invariant in client-rpc getResponse() tripped by 502 error

[dxptqhtlutehvlyxcmtg]

Not technically a bug, but this behavior is less than desirable:

getResponse() requires a 'content-type' header.

In the case of a Bad Gateway response from a reverse proxy (header could be missing, in other words), an invariant is thrown which means a developer lacks error context for presenting retry options to the user.

[barry166]

This matches the client parser path. serverFnFetcher calls getResponse(), and before it can deserialize the body it requires a content-type; a proxy-generated 502 without that header hits Invariant failed: expected content-type header to be set instead of surfacing the 502 context.

For now, the practical workaround is to make the reverse proxy add a content type on its own error responses, e.g. text/plain or application/json, so TanStack Start can get past that invariant and handle the response as an error. The library could still improve this by treating missing-content-type non-2xx responses as plain errors, but the proxy header is the part you can fix without patching Start.