Harden runtime HTTP transport lifecycles

src/__Libraries/StellaOps.Verdict/Oci/OciAttestationPublisher.cs

@@ -122,7 +122,7 @@ public sealed class OciAttestationPublisher : IOciAttestationPublisher
     {
         _options = options ?? throw new ArgumentNullException(nameof(options));
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
-        _httpClient = httpClient ?? new HttpClient();
+        _httpClient = httpClient ?? OciRuntimeHttpClient.SharedClient;
         _timeProvider = timeProvider ?? TimeProvider.System;
     }