fix(durable-functions): preserve invocation correlation on cached clients

packages/azure-functions-durable/CHANGELOG.md

@@ -28,6 +28,11 @@
 
 ### Fixes
 
+- Forward the active Functions invocation ID in client gRPC metadata, including `getClient(context)`
+  and `app.client.*` starters. Invocation-local scoping preserves correlation across awaits and
+  concurrent calls without retaining IDs on cached clients or changing channel reuse. Calls outside
+  a Functions invocation omit the header
+  ([#395](https://github.com/microsoft/durabletask-js/issues/395)).
 - Preserve received failure `properties` in `durable-functions/testing` results, including
   nested failures. This does not collect arbitrary JavaScript `Error` fields.
 - Forward the optional `reason` from the classic `suspend()` / `resume()` aliases to the

packages/azure-functions-durable/src/metadata.ts

@@ -1,19 +1,32 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
+import { app as azFuncApp } from "@azure/functions";
 import * as grpc from "@grpc/grpc-js";
 import { MetadataGenerator } from "@microsoft/durabletask-js";
+import { AsyncLocalStorage } from "node:async_hooks";
 import { getUserAgent } from "./user-agent";
 
-export function createAzureFunctionsMetadataGenerator(
-  taskHubName: string,
-): MetadataGenerator {
+const invocationIds = new AsyncLocalStorage<string>();
+
+azFuncApp.hook.preInvocation((context) => {
+  const invocationId = context.invocationContext.invocationId;
+  const handler = context.functionHandler;
+  // Scope the handler, not the hook: the runtime invokes the handler after pre-invocation hooks.
+  context.functionHandler = (...args) => invocationIds.run(invocationId, handler, ...args);
+});
+
+export function createAzureFunctionsMetadataGenerator(taskHubName: string): MetadataGenerator {
   const userAgent = getUserAgent();
 
   return async (): Promise<grpc.Metadata> => {
     const metadata = new grpc.Metadata();
     metadata.set("taskhub", taskHubName);
     metadata.set("x-user-agent", userAgent);
+    const invocationId = invocationIds.getStore();
+    if (invocationId) {
+      metadata.set("x-azure-functions-invocationid", invocationId);
+    }
     return metadata;
   };
 }