Add changelog for 2.18.0

changelog.md

@@ -6,7 +6,13 @@ The **minimum recommended version is [2.16.2](#2.16.2)**.
 Because version 3 of the Azure Cosmos DB .NET SDK includes updated features and improved performance, we’ll retire version 2.x of this SDK on 31 August 2024.  As a result, you’ll need to update your SDK to version 3 by that date. We recommend following the [instructions](https://docs.microsoft.com/azure/cosmos-db/sql/migrate-dotnet-v3?tabs=dotnet-v3) to migrate to Azure Cosmos DB .NET SDK version 3.
 
 ## Release notes
-### <a name="2.17.0"></a> 2.17.0
+### <a name="2.18.0"></a> 2.18.0
+* Fixed regression introduced in 2.17.0 causing unobserved exception ("System.ObjectDisposedException: The semaphore has been disposed.")
+* Removed noisy session token parse trace message
+* Improved availabilty by using nonblocking cache for partition key ranges
+* Fixed DocumentClient initialization to keep retrying. Previously it would keep returning same cached exception. 
+
+### <a name="2.17.0"></a> 2.17.0 - Unlisted from a regression on broken connection causing unobserved exception. "System.ObjectDisposedException: The semaphore has been disposed."
 
 > :warning: 2.17.0 removes the DefaultTraceListener from the SDK TraceSource for [performance reasons](https://docs.microsoft.com/azure/cosmos-db/sql/performance-tips?tabs=trace-net-core#logging-and-tracing) by default when not running in Debug mode.
 
@@ -22,6 +28,7 @@ Because version 3 of the Azure Cosmos DB .NET SDK includes updated features and
 * Improved client availability by enabling the account information refresh upon client creation, which helps detect regional changes without a required failure happening
 * Improved availability by avoiding retries on replicas that previously failed for that request
 * Improved availability from avoiding replica during cache refreshes
+* Added substatus code to all 503(Service Unavailable) exceptions
 
 ### <a name="2.16.2"></a> 2.16.2
 * Fixed memory leak in query for systems running on Windows x64 using the ServiceInterop.dll