# Tool (asset type) A tool is a single agent-callable function whose schema is its `typed function` signature. Tools are the workflow surface — composed Luau operations that bundle multiple engine APIs into one named call, suitable for agents (and for use from `execute`). Each tool has a declared input shape, return shape, and a strict result envelope (`ZmToolResult`). **Every exported tool function is declared `typed function`.** The `typed` keyword is what makes the signature real: it compiles to a runtime dispatch wrapper that checks each argument against its declared type and raises on a mismatch. A plain `function` — even one carrying Luau type annotations — is checked by nothing at call time, so the tool accepts any input and reports success on garbage. See "The typed signature is the schema" below. ## When to use one - You're composing several engine APIs into a workflow that's worth naming and discovering (`tools.list`, `search_tools`). - You want an agent to be able to call this function by name without reading source code — the typed signature is the API contract. - The operation has clear success / failure modes that fit `{ exitCode, data?, stdout?, message? }`. If the function is just a Luau utility called from other code, use a `.module`. If it's stateful background work, use a `.service`. If it's pure GPU compute, use a compute `.shader`. ## Where it lives Tools nest under a `.toolbox/` parent — toolboxes are the namespace. - Source: `/zero/source/.../<Toolbox>.toolbox/<name>.tool/` - Identity: `<Toolbox>.<name>` (dotted form — the toolbox name is part of the tool identity). - Folder shape: - `init.luau` (or `init.lua`) — exports the function, and carries its schema in `--!desc` / `--!arg` / `--!return` / `--!example` annotations above it. The typed signature IS the tool's signature. **Required.** - `README.md` — instance documentation. **Required.** - `.metadata` — tool-level tier and tags. **Required.** ## How to create one Use the workflow tool that scaffolds the right `.tool/` shape under an existing toolbox: ```luau -- The `tools` global authors a tool inside an existing toolbox: tools.create({ name = "<name>", toolbox = "<Toolbox>", description = "What this tool does, agent-facing.", code = "return shared.ok(true)", -- the function body }) -- Or scaffold the folder manually: local box = asset.resolve("<Toolbox>.toolbox") asset.create("tool", "<name>", { into = box }) ``` Always nest under an existing toolbox — if you don't have one yet, call `tools.createToolbox({ name = "<Name>", description = "..." })` first. ## How it operates 1. **Registration.** Writing `init.luau` into a `.tool/` folder registers the tool with the tools registry. It becomes callable as `tools.use("<toolbox>", "<name>", ...)` from Luau, `use_tool { toolbox, tool, args }` over MCP, and `zero <toolbox> <name> [args]` from the engine shell. 2. **Schema validation.** The `typed function` signature declares the parameter shape. Its runtime dispatch wrapper checks each argument before the body runs and raises a message naming the argument, the expected type, and what arrived. 3. **Return envelope.** Tools MUST return `ZmToolResult`: ``` { exitCode = 0|n, data? = any, stdout? = string, message? = string } ``` `exitCode = 0` means success; non-zero means failure, with `message` carrying the human-readable reason. 4. **Discovery.** The tool surfaces in `tools.list()`, `search_tools { query: "..." }`, and `asset.inspect`'s `exposes:` section (parsed from the typed signature and the `--!` annotations). 5. **Hot reload.** Editing `init.luau` re-registers the tool. Subsequent calls see the new behaviour / schema. ## Discovery - `tools.list()` — every registered tool (any toolbox). - `search_tools { query: "..." }` — MCP-side tool search. - `asset.list("tool")` — same set, asset-style listing. - `asset.inspect("<toolbox>.<name>")` — signature, parameters, return shape, this type README. - `ls /zero/source/<Toolbox>.toolbox/<name>.tool` lists the files the folder holds. ## Authoring conventions - **Implementation lives in `init.luau`.** The tool's full function body — argument validation, the call into engine APIs, the return value — goes in `init.luau`. The toolbox's `shared.module/` is for genuinely cross-tool helpers (`ok` / `fail` constructors, shared parsers / validators), not per-tool logic. Do NOT make `init.luau` a one-line forwarder onto a function defined in `shared.module/`. - Use `shared.module/` in the parent toolbox for `ok` / `fail` result constructors. Don't hand-roll the envelope per tool. Pull it in with `local shared = require(".shared")` from any tool that needs the helpers. - Annotate every public function with `--!desc` / `--!arg` / `--!return` / `--!example` directly above the function — the LSP and toolbox surfaces extract these. - **Declare every exported function `typed function M.name(arg: T, opt: U?): R`.** This is not conditional on the signature being "clear" — a loose argument is the case that needs the checked contract most. Give the argument the type it actually accepts (a union, a named table type, a literal enum) instead of dropping to an unchecked `function`. - Keep tools focused. One tool, one named workflow. Split rather than grow. - Tag tools in the sibling `.metadata` (`{ "tags": [...], "tier": "core|content|specialized" }`) so `search_tools` can find them by domain (e.g. `entity`, `scene`, `assets`, `physics`). ## The typed signature is the schema The `typed` keyword compiles the function into a dispatch wrapper that validates arguments at call time. Without it there is no check at all, so the tool runs its body on whatever arrived and returns a success envelope built from garbage. Type each argument as narrowly as the operation actually accepts: ```luau export type Mode = "edit" | "play" export type SpawnOpts = { position: { number }?, parent: EntityRef?, count: number?, } --!desc Spawn a primitive and return the entities it created. --!arg kind Primitive shape to spawn. --!arg opts Placement and repetition options. --!return The spawned entity refs. --!example "cube", { count = 4 } typed function M.spawn(kind: ("cube" | "sphere" | "plane"), opts: SpawnOpts?): { EntityRef } ``` - **A fixed set of accepted words is a literal union**, never `string`. `("cube" | "sphere")` rejects `"Cube"` at the call and lists the accepted values in the error; `kind: string` accepts `"banana"` and fails somewhere deeper, or not at all. - **A structured argument is a named `export type`**, never `{ [string]: any }`. Naming it puts every field and its type on the tool's page and checks them on entry. - **A named type is only as strong as its fields.** `opts: DrawOpts` where `DrawOpts = { value: any }` passes for a table and checks nothing inside it — the same hole, one level down. The argument checker walks nested fields, so type each one; a type name is not a place to put the work off. - **A dispatch table keyed by an `op` string is several tools.** `{ op: string, [string]: any }` is one unchecked entry point wearing N signatures — split it so each operation carries its own checked arguments. - **An entity or asset argument is `EntityRef` / `AssetRef<kind>`**, never `any` and never a bare name string. - `any` is correct only for a value the tool genuinely does not constrain — a passthrough payload, arbitrary user data. It is not a placeholder for a type not yet written down. ## Common pitfalls - **A plain `function` export.** The tool registers and dispatches, so nothing looks wrong — it just never rejects bad input, and every call reports success. Declare it `typed function`. - **Annotations without `typed`.** `function M.f(x: string)` reads as typed and checks nothing at runtime; the annotation only informs the LSP. The keyword is what enforces it. - **Wrong return envelope.** Returning a raw value instead of `{ exitCode = 0, ... }` will be flagged by callers expecting `ZmToolResult`. - **Tool identity.** The fully-qualified identity is `<toolbox>.<name>`, NOT just `<name>`. Toolbox-less tools don't exist by design. - **Missing dependency.** Tools requiring another package / service must declare it; otherwise the call fails at runtime with a missing-module error. ## Related types - `.toolbox` — the required parent namespace for tools. - `.module` — for Luau libraries with no agent-facing schema. - `.service` — for stateful background work, not callable request/response operations. ## In the Inspector Tool: how the tool is called (its signature), what it does, each argument, what it returns, and its examples, with **Open** for its source.

# shared Module Cross-tool helpers for the `capture` toolbox. Every tool inside this toolbox can pull these in with `require(".shared")`. ## Purpose This module holds the small set of helpers that more than one tool in the toolbox needs — typically the `ok(value, formatted?)` / `fail(message, exitCode?)` constructors that produce the canonical `captureToolResult` shape, plus any toolbox-wide parsers, validators, or shared state. Keep it focused: per-tool implementation stays inside each `<x>.tool/init.luau` (with its own `--!desc` / `--!arg` / `--!return` / `--!example` annotations). ## Usage ```luau local shared = require(".shared") function M.someTool(...) if not ok then return shared.fail("reason", 1) end return shared.ok(value, "") end ``` ## Exports See `init.luau` for the full export surface. Typical exports include `shared.ok(value, formatted?)` and `shared.fail(message, exitCode?)` for building the toolbox's standard result envelope.

# assetType (asset type) The `assetType` is the **type of types** — the meta-type that every `<typename>.assetType/` folder is an instance of, including itself. A `<typename>.assetType/` folder declares a new asset type called `<typename>`: its on-disk shape, its identity rule, and the structural contract instances of the type must satisfy. This type is self-hosting. `assetType.assetType/` conforms to its own schema — a `type.yaml` plus a `README.md` — so the type system is defined in terms of itself rather than a hidden engine special-case (the same way a C compiler is written in C). Every asset in the engine, including each `.assetType` definition, now resolves to a registered assetType: a `.material` resolves to `material.assetType`, and `material.assetType` resolves to `assetType.assetType`, which resolves to itself. ## Why it exists Assets used to be mapped to their type *implicitly*, by matching the folder suffix against a name-keyed registry. That match carried no stored link: nothing on a `Foo.material` recorded *which* `material.assetType` it was written against, so two worlds shipping a same-named type could silently disagree. Making `assetType` a real, resolvable asset closes that gap — the link from an asset to its type is now an explicit reference pinned in the asset's `.refs` sidecar (`via: "asset_type"`), exactly like every other dependency. ## Where it lives - Source: `/zero/source/.../<typename>.assetType/` - Identity: `<typename>` (the `.assetType` suffix strips from the identity; the folder retains the suffix on disk). - Folder shape: - `type.yaml` — the structural spec the validator reads. **Required.** - `README.md` — type-level documentation. **Required.** - `about.yaml` — three short plain-language texts saying what the type is for (see "Say what your type is for" below). Every built-in type ships one. - `behavior.luau` — optional behavior/scaffolding module. - `template/` — optional canonical placeholder body the templater copies into a new asset of the type. - `<name>.module/` — optional shared code the type ships to **every instance** of it, conventionally `shared.module/` (see below). ## Shared code its instances reach (`asset.containing` + `.modules`) A type ships code every instance of it uses by declaring the modules in its own `behavior.luau`, as a map of tracked `require`s: ```luau -- inside <typename>.assetType/behavior.luau M.modules = { shared = require(".shared") } -- the sibling shared.module/ ``` An instance reaches it with one location-independent line: ```luau -- inside any foo.<typename>/init.luau local api = asset.containing(__FILE__).modules.shared ``` `__FILE__` is the chunk's own VFS path; `asset.containing` resolves the calling asset, and `.modules.<name>` follows the instance's pinned `typeRef` (the type's **guid**, recorded in the instance's `.refs` as `via = "asset_type"`) to the module its type declares. Because resolution follows that link rather than a category name, the same line in an instance of a different type resolves to that type's module, and identically-named modules in two types never collide. `asset.typeRef(target)` reads that guid for any target; `asset.resolve(asset.typeRef(target))` gives the full `AssetRef<assetType>`. See `assetTypes/README.md` § "Shared code: type-owned modules" for the full mechanism. ## How to create one Authoring a new asset type is just creating a `<typename>.assetType/` folder under `/zero/source/`. The engine registers `<typename>` as a category **the moment the folder is written** — no engine restart, no Rust change, and it works for built-in (`@builtin/assetTypes/`) and user-defined types identically. Once `<typename>` is registered, `<name>.<typename>/` folders are recognised as assets of that type and resolve their `asset_type` link back to this definition. Creating a `<name>.<typename>/` folder *before* its `<typename>.assetType/` exists fails fast: the suffix has no registered type, so the folder can't be a valid asset. Author the type first. ## Say what your type is for (`about.yaml`) Every type carries a small `about.yaml` beside its `type.yaml`, and the README you write for the type documents how to author an asset of it. Both are required, and both are meant to be written as you make the type, while you know what it is for. `about.yaml` answers three questions in plain words, one key each: ```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. Name the whole range of things it covers, in the words a game maker would use for them. - **`function`** is how it works today: what an asset of the type is made of and what the engine does with it. - **`usage`** is what a person or an agent does with one: how they pick it, place it, call it, or hand it to something else. A few habits keep it useful. Write about the type as a whole, so the text holds for every asset of it, and leave out any one asset's name. Say what the type does right now. Stay with words a game maker would say, and mention a file name or a call only where a game maker would know it. The limits are in bytes: `intent` 800, `function` 1500, `usage` 1200. Each is generous, and a few sentences usually say it. Why bother: agents working in a world read these three texts to learn what your type is for, so they reach for it when it fits and use it the way you meant. People searching find the type by what they want to make, and the three texts let them tell at a glance whether it is the one they need. `asset.create("assetType", name)` scaffolds the file with all three keys, and a README whose first paragraph is a `[[describe]]` note. Each value starts with `[[describe]]` followed by a note on what to write; replace the whole value with your own words. A value or a README line that still starts with `[[describe]]` counts as not written yet, which the push's check of each asset it carries against its type reports, naming the file. A type you leave as it was is not asked, so older types stand. Many types at once, or one you would rather not write by hand: `services describe` lists the types that lack these texts and what filling them costs, and `{ mode = "all" }` writes them into the same files, where you edit them like anything else you wrote. Where the texts show up: `asset.inspect("<typename>", "assetType")` returns them as `detail.about`, `assetTypeRef:getAbout()` returns them as a table with the keys `intent`, `function` and `usage`, the type's `types/<typename>` guide page ends with an "About this type" section holding them, and the Inspector's Type section lists them at the top. The guide page is this README plus that section, so a README that explains the type well and an `about.yaml` that says what it is for read well together. ## Ask your assets to say what they are A type can ask each of its assets to carry a description: a file, written by the author or generated, that says what that asset is and what it is for. The people and agents who find an asset read it to decide whether it fits, and the author knows what it is for at the moment of making it. **1. Declare the file with a `described` check.** This is the whole requirement: ```yaml files: required: - path: "README.md" # any file name works kind: "file" content: - { check: "described", message: "Say what this widget is for and where it goes." } ``` With that in place: - An asset whose file is missing, empty, or still has a line starting with `[[describe]]` does not meet the type's requirements. `asset.validate` names it, `zm status` and `world.publishBlockers()` list it, and a push that carries it is refused with `message`. - `services describe` finds it (`mode = "find"` lists it and the price) and can write the description for it (`mode = "all"`). It writes only this file. For a YAML file that holds several texts, name the keys and their limits in bytes, the way this type does for `about.yaml`: ```yaml content: - check: "described" keys: - { key: "intent", max_bytes: 800 } - { key: "usage", max_bytes: 1200 } message: "Write intent and usage." ``` `headings` names sections a Markdown file must have. `assetTypes/README.md` has the full check. **2. Optionally, steer what gets generated with a `describe:` block:** ```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>" ``` `guidance` says what a description of your type covers, and `examples` names assets whose descriptions show the shape you want. Without the block, generation still works from the general describing guide and the check's `message`. An example is an asset of your type in the library whose description is a true, written one, never a scaffold's placeholder, and never the asset being described. When the library has none, leave `examples` empty rather than name one that is not. A type whose assets the model cannot perceive (a sound it cannot hear, a motion it cannot see) says so in `guidance`: the description comes only from what the asset's own files state, such as its name and the `.metadata` where a generation service records the prompt that made it, and when they state nothing the model answers `cannot` with that reason. `services describe` then fails that one asset with the reason and leaves its file as it was. **3. Start the file unwritten in your template.** Put a heading and one line that starts with `[[describe]]` and a short note on what to write, in `template/<file>`, so a new asset starts unwritten rather than with text that only looks written. Do not put example content in it: every new asset carries the template verbatim, and the same text on many assets makes them impossible to tell apart in search. Types whose assets say what they are through their own content (a mesh, a texture, a sound) leave this out: declare nothing and nothing is asked. ## The `behavior.luau` contract `behavior.luau` is the type's code. It returns ONE table, and the keys below are the ones the framework reads off it for EVERY type — the surface you get by declaring them. Anything else on the table is your own: reachable by name through `require("@builtin::assetTypes.assetType.shared.ref").loadTypeModule("<typename>")` for a system that knows your type (`computeShader` publishes `dispatchKey` that way), and never called by the framework. ```luau local M = {} M.ref = { ... } -- methods on every AssetRef of this type M.modules = { ... } -- shared code the instances reach M.global = {} -- reserved key; ship the empty table function M.onCreate(name, opts) ... end return M ``` ### The tables | Key | Shape | What the engine does with it | |-----|-------|------------------------------| | `M.ref` | `{ [name] = function(self, ...) }` | Every function becomes a method on every `AssetRef` of this type: `ref:name(...)`, with `self` the ref. This is how a type gives its instances an API. Two names in here are contracted — see below. | | `M.modules` | `{ [name] = require(".sibling") }` | Shared code the type's instances reach through `asset.containing(__FILE__).modules.<name>`, resolved by the instance's pinned `typeRef` guid. See the section above. | | `M.refShapes` | `{ [method] = "TypeName" }` | Declares the result type of a `M.ref` method so the LSP can check what a call site does with it. See the `M.refShapes` section below. | | `M.events` | an events schema | The events an ASSET of this type fires, declared the way a component declares its own. Readers subscribe through `ref.events.<name>:connect(...)`; firing authority stays with the type. Keyed by the asset's guid, so every resolver of the same asset shares the signals and a re-resolved ref re-attaches to subscriptions already there. | | `M.namePattern` | a Lua pattern string | The name shape `asset.create` enforces for instances of this type, replacing the default `^[A-Za-z][A-Za-z0-9_]*$`. | | `M.global` | `{}` | Reserved. Ship the empty table. | ### The lifecycle hooks Each is optional; a type that omits one costs nothing. The engine calls them: | Hook | Signature | When it fires | |------|-----------|---------------| | `M.onCreate` | `(name, opts) -> { [filename] = contents }` | On `asset.create("<type>", name, opts)`. Returns the files that scaffold the new instance, as a map of relative path to contents; the framework writes them. The `opts` type annotation is the schema `asset.create` validates the caller's arguments against, so annotate it. | | `M.onReplace` | `(dest, files) -> { [filename] = contents }` | On an `asset.create` that writes over an asset already at `dest`, after `onCreate`. Receives the files `onCreate` produced and returns the files to write, so a type that re-derives its content (a rig re-imported from its source file) can carry what an author added to the asset it replaces. Optional. | | `M.onRegister` | `(self)` | Once per instance, the first time it registers: on `engine.onWorldLoaded` for instances already in the world, immediately on a live `asset.create`, and when an instance arrives after that sweep (installed, pulled, or synced from a peer). Guarded by the instance's path, so a double trigger never double-registers. An instance that leaves the runtime releases the guard, so one arriving at the same path again registers. This is what makes "write an asset into the world and it takes effect live" work for content that registers into a runtime registry. The `@builtin` library is excluded from the sweep. | | `M.onChange` | `(ref, change)` | On every VFS write to a file INSIDE one of this type's instances. `change` is `{ path, asset, type, kind, origin }`: `kind` is `"edited"` or `"seeded"`, `origin` is `"local"` or `"remote"` (an importer runs on the originator only). **Filter on `change.path`**: the hook fires for any file under the folder, so act on the one you care about. It runs as its own task and may wait on what it reads: a `vfs.read` of bytes only the blob store holds (a binary file on the web build) fetches them. The writes to one asset reach the hook in the order they were made, each once the hook before it has finished. A re-entrancy guard suppresses writes back into the same asset routed inline from the hook, and a write the hook makes is routed on a later frame like any other, so the hook must be convergent on its own: diff the meaningful state and short-circuit while your own regeneration is in flight. | | `M.onDelete` | `(ref)` | When an instance of this type leaves the runtime: it is deleted, or the engine swaps away from the world binding that held it. Its files are gone from `/zero/source` by then. A removal routed while the instance's `onChange` is waiting reaches `onDelete` once that hook, and every write queued behind it, has finished. On a swap the instance still exists in the world it belongs to, and a VFS write the hook makes reaches the world now bound. | | `M.validate` | `(assetRef) -> { { code, message, severity? } }` | On `asset.validate`, after the structural `type.yaml` check, for the type's own SEMANTIC validation. `severity` defaults to `"error"`; error-severity problems flip `ok` to false, warnings do not. A hook that raises or returns a non-table is itself reported as a `validate.hook_failed` error. `world.push` runs this per user asset, so declaring it enforces your type's rules at publish time with no further wiring. | ### The two contracted `M.ref` names Most `M.ref` methods are your type's own surface: name them what you like, return what you like. Two are read by the engine and mean the same thing for every type, so their shape is fixed: - **`instantiate(self, target?, opts?) -> (root, idMap)`** — makes an instance part of the scene. Defining it is the whole opt-in: `ref:canInstantiate()` is true exactly when it exists. Its **return is a contract** — see the next section. - **`inspect(self) -> detail`** — the type-specific half of `asset.inspect`. See its section below. ### Names a type cannot shadow Some keys resolve on every `AssetRef` before per-type dispatch, so an `M.ref` entry of the same name is never reached: `canInstantiate`, `getSource` / `getBytes` / `getText`, `exists`, `deps`, `meta`, `runtime`, `events`, `modules`, `typeRef`, and the residency flags `has_backing_asset`, `has_runtime_changes`, `cpu_resident`, `gpu_resident`. These are the behaviours every asset must expose identically, which is why they win. ### Reloading A `behavior.luau` edit ripples to existing refs with no restart: dispatch reads `mod.ref` fresh each time and `require`'s cache is re-run in place. A type whose folder appears at runtime is picked up on the next dispatch — negative results are not cached either. ## The names your type's assets hold (`references:`) An asset that names another asset by a string depends on it: the named asset travels with it into a pack or a pull, and a name nothing answers to is an unresolved dependency `worldValidation` reports and the push gate refuses. The engine reads `require(...)` and the asset lookups on its own; a name your type's format or API carries anywhere else is one you declare, in `type.yaml`: ```yaml references: # A top-level key of this type's own files that holds a name (or a table of them). keys: - { key: "shader", type: "shader" } # A call's argument, counting from 1, wherever the call is written. args: - { call: "g:node", position: 2, type: "procNode" } # A field of the options table a call takes. fields: - { call: "fx.beam", field: "material", type: "material" } ``` `type` is the category the name resolves in, one of `asset.categories()`. An argument declared once per category, at the same `call` and `position`, takes the name from whichever category answers. A key or a field holds one category: declared again with another `type`, it takes the later one. The block is declared as the type registers, when the library or the world holding it is laid into the VFS, so every reference table reads it whatever script has or has not run. `asset.declareReferenceKey`, `asset.declareReferenceArg` and `asset.declareReferenceField` declare the same things from a script, for a surface that is no type's. ## What search does with your type (`indexing:`) A type declares what search embeds for its instances. **This is not optional and there is no useful default**: ZeroMind runs your declaration and adds nothing of its own, so anything you do not point at is absent from the index — silently, and for every instance of the type forever. Twenty types once shipped with no `indexing:` block and every instance of them was unfindable. A type whose instances are never searchable (a run record, a log) says so with `indexing: none`; every other type declares a recipe. A type without an `about.yaml` beside its `type.yaml` refuses every push that carries it, whether or not the push edited the type. Texts in it that are not written yet follow the rule every `described` file follows: they refuse the push that edits, stages or commits the type. Two words carry the whole thing, and they are the same two the search tool exposes: - **`identity`** — what an instance IS. For anything you can look at, that is the picture (`content:` + `modality: image`, matched directly by a text query). For everything else it is the authored text that says what it is. - **`capability`** — what it DOES and how it is made. Code, settings, the model-written summary of them. A type with no behaviour has no `capability` entry. A type with nothing to look at has no image. Leaving a slot empty is a statement; filling it with whatever happens to be lying around is not. The one you have to decide when authoring a type is: *for an instance of this, what is the thing a person would recognise it by, and what is the thing it does?* A texture answers "the image" and "its compression settings". A module answers "its README" and "its code". Write those two answers into `indexing:` and the rest follows. Three specifics worth knowing before you write one: - **`derive` is instructed by this type's own `README.md`.** A model reads an instance's source and writes a description; what it embeds is the description, not the source. It follows your README to know what it is looking at, so a type whose README says what its instances are gets good derivations for free. There is no prompt to name. - **`derive` loses detail.** It keeps the main technique and drops secondary ones. If the source is code you want searchable by its own vocabulary, declare the same files a second time as `capability` with `extractor: verbatim`. Two entries, same role, different failure modes. - **Never `source: { field: name }`.** A filename is one or two words with no usable embedding, and a corpus indexed that way answers "language runtime" with `say_runtime_2.soundClip`. `facets:` is the second stage: a `file:` embedded whole (`.metadata`, so keys nobody declared still get indexed) plus computed keys that state a value for every instance including `false` — the raw file can imply "not rigged" and can never say it. The full schema, every extractor and the facet sources are in [`assetTypes/README.md`](../README.md); the scaffolded block with inline guidance is in [`template/type.yaml`](template/type.yaml). ## A container whose contents work together (`system: true`) A type that is a container can say its contents are one working whole by declaring `system: true` at the top level of its `type.yaml`. `package` declares it: the components, modules, scenes and tools a package ships are parts of one system. The declaration is plain data, read from the decoded `type.yaml` (`require("@builtin::assetTypes.assetType.shared.declaration").of("package").system`), and a type that leaves it out is an ordinary type. ## What your type looks like (`preview:`) A type declares how its instances are pictured, and the engine makes the picture when something needs it: staging an instance whose `preview.png` is missing or pictures content it no longer holds queues a render, a view that shows the instance asks for one, and `ref:preview()` renders one on demand. An edit renders nothing on its own. Each `preview.png` records the content it pictured, which is how a stale one is told from a current one. The preview studio owns the light, the backdrop, the framing and the camera, and nothing in the world reaches it, so an instance pictures the same in every world. Declare one of four recipes: | `kind` | The picture is | Your type provides | |---|---|---| | `instantiate` | the asset stood in the studio through its own `instantiate` | `ref.instantiate` | | `image` | a file the instance holds, fitted to the frame, nothing rendered | `source.files`, the candidate files in order | | `surface` | the asset painted on a builtin mesh | `mesh`, and `ref.previewMaterial(self) -> { material }` | | `custom` | whatever `ref.preview(self, opts)` returns | `ref.preview` | ```yaml preview: kind: surface mesh: sphere ``` A scene-instantiable type that declares nothing still answers `ref:preview()` through its `instantiate`, but persists no picture: the declaration is what makes the engine keep one. List `preview.png` among the type's files so an instance may hold it. The picture is findable only when `indexing.content` names it. The two are separate statements, and neither is derived from the other: ```yaml indexing: content: - role: identity modality: image source: { file: "preview.png" } ``` `@builtin::assetTypes.assetType.shared.previewRecipe` reads the declaration; the scaffolded block with inline guidance is in [`template/type.yaml`](template/type.yaml). ## Typing a result from the instance (`M.refShapes`) Every method on `M.ref` is checked against the type its `--!return` names, and every asset of the type gets the same one. That is right for most methods and wrong for the ones whose result is shaped by the ASSET: a method answering one entry per child folder, per row of a config, per binding an input map declares. The widest true annotation for those is `{ [string]: Thing }`, and an indexer accepts every key — so a caller's typo reads as valid and nothing reports. `M.refShapes` lets the type state the result per instance. Each entry is `function(self) -> (typeExpression, source?)`: a Luau type expression for THIS asset, and the module whose type vocabulary the expression uses. Read the asset; never run it — stating a type must not take effect. ```lua -- inputMap.assetType/behavior.luau — the shipped example. -- `activate()` hands back one handle per control the map declares. 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)` resolves and `map.noexisting` is reported with the map's real controls. Without it, both pass silently. ### What the call site has to say A per-instance type is matched by the asset's IDENTITY, so it applies only where the reference the method is called on says WHICH asset. Two spellings do: ```lua -- a component field, whose declared default names the asset public = { map = Field.assetRef("inputMap", "@builtin::inputMaps.default", Sync) } local controls = public.map:activate() -- typed for THAT map -- an annotation, naming category and identity local m: AssetRef<"inputMap", "@builtin::inputMaps.default"> ``` `asset.resolve("<identity>", "<category>")` carries the CATEGORY, so the methods the category defines are checked on the result — but not which asset it found, so a per-instance result keeps the category's declared return. A reference that names no asset (`asset.resolve(someVariable)`, a value passed in as a parameter) carries neither, and calls on it are unchecked. That is the same rule everywhere: the checker states what the code states, and a name computed at runtime states nothing. ### The result is a value, not a binding The type belongs to the expression, so it travels the way any inferred type travels. Indexing the call's result is checked; stashing it in a module local and indexing it from another function is not, because the local's declared type is what carries across — and `any` (or no annotation) carries nothing: ```lua -- checked: `d.greting` is reported function awake() local d = public.dialogue:lines() d.greeting:say() end -- NOT checked: `lines` is a module local typed `any` local lines: any = nil function awake() lines = public.dialogue:lines() end function start() lines.greting:say() end ``` Bind what you need at the call site and the names stay checked in both places — the asset-derived type at the boundary, ordinary scoping after it: ```lua local lineGreeting = nil function awake() local d = public.dialogue:lines() lineGreeting = d.greeting -- `d.greting` is reported here end function start() lineGreeting:say() end ``` ### When nothing is reported and you expected something From a call site, a type that is correct and a type that was never published look the same: no diagnostic either way. `require("@builtin::assetTypes.assetType.shared.refShapes").published()` answers which it is. It returns two maps — the category surfaces, and the per-asset results keyed by identity and then by method: ```lua local shapes = require("@builtin::assetTypes.assetType.shared.refShapes").published() shapes.categories.dialogue --> "{ lines: () -> any, lineNames: () -> { string } }" shapes.returns.Shopkeeper.lines --> "{ browsing: Line, farewell: Line, greeting: Line, wares: Line }" ``` An identity absent from `returns` was never published for, which is a different thing from published-and-correct — and the reason to look here rather than at the call site. The answers are recomputed when an instance is written, so a control added to a map reaches the checker with no restart. Only types that declare `refShapes` are read per instance, and at most 64 assets of one type are — past that the type keeps its declared return and the engine log names what was dropped. ## The instantiate hook (`M.ref.instantiate`) — a contracted return A type opts into becoming part of the scene by defining `instantiate` on its `ref` table. That is the whole opt-in: `ref:canInstantiate()` is true exactly when the hook exists, so consumers offer a scene path — an `Asset.source` field, a viewport drop, a tool argument — by CAPABILITY rather than by a list of type names. Unlike `inspect`, this hook's **return is a contract**. A caller writes one piece of code against every instantiable type, so what comes back cannot vary by type: ```lua -- behavior.luau local Instantiable = require("@builtin::assetTypes.assetType.shared.instantiable") local M = {} M.ref = { instantiate = function(self, target, opts) local root = Instantiable.root(self, target, opts) -- IN: the base opts -- ... compose whatever this type is, under `root`, NOW ... return Instantiable.result(self, root, idMap) -- OUT: the contract end, } return M ``` **IN.** `target` is an owning entity ref: the instance lands under (or, for a hierarchy type, onto) that owner. With no target the type spawns a fresh root. `position`, `rotation`, `scale`, `name` and `temporary` mean the same for every type — `Instantiable.root` applies them to a root you mint, `Instantiable.place` to one you adopt, so you never re-read the spec. Honour more opts of your own if your type needs them, and document them in the hook's `--!arg` docs. **OUT.** Return `(root, idMap)` through `Instantiable.result`: - **`root`** — the composed root, as an `EntityRef`. Composition is **synchronous**: everything your type builds is live when you return, so the caller can parent to it and read its components in the same statement. Do not defer the work to a component's `awake` and return an empty shell — a root that is not live is refused. - **`idMap`** — the `originalId -> runtimeId` map naming what you spawned, or nil for a type with no addressable children (`result` normalises it to `{}`). **A caller never receives nil.** A component that re-composes your asset on every load keeps this map and passes it back in, which is how a cross-entity reference into the composition survives a reload. `AssetRef` runs every `instantiate` through `result` on the way out whether or not your type called it, so returning something else fails at your own call rather than handing a caller a nil root. Calling it yourself is still how you say what you return, and running it twice changes nothing. `@builtin::assetTypes.assetType.shared.instantiable`'s README is the full reference for both halves. ## The inspect hook (`M.ref.inspect`) `asset.inspect(ref)` resolves `ref`, builds a common envelope shared by every asset (`identity`, `name`, `guid`, `source`, `typeName`, `typeDefinitionPath`, `scope`, `origin`, `description`, `tags`), then calls the resolved type's own inspect hook — `M.ref.inspect(self)` on `behavior.luau` — for the type-specific `detail`. The hook returns *only* `detail`; the framework fills in everything else: ```lua -- behavior.luau local M = {} M.ref = { inspect = function(self) -- self.path is the asset's own folder. Parse the asset's OWN -- files — source text, a native payload header, its `.metadata` -- — never runtime state (a live component instance, a GPU -- upload, a compiled schema): inspect must work on an asset that -- hasn't been compiled, uploaded, or registered yet. return { -- type-specific fields, whatever this type wants to surface } end, } return M ``` A type that omits `M.ref.inspect` yields the generic record: the envelope alone, `detail = nil`. That's a valid, working state — not an error — but it means agents calling `asset.inspect` / `tools.use("assets","describe", ...)` on an instance of the type see only identity and scope, none of what makes an instance of it meaningful. Declaring the hook is what makes a type's instances inspectable for what they actually are. A hook that raises leaves `detail = nil` and sets `record.warning` to the error text — `asset.inspect` itself never raises for a resolved ref. ## Discovery - `asset.list("assetType")` — every registered asset type. - `asset.inspect("<typename>")` — the type's identity, source path, and this README, plus its `about.yaml` texts as `detail.about`. - `asset.resolve("<typename>", "assetType")` — the `<typename>.assetType` asset itself (used by the validator to find the type's `type.yaml`). ## Related - `assetTypes/README.md` — the full `type.yaml` schema and validator rules. - `@builtin::assetTypes.assetType.shared.instantiable` — the instantiation contract's shared implementation, both halves. - Every other `*.assetType/` here — the concrete types built on this meta-type. ## The Inspector a type ships Every type names the file its Inspector sections come from with `inspector: { type: "inspector.luau" }` in its type.yaml. `asset.create("assetType", name)` scaffolds the block and an `inspector.luau` whose Contents section lists an asset's files, built from `ctx.parts`. `asset.validate` on a type that names none reports `assetType.inspector_required` (an error for a `@builtin` type the engine's library authors; a warning for a world's own, and for one the library carries by reference, which the world that published it answers for), and one whose file does not load `assetType.inspector_invalid`. ## In the Inspector Type: what the type.yaml declares (suffix, container, primary files, the settings and inspector blocks), whether the type ships a behavior, how many instances it has, and **Open** for its files. Schema: the settings every instance carries, as read-only typed controls at their defaults (a type whose schema is per instance says where it is declared). Instances: a link to each of the first 20 assets of the type, and how many there are when there are more.

# 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. 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()`. Globals leak across reloads. 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**.

# capture Render a screenshot of the scene from anywhere — an explicit position, a named camera station around an entity, a specific camera, or a mirror of the active viewport — and a grid of them in one image; or read back the frame the engine actually presented, exactly as the player saw it. The picture of the machine's own camera (a webcam, a phone camera) is `cameraInput`, covered by the `topics/camera-input` guide; this toolbox photographs the scene. Every source but `presented` and `window` (see [The presented frame](#the-presented-frame)) spawns an ephemeral offscreen camera, triggers one render, and returns the picture as an image value — returned from a tool, a probe or `execute`, it reaches you as a picture, with what the capture has to say about it (its size, the frame it is of, the cells of a grid) beside it. A PNG is written as well when you pass a `path`. The convenience wrappers render from a world-space position (with optional look-at), frame a target entity, mirror the active viewport camera including its layers, or render a specific camera by name from its exact authored pose and settings (`fromCamera`, with optional per-capture overrides that never touch the camera); they run as a background task that waits for the GPU readback and cleans up — which only works in play mode, since the task scheduler ticks there. The low-level oneshot spawns the camera, triggers one render, and returns the handles synchronously — the only path that works from edit mode, and the one the `capture` MCP tool is built on. A cleanup tool clears the capture output directory. ## Where a shot lands A capture given a `path` writes the PNG there and says where those bytes stand, beside the path it wrote: `durable` is true when the PNG is on the path it names and the next session reads it back, and false when the play shadow took it (live in this session and discarded on a guarded play-exit unless kept, with `survivesRestart` saying whether a restart keeps it and `playShadow` naming the routes that keep it) or when the path is in `/source/tmp/` scratch (gone when the engine stops or restarts, with a `warning` opening `SCRATCH`). Every capture carries it on the picture it returns as `durability`. Shooting gameplay means shooting in play, which is exactly when a `/source` destination is the shadow's, so this is the field that says whether a shot survives leaving play — `vfs.promotePlayShadow(path)` keeps it with play still running. ## The presented frame `source = "presented"` reads back the frame the engine presented to the player instead of rendering one. Nothing is drawn for it: it is the frame the viewport drew, copied out as it was finished, after the post chain, the upscale, the display transform, the content UI and every post-scene pass, at the size it was composed at. So it is the one capture whose temporal antialiasing, motion blur, camera motion, auto exposure and render scale are the real ones, and the source to verify any of them with. `source = "window"` is the whole presented surface (the window, the browser canvas or the headless framebuffer) with everything painted on the window: the editor's chrome and every window-level UI pass. Where no Scene panel shows the viewport, the two are the same image: the scene fills the window and the editor's chrome is painted over it, and each such frame says so in its `note` (a cell of a `presented` capture, a frame `renderer.presentedFrames` returns) for as long as that chrome is on the window. Show the Scene panel (the editor toolbox's `layout` tool) to read the game view alone. `frames = n` (1-32) takes n presented frames, one every `interval` frames (default 1: consecutive), at real gameplay speed, and lays them out as a grid in the order they were presented. Each cell states what its frame was drawn with: `frame` (the renderer's count, so consecutive frames carry consecutive numbers), `rasterWidth` / `rasterHeight` (the size the scene rasterized at), `compositeWidth` / `compositeHeight`, `renderScale` and `scaleMode`, `jitter` (the projection's sub-pixel offset in raster pixels), `exposure` (what the display transform multiplied the scene by) and `historyReset` (the viewport camera's first frame, a cut, or a hand-over to another camera). A single frame comes back at the size it was presented at; `width` / `height` resample it, or size the sheet a grid is laid into. A presented frame is drawn through the camera, layers, lens and chain that drew the screen, so the options that aim, light or shape a rendered frame (`camera`, `entity`, `position`, `viewpoint`, `fov`, `pass`, `renderLayers`, `postProcessing`, `environment`, `mode = "collage"` and the collage axes) are refused for it; aim the camera holding the viewport instead, or take an offscreen capture. A source that renders refuses `frames` and `interval` the same way, since they count presented frames. `deterministic` and `clearAir` hold the clock and the air for the whole engine, so they reach the presented frame too. A diagnostic buffer of the viewport itself, under its real camera motion and history, is read the same way: put the camera holding the viewport on that pass (the camera toolbox's `set` with `debugPass = "motion_vectors"`) and take `source = "presented"`. The viewport's velocity buffer is the frame's travel against the frame before it, so a turning camera reads in it, where an offscreen `pass = "motion_vectors"` holds the objects' own motion alone. The `motion_vectors` picture is a visualization: each channel is the square root of 100 times the stored displacement's size on its axis (R horizontal, G vertical, B the length), the sign is dropped, and R reads 255 from `width / 200` px of horizontal travel, G from `height / 200` px of vertical travel (raster pixels). The rendering guide's "What the `motion_vectors` picture encodes" states it in full. The same frames, with their pixels as `TextureCpuHandle`s, come from `renderer.presentedFrames({ scope = "viewport" | "window", frames, interval })`, and `velocity = true` adds the viewport's velocity buffer from each frame as numbers (`frame.velocity`, a `VelocityField`): each pixel's travel in pixels per frame, x right and y down, signed and unclamped, read with `field:at(x, y)`, `field:row(y)` and `field:region(rect)`. ## The feed Every capture publishes the frame it made to `@builtin::tools.capture.feed`, so a viewer can show the newest one without taking a shot of its own. `Feed.latest()` is that frame: a `src` an image widget draws (the render target's guid while the engine still holds it, the written path when the capture produced a file), with the size, the source and the pass beside it. `Feed.watch(fn)` calls `fn` as each new frame arrives. The editor's Capture panel is built on it, and the `watch` layout puts that panel under the scene. A viewer calls `Feed.shown()` to say it is drawing frames from the feed. From then on the feed holds the newest capture's render target so the picture stays up after the capture that made it is finished with it, and lets it go when a later frame replaces it; `Feed.shown(false)` stops. With nobody drawing, a capture's target is released the moment its capture is done, and nothing is held. ## Viewpoints A **viewpoint** names where the camera stands and which way is up in the image: `front`, `back`, `left`, `right`, `top`, `bottom`, `iso`. It replaces reverse-engineering a `{yaw, pitch}` pair, and names the seven stations that answer "is this built correctly". `basis` says which axes the name is measured against, and it is **required** alongside a viewpoint when a subject is being framed: - **`"local"`** — the subject's own axes. `front` is the side it faces however it is turned, and the frame is fitted to its own extents rather than to the world-axis box around them. - **`"world"`** — the world axes. `front` is whatever faces world +Z. For a crate turned 40 degrees those are different pictures, so the call says which one it wants. Framing a world position rather than an entity, both values mean the world axes and either is accepted. ## Passes `pass` names **what** the frame holds, by name. `"final"` is the lit picture; a built-in diagnostic pass (`albedo`, `normal`, `depth`, `motion_vectors`, …) replaces the shaded image with the buffer behind it; and any capture **view** a render feature has published (`renderer.captureView.list()` enumerates them) is selectable by its own name. A name that is neither is refused against the list of what is registered. The name carries two decisions: which channel the camera renders, and which render layers that channel is legible under. A diagnostic buffer is read flat, so the sky behind it and the post-process chain over it come off; a view that draws its own geometry declares the layers it needs and is rendered under them. Stating `renderLayers` answers that second question yourself, for the one call. `passes` spreads the same vocabulary across the cells of a collage, and each cell reports the layers it was read under. ## Projection `projection = "orthographic"` covers a fixed world-space height at every distance. Parallel edges stay parallel and two equal-size objects at different depths cover equal pixels, which is what makes it the projection to check a shape or compare sizes under — a perspective frame's convergence hides both. `orthoHeight` sets that height; omit it and it is fitted to what is being framed. Any camera can be orthographic, not only a capture: it is a field on the `Camera` component. A capture through a camera the scene holds (`fromCamera`, `viewport`, and `source = "camera"`, `"screen"` or the scene camera) takes that camera's `projection` and `orthoHeight` with the rest of its lens, and its lighting `environment` with an `isolated` camera's background and ambient; a `projection` or `orthoHeight` stated for the call stands over the camera's. ## Which entity a capture framed A capture names an entity, or a camera to render from, by its id or by its name. A name exactly one entity carries means that entity. A name several entities carry means none of them on its own, so the capture is refused, and the refusal says how many entities carry it and names each by name and id; pass the id of the one you mean. A player is drawn as its body, so a capture of a player identity (an entity carrying `UserIdentity`, named `user`) frames the body its `avatar` names. A player prototype is absent from the live scene while it plays, so its name reaches no entity there: a capture of that name is refused, and the refusal names each player spawned from the prototype, by its identity and its body, with their ids. Every cell of a capture aimed at an entity reports what it framed under `subjects`: one `{ id, name }` per subject, carrying `playerIdentity = { id, name }` when the picture is the body of the identity the capture named. ## Isolate Framing a subject fits the **frame** to it; it does not decide what is drawn in that frame. Everything else standing there is still rendered — and a scene's default player spawn sits at the world **origin**, which is exactly where a prop usually gets built, so a tight shot of a new prop at the origin can come back showing the player instead. `isolate = true` draws the subject without the other geometry. It changes exactly that — lighting, sky and post-process are untouched, so a final frame stays a final frame, and a flat read of the geometry is a `pass`. Excluded geometry still casts shadows onto the subject and still bounces light into it, the same as any render-layer exclusion. In a `setups` collage each cell shows the entity its own set-up frames alone, and a set-up can state `isolate` for its own cell; a set-up aimed from a position or a camera frames no entity and is refused when it is to be isolated. ## The tone the frame carries Every capture reports `luma` on its cell record: the tone of the pixels it just encoded, in code values on the 0-255 scale the image is delivered at. ``` luma = { pixels, min, max, mean, p1, p5, p50, p95, p99, span, spread, crushed, clipped } ``` `span` is `max - min` — the whole range, a single stray pixel included. `spread` is `p95 - p5` — the range the body of the picture occupies, which is the reading that answers whether a shot is legible. `crushed` and `clipped` are the shares of the picture sitting at code 0 and at code 255. A frame's mean cannot answer that question: half a picture at 40 and half at 200 carries the same mean as a flat field at 120, and only one of them has anything in it. A subject can be modelled, shaded, lit and drawn and still arrive inside a handful of code values, in which case the image looks like a wash and every other field here reports success. `spread` is the number that says so. The same reading is available anywhere pixels are: `cpu:tone()` on a `TextureCpuHandle` — from `renderer.texture.readback(rtHandle)` on a capture handle, from a render-to-texture camera's target, from a CPU canvas — and `cpu:histogram()` under it, the per-code-value counts for luminance and for each of the three channels, which every reading above is a sum over. `cpu:histogram(x, y, w, h)` counts one rectangle of the picture alone, so a reading per region of the frame — how much of each cell is dark, lit or a given colour — is one call per region. `cpu:flip(reference)` holds the picture against another of its size by NVIDIA FLIP, the comparison a golden is judged by; `@builtin::modules.postMetrics` carries it with the golden runner, the pixel metrics (banding, temporal variance, halo overshoot, ring energy, hue drift) and the scopes, each reading a presented frame or a capture result as it comes. ## The grade an offscreen frame carries A capture spawns its own camera and renders offscreen, and the post-process chain runs over that frame the way it runs over the viewport's — for a station, for an orbit around an entity, for a named camera, for a render-to-texture camera alike. Inside an effect, `engine.view_proj` / `engine.prev_view_proj` / `engine.inv_view_proj` are the camera THAT render was drawn from and `engine.resolution` is that target's own size, so a grade that reconstructs world space from scene depth reconstructs against the station and lens the capture asked for. That makes an offscreen capture an oracle for an authored look: it photographs a chosen station and lens without taking the on-screen camera away from whoever else is driving the scene, and moving that camera somewhere else does not move the frame this one returns. An offscreen render keeps no view history of its own, so `engine.prev_view_proj` there holds that same matrix rather than the frame before it, and a pass taking camera motion from the two reads none. On the viewport the pair is a frame apart, so a camera's motion (and the blur and temporal reconstruction built on it) is read from the presented frame: `source = "presented"`. A render feature's passes reach an offscreen render the same way, against the same camera — the `renderFeature` assetType README carries that half, including `@frame.camera`, its own per-target camera input. `render(ctx)` itself runs once a frame for the main viewport, so `ctx.viewport` is the window's size rather than the captured target's; a feature sizes its scratch with `screen = true` and lets the engine track the drawn target. `postProcessing = false` takes the chain off the frame a capture returns, and with it the film a render feature draws — the flare and grain, a short focus's bokeh, the shutter's smear. It is a `Camera` property rather than a render layer, so `renderLayers` does not reach it. A capture naming a diagnostic `pass` drops the chain by default, so the buffer comes back as the value it encodes. ## Collage `collage` renders a grid of frames into one image. What varies across its cells is what you pass — `setups` for a cell per whole camera set-up, `viewpoints` for a cell per view of one subject (or `"sides"` for all six), `passes` for a cell per render pass, `duration` for a cell per sample over time. A collage with no axis is refused rather than quietly sampling time. `setups` is the shot list: each entry is written the way a single capture is aimed (`source`, `camera`, `entity`/`entities`, `position`, `lookAt`, `rotation`, `distance`, `angle`, `margin`, `viewpoint`, `basis`, `projection`, `orthoHeight`, `fov`, `near`, `far`), plus `label` to name the shot on the result, and a field an entry leaves out comes from the collage's own options. `setups` and `viewpoints` are one axis — both say where the camera stands — so a request names one of them; either crosses with `passes` into a 2D grid, a row per station and a column per pass. The shot most of this exists for is one call: six sides of one object, each an orthographic elevation, nothing else in frame. Authoring the cameras themselves — creating, listing, aiming, framing, and setting their parameters — is the `camera` toolbox.

# 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.

# 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.

# ik.reach How far a limb can extend, and how far away a point is, in the same units — plus whether that point falls inside the reachable band. Part of `ik.toolbox`; surfaces as `ik.reach`. This is the first thing to check when an IK solve looks inert. A limb reaches as far as its bones are long and no further: a target beyond that has no solution, so the chain extends straight toward it and stops. That is correct behaviour and it is indistinguishable from a broken solver by eye. There is a lower bound too — a two-bone chain cannot fold its tip closer to the root than the difference between its segment lengths. Everything is reported in world units, so the rig's model space never has to be reasoned about. That matters because a limb's `reach` as the component reports it is in model space, where a 0.61 m arm reads as about 61, and the scale factor usually lives on a node inside the imported body rather than on the entity you set `localScale` on. Takes either a canonical limb role (`leftarm`, `rightarm`, `leftleg`, `rightleg`) or a `"rootBone..tipBone"` pair, so it works on rigs that carry no retarget profile at all.

# assetType runtime The machinery that reads a `<typename>.assetType/behavior.luau` and turns its declarations into live behaviour. A `behavior.luau` is a table of declarations — `ref` methods, `modules` shared code, an `events` schema, a `namePattern`, `refShapes`, and the `onCreate` / `onRegister` / `onChange` / `onDelete` / `validate` / `settingsDefaults` / `settingsCorrections` hooks. None of it runs itself. This is the code that runs it, and it lives here because reading a type's declarations is the **assetType type's own behaviour** — the same way `material.assetType` owns what a `.material` does. ## Sub-modules | Module | Reads | Responsibility | |---|---|---| | `ref.module` | `ref`, `modules` | Builds every `AssetRef` envelope, attaches the shared metatable, and dispatches per-type methods and shared modules onto it. Also owns edit-mode write-behind persistence. | | `create.module` | `onCreate`, `namePattern`, `validate` | Backs `asset.create`: resolves the type, checks the name against its pattern, runs `onCreate` (or clones `template/`), and writes the instance. `validate.module` beside it checks a creation `opts` table against the type's `createSchema`. Before running `onCreate`, resolves the type's settings chain (below) and hands the result to the hook as `opts.settings`. | | `settings.module` | `settings`, `settingsDefaults`, `settingsCorrections` | A type's declared settings schema and where its values live (`type.yaml`'s `settings:` block). `Settings.resolveForCreate` layers the schema's own defaults, the type's own `settingsDefaults(name, opts, asked)` hook (a DEFAULT the schema can't express — a name-derived convention, a fact read off a payload the caller handed it, a value following a field `asked` shows a higher layer naming; any later layer overrides it), the Preset Manager, an importer's settings, the caller's `settings` table, then the type's own `settingsCorrections(values, name, opts)` hook (a CROSS-FIELD CONSTRAINT the schema can't express, applied last over the fully merged values). A correction over a default/preset/importer value lands silently; a correction that would override what the caller's own `settings` table explicitly asked for refuses the creation instead, naming the field and why. Neither hook is ever handed a table to mutate; each returns what it wants changed (`settingsCorrections` may also return a `{ [field]: reason }` table for that refusal message). `Settings.cloneValues` deep-copies a values table — `create.module` hands `onCreate` a copy, never the table it stamps. `Settings.valuesOf` / `writeValues` read and write an asset's own values file. | | `typeYaml.module` | `type.yaml` | The folder a type lives in and its parsed `type.yaml`, decoded once per content version of the file. `settings.module` and `inspector.module` read their blocks through it. `about` / `aboutAt` read a type's `about.yaml` (`intent`, `function`, `usage`), leaving out any key that is empty or still starts with `[[describe]]`; `aboutRows` and `aboutMarkdown` lay the texts out for the Inspector and the `types/<name>` guide. | | `inspector.module` | `type.yaml`'s `inspector:` block | Which inspector a type declares for its assets (`inspector: { type: ... }` or `{ instance: ... }`), and the declaration that file returns — the sections it adds, the generic ones it replaces, and their order — or the problem that kept it from loading. | | `onRegister.module` | `onRegister` | Fires an instance's once-only registration hook — on arrival, on world load, and for `@builtin` library instances. | | `changeDispatch.module` | `onChange`, `onDelete`, `refShapes` | Routes a VFS source write or a folder delete to the enclosing typed asset's type hooks. | | `refShapes.module` | `refShapes`, `ref` | Publishes what every `AssetRef<category>` answers to, so a member read on an asset-typed value is checked against that category's real surface. | | `events.module` | `events` | The per-asset event runtime behind `ref.events`. | | `instantiable.module` | `ref.instantiate` | The instantiation contract an asset type opts into: `root` stands the root entity, `place` applies the base placement opts to one the type adopted, and `result` shapes the `(root, idMap)` every `instantiate` returns. Also registers the `sceneInstantiable` field-constraint validator. | | `declaration.module` | `type.yaml` | The type's decoded declaration, read once and held until a write inside an `.assetType` folder; what every question about a type as a whole reads. | | `previewRecipe.module` | `type.yaml` `preview:` | How an instance's `preview.png` is produced: which of the four recipes (`instantiate`, `image`, `surface`, `custom`) the type declares, and what that recipe needs. | ## Reaching it ```luau local rt = require("@builtin::assetTypes.assetType.shared") rt.ref.loadTypeBehavior("material") ``` Fields resolve lazily. The prelude requires the sub-modules directly, in dependency order (`ref`, then `changeDispatch`, `onRegister.install()`, `refShapes.install()`) — a table that required all six on load would take that ordering away from it.