style: align with MS C# coding conventions

- Set max_line_length = 120 in .editorconfig for *.cs
- Filter OperationCanceledException out of sweep-loop best-effort catch
  in ArtifactStore so shutdown cancellation propagates
- Use collection expressions ([] / [x]) in ARCPRuntime and
  SubscriptionManager

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nficano

.editorconfig

@@ -19,6 +19,7 @@ trim_trailing_whitespace = false
 
 [*.cs]
 indent_size = 4
+max_line_length = 120
 
 # Naming
 dotnet_naming_rule.types_should_be_pascal_case.severity = warning

src/ARCP/Runtime/ARCPRuntime.cs

@@ -44,7 +44,7 @@ public ARCPRuntime(ARCPRuntimeOptions options, ILogger<ARCPRuntime>? logger = nu
         _messageRegistry = options.MessageRegistry ?? MessageTypeRegistry.CoreCatalog();
         _jsonOptions = EnvelopeJson.CreateOptions(_messageRegistry, options.ExtensionRegistry);
         _verifiers = new ConcurrentDictionary<AuthScheme, IAuthVerifier>();
-        foreach (IAuthVerifier verifier in options.AuthVerifiers ?? Array.Empty<IAuthVerifier>())
+        foreach (IAuthVerifier verifier in options.AuthVerifiers ?? [])
         {
             _verifiers[verifier.Scheme] = verifier;
         }

src/ARCP/Runtime/ArtifactStore.cs

@@ -269,7 +269,7 @@ private async Task SweepLoopAsync()
                 {
                     await SweepExpiredAsync(_shutdown.Token).ConfigureAwait(false);
                 }
-                catch (Exception)
+                catch (Exception ex) when (ex is not OperationCanceledException)
                 {
                     // best effort
                 }

src/ARCP/Runtime/SubscriptionManager.cs

@@ -80,7 +80,7 @@ public SubscriptionManager(EventLog log, TimeProvider? time = null)
         }
         else
         {
-            filter = filter with { SessionId = new[] { subscriberSessionId.Value } };
+            filter = filter with { SessionId = [subscriberSessionId.Value] };
         }
 
         SubscriptionId id = SubscriptionId.New();