refactor: extract MainScaffold for better separation of navigation chrome logic

shared/src/commonMain/kotlin/bzh/ajaury/chombev/App.kt

@@ -1,8 +1,6 @@
 package bzh.ajaury.chombev
 
 import androidx.compose.foundation.isSystemInDarkTheme
-import androidx.compose.foundation.layout.WindowInsets
-import androidx.compose.material3.Scaffold
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.mutableStateListOf
 import androidx.compose.runtime.saveable.rememberSerializable
@@ -13,8 +11,7 @@ import androidx.savedstate.compose.serialization.serializers.SnapshotStateListSe
 import bzh.ajaury.chombev.core.coroutines.di.coroutinesModule
 import bzh.ajaury.chombev.core.logging.di.loggingModule
 import bzh.ajaury.chombev.di.sharedModule
-import bzh.ajaury.chombev.navigation.MainBottomBar
-import bzh.ajaury.chombev.navigation.MainTopBar
+import bzh.ajaury.chombev.navigation.MainScaffold
 import bzh.ajaury.chombev.navigation.Route
 import bzh.ajaury.chombev.navigation.WebPages
 import bzh.ajaury.chombev.player.ui.PlayerScreen
@@ -49,38 +46,21 @@ fun App() {
 
         val darkTheme = isSystemInDarkTheme()
 
-        // The current top destination drives the shared chrome: the top and bottom bars are shown
-        // only on the main screens (Records and the web pages), not on the Player detail screen.
-        val currentRoute = backStack.lastOrNull()
-        val selectedPage = (currentRoute as? Route.Web)?.page
-        val isMainScreen = currentRoute is Route.Records || currentRoute is Route.Web
-
         ChomBevTheme(darkTheme = darkTheme) {
-            Scaffold(
-                // Let each screen's bars/insets apply; keeps the Player's own scaffold from double-padding.
-                contentWindowInsets = WindowInsets(0, 0, 0, 0),
-                topBar = {
-                    if (isMainScreen) {
-                        MainTopBar()
-                    }
-                },
-                bottomBar = {
-                    if (isMainScreen) {
-                        MainBottomBar(
-                            selectedPage = selectedPage,
-                            onRecordsClick = { backStack.selectMainTab(null) },
-                            onDeepenClick = { backStack.selectMainTab(WebPages.DEEPEN) },
-                            onAboutClick = { backStack.selectMainTab(WebPages.ABOUT) },
-                        )
-                    }
-                },
-            ) { innerPadding ->
-                NavDisplay(
-                    backStack = backStack,
-                    onBack = { backStack.removeLastOrNull() },
-                    entryProvider = { key ->
-                        when (key) {
-                            is Route.Records -> NavEntry(key) {
+            // Each destination owns its chrome (see MainScaffold) so navigating to the full-screen
+            // player animates as a whole scene without the main bars reflowing the outgoing screen.
+            NavDisplay(
+                backStack = backStack,
+                onBack = { backStack.removeLastOrNull() },
+                entryProvider = { key ->
+                    when (key) {
+                        is Route.Records -> NavEntry(key) {
+                            MainScaffold(
+                                selectedPage = null,
+                                onRecordsClick = { backStack.selectMainTab(null) },
+                                onDeepenClick = { backStack.selectMainTab(WebPages.DEEPEN) },
+                                onAboutClick = { backStack.selectMainTab(WebPages.ABOUT) },
+                            ) { innerPadding ->
                                 RecordsScreen(
                                     contentPadding = innerPadding,
                                     onRecordClick = { record ->
@@ -88,15 +68,22 @@ fun App() {
                                     },
                                 )
                             }
+                        }
 
-                            is Route.Player -> NavEntry(key) {
-                                PlayerScreen(
-                                    recordId = key.recordId,
-                                    onBackClicked = { backStack.removeLastOrNull() },
-                                )
-                            }
+                        is Route.Player -> NavEntry(key) {
+                            PlayerScreen(
+                                recordId = key.recordId,
+                                onBackClicked = { backStack.removeLastOrNull() },
+                            )
+                        }
 
-                            is Route.Web -> NavEntry(key) {
+                        is Route.Web -> NavEntry(key) {
+                            MainScaffold(
+                                selectedPage = key.page,
+                                onRecordsClick = { backStack.selectMainTab(null) },
+                                onDeepenClick = { backStack.selectMainTab(WebPages.DEEPEN) },
+                                onAboutClick = { backStack.selectMainTab(WebPages.ABOUT) },
+                            ) { innerPadding ->
                                 WebViewScreen(
                                     page = key.page,
                                     contentPadding = innerPadding,
@@ -104,9 +91,9 @@ fun App() {
                                 )
                             }
                         }
-                    },
-                )
-            }
+                    }
+                },
+            )
         }
     }
 }

shared/src/commonMain/kotlin/bzh/ajaury/chombev/navigation/MainScaffold.kt

@@ -0,0 +1,40 @@
+package bzh.ajaury.chombev.navigation
+
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.WindowInsets
+import androidx.compose.material3.Scaffold
+import androidx.compose.runtime.Composable
+import bzh.ajaury.chombev.web.model.WebPage
+
+/**
+ * Scaffold shared by the main destinations (Records, Deepen, About): the app [MainTopBar] and the
+ * [MainBottomBar].
+ *
+ * Each main destination wraps its own content in a [MainScaffold] rather than sitting inside one
+ * shared outer scaffold. This keeps the chrome part of the destination, so it animates with it and
+ * its content padding stays stable during navigation — avoiding the layout jump that happened when
+ * pushing a full-screen detail (the player) instantly removed the shared bars.
+ */
+@Composable
+fun MainScaffold(
+    selectedPage: WebPage?,
+    onRecordsClick: () -> Unit = {},
+    onDeepenClick: () -> Unit = {},
+    onAboutClick: () -> Unit = {},
+    content: @Composable (PaddingValues) -> Unit,
+) {
+    Scaffold(
+        // Let each bar apply its own insets; matches the player's standalone scaffold.
+        contentWindowInsets = WindowInsets(0, 0, 0, 0),
+        topBar = { MainTopBar() },
+        bottomBar = {
+            MainBottomBar(
+                selectedPage = selectedPage,
+                onRecordsClick = onRecordsClick,
+                onDeepenClick = onDeepenClick,
+                onAboutClick = onAboutClick,
+            )
+        },
+        content = content,
+    )
+}