Typegen fails to resolve `.mdx` files

[nikolailehbrink]

Reproduction

https://stackblitz.com/edit/github-pvha4jzr-ionx6pm8

1. Run the typegen command with pnpm typecheck and see the errors regarding the "mdx" file.

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 20.19.1 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @react-router/dev: ^7.6.3 => 7.6.3 
    @react-router/node: 7.6.3 => 7.6.3 
    @react-router/serve: ^7.6.3 => 7.6.3 
    react-router: ^7.6.3 => 7.6.3 
    vite: ^6.3.3 => 6.3.5

Used Package Manager

pnpm

Expected Behavior

When running type generation in a project with MDX routes, the generated +types/*.ts files reference the .mdx files directly:

type Module = typeof import("../home.mdx")

This causes TypeScript errors:

.react-router/types/app/routes/+types/home.ts:5:29 - error TS2307: Cannot find module '../home.mdx' or its corresponding type declarations.

Actual Behavior

No errors should be shown, because it is working properly.