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chore(plugin-mcp): improve schema sanitization and test coverage (#15704)
- Improve Schema validation — verifies that the MCP tools/list response generates correct input schemas for each field type (correct type, enum values, nested properties, layout field flattening, etc.) - Adds a new FieldTypes collection test suite covering the full range of Payload field types over MCP
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‎packages/plugin-mcp/src/utils/schemaConversion/sanitizeJsonSchema.ts‎

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@@ -4,6 +4,11 @@ import type { JSONSchema4 } from 'json-schema'
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* Removes internal Payload properties (id, createdAt, updatedAt) from a
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* JSON Schema so they don't appear in the generated Zod validation schema.
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* Also strips `id` from the `required` array when present.
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*
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* Additionally normalizes nullable type arrays (e.g. `['array', 'null']` →
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* `'array'`) throughout the schema tree. Without this, `json-schema-to-zod`
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* emits a Zod union which the MCP SDK serialises back as `anyOf`, stripping
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* the concrete `type` from the output and breaking schema introspection.
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*/
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export function sanitizeJsonSchema(schema: JSONSchema4): JSONSchema4 {
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delete schema?.properties?.id
@@ -17,5 +22,41 @@ export function sanitizeJsonSchema(schema: JSONSchema4): JSONSchema4 {
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}
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}
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if (schema.properties && typeof schema.properties === 'object') {
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for (const key of Object.keys(schema.properties)) {
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const prop = schema.properties[key] as JSONSchema4
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if (!prop || typeof prop !== 'object') {
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continue
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}
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normalizeNullableType(prop)
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if (prop.properties) {
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sanitizeJsonSchema(prop)
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}
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if (prop.items && typeof prop.items === 'object' && !Array.isArray(prop.items)) {
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sanitizeJsonSchema(prop.items)
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}
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}
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}
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return schema
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}
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/**
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* Strips `'null'` from a `type` array only when the remaining type is a
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* complex structural type (`array` or `object`).
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*
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* Simple scalar types (`string`, `number`, `boolean`) are intentionally
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* preserved as `['string', 'null']` so that the MCP SDK serialises them as a
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* compact inline `type` array. Complex types however cause `zodToJsonSchema`
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* to emit `anyOf: [{ type: 'array', items: ... }, { type: 'null' }]`, which
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* has no top-level `type` property and breaks schema introspection by clients.
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*/
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function normalizeNullableType(schema: JSONSchema4): void {
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if (!Array.isArray(schema.type)) {
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return
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}
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const nonNullTypes = schema.type.filter((t) => t !== 'null')
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if (nonNullTypes.length === 1 && (nonNullTypes[0] === 'array' || nonNullTypes[0] === 'object')) {
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schema.type = nonNullTypes[0]
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}
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}

‎test/plugin-mcp/collections/FieldTypes.ts‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,210 @@
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import type { CollectionConfig } from 'payload'
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export const fieldTypesSlug = 'field-types'
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export const FieldTypes: CollectionConfig = {
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slug: fieldTypesSlug,
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fields: [
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// Atomic data fields
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{
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name: 'textField',
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type: 'text',
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admin: {
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description: 'A simple text field',
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},
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},
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{
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name: 'textareaField',
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type: 'textarea',
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admin: {
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description: 'A textarea field',
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},
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},
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{
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name: 'numberField',
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type: 'number',
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admin: {
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description: 'A number field',
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},
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},
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{
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name: 'emailField',
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type: 'email',
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admin: {
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description: 'An email field',
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},
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},
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{
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name: 'checkboxField',
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type: 'checkbox',
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admin: {
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description: 'A checkbox field',
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},
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},
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{
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name: 'dateField',
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type: 'date',
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admin: {
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description: 'A date field',
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},
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},
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{
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name: 'codeField',
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type: 'code',
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admin: {
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description: 'A code field',
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},
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},
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{
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name: 'jsonField',
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type: 'json',
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admin: {
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description: 'A JSON field',
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},
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},
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{
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name: 'selectField',
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type: 'select',
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admin: {
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description: 'A select field',
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},
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options: [
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{ label: 'Option One', value: 'option1' },
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{ label: 'Option Two', value: 'option2' },
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{ label: 'Option Three', value: 'option3' },
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],
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},
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{
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name: 'radioField',
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type: 'radio',
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admin: {
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description: 'A radio field',
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},
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options: [
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{ label: 'Radio One', value: 'radio1' },
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{ label: 'Radio Two', value: 'radio2' },
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{ label: 'Radio Three', value: 'radio3' },
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],
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},
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// Array field
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{
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name: 'arrayField',
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type: 'array',
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admin: {
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description: 'An array field with nested items',
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},
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fields: [
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{
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name: 'item',
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type: 'text',
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},
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{
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name: 'itemNumber',
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type: 'number',
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},
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],
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},
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// Group field (stored as nested object)
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{
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name: 'groupField',
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type: 'group',
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admin: {
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description: 'A group field with nested properties',
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},
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fields: [
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{
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name: 'groupText',
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type: 'text',
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},
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{
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name: 'groupNumber',
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type: 'number',
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},
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],
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},
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// Upload field
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{
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name: 'uploadField',
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type: 'upload',
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admin: {
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description: 'An upload field',
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},
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relationTo: 'media',
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},
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// UI field (display-only, not stored, should be absent from create/update schema)
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{
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name: 'uiField',
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type: 'ui',
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admin: {
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components: {},
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},
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},
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// Collapsible layout field (children are flattened to top level in the document)
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{
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type: 'collapsible',
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label: 'Collapsible Section',
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fields: [
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{
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name: 'collapsibleText',
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type: 'text',
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admin: {
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description: 'Text field inside a collapsible container',
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},
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},
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],
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},
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// Row layout field (children are flattened to top level in the document)
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{
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type: 'row',
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fields: [
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{
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name: 'rowText',
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type: 'text',
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admin: {
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description: 'Text field inside a row container',
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},
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},
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],
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},
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// Tabs field with both named and unnamed tabs
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{
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type: 'tabs',
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tabs: [
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// Named tab - stored as a nested object at `namedTab.namedTabText`
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{
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name: 'namedTab',
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label: 'Named Tab',
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fields: [
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{
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name: 'namedTabText',
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type: 'text',
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admin: {
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description: 'Text field inside a named tab',
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},
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},
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],
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},
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// Unnamed tab - children are flattened to the top level of the document
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{
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label: 'Unnamed Tab',
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fields: [
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{
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name: 'unnamedTabText',
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type: 'text',
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admin: {
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description: 'Text field inside an unnamed tab',
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},
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},
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],
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},
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],
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},
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],
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}

‎test/plugin-mcp/config.ts‎

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Original file line numberDiff line numberDiff line change
@@ -5,6 +5,7 @@ import { fileURLToPath } from 'url'
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import { z } from 'zod'
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import { buildConfigWithDefaults } from '../buildConfigWithDefaults.js'
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import { FieldTypes } from './collections/FieldTypes.js'
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import { Media } from './collections/Media.js'
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import { ModifiedPrompts } from './collections/ModifiedPrompts.js'
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import { Pages } from './collections/Pages.js'
@@ -27,7 +28,17 @@ export default buildConfigWithDefaults({
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baseDir: path.resolve(dirname),
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},
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},
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collections: [Users, Media, Posts, Products, Rolls, ModifiedPrompts, ReturnedResources, Pages],
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collections: [
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Users,
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Media,
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Posts,
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Products,
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Rolls,
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ModifiedPrompts,
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ReturnedResources,
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Pages,
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FieldTypes,
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],
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localization: {
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defaultLocale: 'en',
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fallback: true,
@@ -96,6 +107,15 @@ export default buildConfigWithDefaults({
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[Products.slug]: {
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enabled: true,
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},
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'field-types': {
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enabled: {
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find: true,
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create: true,
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update: true,
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delete: true,
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},
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description: 'A collection covering all Payload field types for MCP schema testing.',
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},
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pages: {
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enabled: {
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find: true,

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