close raw app preview pop-out when the editor tab reloads or closes (#11607)

frontend/src/lib/components/raw_apps/RawAppEditor.svelte

@@ -1839,13 +1839,15 @@ addEventListener('message', function (e) {
 		syncExternalPreviewNotice()
 		syncExternalPreview()
 	}
-
-	onDestroy(() => {
-		// Don't leave a detached preview behind when the editor unmounts: it
-		// would stop receiving builds and, once refreshed, has no opener to
+
+	// Don't leave a detached preview behind when the editor goes away, by
+	// unmounting or by its tab reloading or closing (`pagehide`, which skips
+	// `onDestroy`): it would stop receiving builds, and its document is a blob
+	// URL owned by this page, so refreshing it gives "not found".
 	function closeExternalPreview() {
 		if (externalPreviewWindow && !externalPreviewWindow.closed) externalPreviewWindow.close()
-		externalPreviewWindow = null
+		externalPreviewWindow = null
+	}
 	onDestroy(closeExternalPreview)
 
 	function openExternalPreview() {
@@ -2512,7 +2514,7 @@ addEventListener('message', function (e) {
 		}
 	}
 </script>
-
+
 <svelte:window onmessage={listener} onkeydown={handleKeydown} onpagehide={closeExternalPreview} />
 <DarkModeObserver
 	bind:darkMode