.NET: Bug fixes for AGUI hosting and workflows (#6311)

* Add mcp tool execution fix

* Apply IsolationKeyScopedAgentSessionStore to MapAGUI by default if not yet set and improve comments in samples

* Address PR comments

* Fix formatting

dotnet/samples/02-agents/AGUI/Step04_HumanInLoop/Server/Program.cs

@@ -27,6 +27,11 @@ builder.Services.ConfigureHttpJsonOptions(options =>
     options.SerializerOptions.TypeInfoResolverChain.Add(ApprovalJsonContext.Default));
 builder.Services.AddAGUI();
 
+// WARNING: When adding session persistence (e.g., WithInMemorySessionStore), or running in production,
+// make sure to also register a SessionIsolationKeyProvider to scope sessions by principal in multi-user
+// deployments, e.g.:
+// builder.Services.UseClaimsBasedSessionIsolation(new() { ClaimType = ClaimTypes.NameIdentifier });
+
 WebApplication app = builder.Build();
 
 app.UseHttpLogging();