docs: document duplicating data apps

guides/data-apps.mdx

@@ -68,6 +68,32 @@ Restoring duplicates the selected version to the head of the timeline as a new l
 
 
 
+### Duplicating an app
+
+If you want to fork an app - to experiment with a different direction, use it as a starting point for a new app, or grab a personal copy of something a teammate built - you can duplicate it.
+
+You can duplicate any app you can view. The duplicate lands in your **Settings \> My apps** as a personal app you own, regardless of where the original lives. The original is untouched.
+
+To duplicate an app:
+
+- From the apps list, open the **⋯** menu on any app card and select **Duplicate**.
+- Or, from inside an app, open the **⋯** menu in the chat header and select **Duplicate**.
+
+The duplicate starts at version 1, seeded from the source app's latest ready version. The following is carried over:
+
+- The generated app code (the version you see in the preview).
+- The template the source app was built from.
+- Any chart and dashboard resource references attached to the source app.
+
+The following is **not** carried over:
+
+- Prior version history - the duplicate starts fresh at v1.
+- Images attached to earlier prompts.
+- Pending clarifications from in-progress builds.
+- The running sandbox - a fresh sandbox spins up on your first prompt.
+
+To duplicate, you need **view** access on the source app and **create** permission for data apps on the project.
+
 ### Query inspector
 
 When an app runs a query, it will appear in the query inspector. Open it to see every query the running app is making - the underlying metric query, the fields it's pulling, and the results it gets back. Use it to verify the app is asking for the right data, debug unexpected numbers, or sanity-check performance.