Problem:
The withHeaderCarrier generic function had a type mismatch that caused compilation
errors in CI. The function used `T proto.Message` constraint, but Connect's Response
type expects the non-pointer message type while protobuf methods return pointers.

Error from CI:
  type T of resp does not match *T (cannot infer T)

This occurred because:
- Connect methods expect: *connect.Response[v1pb.CreateSessionResponse]
- Service methods return: (*v1pb.CreateSessionResponse, error)
- Old signature: fn func(context.Context) (T, error) with T proto.Message
- This caused T to be inferred as *v1pb.CreateSessionResponse
- Leading to return type: *connect.Response[*v1pb.CreateSessionResponse] (wrong!)

Solution:
Changed generic signature to explicitly handle the pointer/non-pointer distinction:
- New signature: fn func(context.Context) (*T, error) with T any
- T is now the non-pointer type (e.g., v1pb.CreateSessionResponse)
- fn returns *T (e.g., *v1pb.CreateSessionResponse)
- Return type is correctly: *connect.Response[T] (e.g., *connect.Response[v1pb.CreateSessionResponse])

Also removed unused "google.golang.org/protobuf/proto" import and improved documentation
to clarify the T vs *T distinction.

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>