different generated types for ActionData based on how we return the data (directly or indirectly)

Describe the bug

I have an async method that returns a Union of types A and B (they might or might not have something in common). If I do

const a = await asyncFun()
return a;

then typings on ActionData will be correct (typeof ActionData will be {typeof A & AllUndefined<B> | typeof B & AllUndefined<A>), but if I do

return await asyncFunc()

then all typings will be wrong (typeof ActionData will be {} | null)

Reproduction

1- clone weird-type-generation brach of this repository
2- run npm i
3- run npm run check
4- at this step everything should be fine, goto src/routes/user/todos and the type of ActionData is

{
    success?: undefined;
    result?: undefined;
    message: ErrorMessage;
    error: {
        title?: string[] | undefined;
        description?: string[] | undefined;
        is_done?: string[] | undefined;
    };
} | {
    success?: undefined;
    result?: undefined;
    message: ErrorMessage;
    error: {
        title: string;
        description: string;
        is_done: boolean;
    };
} | {
    message?: undefined;
    error?: undefined;
    success: true;
    result: Todo;
} | null

5- goto src/routes/user/todos/+page.server.ts and uncommend the lines 47 to 54 where we immediatly return the awaited async funtion (I've also described the problem in the comments of mentioned lines) and comment lines 36 to 44 where we first store it in a variable and then return the variable.
6- run npm run check again.
7- now goto the corresponding +page.svelte (src/routes/user/todos/+page.svelte) and see the type of ActionData. it is {} | null now!
*** this problem exists in src/routes/signup as well (but not in src/routes/login).

Logs

No response

System Info

System:
    OS: Linux 5.15 Ubuntu 22.04.3 LTS 22.04.3 LTS (Jammy Jellyfish)
    CPU: (16) x64 AMD Ryzen 7 4800H with Radeon Graphics
    Memory: 10.25 GB / 15.33 GB
    Container: Yes
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 18.16.1 - ~/.nvm/versions/node/v18.16.1/bin/node
    npm: 9.5.1 - ~/.nvm/versions/node/v18.16.1/bin/npm
  Browsers:
    Chrome: 115.0.5790.170
  npmPackages:
    @sveltejs/adapter-auto: ^2.0.0 => 2.1.0 
    @sveltejs/kit: ^1.20.4 => 1.22.4 
    svelte: ^4.0.5 => 4.1.2 
    vite: ^4.4.2 => 4.4.9

Severity

serious, but I can work around it

Additional Information

No response

Reproduce the issue from the linked weird-type-generation branch with npm i and npm run check. Compare src/routes/user/todos/+page.server.ts with src/routes/user/todos/+page.svelte, including the analogous signup route, then trace how ActionData types are generated. Done means direct and indirect awaited returns produce the same correct union type.