---

This section details on the original issue you should resolve

<issue_title>[13.0] EndpointReference environment variable evaluating to http://: (i.e. missing host & port)</issue_title>
<issue_description>### Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I have a test in 9.5, in which I needed to run an in memory server on a port, and make sure a dependency connects to it. (Specifically the otel connector)

After upgrading to 13.0, the endpoint is not being resolved correctly, and rather than failing, is ending up with an empty host and port http://:.

Whilst this could be a problem with my test code, it does feel like WithEnvironment() should never be able to resolve with an empty port/host, so maybe something else is wrong.

Expected Behavior

The reference should contain the port & host from the allocated endpoint.

But even more so, I wouldn't expect the final environment value to end up with missing host or port - I'd expect some kind of error to be thrown if either of these evaluated to null/empty.

Steps To Reproduce

   [Test]
   public async Task test()
   {
      var builder = DistributedApplicationTestingBuilder.Create();

      var dependency = builder
         .AddResource(new FakeResource())
         .WithHttpEndpoint();

      var consumer = builder
         .AddContainer("test", "redis")
         .WithImageRegistry("docker.io")
         .WithReference(dependency.GetEndpoint("http"));

      var endpointAnnotation = dependency.Resource.Annotations.OfType<EndpointAnnotation>().Single();
      endpointAnnotation.AllocatedEndpoint = new AllocatedEndpoint(endpointAnnotation, "localhost", 1234);

      using var app = builder.Build();
      await app.StartAsync();

      var envVars = await consumer.Resource.GetEnvironmentVariableValuesAsync();
      Assert.That(envVars["services__fake__http__0"], Is.EqualTo("http://localhost:1234"));
      // Actual: `http://:`
   }

   public class FakeResource() : Resource("fake"), IResourceWithEndpoints { }

Exceptions (if any)

  Assert.That(envVars["services__fake__http__0"], Is.EqualTo("http://localhost:1234"))
  Expected string length 21 but was 8. Strings differ at index 7.
  Expected: "http://localhost:1234"
  But was:  "http://:"

.NET Version info

No response

Anything else?

No response</issue_description>

<agent_instructions>Import the test case in the issue (not the comment) into Aspire.Hosting.Tests. Do not attempt to fix the issue yet, lets just verify the failing behavior inside the repo and then we can look at understanding the cause.</agent_instructions>

Comments on the Issue (you are @copilot in this section)