fix: case-insensitive SessionId and reserved-header handling for ASB (#4054)

Brighter's JSON serialization camelCases header bag keys, so a "SessionId"
key returns as "sessionId" after an Outbox round-trip. The publisher's
exact-match lookup missed it (session never set) and the case-sensitive
reserved-header filter let it leak into ApplicationProperties. Both lookups
are now OrdinalIgnoreCase.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: iancooper

src/Paramore.Brighter.MessagingGateway.AzureServiceBus/AzureServiceBusMessagePublisher.cs

@@ -1,4 +1,5 @@
-using System.Linq;
+using System;
+using System.Linq;
 using System.Net.Mime;
 using Azure.Messaging.ServiceBus;
 using Paramore.Brighter.Extensions;
@@ -59,11 +60,17 @@ private static void AddBrighterHeaders(Message message, ServiceBusMessage azureS
             azureServiceBusMessage.CorrelationId = message.Header.CorrelationId;
         if (!string.IsNullOrEmpty(message.Header.ReplyTo!))
             azureServiceBusMessage.ReplyTo = message.Header.ReplyTo?.Value;
-        if (message.Header.Bag.TryGetValue(ASBConstants.SessionIdKey, out object? value))
-            azureServiceBusMessage.SessionId = value.ToString();
+        //Brighter's JSON serialization camelCases bag keys (JsonNamingPolicy.CamelCase), so a key
+        //written as "SessionId" returns as "sessionId" after a round-trip (e.g. via an Outbox).
+        //Resolve the SessionId regardless of casing.
+        var sessionId = message.Header.Bag
+            .FirstOrDefault(h => string.Equals(h.Key, ASBConstants.SessionIdKey, StringComparison.OrdinalIgnoreCase))
+            .Value;
+        if (sessionId is not null)
+            azureServiceBusMessage.SessionId = sessionId.ToString();
 
         foreach (var header in message.Header.Bag.Where(h =>
-                     !ASBConstants.ReservedHeaders.Contains(h.Key)
+                     !ASBConstants.ReservedHeaders.Contains(h.Key, StringComparer.OrdinalIgnoreCase)
                      && !MessageHeader.IsLocalHeader(h.Key)))
         {
             azureServiceBusMessage.ApplicationProperties[header.Key] = header.Value;

tests/Paramore.Brighter.AzureServiceBus.Tests/MessagingGateway/When_Converting_A_Message_With_A_Session_Id.cs

@@ -0,0 +1,35 @@
+using System;
+using Paramore.Brighter.MessagingGateway.AzureServiceBus;
+using Xunit;
+
+namespace Paramore.Brighter.AzureServiceBus.Tests.MessagingGateway;
+
+[Trait("Category", "ASB")]
+public class AzureServiceBusMessagePublisherSessionIdTests
+{
+    [Theory]
+    [InlineData("SessionId")] // as written by application code
+    [InlineData("sessionId")] // as it returns from a camelCasing serialization round-trip (e.g. via the Outbox)
+    public void When_Converting_A_Message_With_A_SessionId_Bag_Key_Of_Any_Casing_The_SessionId_Is_Set(string sessionIdKey)
+    {
+        // Brighter's JSON serialization uses JsonNamingPolicy.CamelCase, so a bag key written as
+        // "SessionId" comes back as "sessionId" once the message round-trips through serialization
+        // (for example when stored in and read back from an Outbox). The publisher must resolve the
+        // SessionId regardless of the key's casing — and the reserved key must not leak onto the wire.
+        const string expectedSessionId = "order-42";
+        var header = new MessageHeader(
+            messageId: Guid.NewGuid().ToString(),
+            topic: new RoutingKey("test.topic"),
+            messageType: MessageType.MT_COMMAND);
+        header.Bag[sessionIdKey] = expectedSessionId;
+
+        var message = new Message(header, new MessageBody("body"));
+
+        var asbMessage = AzureServiceBusMessagePublisher.ConvertToServiceBusMessage(message);
+
+        // the session id is set on the outgoing message...
+        Assert.Equal(expectedSessionId, asbMessage.SessionId);
+        // ...and the reserved header does not leak into ApplicationProperties
+        Assert.False(asbMessage.ApplicationProperties.ContainsKey(sessionIdKey));
+    }
+}