Also, can you test out what is the output if merging of route happens? How does the metadata look like?

Also, can you test out what is the output if merging of route happens? How does the metadata look like?

Tested this. When two route rules merge into a single Envoy route, addRouteSourceMetadata
is called sequentially on the same metadata object. Because the function overwrites the
dev.kgateway.route_source key unconditionally:

metadata.FilterMetadata[routeSourceMetadataKey] = &structpb.Struct{Fields: fields}

the last rule processed wins. Actual test output:

{
  "filter_metadata": {
    "dev.kgateway.route_source": {
      "group": "gateway.networking.k8s.io",
      "kind": "HTTPRoute",
      "name": "test-route",
      "namespace": "default",
      "rule": "rule2-merged"
    }
  }
}

So if rule1 and rule2 merge, only rule2's source is reported — rule1 is silently dropped.
Happy to change this behavior (e.g. keep the first rule, or store a list) if you'd prefer
different semantics for merged routes.

@mihir-dixit2k27 Thank you again for the contribution. Can you add translator test to this now that we don't have to modify all the golden file.

Ready for re-review @andy-fong

re: will route replacement carry metadata?

It depends

1. Per-route replacement — keeps the metadata ✅

When a single route is invalid (bad builtin filter, invalid config, validateRoutePreEnvoy
failure, etc.), finalizeRoute (route.go:338-374) mutates the same out object in place: it swaps
Action to a 500 direct response and clears headers/TPFC — but it does not touch Metadata. Since
envoyRoutes set out.Metadata at line 253 before the action was computed, the replaced route
retains it.

2. Whole-vhost / whole-RouteConfiguration replacement — loses the metadata.

When a vhost-plugin fails, strict batch validation fails, or route-config plugins fail
(route.go:114, :194, :426), the entire vhost/RC is discarded and replaced by setFallBackConfig —
a brand-new synthetic catch-all / → 500 route with no Metadata. All per-route source metadata is
gone, because many routes collapse into one synthetic route with no single source to attribute.

This is correct because the fallback route isn't produced by any xRoute — it's a synthetic error route that kgateway emits because a listener/vhost/RC-level policy failed