[Start] Rendered notFound route then redirects to basepath with trailing slash when basepath is set

[hokkyss]

Which project does this relate to?

Start

Describe the bug

When customizing basepath in createRouter and visiting /, the router first renders not found and then redirects to /basepath/ (with trailing slash even though trailing slash is disabled)

Your Example Website or App

https://codesandbox.io/p/devbox/unruffled-hodgkin-8y6p2q?workspaceId=ws_3crUW8RxweSdTKWh8AMbfP

Steps to Reproduce the Bug or Issue

Remove /basepath from URL manually.

Expected behavior

One of the two:

1. Smoothly rendering /basepath/ without showing not found
2. Render not found and not redirecting to /basepath/

Screenshots or Videos

Screen.Recording.2025-05-07.at.11.58.42.mov

Platform

tanstack start basic example

• OS: MacOS
• Browser: Chrome
• Version: 1.120.2

Additional context

No response