Fix Azure Functions span parenting via HttpContext.Items

AsyncLocal context doesn't flow through Azure Functions middleware,
causing worker's azure_functions.invoke span to be incorrectly
parented. Use HttpContext.Items as an explicit bridge to pass the
AspNetCore scope to the Azure Functions middleware.

Changes:
- Store AspNetCore scope in HttpContext.Items after creation
- Add Items property to IFunctionContext duck type interface
- Retrieve scope from HttpContext.Items when creating azure_functions.invoke span
- Only use HttpContext.Items fallback when tracer.InternalActiveScope is null

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: lucaspimentel

tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/Azure/Functions/AzureFunctionsCommon.cs

@@ -261,13 +261,44 @@ _ when type.StartsWith("eventGrid", StringComparison.OrdinalIgnoreCase) => "Even
 
                 if (tracer.InternalActiveScope == null)
                 {
-                    // This is the root scope
-                    tags.SetAnalyticsSampleRate(IntegrationId, tracer.CurrentTraceSettings.Settings, enabledWithGlobalSetting: false);
-                    scope = tracer.StartActiveInternal(OperationName, tags: tags, parent: extractedContext.SpanContext);
+                    // AsyncLocal context didn't flow - try to get parent scope from HttpContext.Items
+                    // This happens in Azure Functions isolated worker where middleware breaks AsyncLocal flow
+                    Scope? parentScope = null;
+                    try
+                    {
+                        // HttpContext is stored in FunctionContext.Items with key "__AspNetCoreHttpContext__"
+                        if (context.Items?.TryGetValue("__AspNetCoreHttpContext__", out var httpContextObj) == true
+                            && httpContextObj is Microsoft.AspNetCore.Http.HttpContext httpContext)
+                        {
+                            // Retrieve the scope stored by AspNetCoreHttpRequestHandler
+                            if (httpContext.Items.TryGetValue("__Datadog.Trace.AspNetCore.ActiveScope", out var scopeObj)
+                                && scopeObj is Scope aspNetCoreScope)
+                            {
+                                parentScope = aspNetCoreScope;
+                                Log.Debug("Retrieved AspNetCore scope from HttpContext.Items for Azure Functions span parenting");
+                            }
+                        }
+                    }
+                    catch (Exception ex)
+                    {
+                        Log.Debug(ex, "Error retrieving AspNetCore scope from HttpContext.Items");
+                    }
+
+                    if (parentScope != null)
+                    {
+                        // Use the AspNetCore scope as parent
+                        scope = tracer.StartActiveInternal(OperationName, parent: parentScope.Span.Context, tags: tags);
+                    }
+                    else
+                    {
+                        // This is the root scope - use extracted context from headers
+                        tags.SetAnalyticsSampleRate(IntegrationId, tracer.CurrentTraceSettings.Settings, enabledWithGlobalSetting: false);
+                        scope = tracer.StartActiveInternal(OperationName, tags: tags, parent: extractedContext.SpanContext);
+                    }
                 }
                 else
                 {
-                    // shouldn't be hit, but better safe than sorry
+                    // AsyncLocal is working - use it as parent
                     scope = tracer.StartActiveInternal(OperationName);
                     var rootSpan = scope.Root.Span;
                     AzureFunctionsTags.SetRootSpanTags(

tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/Azure/Functions/Isolated/IFunctionContext.cs

@@ -18,6 +18,8 @@ internal interface IFunctionContext
     FunctionDefinitionStruct FunctionDefinition { get; }
 
     IEnumerable<KeyValuePair<Type, object?>>? Features { get; }
+
+    IDictionary<object, object>? Items { get; }
 }
 
 #endif

tracer/src/Datadog.Trace/PlatformHelpers/AspNetCoreHttpRequestHandler.cs

@@ -137,6 +137,10 @@ public Scope StartAspNetCorePipelineScope(Tracer tracer, Security security, Http
 
             httpContext.Features.Set(requestTrackingFeature);
 
+            // Store scope in HttpContext.Items for Azure Functions middleware to retrieve
+            // Use __ prefix to avoid conflicts with user code (same pattern as TracingHttpModule)
+            httpContext.Items["__Datadog.Trace.AspNetCore.ActiveScope"] = scope;
+
             if (tracer.Settings.IpHeaderEnabled || security.AppsecEnabled)
             {
                 var peerIp = new Headers.Ip.IpInfo(httpContext.Connection.RemoteIpAddress?.ToString(), httpContext.Connection.RemotePort);