diff --git a/app/src/main/java/com/ubisam/ubgitea/MainActivity.kt b/app/src/main/java/com/ubisam/ubgitea/MainActivity.kt
index 821c44f..af5c207 100644
--- a/app/src/main/java/com/ubisam/ubgitea/MainActivity.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/MainActivity.kt
@@ -400,6 +400,7 @@ class MainActivity : ComponentActivity() {
                             onSetCodeWordWrap = settingsViewModel::setCodeWordWrapEnabled,
                             onSetCodeFontSize = settingsViewModel::setCodeFontSizeSp,
                             onOpenSibling = codeBrowserViewModel::openSibling,
+                            onToggleFolder = codeBrowserViewModel::toggleFolder,
                             onLoadCounterpart = codeBrowserViewModel::loadCounterpart,
                             historyState = historyState,
                             onCommitSelected = historyViewModel::openCommit,
diff --git a/app/src/main/java/com/ubisam/ubgitea/core/settings/AppSettingsStore.kt b/app/src/main/java/com/ubisam/ubgitea/core/settings/AppSettingsStore.kt
index a736e2c..cfb9ced 100644
--- a/app/src/main/java/com/ubisam/ubgitea/core/settings/AppSettingsStore.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/core/settings/AppSettingsStore.kt
@@ -37,6 +37,11 @@ interface AppSettingsStore {
     fun themeMode(): ThemeMode = ThemeMode.SYSTEM
     fun setThemeMode(mode: ThemeMode) = Unit
 
+    // Which half of the viewer's side pane is on top (TASK-057): the folder tree by default, the
+    // classes and functions when the reader has swapped them.
+    fun isOutlineAboveFolders(): Boolean = false
+    fun setOutlineAboveFolders(above: Boolean) = Unit
+
     companion object {
         const val DEFAULT_CODE_FONT_SIZE_SP = 13
         val CODE_FONT_SIZES_SP = listOf(11, 12, 13, 14, 16)
@@ -88,7 +93,14 @@ class SharedPreferencesAppSettingsStore(context: Context) : AppSettingsStore {
         preferences.edit().putString(KEY_THEME_MODE, mode.name).apply()
     }
 
+    override fun isOutlineAboveFolders(): Boolean = preferences.getBoolean(KEY_OUTLINE_ABOVE_FOLDERS, false)
+
+    override fun setOutlineAboveFolders(above: Boolean) {
+        preferences.edit().putBoolean(KEY_OUTLINE_ABOVE_FOLDERS, above).apply()
+    }
+
     private companion object {
+        const val KEY_OUTLINE_ABOVE_FOLDERS = "code_outline_above_folders"
         const val KEY_HOME_SOURCE = "home_source"
         const val KEY_THEME_MODE = "theme_mode"
         const val KEY_CODE_WORD_WRAP = "code_word_wrap_enabled"
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/branchdetail/BranchDetailScreen.kt b/app/src/main/java/com/ubisam/ubgitea/feature/branchdetail/BranchDetailScreen.kt
index 752f692..812a516 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/branchdetail/BranchDetailScreen.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/branchdetail/BranchDetailScreen.kt
@@ -55,6 +55,7 @@ fun BranchDetailScreen(
     onSetCodeWordWrap: (Boolean) -> Unit,
     onSetCodeFontSize: (Int) -> Unit,
     onOpenSibling: (RepositoryPath, String?) -> Unit,
+    onToggleFolder: (RepositoryPath) -> Unit,
     onLoadCounterpart: () -> Unit,
     historyState: HistoryUiState,
     onCommitSelected: (CommitSummary) -> Unit,
@@ -86,6 +87,7 @@ fun BranchDetailScreen(
             onSetWordWrap = onSetCodeWordWrap,
             onSetFontSize = onSetCodeFontSize,
             onOpenSibling = onOpenSibling,
+            onToggleFolder = onToggleFolder,
             onOpenEntry = onEntrySelected,
             onLoadCounterpart = onLoadCounterpart,
             modifier = modifier,
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserScreen.kt b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserScreen.kt
index 87a320a..fff3d6d 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserScreen.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserScreen.kt
@@ -159,14 +159,15 @@ fun FileViewerScreen(
     onSetWordWrap: (Boolean) -> Unit,
     onSetFontSize: (Int) -> Unit,
     onOpenSibling: (RepositoryPath, String?) -> Unit,
+    onToggleFolder: (RepositoryPath) -> Unit,
     onOpenEntry: (TreeEntry) -> Unit,
     onLoadCounterpart: () -> Unit,
     modifier: Modifier = Modifier,
 ) {
     if (state is CodeBrowserUiState.File && state.content is ContentClassification.Text) {
         CodeViewerScreen(
-            state, state.content, preferences, onBack, onSetWordWrap, onSetFontSize, onOpenSibling, onOpenEntry,
-            onLoadCounterpart, modifier,
+            state, state.content, preferences, onBack, onSetWordWrap, onSetFontSize, onOpenSibling, onToggleFolder,
+            onOpenEntry, onLoadCounterpart, modifier,
         )
         return
     }
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserViewModel.kt b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserViewModel.kt
index 3f8fb73..990b126 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserViewModel.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserViewModel.kt
@@ -93,6 +93,9 @@ sealed interface CodeBrowserUiState {
         // A symbol to bring into view once the file is shown: set when the file was reached by
         // following a symbol from its counterpart.
         val focusSymbol: String? = null,
+        // The folder tree beside the code. It starts as the directory the file was opened from and
+        // keeps its open folders while the reader moves between files in it.
+        val tree: FileTree = FileTree(CodeBrowserNavigation.parent(path), siblingEntries),
     ) : CodeBrowserUiState
     data class UnsupportedEntry(
         val target: CodeBrowserTarget,
@@ -125,6 +128,7 @@ class CodeBrowserViewModel(
     val state: StateFlow<CodeBrowserUiState> = mutableState.asStateFlow()
     private var operation: Job? = null
     private var counterpartOperation: Job? = null
+    private val folderOperations = mutableMapOf<RepositoryPath, Job>()
 
     fun open(target: CodeBrowserTarget) = loadDirectory(target, RepositoryPath.Root)
 
@@ -149,14 +153,47 @@ class CodeBrowserViewModel(
         if (index == -1) return
         val newIndex = index + delta
         if (newIndex !in siblings.indices) return
-        loadFile(current.target, siblings[newIndex], current.siblingEntries)
+        loadFile(current.target, siblings[newIndex], current.siblingEntries, tree = current.tree)
     }
 
-    /** Opens another file of the directory the current file came from, optionally at a symbol. */
+    /**
+     * Opens another file of the folder tree -- of the current file's directory, or of a folder
+     * opened in the tree -- optionally at a symbol.
+     */
     fun openSibling(path: RepositoryPath, focusSymbol: String? = null) {
         val current = mutableState.value as? CodeBrowserUiState.File ?: return
         if (path == current.path) return
-        loadFile(current.target, path, current.siblingEntries, focusSymbol)
+        val directory = current.tree.entriesOf(CodeBrowserNavigation.parent(path)) ?: current.siblingEntries
+        loadFile(current.target, path, directory, focusSymbol, current.tree)
+    }
+
+    /** Opens a folder of the tree beside the code in place, or closes it if it is open. */
+    fun toggleFolder(folder: RepositoryPath) {
+        val current = mutableState.value as? CodeBrowserUiState.File ?: return
+        folderOperations.remove(folder)?.cancel()
+        if (folder in current.tree.folders) {
+            mutableState.value = current.copy(tree = current.tree.without(folder))
+            return
+        }
+        mutableState.value = current.copy(tree = current.tree.with(folder, FolderUiState.Loading))
+        folderOperations[folder] = viewModelScope.launch {
+            val result = try {
+                val entries = withContext(defaultDispatcher) {
+                    loadAllPages { page -> browser.listTree(current.target.repository, current.target.ref, folder, page, PAGE_SIZE) }
+                        .distinctBy(TreeEntry::path)
+                        .sortedWith(LISTING_ORDER)
+                }
+                FolderUiState.Loaded(entries)
+            } catch (failure: Throwable) {
+                if (failure is CancellationException) throw failure
+                FolderUiState.Failed
+            }
+            // Only if the folder is still waiting: it may have been closed, or the file left.
+            val latest = mutableState.value as? CodeBrowserUiState.File ?: return@launch
+            if (latest.tree.folders[folder] == FolderUiState.Loading) {
+                mutableState.value = latest.copy(tree = latest.tree.with(folder, result))
+            }
+        }
     }
 
     /** Fetches the current file's counterpart so both can be shown side by side. */
@@ -207,6 +244,8 @@ class CodeBrowserViewModel(
         operation?.cancel()
         operation = null
         counterpartOperation?.cancel()
+        folderOperations.values.forEach(Job::cancel)
+        folderOperations.clear()
         mutableState.value = CodeBrowserUiState.Idle
     }
 
@@ -234,7 +273,7 @@ class CodeBrowserViewModel(
                         }
                     }
                 }.distinctBy(TreeEntry::path)
-                    .sortedWith(compareBy<TreeEntry> { it.type != TreeEntryType.DIRECTORY }.thenBy { it.name.lowercase() })
+                    .sortedWith(LISTING_ORDER)
             }
             mutableState.value = CodeBrowserUiState.Directory(target, path, entries)
         } catch (failure: Throwable) {
@@ -247,6 +286,7 @@ class CodeBrowserViewModel(
         path: RepositoryPath,
         siblingEntries: List<TreeEntry> = emptyList(),
         focusSymbol: String? = null,
+        tree: FileTree? = null,
     ) = startOperation {
         counterpartOperation?.cancel()
         mutableState.value = CodeBrowserUiState.Loading(target, path, isFile = true)
@@ -264,6 +304,8 @@ class CodeBrowserViewModel(
                 siblingEntries = siblingEntries,
                 counterpartPath = counterpartOf(path, siblingFiles),
                 focusSymbol = focusSymbol,
+                // A folder still being fetched would never hear back in the new state.
+                tree = tree?.settled() ?: FileTree(CodeBrowserNavigation.parent(path), siblingEntries),
             )
         } catch (failure: Throwable) {
             handleFailure(target, path, failure, isFile = true)
@@ -332,6 +374,7 @@ class CodeBrowserViewModel(
     private companion object {
         const val PAGE_SIZE = 100
         const val MAX_PAGES = 100
+        val LISTING_ORDER = compareBy<TreeEntry> { it.type != TreeEntryType.DIRECTORY }.thenBy { it.name.lowercase() }
     }
 }
 
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt
index f567188..acbd407 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt
@@ -1,5 +1,6 @@
 package com.ubisam.ubgitea.feature.codebrowser
 
+import android.app.Application
 import androidx.activity.compose.BackHandler
 import androidx.annotation.DrawableRes
 import androidx.annotation.StringRes
@@ -70,6 +71,8 @@ import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.focus.FocusRequester
 import androidx.compose.ui.focus.focusRequester
 import androidx.compose.ui.input.pointer.PointerEventPass
@@ -94,6 +97,7 @@ import androidx.compose.ui.unit.Dp
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import com.ubisam.ubgitea.R
+import com.ubisam.ubgitea.core.settings.AppSettingsSession
 import com.ubisam.ubgitea.core.settings.AppSettingsStore
 import com.ubisam.ubgitea.domain.model.RepositoryPath
 import com.ubisam.ubgitea.domain.model.TreeEntry
@@ -141,7 +145,8 @@ private enum class ViewerLayout {
 }
 
 private val CompactHeightBreakpoint = 480.dp
-private val SidePaneWidth = 268.dp
+private val SidePaneWidth = 288.dp
+private val TreeIndent = 14.dp
 private val NarrowSidePaneWidth = 220.dp
 private val NarrowWideBreakpoint = 700.dp
 
@@ -160,11 +165,20 @@ fun CodeViewerScreen(
     onSetWordWrap: (Boolean) -> Unit,
     onSetFontSize: (Int) -> Unit,
     onOpenSibling: (RepositoryPath, String?) -> Unit,
+    onToggleFolder: (RepositoryPath) -> Unit,
     onOpenEntry: (TreeEntry) -> Unit,
     onLoadCounterpart: () -> Unit,
     modifier: Modifier = Modifier,
 ) {
     val document = rememberCodeDocument(state.path, text.renderedText)
+    // Which half of the side pane is on top is the reader's choice and is kept. It is read and
+    // written here rather than passed down through every screen above: nothing else uses it.
+    val settings = AppSettingsSession.store(LocalContext.current.applicationContext as Application)
+    var outlineFirst by remember { mutableStateOf(settings.isOutlineAboveFolders()) }
+    val swapPanes = {
+        outlineFirst = !outlineFirst
+        settings.setOutlineAboveFolders(outlineFirst)
+    }
     val listState = remember(state.path) { LazyListState() }
     val scope = rememberCoroutineScope()
     val firstVisibleLine by rememberFirstVisibleLine(listState)
@@ -279,7 +293,8 @@ fun CodeViewerScreen(
             drawerContent = {
                 if (!sidePaneIsShown) {
                     ModalDrawerSheet(
-                        drawerContainerColor = MaterialTheme.colorScheme.surface,
+                        drawerContainerColor = MaterialTheme.colorScheme.background,
+                        drawerShape = RoundedCornerShape(topEnd = 28.dp, bottomEnd = 28.dp),
                         modifier = Modifier.width(drawerWidth),
                     ) {
                         SidePane(
@@ -293,6 +308,9 @@ fun CodeViewerScreen(
                                 onOpenSibling(it, null)
                             },
                             onOpenEntry = onOpenEntry,
+                            onToggleFolder = onToggleFolder,
+                            outlineFirst = outlineFirst,
+                            onSwap = swapPanes,
                             onSymbolSelected = {
                                 scope.launch { drawerState.close() }
                                 goToSymbol(it)
@@ -364,6 +382,9 @@ fun CodeViewerScreen(
                                 onToggleCollapsed = toggleCollapsed,
                                 onOpenFile = { onOpenSibling(it, null) },
                                 onOpenEntry = onOpenEntry,
+                                onToggleFolder = onToggleFolder,
+                                outlineFirst = outlineFirst,
+                                onSwap = swapPanes,
                                 onSymbolSelected = { goToSymbol(it) },
                                 modifier = Modifier.width(sidePaneWidth).fillMaxHeight(),
                             )
@@ -971,31 +992,99 @@ private fun SidePane(
     collapsed: Set<Int>,
     onToggleCollapsed: (CodeSymbol) -> Unit,
     onOpenFile: (RepositoryPath) -> Unit,
+    onToggleFolder: (RepositoryPath) -> Unit,
     onOpenEntry: (TreeEntry) -> Unit,
     onSymbolSelected: (CodeSymbol) -> Unit,
+    outlineFirst: Boolean,
+    onSwap: () -> Unit,
     modifier: Modifier = Modifier,
 ) {
-    val tree = remember(document.symbols, collapsed) { outlineTree(document.symbols, collapsed) }
-    val current = currentIn(tree, document.symbols, currentLine)
-    LazyColumn(modifier.background(MaterialTheme.colorScheme.surface), contentPadding = PaddingValues(vertical = 8.dp)) {
-        if (state.siblingEntries.isNotEmpty()) {
-            item(key = "files-title") { SidePaneTitle(stringResource(R.string.codeviewer_files_title)) }
-            items(state.siblingEntries, key = { "file:" + it.path.value }) { entry ->
-                val isFile = entry.type == TreeEntryType.FILE
-                val isCurrent = entry.path == state.path
-                SidePaneRow(
-                    icon = if (entry.type == TreeEntryType.DIRECTORY) R.drawable.ic_ub_folder else R.drawable.ic_ub_file,
-                    text = entry.name,
-                    isCurrent = isCurrent,
-                    accent = entry.type == TreeEntryType.DIRECTORY,
-                    onClick = { if (isFile) onOpenFile(entry.path) else onOpenEntry(entry) },
-                )
+    val outline = remember(document.symbols, collapsed) { outlineTree(document.symbols, collapsed) }
+    val rows = remember(state.tree) { state.tree.rows() }
+    val folders: @Composable (Modifier) -> Unit = { FolderCard(state, rows, onOpenFile, onToggleFolder, onOpenEntry, it) }
+    val symbols: @Composable (Modifier) -> Unit = {
+        SymbolCard(document, outline, currentLine, collapsed, onToggleCollapsed, onSymbolSelected, it)
+    }
+    Column(modifier.background(MaterialTheme.colorScheme.background).padding(horizontal = 10.dp, vertical = 10.dp)) {
+        val half = Modifier.weight(1f).fillMaxWidth()
+        when {
+            // A file that was not opened from a listing has no folder to show.
+            rows.isEmpty() -> symbols(half)
+            else -> {
+                if (outlineFirst) symbols(half) else folders(half)
+                SwapButton(onSwap)
+                if (outlineFirst) folders(half) else symbols(half)
             }
-            item(key = "divider") { HorizontalDivider(Modifier.padding(vertical = 8.dp), color = MaterialTheme.colorScheme.outlineVariant) }
         }
-        if (tree.isNotEmpty()) {
-            item(key = "outline-title") { SidePaneTitle(stringResource(R.string.codeviewer_outline_title)) }
-            items(tree, key = { "symbol:" + it.line + ":" + it.name }) { symbol ->
+    }
+}
+
+@Composable
+private fun FolderCard(
+    state: CodeBrowserUiState.File,
+    rows: List<FileTreeRow>,
+    onOpenFile: (RepositoryPath) -> Unit,
+    onToggleFolder: (RepositoryPath) -> Unit,
+    onOpenEntry: (TreeEntry) -> Unit,
+    modifier: Modifier,
+) {
+    PaneCard(
+        icon = R.drawable.ic_ub_folder,
+        title = stringResource(R.string.codeviewer_files_title),
+        caption = state.tree.root.value.ifEmpty { stringResource(R.string.codebrowser_root) },
+        modifier = modifier,
+    ) {
+        val listState = rememberLazyListState()
+        // Open on the file being read, not on the top of a long folder.
+        LaunchedEffect(state.path) {
+            val index = rows.indexOfFirst { it is FileTreeRow.Entry && it.entry.path == state.path }
+            if (index > 0) listState.scrollToItem((index - 2).coerceAtLeast(0))
+        }
+        LazyColumn(state = listState, contentPadding = PaddingValues(vertical = 6.dp)) {
+            items(rows, key = { if (it is FileTreeRow.Entry) "e:" + it.entry.path.value else "n:" + (it as FileTreeRow.Note).folder.value }) { row ->
+                when (row) {
+                    is FileTreeRow.Entry -> FolderTreeRow(row, isCurrent = row.entry.path == state.path) {
+                        when (row.entry.type) {
+                            TreeEntryType.DIRECTORY -> onToggleFolder(row.entry.path)
+                            TreeEntryType.FILE -> onOpenFile(row.entry.path)
+                            else -> onOpenEntry(row.entry)
+                        }
+                    }
+                    is FileTreeRow.Note -> FolderNoteRow(row)
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun SymbolCard(
+    document: CodeDocument,
+    outline: List<CodeSymbol>,
+    currentLine: Int,
+    collapsed: Set<Int>,
+    onToggleCollapsed: (CodeSymbol) -> Unit,
+    onSymbolSelected: (CodeSymbol) -> Unit,
+    modifier: Modifier,
+) {
+    val current = currentIn(outline, document.symbols, currentLine)
+    PaneCard(
+        icon = R.drawable.ic_ub_list,
+        title = stringResource(R.string.codeviewer_symbols_title),
+        caption = document.name,
+        modifier = modifier,
+    ) {
+        if (outline.isEmpty()) {
+            Text(
+                stringResource(R.string.codeviewer_symbols_empty),
+                style = MaterialTheme.typography.bodySmall,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                modifier = Modifier.padding(14.dp),
+            )
+            return@PaneCard
+        }
+        LazyColumn(contentPadding = PaddingValues(vertical = 6.dp)) {
+            items(outline, key = { "symbol:" + it.line + ":" + it.name }) { symbol ->
                 SymbolRow(
                     symbol = symbol,
                     isCurrent = symbol == current,
@@ -1009,41 +1098,139 @@ private fun SidePane(
     }
 }
 
+/** One half of the side pane: a white card on the page color, named at the top. */
 @Composable
-private fun SidePaneTitle(text: String) {
-    Text(
-        text,
-        style = MaterialTheme.typography.labelLarge,
-        fontWeight = FontWeight.Bold,
-        color = MaterialTheme.colorScheme.onSurfaceVariant,
-        modifier = Modifier.padding(horizontal = 14.dp, vertical = 6.dp).semantics { heading() },
-    )
+private fun PaneCard(
+    @DrawableRes icon: Int,
+    title: String,
+    caption: String,
+    modifier: Modifier,
+    content: @Composable () -> Unit,
+) {
+    Surface(
+        color = MaterialTheme.colorScheme.surface,
+        shape = RoundedCornerShape(18.dp),
+        border = BorderStroke(1.dp, MaterialTheme.colorScheme.outlineVariant),
+        modifier = modifier,
+    ) {
+        Column {
+            Row(
+                Modifier.fillMaxWidth().padding(start = 12.dp, end = 12.dp, top = 10.dp, bottom = 8.dp),
+                verticalAlignment = Alignment.CenterVertically,
+                horizontalArrangement = Arrangement.spacedBy(8.dp),
+            ) {
+                Box(
+                    Modifier.size(28.dp).background(MaterialTheme.colorScheme.primaryContainer, CircleShape),
+                    contentAlignment = Alignment.Center,
+                ) {
+                    UBIcon(icon, null, size = 16.dp, tint = MaterialTheme.colorScheme.primary)
+                }
+                Text(
+                    title,
+                    style = MaterialTheme.typography.titleSmall,
+                    fontWeight = FontWeight.Bold,
+                    maxLines = 1,
+                    modifier = Modifier.semantics { heading() },
+                )
+                Text(
+                    caption,
+                    style = MaterialTheme.typography.bodySmall,
+                    fontFamily = FontFamily.Monospace,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    maxLines = 1,
+                    overflow = TextOverflow.StartEllipsis,
+                    modifier = Modifier.weight(1f),
+                )
+            }
+            HorizontalDivider(color = MaterialTheme.colorScheme.outlineVariant)
+            content()
+        }
+    }
 }
 
 @Composable
-private fun SidePaneRow(@DrawableRes icon: Int, text: String, isCurrent: Boolean, accent: Boolean, onClick: () -> Unit) {
+private fun SwapButton(onSwap: () -> Unit) {
+    Box(Modifier.fillMaxWidth(), contentAlignment = Alignment.Center) {
+        Surface(
+            onClick = onSwap,
+            shape = CircleShape,
+            color = MaterialTheme.colorScheme.primaryContainer,
+            contentColor = MaterialTheme.colorScheme.onPrimaryContainer,
+        ) {
+            Row(
+                Modifier.padding(horizontal = 14.dp, vertical = 6.dp),
+                verticalAlignment = Alignment.CenterVertically,
+                horizontalArrangement = Arrangement.spacedBy(6.dp),
+            ) {
+                UBIcon(R.drawable.ic_ub_swap_vertical, null, size = 16.dp)
+                Text(stringResource(R.string.codeviewer_pane_swap), style = MaterialTheme.typography.labelMedium, fontWeight = FontWeight.Bold)
+            }
+        }
+    }
+}
+
+@Composable
+private fun FolderTreeRow(row: FileTreeRow.Entry, isCurrent: Boolean, onClick: () -> Unit) {
+    val isFolder = row.entry.type == TreeEntryType.DIRECTORY
+    val folderState = if (!isFolder) null else stringResource(if (row.isOpen) R.string.codeviewer_folder_open else R.string.codeviewer_folder_closed)
     Row(
         Modifier.fillMaxWidth()
-            .background(if (isCurrent) MaterialTheme.colorScheme.primaryContainer else MaterialTheme.colorScheme.surface)
+            .padding(horizontal = 6.dp)
+            .clip(RoundedCornerShape(10.dp))
+            .background(if (isCurrent) MaterialTheme.colorScheme.primaryContainer else Color.Transparent)
             .clickable(role = Role.Button, onClick = onClick)
-            .semantics { selected = isCurrent }
+            .semantics {
+                selected = isCurrent
+                if (folderState != null) stateDescription = folderState
+            }
             .heightIn(min = 44.dp)
-            .padding(horizontal = 14.dp),
+            .padding(start = 6.dp + TreeIndent * row.depth, end = 8.dp),
         verticalAlignment = Alignment.CenterVertically,
-        horizontalArrangement = Arrangement.spacedBy(8.dp),
+        horizontalArrangement = Arrangement.spacedBy(6.dp),
     ) {
-        UBIcon(icon, null, size = 18.dp, tint = if (accent) MaterialTheme.colorScheme.primary else MaterialTheme.colorScheme.onSurfaceVariant)
+        if (isFolder) {
+            UBIcon(
+                if (row.isOpen) R.drawable.ic_ub_chevron_down else R.drawable.ic_ub_chevron_right,
+                null,
+                size = 16.dp,
+                tint = MaterialTheme.colorScheme.onSurfaceVariant,
+            )
+        } else {
+            Spacer(Modifier.size(16.dp))
+        }
+        UBIcon(
+            if (isFolder) R.drawable.ic_ub_folder else R.drawable.ic_ub_file,
+            null,
+            size = 18.dp,
+            tint = if (isFolder || isCurrent) MaterialTheme.colorScheme.primary else MaterialTheme.colorScheme.onSurfaceVariant,
+        )
         Text(
-            text,
+            row.entry.name,
             fontFamily = FontFamily.Monospace,
             fontSize = 13.sp,
-            fontWeight = if (isCurrent) FontWeight.Bold else FontWeight.Medium,
+            fontWeight = if (isCurrent || isFolder) FontWeight.Bold else FontWeight.Medium,
             maxLines = 1,
             overflow = TextOverflow.Ellipsis,
         )
     }
 }
 
+@Composable
+private fun FolderNoteRow(row: FileTreeRow.Note) {
+    Text(
+        stringResource(
+            when (row.note) {
+                FolderNote.LOADING -> R.string.codeviewer_folder_loading
+                FolderNote.FAILED -> R.string.codeviewer_folder_failed
+                FolderNote.EMPTY -> R.string.codeviewer_folder_empty
+            },
+        ),
+        style = MaterialTheme.typography.bodySmall,
+        color = if (row.note == FolderNote.FAILED) MaterialTheme.colorScheme.error else MaterialTheme.colorScheme.onSurfaceVariant,
+        modifier = Modifier.padding(start = 34.dp + TreeIndent * row.depth, end = 12.dp, top = 8.dp, bottom = 8.dp),
+    )
+}
+
 /**
  * The row to mark as "you are here": the innermost enclosing symbol that is on screen in the tree.
  * Inside a folded class that is the class itself, since its methods are hidden.
@@ -1073,11 +1260,13 @@ private fun SymbolRow(
     val base: Dp = if (compact) 14.dp else 20.dp
     Row(
         Modifier.fillMaxWidth()
-            .background(if (isCurrent) MaterialTheme.colorScheme.primaryContainer else MaterialTheme.colorScheme.surface)
+            // In the side pane a row is a rounded pill inside its card; in the sheet it spans it.
+            .then(if (compact) Modifier.padding(horizontal = 6.dp).clip(RoundedCornerShape(10.dp)) else Modifier)
+            .background(if (isCurrent) MaterialTheme.colorScheme.primaryContainer else Color.Transparent)
             .clickable(role = Role.Button, onClick = onClick)
             .semantics { selected = isCurrent }
             .heightIn(min = if (compact) 44.dp else 48.dp)
-            .padding(start = (base - 8.dp) + step * symbol.depth, end = if (compact) 4.dp else base),
+            .padding(start = (if (compact) 0.dp else base - 8.dp) + step * symbol.depth, end = if (compact) 4.dp else base),
         verticalAlignment = Alignment.CenterVertically,
         horizontalArrangement = Arrangement.spacedBy(6.dp),
     ) {
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/FileTree.kt b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/FileTree.kt
new file mode 100644
index 0000000..c3562ef
--- /dev/null
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/FileTree.kt
@@ -0,0 +1,67 @@
+package com.ubisam.ubgitea.feature.codebrowser
+
+import com.ubisam.ubgitea.domain.model.RepositoryPath
+import com.ubisam.ubgitea.domain.model.TreeEntry
+import com.ubisam.ubgitea.domain.model.TreeEntryType
+
+/** What is known about a folder that has been opened in the viewer's folder tree. */
+sealed interface FolderUiState {
+    data object Loading : FolderUiState
+    data class Loaded(val entries: List<TreeEntry>) : FolderUiState
+    data object Failed : FolderUiState
+}
+
+/**
+ * The folder tree beside the code (TASK-057): the directory the file was opened from, and under it
+ * whichever folders have been opened since. A folder is in [folders] exactly while it is open.
+ */
+data class FileTree(
+    val root: RepositoryPath,
+    val entries: List<TreeEntry>,
+    val folders: Map<RepositoryPath, FolderUiState> = emptyMap(),
+) {
+    /** The listing of [directory], if this tree holds it. */
+    fun entriesOf(directory: RepositoryPath): List<TreeEntry>? =
+        if (directory == root) entries else (folders[directory] as? FolderUiState.Loaded)?.entries
+
+    fun with(folder: RepositoryPath, state: FolderUiState): FileTree = copy(folders = folders + (folder to state))
+
+    /** Closes [folder], and with it every folder that was open inside it. */
+    fun without(folder: RepositoryPath): FileTree =
+        copy(folders = folders.filterKeys { it != folder && !it.value.startsWith(folder.value + "/") })
+
+    /** Without the folders still being fetched: what can be carried over to another file. */
+    fun settled(): FileTree = copy(folders = folders.filterValues { it != FolderUiState.Loading })
+}
+
+enum class FolderNote { LOADING, FAILED, EMPTY }
+
+sealed interface FileTreeRow {
+    val depth: Int
+
+    data class Entry(val entry: TreeEntry, override val depth: Int, val isOpen: Boolean) : FileTreeRow
+
+    /** Stands where an open folder's contents would be, when there are none to show. */
+    data class Note(val folder: RepositoryPath, override val depth: Int, val note: FolderNote) : FileTreeRow
+}
+
+/** The tree as the rows of a list, top to bottom, each open folder followed by what is in it. */
+fun FileTree.rows(): List<FileTreeRow> = buildList { addRows(this@rows, entries, depth = 0) }
+
+private fun MutableList<FileTreeRow>.addRows(tree: FileTree, entries: List<TreeEntry>, depth: Int) {
+    for (entry in entries) {
+        val folder = if (entry.type == TreeEntryType.DIRECTORY) tree.folders[entry.path] else null
+        add(FileTreeRow.Entry(entry, depth, isOpen = folder != null))
+        when (folder) {
+            null -> Unit
+            FolderUiState.Loading -> add(FileTreeRow.Note(entry.path, depth + 1, FolderNote.LOADING))
+            FolderUiState.Failed -> add(FileTreeRow.Note(entry.path, depth + 1, FolderNote.FAILED))
+            is FolderUiState.Loaded ->
+                if (folder.entries.isEmpty()) add(FileTreeRow.Note(entry.path, depth + 1, FolderNote.EMPTY))
+                // A depth limit so that a listing that names itself cannot recurse without end.
+                else if (depth < MAX_TREE_DEPTH) addRows(tree, folder.entries, depth + 1)
+        }
+    }
+}
+
+private const val MAX_TREE_DEPTH = 32
diff --git a/app/src/main/java/com/ubisam/ubgitea/feature/home/HomeScreen.kt b/app/src/main/java/com/ubisam/ubgitea/feature/home/HomeScreen.kt
index a893889..075b744 100644
--- a/app/src/main/java/com/ubisam/ubgitea/feature/home/HomeScreen.kt
+++ b/app/src/main/java/com/ubisam/ubgitea/feature/home/HomeScreen.kt
@@ -156,13 +156,14 @@ private fun HomeContent(
             // Unfolded: the overview stays put on the left while the timeline scrolls on the right,
             // so the whole picture is on screen at once.
             Row(Modifier.fillMaxSize()) {
-                LazyColumn(Modifier.weight(0.46f).fillMaxHeight(), contentPadding = PaddingValues(bottom = 24.dp)) {
+                LazyColumn(Modifier.weight(0.5f).fillMaxHeight(), contentPadding = PaddingValues(bottom = 24.dp)) {
                     overview(state, vertical = true, onNavigate, onSelectSource, showToday)
                 }
                 LazyColumn(
-                    Modifier.weight(0.54f).fillMaxHeight(),
+                    Modifier.weight(0.5f).fillMaxHeight(),
                     state = timelineState,
-                    contentPadding = PaddingValues(bottom = 24.dp),
+                    // Starts level with the headline card on the left.
+                    contentPadding = PaddingValues(top = 8.dp, bottom = 24.dp),
                 ) {
                     timeline(state, onNavigate, onSelectFilter, onSetTodayOnly, onLoadMore)
                 }
@@ -184,10 +185,14 @@ private fun LazyListScope.overview(
     onShowToday: (ActivityCategory) -> Unit,
 ) {
     item(key = "headline") {
+        // On a phone the headline hangs from the top bar, edge to edge. Unfolded it has only the
+        // left column to hang from, and a white block that stops at the middle of the screen
+        // reads as a different design from the timeline beside it -- so there it is a card on the
+        // page like every other block in both columns.
         Surface(
             color = MaterialTheme.colorScheme.surface,
-            shape = RoundedCornerShape(bottomStart = 28.dp, bottomEnd = 28.dp),
-            modifier = Modifier.fillMaxWidth(),
+            shape = if (vertical) RoundedCornerShape(24.dp) else RoundedCornerShape(bottomStart = 28.dp, bottomEnd = 28.dp),
+            modifier = if (vertical) Modifier.fillMaxWidth().padding(start = 20.dp, end = 20.dp, top = 16.dp) else Modifier.fillMaxWidth(),
         ) {
             Column(Modifier.padding(bottom = 20.dp)) {
                 TabTitle(
diff --git a/app/src/main/res/drawable/ic_ub_swap_vertical.xml b/app/src/main/res/drawable/ic_ub_swap_vertical.xml
new file mode 100644
index 0000000..f15cde2
--- /dev/null
+++ b/app/src/main/res/drawable/ic_ub_swap_vertical.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="#00000000"
+        android:strokeColor="#FF000000"
+        android:strokeLineCap="round"
+        android:strokeLineJoin="round"
+        android:strokeWidth="1.8"
+        android:pathData="M8,19V5M4,9l4,-4 4,4" />
+    <path
+        android:fillColor="#00000000"
+        android:strokeColor="#FF000000"
+        android:strokeLineCap="round"
+        android:strokeLineJoin="round"
+        android:strokeWidth="1.8"
+        android:pathData="M16,5v14M12,15l4,4 4,-4" />
+</vector>
diff --git a/app/src/main/res/values/strings_codebrowser.xml b/app/src/main/res/values/strings_codebrowser.xml
index 7dba76c..55f75e1 100644
--- a/app/src/main/res/values/strings_codebrowser.xml
+++ b/app/src/main/res/values/strings_codebrowser.xml
@@ -66,7 +66,15 @@
     <string name="codeviewer_symbol_type">타입</string>
     <string name="codeviewer_symbol_method">메서드</string>
     <string name="codeviewer_symbol_field">필드</string>
-    <string name="codeviewer_files_title">파일</string>
+    <string name="codeviewer_files_title">폴더 구조</string>
+    <string name="codeviewer_symbols_title">클래스 · 함수</string>
+    <string name="codeviewer_symbols_empty">이 파일에는 표시할 클래스나 함수가 없습니다.</string>
+    <string name="codeviewer_pane_swap">위아래 바꾸기</string>
+    <string name="codeviewer_folder_open">펼쳐짐</string>
+    <string name="codeviewer_folder_closed">접힘</string>
+    <string name="codeviewer_folder_loading">불러오는 중…</string>
+    <string name="codeviewer_folder_failed">불러오지 못했습니다. 폴더를 다시 눌러 주세요.</string>
+    <string name="codeviewer_folder_empty">비어 있음</string>
     <string name="codeviewer_pair_label">짝 파일</string>
     <string name="codeviewer_pair_header">선언</string>
     <string name="codeviewer_pair_source">구현</string>
diff --git a/app/src/test/java/com/ubisam/ubgitea/feature/codebrowser/FileTreeTest.kt b/app/src/test/java/com/ubisam/ubgitea/feature/codebrowser/FileTreeTest.kt
new file mode 100644
index 0000000..5445914
--- /dev/null
+++ b/app/src/test/java/com/ubisam/ubgitea/feature/codebrowser/FileTreeTest.kt
@@ -0,0 +1,68 @@
+package com.ubisam.ubgitea.feature.codebrowser
+
+import com.ubisam.ubgitea.domain.model.RepositoryPath
+import com.ubisam.ubgitea.domain.model.TreeEntry
+import com.ubisam.ubgitea.domain.model.TreeEntryType
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class FileTreeTest {
+    private fun dir(path: String) = TreeEntry(path.substringAfterLast('/'), RepositoryPath.of(path), TreeEntryType.DIRECTORY, null)
+    private fun file(path: String) = TreeEntry(path.substringAfterLast('/'), RepositoryPath.of(path), TreeEntryType.FILE, 1L)
+
+    private val tree = FileTree(RepositoryPath.of("src"), listOf(dir("src/core"), dir("src/ui"), file("src/Main.cpp")))
+
+    private fun describe(tree: FileTree) = tree.rows().map {
+        when (it) {
+            is FileTreeRow.Entry -> "${it.depth}:${it.entry.name}" + if (it.isOpen) "+" else ""
+            is FileTreeRow.Note -> "${it.depth}:<${it.note}>"
+        }
+    }
+
+    @Test
+    fun `a closed tree is its entries`() {
+        assertEquals(listOf("0:core", "0:ui", "0:Main.cpp"), describe(tree))
+    }
+
+    @Test
+    fun `an open folder is followed by what is in it, one level in`() {
+        val open = tree
+            .with(RepositoryPath.of("src/core"), FolderUiState.Loaded(listOf(dir("src/core/net"), file("src/core/A.h"))))
+            .with(RepositoryPath.of("src/core/net"), FolderUiState.Loaded(listOf(file("src/core/net/B.h"))))
+
+        assertEquals(listOf("0:core+", "1:net+", "2:B.h", "1:A.h", "0:ui", "0:Main.cpp"), describe(open))
+    }
+
+    @Test
+    fun `a folder with nothing to show says why`() {
+        val open = tree
+            .with(RepositoryPath.of("src/core"), FolderUiState.Loading)
+            .with(RepositoryPath.of("src/ui"), FolderUiState.Loaded(emptyList()))
+
+        assertEquals(listOf("0:core+", "1:<LOADING>", "0:ui+", "1:<EMPTY>", "0:Main.cpp"), describe(open))
+        assertEquals(listOf("0:core+", "1:<FAILED>", "0:ui", "0:Main.cpp"), describe(tree.with(RepositoryPath.of("src/core"), FolderUiState.Failed)))
+    }
+
+    @Test
+    fun `closing a folder closes the folders inside it but not one that only shares its prefix`() {
+        val open = tree
+            .with(RepositoryPath.of("src/core"), FolderUiState.Loaded(listOf(dir("src/core/net"))))
+            .with(RepositoryPath.of("src/core/net"), FolderUiState.Loaded(emptyList()))
+            .with(RepositoryPath.of("src/core2"), FolderUiState.Loaded(emptyList()))
+
+        assertEquals(setOf(RepositoryPath.of("src/core2")), open.without(RepositoryPath.of("src/core")).folders.keys)
+    }
+
+    @Test
+    fun `entries are found for the root and for loaded folders only`() {
+        val open = tree
+            .with(RepositoryPath.of("src/core"), FolderUiState.Loaded(listOf(file("src/core/A.h"))))
+            .with(RepositoryPath.of("src/ui"), FolderUiState.Loading)
+
+        assertEquals(3, open.entriesOf(RepositoryPath.of("src"))?.size)
+        assertEquals(1, open.entriesOf(RepositoryPath.of("src/core"))?.size)
+        assertNull(open.entriesOf(RepositoryPath.of("src/ui")))
+        assertEquals(setOf(RepositoryPath.of("src/core")), open.settled().folders.keys)
+    }
+}
diff --git a/docs/UBGitea_기술소개.pptx b/docs/UBGitea_기술소개.pptx
index 6650630..e3b577f 100644
Binary files a/docs/UBGitea_기술소개.pptx and b/docs/UBGitea_기술소개.pptx differ
diff --git a/docs/development-log.md b/docs/development-log.md
index 4ce5eec..e37ec35 100644
--- a/docs/development-log.md
+++ b/docs/development-log.md
@@ -1367,3 +1367,17 @@ This is the append-only implementation and handoff record shared by Codex and Cl
 - Live verification: installed on the SM-F966N. Nothing in this task has been seen working on the
   device by the implementer; endpoint timings were taken from a PC.
 - Next owner: the product owner, to confirm on the device.
+
+## 2026-09-28 (continued) — TASK-057: side pane redesign, folder tree, unfolded Home
+
+- Request: the human product owner confirmed the faster listing, then asked for the pane drawn
+  from the left edge to be redesigned (it was a plain rectangle), split into folder structure and
+  classes/functions with the two halves swappable, and reported that on the unfolded Home the
+  left and right halves did not look like one design.
+- What changed: see `tasks/057-side-pane-redesign-and-folder-tree.md`.
+- Why the unfolded Home looked split: the headline was drawn edge to edge, hanging from the top
+  bar, which is right on a phone; unfolded, it covered only the left column.
+- Checks and results: the required checks pass; 432 unit tests, 0 failures; lint 0 errors.
+- Live verification: installed on the SM-F966N. None of it has been seen on a screen by the
+  implementer.
+- Next owner: the product owner, to confirm on the device.
diff --git a/tasks/057-side-pane-redesign-and-folder-tree.md b/tasks/057-side-pane-redesign-and-folder-tree.md
new file mode 100644
index 0000000..d307c92
--- /dev/null
+++ b/tasks/057-side-pane-redesign-and-folder-tree.md
@@ -0,0 +1,80 @@
+# TASK-057: Side pane redesign, folder tree, and the unfolded Home
+
+Status: implemented; required checks pass; installed on the product owner's Z Fold7, awaiting their confirmation
+Owner: Claude
+Reviewer: human product owner
+
+## Outcome
+
+Third round of requests from the human product owner after using the app on their Galaxy Z Fold7
+(SM-F966N), 2026-09-28. They confirmed that directory listing (TASK-056) is now much faster.
+
+## Scope
+
+- Included:
+  1. The pane drawn out from the left edge of the code viewer is no longer a plain rectangle: the
+     drawer has rounded outer corners and the page color, and holds two white cards.
+  2. The pane is split in half: the folder structure, and the open file's classes and functions.
+     Choosing a class or function goes to it.
+  3. A "위아래 바꾸기" button between the halves swaps them. The choice is kept across launches.
+  4. The folder half is a tree: a folder opens in place, one level at a time, and a file inside it
+     opens from there. Before, choosing a folder left the viewer for the directory list.
+  5. Home, unfolded: the headline block is a card like the rest, and the two columns are equal.
+     Before, it was a white block hanging from the top bar over the left column only, so the left
+     and right halves of the screen looked like two designs.
+- Excluded:
+  - Dragging the boundary between the two halves; they are equal.
+  - Showing folders above the directory the file was opened from. The tree starts there.
+
+## Writable paths
+
+- `app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/`
+- `app/src/main/java/com/ubisam/ubgitea/feature/home/HomeScreen.kt`
+- `app/src/main/java/com/ubisam/ubgitea/feature/branchdetail/BranchDetailScreen.kt`
+- `app/src/main/java/com/ubisam/ubgitea/core/settings/AppSettingsStore.kt`
+- `app/src/main/java/com/ubisam/ubgitea/MainActivity.kt`
+- `app/src/main/res/`
+- `app/src/test/java/com/ubisam/ubgitea/feature/codebrowser/`
+- `tasks/`, `docs/`
+
+## Acceptance criteria
+
+- [x] The same pane is used in the drawer (phone, landscape, side-by-side pair) and beside the code
+      on a wide window.
+- [x] A folder shows that it is loading, that it is empty, or that it failed; choosing a failed
+      folder twice tries again.
+- [x] Closing a folder closes the folders open inside it.
+- [x] Open folders are kept while moving between files of the tree.
+- [x] A file opened from a folder of the tree finds its `.h`/`.cpp` counterpart in that folder.
+- [x] A file with no classes or functions says so instead of showing an empty card.
+- [x] Unit tests cover the tree's rows, closing, and lookup (`FileTreeTest`).
+
+## Security and privacy
+
+No additional concerns. The only thing stored is which half is on top, a boolean in the existing
+settings preferences.
+
+## Required checks
+
+```text
+./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug
+```
+
+## Evidence
+
+- Required checks pass: 432 unit tests, 0 failures; lint 0 errors.
+- Installed on the SM-F966N over wireless `adb`.
+- Not seen by the implementer on any screen: the drawer's new look, the tree, the swap, and the
+  unfolded Home. The Home change was made from reading the layout code, not from a screenshot.
+
+## Known limitations
+
+- `toggleFolder` in the view model has no unit test of its own; the tree it edits has.
+- On the unfolded Home the three summary tiles are narrower than before, because the headline
+  card is now inset. A long label may wrap to two lines.
+- The preference for which half is on top is read in the viewer itself rather than passed down
+  from `MainActivity` like the other viewer preferences.
+
+## Review findings
+
+None yet.