Adjacent folder fallthrough pages swallow endpoint request

[adamjkb]

Describe the bug
The following routes folder structure will result in page /b being a 404 however /b.json is reachable when requested directly. (Both [a].svelte and [b].svelte try to fetch their respective endpoint from the load function.)
The issue only comes up when the address is accessed directly; navigating to /b is still working (see root page).

├── [a]
│   ├── index.json.js
│   └── index.svelte
├── [b]
│   ├── index.json.js
│   └── index.svelte
└── index.svelte

---

The same routes flattened as such will work as expected:

├── [c].json.js
├── [c].svelte
├── [d].json.js
├── [d].svelte
└── index.svelte

Logs
Retracing /b request by logging paths from each endpoint and page:

Page A (/b)
Endpoint A (/b.json)
Page B (/b)
Endpoint A (/b.json)
Page A (/b.json)
Endpoint A (/b.json.json)

To Reproduce
Repo: https://github.com/adamjkb/sveltekit-adjacent-fallthrough-routes

Type localhost:3000/b in address bar.

Expected behavior
To reach all endpoints/pages if its requirements are met.

Severity
Low–medium. Has work around.

[adamjkb]

Closing as this has been fixed alongside of #2041