIFIED (copy-on-write fork) | | false | true | RUNTIME-GENERATED | `cpu_resident` and `gpu_resident` are orthogonal to those three, and to each other. `cpu_resident` asks *"is this asset referenced from a live script-component context, so its bytes are warmed in memory?"* (the `/runtime/assets/` CPU layer); `gpu_resident` asks whether the device holds a texture or mesh under the asset's guid. They are separate pools and an asset can be in one and not the other — `asset.observe()` lists both. See `docs/specs/runtime-asset-copying.md` — "CPU residency vs GPU residency". The backing/runtime flags are derived from where the asset lives — source under `/zero/source/…` (backed), a copy-on-write fork / runtime-generated asset under `/zero/runtime/assets/<identity>.<category>/` (runtime change) — using the canonical `<identity>.<category>/` suffix shape, generic over any category. `cpu_resident` and `gpu_resident` are live queries through `asset.cpuResident` and `asset.gpuResident`.

# opts The contract an options table is held to. A call that reads a fixed set of keys acts on those keys and no others, so a key it does not know names a change the caller asked for and never got — a cube asked for `size = 3` that comes back one unit wide, reporting success. `Opts.check` makes that a refusal carrying what to write instead: the key, the accepted set, and the nearest accepted spelling. The same three parts answer for a name of any kind — `tools.use` names the near-miss toolbox, `MaterialAuthor` names the near-miss shader property — so the distance search lives here too, and every caller ranks candidates the same way. Pure Luau, no engine dependencies. ## Exports - `Opts.check(where: string, value: any, accepted: { string }, inTable?: string)` — raise unless every key of `value` is named by `accepted`. `nil` accepts. - `Opts.forward(where: string, own: { string }, fn, ...) -> ...` — call `fn(...)`, and when it refuses an option, append the vocabulary `where` itself takes. - `Opts.unknown(value, accepted) -> { string }` — the keys `value` carries that `accepted` does not name, sorted. - `Opts.nearest(key: string, candidates: { string }) -> string?` — the candidate `key` is most plausibly a misspelling of, or nil. - `Opts.editDistance(a: string, b: string, limit: number) -> number` — single-character edits between two names, capped at `limit + 1`. ## Usage ```luau local Opts = require("@builtin::modules.opts") -- The keys this call reads, named once. local CUBE_OPTS = { "animate", "scale" } function M.cube(name, x, y, z, opts) Opts.check("primitives.cube", opts, CUBE_OPTS) -- primitives.cube: unknown option 'scail'. Accepted: animate, scale. Did you mean 'scale'? -- The spawn target is handed to `entity.spawn`, so it is that call's -- contract a key is checked against — `own` says what this one takes. local e = Opts.forward("primitives.cube", { "opts.scale", "opts.animate" }, entity.spawn, name) -- entity.spawn: unknown option 'size'. Valid options: name, hidden, … -- (primitives.cube itself takes: opts.scale, opts.animate) end ``` A call taking more than one table names which one the key was written in: ```luau Opts.check("primitives.ground", color, { "r", "g", "b", "a" }, "color") -- primitives.ground: unknown option 'red' in color. Accepted: r, g, b, a. Did you mean 'r'? ``` ## Notes - Refusals raise at level 0: the message is the whole error, so a caller reads the contract rather than the line inside the library that checked it. - A key of any type is reported by how it is written, so the positional form of a named shape (`{ 200, 50, 50 }` for `{ r = , g = , b = }`) names its indices rather than passing as a table with nothing the call reads. - `nearest` is case-insensitive, and a candidate containing the key scores by how much longer it is, so `roughnes` prefers `roughness` over `clearcoat_roughness`. How far a plain misspelling may stray scales with the key's own length — a four-letter key admits two edits, a longer one three — so a short key is not answered with an unrelated short name. - Equal scores go to the shorter candidate, then the alphabetically earlier one, so the answer never depends on the order candidates were listed in. - `forward` matches the phrase both this module and the engine's own option checks use for the condition (`unknown option '<key>'`). Every other error passes through as raised.

# luau_introspect (module) Parses Luau/asset source TEXT into structured declarations. Pure string/pattern parsing (`string.find` / `string.match` / `string.gmatch`) over the literal source — no compiling, no VM spawn, no runtime state, no engine FFI. Given source text, it extracts what is written in the file. This is the shared parser every per-assetType `M.ref.inspect` hook uses to turn a component/module/tool's own source into the structured record `asset.inspect` returns. ## Exports - `docstrings(src) -> DocMap` — scans `--!desc` / `--!arg` / `--!return` / `--!example` comment runs and binds each run to the name of the declaration on the next non-comment line (the identifier after `function`, `public:`, `local function`, or `M.`). - `publicFields(src) -> { FieldEntry }` — parses `public = { name = Field.<kind>(default, mode), ... }` table-literal entries and module-scope `public.<name> = Field.<kind>(...)` assignments. - `events(src) -> { EventEntry }` — parses `events = { name = Event(payloadSchema?, syncMode?), ... }` table-literal entries. - `methods(src) -> { MethodEntry }` — parses `function public:<name>(...)` / `typed function public:<name>(...)` declarations (params + optional return type). - `lifecycleHooks(src, catalog) -> { string }` — top-level `function <name>(` declarations whose name is in the caller-supplied `catalog` array. - `moduleExports(src) -> { ExportEntry }` — parses `M.<name> = function` assignments, `function M.<name>(...)` declarations, and a trailing `return { foo = foo, ... }` export table. - `forSource(src, computeFn) -> any` — memoises `computeFn(src)` keyed on `src` itself in a module-local table. The same source text returns the cached result without re-running `computeFn`; different source text recomputes. Keyed on the source content (not an asset checksum) because composite/container assets (component folders, scene folders, etc.) all hash to the empty-string checksum — a checksum-keyed cache collapses every such asset's detail onto whichever one was inspected first. ## Usage ```luau local Introspect = require("modules.luau_introspect") local src = self:getInitScript() local detail = Introspect.forSource(src, function(s) return { fields = Introspect.publicFields(s), events = Introspect.events(s), methods = Introspect.methods(s), hooks = Introspect.lifecycleHooks(s, lifecycleCatalog), } end) ``` ## Notes - Every function is a pure string→table transform: same source text in, same structured table out, every time. No reads of live component state, no entity/world queries. - Structural scanning runs over a comment- and string-aware **mask** of the source (a same-length copy where comment bodies and string-literal contents are blanked to spaces, delimiters and newlines preserved). Pattern matches and brace/paren balancing run on the mask — so a brace, `Field.`, `Event(`, or a whole entry that appears inside a comment or a string literal never registers — while captured values are sliced from the original source at the same (aligned) indices. This makes the parser robust to apostrophes in comments, commented-out entries, string defaults containing `}` / `Field.` / `Event(`, and `[[ ]]` long strings. - `default` / `category` are raw trimmed source-text slices (with any trailing comment stripped), not evaluated values. - For a **ref constructor** (`Field.assetRef` / `dataRef` / `resource` / `componentRef`) the FIRST positional argument is the category / contract / componentType selector, captured under `category`; the SECOND argument is captured under `default`. - For every **other** Field kind the first argument is the `default` and `category` is nil. - A trailing `Sync` / `NoSync` identifier is captured as `sync`, tolerating a trailing comma or a trailing comment after the last argument. - Field/Event entries whose key is a computed or indirect expression (`[expr] = Field.number(...)`) are omitted — only literal identifier keys are recognised. - `methods` captures a `...` variadic parameter (as `name = "..."`), with its `: <type>` annotation when present. - A `--!desc` written above a field/event declaration (`<name> = Field.<kind>(...)` / `<name> = Event(...)`) or a `public.<name> =` assignment binds to that name in `docstrings`, and is folded into the corresponding `publicFields` / `events` entry's `desc`. - `lifecycleHooks` never hardcodes the lifecycle-callback catalog; the caller passes the list of names to match against. - `forSource`'s memo is bounded (oldest-key eviction) so a long session touching many distinct asset versions can't grow it without limit.

# defaults The Preset Manager: the world's ordered `[[presets]]` rows in `/zero/source/.world_settings`. A row names one declarer (`target`), one preset for that declarer (`preset`) and a path glob (`filter`). When something a declarer governs is created — an asset of an assetType, an import an importer runs, a component added to an entity — the first row naming that declarer whose filter matches the new thing's path gives a layer of its settings. Rows are read only at creation. A component row's filter reads the entity's hierarchy path (names from the root down, joined with `/`). What a scene build's capture scope adds takes the rows in any mode, whoever runs the build; outside a build, a component takes a row when it is added in edit mode. A component put back from existing content takes none: one added inside `materializing` (a saved scene, a peer's record, a template clone, a bundle's hierarchy, a build's records), and one a component's own code adds outside a build, on any coroutine that code runs. A scene build records which fields the rows gave each component, and a rebuild restates a component only when the code states it differently, so a row edit alone changes nothing a build already placed. Rows are written as guid envelopes and checked as a whole. A row is refused when its target does not resolve, is consulted at no creation, or declares no settings; when its preset does not resolve, is not a preset, or targets another declarer; or when its filter is not a string. A write replaces the `[[presets]]` block and keeps the rest of the file byte for byte. ## The row format ```toml [[presets]] target = { __ref = "8cc28fc8-ed63-48ee-83a6-15f4192e27e1", type = "importer", name = "texture" } preset = { __ref = "0b6c1f0e-5d0c-4d5e-9d64-3c1b7f2a9e11", type = "preset", name = "pixel_art" } filter = "sprites/**" ``` `target` and `preset` are guid envelopes: `__ref` is the guid, and `type` and `name` tell a person reading the file what it names. A row written by hand may name either by identity or guid; the next write rewrites it as envelopes. `.world_settings`'s `.refs` pins each row's target and preset by guid. ## Matching For a new thing a declarer governs, the rows are read in order and the first naming that declarer whose filter matches the thing's path applies; the rest are not consulted. A filter is a glob (`preset.glob`) over the path relative to `/source` with forward slashes, or an entity's hierarchy path for a component row; the empty filter matches everything, and a filter that is not a string matches nothing. A matching row whose preset does not resolve, or targets another declarer, is the match and contributes nothing, with one warning. A preset value the declarer's schema rejects is left out and the rest apply. ## Sync The rows are part of `.world_settings`, so they sync with the world like any other file and every peer reads the same rows. A row applies where the creation happens, when it happens: a peer's edit reaches only what is created after it arrives, and what was created before keeps the settings it was stamped with. A runtime asset lives for the engine process; a peer that started before a row edit keeps its old settings on a re-created runtime identity until it restarts. ## Exports - `Defaults.PATH`, `Defaults.BLOCK` — the file and the array-of-tables name. - `Defaults.SCHEMA` — the block's Field schema, `{ presets = Field.list(row) }`. - `Defaults.rows() -> { Row }` — every row, resolved, with its problems. - `Defaults.write(rows)` — normalise, check, and replace the rows. - `Defaults.normalize(input) -> StoredRow` - `Defaults.rowProblems(row) -> (problems, targetRef, presetRef)` - `Defaults.consultedAt(declarer) -> "asset.create" | "import" | "component.add" | nil` - `Defaults.relativePathOf(path) -> string?` — the path a filter reads. - `Defaults.match(declarerGuid, relPath) -> (Row?, index?)` - `Defaults.layerFor(declarerGuid, relPath) -> (values?, Match?)` - `Defaults.check(value, constraint) -> (ok, reason)` — the `presetDefaultRow` constraint. - `Defaults.removeAt(index)` — remove one row, writing every other row back as the file holds it. - `Defaults.importerSettings(importerRef, sourcePath) -> (settings, Match?)` - `Defaults.materializing(fn, ...) -> ...` — run `fn` with no row reaching a component add. - `Defaults.entityPath(id) -> string` — the hierarchy path a component row's filter reads. - `Defaults.forComponent(entityId, typeName, data?) -> data?` — the data a component add takes. - `Defaults.batchLayers(targets, typeName, data?) -> { { targets, data } }` — a batch add split into runs. - `Defaults.resolveValue(v) -> AssetRef?` — a row value as the asset it names. - `Defaults.recordingStamps(fn, ...) -> (stamps, ...)` — run `fn` and return what the rows gave the components a capture scope added meanwhile, per `stampKey`. - `Defaults.stampKey(entityId, componentGuid, instanceName?) -> string` The `preset` global exposes the rows as `preset.defaults`, `preset.setDefaults`, `preset.addDefault`, `preset.removeDefault` and `preset.defaultFor`.

# json JSON encode/decode library for Luau. Encodes Lua values to JSON strings and decodes JSON strings back to Lua values. Used for communication with the Rust side of the engine, the VFS read/write bridge, and any wire-format that needs JSON. Pure Luau, no engine dependencies. Compact and pretty-printed encoders, plus a hand-rolled decoder that streams the input by position so it works under WASM as well as native. ## Exports - `Json.encode(value: any, indent?: string, currentIndent?: string) -> string` — compact encode. Functions / unknown types and NaN/Inf encode as `null`. - `Json.encodePretty(value: any, indentStr?: string) -> string` — pretty-printed encode with sorted object keys (diff-friendly). - `Json.encodeArgs(...: any) -> string` — encode varargs as a JSON array. - `Json.decode(str: string) -> any` — decode a JSON string. Returns the decoded value, or `nil` + error message on failure. ## Usage ```luau local Json = require("@builtin::modules.json") local widget = { type = "button", text = "Click Me" } local compact = Json.encode(widget) -- '{"text":"Click Me","type":"button"}' local pretty = Json.encodePretty(widget, " ") local decoded = Json.decode(compact) local v, err = Json.decode("oops") -- v = nil, err = error message ``` ## Notes - Object keys are sorted alphabetically in both encoders for consistent output across runs. - Numeric keys on objects are stringified at encode time (JSON has no numeric keys). Pure-integer key sets get detected as arrays via `isArray` and encoded with brackets. - NaN, +Inf, -Inf encode as `null` — JSON has no representation. Round trips through `decode` recover `null` (Lua `nil`), so they don't preserve. - Unicode `\uXXXX` escapes decode to UTF-8 by hand to stay WASM-safe. Only the BMP is covered; supplementary planes via surrogate pairs are not. - Functions encode as `null`. - Decode is character-streamed — no regex, no `string.match` patterns on the whole input — so the line-and-column information needs to be reconstructed from the position offset.