Describe the Bug

Since PR #15675 (fix(plugin-mcp): use inline block schemas in JSON output), the generate:types command inlines all block type definitions at every usage site instead of referencing the named interfaceName interfaces.

Previously, when a block had an interfaceName set, the generated types would reference that interface:

// Before (3.75): compact references
blocks?: (CmsSectionProps | CmsTripSectionProps | CmsAlertSectionProps | ...)[] | null;
imageSlider?: CmsImageSliderProps[] | null;

Now, the full block schema is inlined everywhere:

// After (3.78): every block is fully inlined
blocks?: ({
    title?: string | null;
    richText?: { root: { type: string; children: { ... }[]; ... } } | null;
    blocks?: (...)[] | null;
    blockType: 'cmsSection';
  } | {
    title?: string | null;
    items: { ... }[];
    blockType: 'cmsSectionList';
  } | ...)[] | null;

The named interfaces (e.g. CmsSectionProps) are still generated in the file, but they are no longer referenced inside collection/global types. This causes massive duplication.

Impact on our project:

• payload-types.ts grew from 5,657 lines to 7,525 lines (+33%)
• Diff: +2,788 / -920 lines
• blockType occurrences went from 42 to 126 (3x), as every block definition is duplicated at every usage site

The root cause is in configToJSONSchema.ts where $ref references were replaced with inline schemas to fix MCP compatibility (#15399). However, this also affects generate:types which doesn't need inline schemas.

Suggestion: The $ref → inline change could be scoped to MCP JSON Schema output only, while keeping $ref references for TypeScript type generation.

Link to the code that reproduces this issue

https://github.com/payloadcms/payload/pull/15675/files#diff-e31c3f38e2d3b4e4db3c8bf8e3edaa35

The change in packages/payload/src/utilities/configToJSONSchema.ts (lines 327-368) replaces $ref with inline schemas unconditionally. Any project using blocks with interfaceName will reproduce this by running generate:types on 3.76+.

Reproduction Steps

1. Create a Payload project with multiple blocks that use interfaceName
2. Run pnpm payload generate:types on Payload 3.75 — observe compact type references
3. Upgrade to Payload 3.78
4. Run pnpm payload generate:types again — observe all block types are now inlined at every usage site
5. Compare the two payload-types.ts files

Which area(s) are affected?

area: core, plugin: mcp

Environment Info

• Payload: 3.78.0
• Node.js: v22
• Next.js: 15