Type system

The recursive type tree for store fields, hook fields, schemas, registry props, and callable signatures.

Every typed slot is a field whose type is a recursive type. Leaves are primitives; composites carry payload (object.fields, array.item, ref.refId, and.operands). The discriminator is kind.

The same field shape is used on stores, schemas, components, and form hook fields.

Field

Name	Type	Default	Description
`name`	string	—	Field name. Used in `{{stores.<store>.<name>}}` and `set-property`.
`type`	type	—	See kinds below.
`defaultValue`	matches type, or `{{…}}`	—	Initial value. An expression plus `editable: false` makes a computed field.
`editable`	boolean	`true`	Set `false` with an expression `defaultValue` for derived fields. Do not `set-property` those.
`id`	string	—	Present on top-level store / schema / form fields. Omit on nested object fields and registry slots.
`label`	string	—	Editor label.
`validation`	object	—	`required`, `min`, `max`, `minLength`, `maxLength`, `message`.
`hidden`	boolean	—	Declared but hidden from the props form (`className` lives on the Style panel).
`options`	list	—	Choices for select-style widgets.
`editor`	string	—	Widget override: `input`, `multiline`, `select`, `image-generate`. Not a type.
`discriminator` / `variants`	—	—	Used with `kind: "oneof"` for a form toggle-group.

Where types appear

Surface	What `type` describes
Store `fields`	Runtime state. Read `{{stores.<name>.<field>}}`; write with `set-property`.
Schema `fields`	A named reusable shape. Reference with `{ kind: "ref", refId: "<schemaId>" }`.
Component / primitive registry props	The element's prop bag, including Function slots.
Hook config	`useForm.fields` (same field list); other kinds use a type on their config keys.
Action `params` / `returns`	The store action's signature. Primitive param catalogs are the same field list.
Hook `returns`	The object at `{{hooks.<alias>.*}}`. Callable members are `kind: "function"` — those become `"<hookId>.<method>"` actions.

`kind` values

`kind`	Type	Default	Description
`text`	`{ kind: "text", flavor?: "inline" \| "rich" }`	—	String. `flavor` is how much markup the widget allows.
`number`	`{ kind: "number" }`	`0`	Number.
`boolean`	`{ kind: "boolean" }`	`false`	Boolean.
`date`	`{ kind: "date" }`	—	Date.
`file`	`{ kind: "file", accept?: string }`	—	A file value `{ fileId, name?, format? }` — not a URL string. `accept` is a MIME glob (`image/`, `video/`). An expression that evaluates to a URL is also legal here because the vendor slot is `src`.
`object`	`{ kind: "object", fields }`	—	Nested record. `fields` is a field list. Holds a value of a shape.
`array`	`{ kind: "array", item: type }`	—	List. `item` is any nested type. UI label: List.
`ref`	`{ kind: "ref", refId: string }`	—	An app schema. UI label: Custom Type.
`and`	`{ kind: "and", operands: type[] }`	—	Intersection. Last operand wins on the same field name. UI label: Combined Type.
`or`	`{ kind: "or", operands: type[] }`	—	Type-level union (`string \| string[] \| void`). No stored discriminator.
`oneof`	`{ kind: "oneof" }` plus field `discriminator` / `variants`	—	Form toggle-group: named variants, each with fields. Distinct from `or`.
`element`	`{ kind: "element" }`	—	`{ elementId }`. The renderer hands the vendor a ref; dispatch resolves it to the DOM node (e.g. toast `anchor`).
`component`	`{ kind: "component" }`	—	`{ componentId, instanceProps? }`.
`function`	`{ kind: "function", params?, returns?, async?, identity? }`	—	A function call `{ functionId, instanceParams?, when? }`. See below.
`renderprop`	`{ kind: "renderprop", params }`	—	Nothing is stored on the slot. The element's children are the callback body; declared `params` (a field list) bind as `{{render.<name>}}` (typically `item` / `index`). Return is rendered, not consumed as a value.
`void`	`{ kind: "void" }`	—	Nothing. Only meaningful as a callable's `returns`. Distinct from omitted `returns` (undeclared). UI label: Nothing.
`interface`	`{ kind: "interface" }`	—	The value is a field list (a shape). `useForm`'s `fields` config is this: Object holds a value of a shape; Interface holds the shape.

Schemas (custom types)

Tool	What you use it for
`list_schemas`	List schemas. Pass `schemaId` for the full field tree.
`create_schema`	`{ name, fields }`. Name is PascalCase.
`update_schema`	Replaces the whole `fields` array.

After create, use the schema id as refId — renaming the schema does not break refs.

To describe	Type
That schema	`{ kind: "ref", refId: "<schemaId>" }`
A list of that schema	`{ kind: "array", item: { kind: "ref", refId: "<schemaId>" } }`
That schema plus extra fields	`{ kind: "and", operands: [ { kind: "ref", refId }, { kind: "object", fields } ] }`

A refId that transitively points back at this schema is rejected. Dangling refs are not cycles.

update_schema wholesale-replaces fields. list_schemas first, then send the whole array.

`kind: "function"` — the signature

A Function type carries an optional signature:

Name	Type	Default	Description
`params`	field list	omitted = React `event`	Declaration order.
`returns`	type	omitted = undeclared	`{ kind: "void" }` means returns nothing.
`async`	boolean	—	`false` means the host reads the return now; only a synchronous `code-action` store action may bind.
`identity`	boolean	omitted = wrap as handler	`true` passes the compiled store callable (`filter`, `validate`, …).

The value on that slot is always a function call, never a body. See Function.

A store action or primitive that knows its shape carries the non-partial signature (params / returns on the action; param catalogs on primitives).

Literal vs expression values

A field's defaultValue (and any prop / instanceParams value) is a literal or an expression — type says what the value is, not whether it is bound.

A whole-binding string "{{stores.cart.price}}" is stored as an expression. Mixed text interpolates as a string.

A field is computed when that expression is paired with editable: false. The pairing is the discriminator — computed is not its own kind. The store keeps the expression as the field's value and evaluates it on every {{stores.*}} read. set-property must not write it.

Name	Example
`name`	`total`
`type`	`{ kind: "number" }`
`defaultValue`	`"{{stores.cart.price * stores.cart.quantity}}"`
`editable`	`false`

An expression defaultValue without editable: false is rejected.

Validation

Name	Example
`name`	`email`
`type`	`{ kind: "text" }`
`label`	`Email`
`validation`	`required: true`, `message: "Email is required"`

update_store wholesale-replaces fields (and actions). update_hook(config) wholesale-replaces the hook config, including useForm.fields. Always list_* first, then send the full array.