fix(navigation): keep article content during exit animation

On back navigation the article state was cleared before the exit animation ran, so the panel animated out empty except for the back arrow. The overlay now retains the last shown article state until the exit transition completes.

app/src/main/java/com/example/research/ui/article/ArticleScreen.kt

@@ -25,33 +25,10 @@ import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.text.style.LineHeightStyle
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.IntSize
-import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import com.example.research.R
 import com.example.research.common.ui.theme.dictionaryTitleLarge
-import com.example.research.feature.search.SearchAction
 import com.example.research.ui.theme.Spacing
 import com.example.research.ui.theme.AppWindowInsets
-import com.example.research.feature.search.SearchViewModel
-import androidx.compose.runtime.getValue
-
-@Composable
-fun ArticleRoute(
-    searchViewModel: SearchViewModel,
-    onNavigateBack: () -> Unit
-) {
-    val articleState by searchViewModel.selectedArticle.collectAsStateWithLifecycle()
-
-    ArticleScreen(
-        articleState = articleState,
-        onNavigateBack = onNavigateBack,
-        onRefClick = { word ->
-            searchViewModel.onAction(SearchAction.SearchAndLoadArticle(word))
-        },
-        onScrollPositionChanged = { index, offset ->
-            searchViewModel.updateArticleScrollPosition(index, offset)
-        },
-    )
-}
 
 private const val MERGED_BLOCK_MAX_CHARS = 1500
 private const val MERGED_BLOCK_MAX_ITEMS = 12

app/src/main/java/com/example/research/ui/navigation/AppNavigation.kt

@@ -23,7 +23,8 @@ import androidx.window.core.layout.WindowSizeClass.Companion.WIDTH_DP_MEDIUM_LOW
 import com.example.research.feature.search.SearchAction
 import com.example.research.feature.search.SearchViewModel
 import com.example.research.ui.about.AboutScreen
-import com.example.research.ui.article.ArticleRoute
+import com.example.research.ui.article.ArticleScreen
+import com.example.research.ui.article.ArticleState
 import com.example.research.ui.main.MainRoute
 import com.example.research.ui.settings.SettingsRoute
 import com.example.research.ui.settings.SettingsViewModel
@@ -104,6 +105,10 @@ fun AppNavigation(
     }
 
     val articleState by searchViewModel.selectedArticle.collectAsStateWithLifecycle()
+    var lastShownArticle by remember { mutableStateOf<ArticleState?>(null) }
+    LaunchedEffect(articleState) {
+        if (articleState != null) lastShownArticle = articleState
+    }
 
     val effectiveScreen = when {
         currentScreen == Screen.About -> Screen.About
@@ -178,15 +183,20 @@ fun AppNavigation(
             modifier = Modifier.fillMaxSize(),
             color = MaterialTheme.colorScheme.surface
         ) {
-            ArticleRoute(
-                searchViewModel = searchViewModel,
+            ArticleScreen(
+                articleState = articleState ?: lastShownArticle,
                 onNavigateBack = {
-                    if (searchViewModel.navigateBackFromArticle()) {
-                        return@ArticleRoute
+                    if (!searchViewModel.navigateBackFromArticle()) {
+                        searchViewModel.onAction(SearchAction.ClearArticle)
+                        if (screenStack.size > 1) screenStack.removeAt(screenStack.lastIndex)
                     }
-                    searchViewModel.onAction(SearchAction.ClearArticle)
-                    if (screenStack.size > 1) screenStack.removeAt(screenStack.lastIndex)
-                }
+                },
+                onRefClick = { word ->
+                    searchViewModel.onAction(SearchAction.SearchAndLoadArticle(word))
+                },
+                onScrollPositionChanged = { index, offset ->
+                    searchViewModel.updateArticleScrollPosition(index, offset)
+                },
             )
         }
     }