ResolvedRefs error not helpful when ref'ing to incorrect port on Service

[lgadban]

kgateway version

main

Kubernetes Version

n/a

Describe the bug

Need to confirm but found in translator test, having a backendRef to a service but the incorrect port results in an error like

condition error for httproute: default/foo-route ref: 0 condition: {ResolvedRefs False 0 2025-08-13 21:13:46.740397 -0500 CDT m=+0.687139126 BackendNotFound Service "foo-svc" not found}

In this case foo-svc does exist it just refers to an incorrect port

Expected Behavior

The error message should not the service does not exist, because it does, but have some sort of pointer that it's related to the port.

Steps to reproduce the bug

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: foo-route
spec:
  parentRefs:
  - name: foo-listenerset
    group: gateway.networking.x-k8s.io
    kind: XListenerSet
  hostnames:
  - "foo.example.com"
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    backendRefs:
    - name: foo-svc
      port: 800
---
apiVersion: v1
kind: Service
metadata:
  name: foo-svc
spec:
  selector:
    test: test
  ports:
    - protocol: HTTP
      port: 8080
      targetPort: test

Additional Environment Detail

No response

Additional Context

No response

[corsairier]

@lgadban Can I work on this?

[ashleywang1]

See #12021 (review) for a proposed way to do this.

[yaten2302]

Hi @lgadban @ashleywang1 , I would like to work on this issue, kindly assign this to me :)
If, I've understood this correctly, then if the user specifies the port and if the service exists (with incorrect port), we should show a msgs that:

return fmt.Errorf("Service %q found, but port %v not defined", Name, Port)

else if the service doesn't exists, then:

return fmt.Errorf("Service %q not found", Name)

[yaten2302]

Hi @ymesika , raised a PR here - #13178, kindly review :)
Thanks!