Changelog: Adds entry for metadata-detached executor fix

Adds a new Unreleased Preview section (per the pattern established in PR #5815) with a Fixed entry for PR #5844. Customer-facing description focuses on the symptom (premature OperationCanceledException preempting cross-region failover during metadata-cache reads) rather than the implementation detail (the new MetadataDetachedExecutor).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: NaluTripician

changelog.md

@@ -15,6 +15,12 @@ Preview features are treated as a separate branch and will not be included in th
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+### <a name="unreleased"/> Unreleased Preview
+
+#### Fixed
+
+- [5844](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/5844) Routing: Fixes premature OperationCanceledException that preempted cross-region failover during metadata-cache reads
+
 ### <a name="3.60.0-preview.0"/> [3.60.0-preview.0](https://www.nuget.org/packages/Microsoft.Azure.Cosmos/3.60.0-preview.0) - 2026-4-24
 
 #### Added