returning `unknown` properties from loader causes TypeScript error even in spa mode and when parent layout has `ssr: false`

[MTG2000]

Which project does this relate to?

Start

Describe the bug

Might be related to this #5222
As it's showing the same error.

So in my project, I have spa mode enabled.
The __root route has ssr: false

The root layout has ssr: false too:

// post.tsx

export const Route = createFileRoute('/posts')({
  ssr: false,
  loader: async () => fetchPosts(),
  component: PostsComponent,
})

function PostsComponent() {}

Then, if I have a page like this:

// posts.$postId.$something.tsx

export const Route = createFileRoute('/posts/$postId/$something')({
  loader: ({ params: { postId } }) => "hello" as unknown,
  component: ()=>{},
})

The loader would throw the same error linked above:

Call signature return types '{ obj: TypeWithUnknown; }' and '{ obj: { value: {}; }; }' are incompatible.
    The types of 'obj.value' are incompatible between these types.
      Type 'unknown' is not assignable to type '{}'.

If I put ssr: false on the posts.$postId.tsx, then the error goes away.
But I shouldn't need to have to put that when it's already on the __root and the posts.tsx routes, right?

Your Example Website or App

https://github.com/MTG2000/tanstack-router/tree/type-unknown-issue

Steps to Reproduce the Bug or Issue

Go to start-basic example and see the changes that I mentioned above.
And you will see the error in this file: https://github.com/MTG2000/tanstack-router/blob/type-unknown-issue/examples/react/start-basic/src/routes/posts.%24postId.%24something.tsx

Expected behavior

No type error when ssr is disabled on a parent layout or root layout.

Screenshots or Videos

No response

Platform

• Router / Start Version: 1.133.15
• OS: [e.g. macOS, Windows, Linux]
• Browser: [e.g. Chrome, Safari, Firefox]
• Browser Version: [e.g. 91.1]
• Bundler: vite
• Bundler Version: [e.g. 7.0.0]

Additional context

No response

[MTG2000]

Looking at the generated routes tree file, I see that for some reason, ssr is enabled on the Register interface:

declare module '@tanstack/react-start' {
  interface Register {
    ssr: true
    router: Awaited<ReturnType<typeof getRouter>>
  }
}

Even though I don't have ssr set to true anywhere in the app.
If I manually make it false here, the error goes away. (But it will be overwritten the next time I run the app of course)