@tanstack/start issue - An error outside of the Outlet can't be caught and doesn't show error boundry

Which project does this relate to?

Start

Describe the bug

In my app I have a two providers which require a fetch from an API. During a release/startup the API might not have fully booted up yet causing this fetch to fail. The providers are defined in the _root.tsx before .

The result is that the server returns a JSON response:
{"status":500,"unhandled":true,"message":"HTTPError"}

I would have expected at least one error page to show (either from __root or the defaultErrorComponent from the router). No amount of error boundaries seem to help.

The biggest problem is that, because it can't be handled gracefully, the query can't be refetched and as such the server keeps throwing an error 500 even if the API has become available.

Your Example Website or App

https://github.com/Da-Teach/start-basic-react-query-error

Steps to Reproduce the Bug or Issue

The example git repo will immediately throw the error.

Expected behavior

I expect to see an error page but seeing a JSON error instead.

Screenshots or Videos

No response

Platform

Browser doesn't matter, nor platform.

"@tanstack/react-query": "^5.97.0",
"@tanstack/react-query-devtools": "^5.97.0",
"@tanstack/react-router": "^1.168.10",
"@tanstack/react-router-devtools": "^1.166.11",
"@tanstack/react-router-ssr-query": "^1.166.10",
"@tanstack/react-start": "^1.167.16",
"react": "^19.2.5",
"react-dom": "^19.2.5",
"redaxios": "^0.5.1",
"tailwind-merge": "^2.6.1"

Additional context

No response

Start with the linked start-basic-react-query-error reproduction and inspect the providers in _root.tsx relative to . Reproduce the failed startup fetch, then trace TanStack Start's server error handling for errors thrown before the Outlet renders. Done means the failure shows an error page rather than the JSON 500 response and can be retried after the API becomes available.