[All hosts] (event-based activation) Update Cache-Control header guidance (#5457)

* Update Cache-Control header guidance

* Apply suggestion from review

Co-authored-by: Alex Jerabek <38896772+AlexJerabek@users.noreply.github.com>

* Apply suggestion from review

---------

Co-authored-by: Alex Jerabek <38896772+AlexJerabek@users.noreply.github.com>

Author: samantharamon

docs/develop/add-in-manifests.md

@@ -2,7 +2,7 @@
 title: Office Add-ins manifest
 description: Get an overview of the Office Add-in manifest and its uses.
 ms.topic: overview
-ms.date: 10/10/2025
+ms.date: 11/06/2025
 ms.localizationpriority: high
 ---
 
@@ -41,7 +41,11 @@ A manifest file enables an Office Add-in to do the following:
 
 ## Hosting requirements
 
-All image URIs, such as those used for [add-in commands](../design/add-in-commands.md), must support caching in production. The server hosting the image shouldn't return a `Cache-Control` header specifying `no-cache`, `no-store`, or similar options in the HTTP response. However, when you're developing the add-in and making changes to image files, the caching can prevent you from seeing your changes, so using `Cache-Control` headers is advisable in development.
+The following URIs must support caching in production.
+- All image URIs, such as those used for [add-in commands](../design/add-in-commands.md).
+- The event-handling file of an [event-based activation](event-based-activation.md) add-in that runs in a JavaScript-only runtime.
+
+The server hosting the image or event-handling file shouldn't return a `Cache-Control` header specifying `no-cache`, `no-store`, or similar options in the HTTP response.
 
 All URLs to code or content files in the add-in should be **SSL-secured (HTTPS)**. [!INCLUDE [HTTPS guidance](../includes/https-guidance.md)]
 

docs/develop/event-based-activation.md

@@ -1,7 +1,7 @@
 ---
 title: Activate add-ins with events
 description: Learn how to develop an Office Add-in that implements event-based activation.
-ms.date: 10/28/2025
+ms.date: 11/06/2025
 ms.topic: concept-article
 ms.localizationpriority: medium
 ---
@@ -122,6 +122,7 @@ When developing an event-based add-in to run on a Windows client, be mindful of
 
   Note that a large JavaScript bundle may cause issues with the performance of your add-in. We recommend preprocessing heavy operations, so that they're not included in your event-handling code.
 - When the JavaScript function specified in the manifest to handle an event runs, code in `Office.onReady()` and `Office.initialize` isn't run. We recommend adding any startup logic needed by event handlers, such as checking the user's client version, to the event handlers instead.
+- The event-handling file and the **bundle.js** file must support caching in production. The server hosting these files shouldn't return a `Cache-Control` header specifying `no-cache` or similar options in the HTTP response. For more information, see the "Hosting requirements" section of [Office Add-ins manifest](add-in-manifests.md#hosting-requirements).
 
 ### Event-based add-in limitations in Excel, PowerPoint, and Word
 

docs/testing/troubleshoot-event-based-and-spam-reporting-add-ins.md

@@ -1,7 +1,7 @@
 ---
 title: Troubleshoot event-based and spam-reporting add-ins
 description: Learn how to troubleshoot development errors in Office Add-ins that implement event-based activation or integrated spam reporting.
-ms.date: 10/14/2025
+ms.date: 11/06/2025
 ms.topic: troubleshooting
 ms.localizationpriority: medium
 ---
@@ -28,7 +28,7 @@ As you develop your [event-based](../develop/event-based-activation.md) or [spam
   - Verify that the `<Runtimes>` element (add-in only manifest) or `"extensions.runtimes.code"` property (unified manifest) correctly references the HTML or JavaScript file containing the event handlers. Classic Outlook on Windows and other Windows-based Office applications use the JavaScript file during runtime, while Office on the web, the new Outlook Mac UI, and [new Outlook on Windows](https://support.microsoft.com/office/656bb8d9-5a60-49b2-a98b-ba7822bc7627) use the HTML file. For an example of how this is configured in the manifest, see the "Configure the manifest" section of [Automatically set the subject of a new message or appointment](../outlook/on-new-compose-events-walkthrough.md#configure-the-manifest).
 
     For Windows clients (except for new Outlook on Windows), you must bundle all your event-handling JavaScript code into this JavaScript file referenced in the manifest. Note that a large JavaScript bundle may cause issues with the performance of your add-in. We recommend preprocessing heavy operations, so that they're not included in your event-handling code.
-
+  - For the JavaScript-only runtime, the event-handling file and the **bundle.js** file must support caching in production. The server hosting these files shouldn't return a `Cache-Control` header specifying `no-cache` or similar options in the HTTP response. If caching is preventing you from seeing your changes during testing, try [clearing your cache](clear-cache.md#clear-the-office-cache-on-windows).
 - For Windows clients (except for new Outlook on Windows), when the JavaScript function specified in the manifest to handle an event runs, code in `Office.onReady()` and `Office.initialize` isn't run. We recommend adding any startup logic needed by event handlers, such as checking the user's client version, to the event handlers instead.
 
 - Verify that your event-handling JavaScript file calls `Office.actions.associate`. This ensures that the event handler name specified in the manifest is mapped to its JavaScript counterpart. The following code is an example.