Merge TASK-065 and TASK-066 into the reviewed branch

Agent: main (opus)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/build.gradle.kts

@@ -14,8 +14,10 @@ android {
         applicationId = "com.ubisam.ubgitea"
         minSdk = 28
         targetSdk = 36
-        versionCode = 1
+        // Raised for every build published to the download page (TASK-066), or the app will not
-        versionName = "0.1.0"
+        // see it as newer.
+        versionCode = 2
+        versionName = "0.2.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }

app/src/main/java/com/ubisam/ubgitea/MainActivity.kt

@@ -7,6 +7,7 @@ import android.graphics.Color
 import android.net.Uri
 import android.os.Build
 import android.os.Bundle
+import android.widget.Toast
 import androidx.activity.ComponentActivity
 import androidx.activity.SystemBarStyle
 import androidx.activity.compose.BackHandler
@@ -18,15 +19,23 @@ import androidx.browser.customtabs.CustomTabsIntent
 import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.runtime.saveable.rememberSaveable
 import com.ubisam.ubgitea.core.auth.protocol.UBGiteaOAuthDefaults
 import com.ubisam.ubgitea.core.notifications.FavoritePushNotifier
 import com.ubisam.ubgitea.core.settings.ThemeMode
+import com.ubisam.ubgitea.core.update.AppUpdateLocations
+import com.ubisam.ubgitea.core.update.AppUpdateViewModel
+import androidx.compose.material3.AlertDialog
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.ui.res.stringResource
 import com.ubisam.ubgitea.core.notifications.FavoritePushScheduler
 import com.ubisam.ubgitea.domain.model.RepositoryCoordinates
 import com.ubisam.ubgitea.domain.model.RepositoryRef
@@ -37,6 +46,16 @@ import com.ubisam.ubgitea.feature.codebrowser.CodeBrowserTarget
 import com.ubisam.ubgitea.feature.codebrowser.CodeBrowserViewModel
 import com.ubisam.ubgitea.feature.codebrowser.CodeReferenceKind
 import com.ubisam.ubgitea.feature.codebrowser.CodeViewerPreferences
+import com.ubisam.ubgitea.feature.codebrowser.CodeBrowserUiState
+import com.ubisam.ubgitea.domain.model.RepositoryPath
+import com.ubisam.ubgitea.feature.compare.CodeTabStrip
+import com.ubisam.ubgitea.feature.compare.CodeWorkbench
+import com.ubisam.ubgitea.feature.compare.CodeWorkbenchViewModel
+import com.ubisam.ubgitea.feature.compare.CompareScreen
+import com.ubisam.ubgitea.feature.compare.CompareUiState
+import com.ubisam.ubgitea.feature.compare.LocalCodeWorkbench
+import com.ubisam.ubgitea.feature.compare.SavedCodeTab
+import com.ubisam.ubgitea.feature.compare.WorkbenchMessage
 import com.ubisam.ubgitea.feature.history.HistoryTarget
 import com.ubisam.ubgitea.feature.history.HistoryViewModel
 import com.ubisam.ubgitea.feature.home.HomeDestination
@@ -87,6 +106,12 @@ class MainActivity : ComponentActivity() {
     private val workViewModel: WorkViewModel by viewModels {
         WorkViewModel.Factory(application)
     }
+    private val workbenchViewModel: CodeWorkbenchViewModel by viewModels {
+        CodeWorkbenchViewModel.Factory(application)
+    }
+    private val updateViewModel: AppUpdateViewModel by viewModels {
+        AppUpdateViewModel.Factory()
+    }
 
     // TASK-036: no-op if already granted or already permanently denied -- the OS itself decides
     // whether to actually show a prompt, this call is safe to make on every launch. Must be
@@ -117,6 +142,10 @@ class MainActivity : ComponentActivity() {
             val settingsState by settingsViewModel.state.collectAsState()
             val homeState by homeViewModel.state.collectAsState()
             val workState by workViewModel.state.collectAsState()
+            val workbenchState by workbenchViewModel.state.collectAsState()
+            val updateState by updateViewModel.state.collectAsState()
+            // TASK-066: whether a newer build is published, once per launch.
+            LaunchedEffect(Unit) { updateViewModel.checkAtLaunch() }
 
             var routeStack by rememberSaveable(stateSaver = RouteStackSaver) {
                 mutableStateOf(listOf<Route>(Route.Home))
@@ -147,8 +176,13 @@ class MainActivity : ComponentActivity() {
                 }
             }
 
+            // The route shown before this one: coming back from a comparison leaves the code as it was.
+            val lastRoute = remember { arrayOfNulls<Route>(1) }
             LaunchedEffect(currentRoute, sessionReady) {
+                val previous = lastRoute[0]
+                lastRoute[0] = currentRoute
                 if (!sessionReady) return@LaunchedEffect
+                if (previous == Route.Compare && currentRoute is Route.BranchDetail) return@LaunchedEffect
                 if (currentRoute.isTab) notificationsViewModel.refreshUnreadCount()
                 when (val route = currentRoute) {
                     Route.Home -> homeViewModel.open()
@@ -157,7 +191,12 @@ class MainActivity : ComponentActivity() {
                     is Route.BranchDetail -> {
                         val repository = RepositoryCoordinates.of(route.owner, route.name)
                         val ref = RepositoryRef.of(route.ref)
-                        codeBrowserViewModel.open(CodeBrowserTarget(repository, ref, CodeReferenceKind.valueOf(route.refKind)))
+                        val target = CodeBrowserTarget(repository, ref, CodeReferenceKind.valueOf(route.refKind))
+                        if (route.path != null) {
+                            codeBrowserViewModel.openFile(target, RepositoryPath.of(route.path))
+                        } else {
+                            codeBrowserViewModel.open(target)
+                        }
                         historyViewModel.open(HistoryTarget(repository, ref))
                     }
                     is Route.WorkItems -> {
@@ -170,9 +209,32 @@ class MainActivity : ComponentActivity() {
                     }
                     Route.Notifications -> notificationsViewModel.open()
                     Route.Settings -> Unit // SettingsViewModel reads its (synchronous) store at construction.
+                    Route.Compare -> Unit // CodeWorkbenchViewModel already holds what is compared.
                 }
             }
 
+            // TASK-065: a comparison that has started is shown on its own screen; one that is gone
+            // (closed, or lost with the process) takes that screen away.
+            val comparing = workbenchState.compare != CompareUiState.None
+            LaunchedEffect(comparing) {
+                if (comparing && currentRoute != Route.Compare) push(Route.Compare)
+            }
+            LaunchedEffect(currentRoute, comparing) {
+                if (currentRoute == Route.Compare && !comparing) pop()
+            }
+            val context = androidx.compose.ui.platform.LocalContext.current
+            LaunchedEffect(workbenchState.message) {
+                val message = workbenchState.message ?: return@LaunchedEffect
+                val text = when (message) {
+                    WorkbenchMessage.TABS_FULL -> context.getString(R.string.workbench_tabs_full, SavedCodeTab.MAX_TABS)
+                    WorkbenchMessage.FILE_UNAVAILABLE -> context.getString(R.string.compare_file_unavailable)
+                    WorkbenchMessage.FILE_NOT_TEXT -> context.getString(R.string.compare_file_not_text)
+                    WorkbenchMessage.SAME_FILE -> context.getString(R.string.compare_same_file)
+                }
+                Toast.makeText(context, text, Toast.LENGTH_SHORT).show()
+                workbenchViewModel.messageShown()
+            }
+
             fun closeFeatures() {
                 codeBrowserViewModel.close()
                 historyViewModel.close()
@@ -197,10 +259,61 @@ class MainActivity : ComponentActivity() {
             val codeViewerPreferences = CodeViewerPreferences(settingsState.codeWordWrapEnabled, settingsState.codeFontSizeSp)
             val showNavigation = sessionReady && when (currentRoute) {
                 is Route.BranchDetail -> !isReadingFullScreen(codeBrowserState, historyState)
-                Route.Settings -> false
+                Route.Settings, Route.Compare -> false
                 else -> true
             }
 
+            // A saved tab: the file in place when this screen already shows its repository and
+            // ref, otherwise this screen on that file in place of the code being read.
+            fun openTab(tab: SavedCodeTab) {
+                val route = currentRoute
+                val target = CodeBrowserTarget(
+                    RepositoryCoordinates.of(tab.owner, tab.name),
+                    RepositoryRef.of(tab.ref),
+                    CodeReferenceKind.valueOf(tab.refKind),
+                )
+                if (route is Route.BranchDetail && route.owner == tab.owner && route.name == tab.name &&
+                    route.refKind == tab.refKind && route.ref == tab.ref
+                ) {
+                    codeBrowserViewModel.openFile(target, RepositoryPath.of(tab.path))
+                    return
+                }
+                val next = Route.BranchDetail(tab.owner, tab.name, tab.refKind, tab.ref, tab.path)
+                if (route is Route.BranchDetail) {
+                    codeBrowserViewModel.close()
+                    historyViewModel.close()
+                    routeStack = routeStack.dropLast(1) + next
+                } else {
+                    push(next)
+                }
+            }
+            val shownFile = codeBrowserState as? CodeBrowserUiState.File
+            val currentCodeTab = (currentRoute as? Route.BranchDetail)?.let { route ->
+                shownFile?.takeIf { it.target.repository == RepositoryCoordinates.of(route.owner, route.name) }?.let {
+                    SavedCodeTab(route.owner, route.name, it.target.kind.name, it.target.ref.value, it.path.value)
+                }
+            }
+            val workbench = if (sessionReady) {
+                CodeWorkbench(
+                    tabs = workbenchState.tabs,
+                    pending = workbenchState.pending,
+                    fetching = workbenchState.fetching,
+                    onToggleTab = workbenchViewModel::toggleTab,
+                    onPin = workbenchViewModel::pin,
+                    onCompareWith = workbenchViewModel::compareWith,
+                    onClearPin = workbenchViewModel::clearPin,
+                    onUseCommitFile = { commitId, shortId, path, side ->
+                        (currentRoute as? Route.BranchDetail)?.let { route ->
+                            workbenchViewModel.useCommitFile(RepositoryCoordinates.of(route.owner, route.name), commitId, shortId, path, side)
+                        }
+                    },
+                )
+            } else {
+                null
+            }
+            val showStrip = sessionReady && currentRoute != Route.Settings && currentRoute != Route.Compare &&
+                (workbenchState.tabs.isNotEmpty() || workbenchState.pending != null || workbenchState.fetching)
+
             val darkTheme = when (settingsState.themeMode) {
                 ThemeMode.SYSTEM -> isSystemInDarkTheme()
                 ThemeMode.LIGHT -> false
@@ -219,17 +332,44 @@ class MainActivity : ComponentActivity() {
             }
 
             UBGiteaTheme(darkTheme = darkTheme) {
+              CompositionLocalProvider(LocalCodeWorkbench provides workbench) {
                 AppShell(
                     selectedTab = currentTab,
                     showNavigation = showNavigation,
                     unreadNotifications = unreadNotifications,
                     onTabSelected = { tab ->
+                        // The Repositories tab pressed again steps back toward the list: from a
+                        // repository's code to its branches' list page, from there to the first page.
+                        val reselected = tab == AppTab.REPOSITORIES && currentTab == AppTab.REPOSITORIES
                         if (currentRoute is Route.BranchDetail) {
                             codeBrowserViewModel.close()
                             historyViewModel.close()
                         }
                         if (currentRoute is Route.WorkItems) workItemsViewModel.close()
+                        when {
+                            !reselected -> selectTab(tab)
+                            currentRoute == Route.Repositories -> viewModel.reselect()
+                            else -> {
+                                if (currentRoute == Route.Compare) workbenchViewModel.closeCompare()
                                 selectTab(tab)
+                                viewModel.backToRepositories()
+                            }
+                        }
+                    },
+                    strip = if (showStrip) {
+                        {
+                            CodeTabStrip(
+                                tabs = workbenchState.tabs,
+                                current = currentCodeTab,
+                                pending = workbenchState.pending,
+                                fetching = workbenchState.fetching,
+                                onOpen = ::openTab,
+                                onClose = workbenchViewModel::removeTab,
+                                onClearPin = workbenchViewModel::clearPin,
+                            )
+                        }
+                    } else {
+                        null
                     },
                 ) { isWide ->
                     // Back on any tab but Home goes Home; back on Home leaves the app.
@@ -337,6 +477,9 @@ class MainActivity : ComponentActivity() {
                             onSetThemeMode = settingsViewModel::setThemeMode,
                             onLogout = ::signOut,
                             onBack = { pop() },
+                            update = updateState,
+                            onCheckUpdate = updateViewModel::checkNow,
+                            onOpenDownloadPage = ::openDownloadPage,
                         )
                         Route.Notifications -> NotificationsScreen(
                             state = notificationsState,
@@ -419,11 +562,37 @@ class MainActivity : ComponentActivity() {
                             onAuthenticationExpired = ::signOut,
                         )
                         Route.Repositories -> repositoryList()
+                        Route.Compare -> CompareScreen(
+                            state = workbenchState.compare,
+                            fontSizeSp = settingsState.codeFontSizeSp,
+                            onSwap = workbenchViewModel::swapSides,
+                            onClose = workbenchViewModel::closeCompare,
+                        )
+                    }
                 }
               }
                 LaunchedEffect(viewModel) {
                     viewModel.browserRequests.collect(::openAuthorizationTab)
                 }
+                updateState.prompt?.let { release ->
+                    AlertDialog(
+                        onDismissRequest = updateViewModel::dismissPrompt,
+                        title = { Text(stringResource(R.string.update_dialog_title)) },
+                        text = {
+                            val body = stringResource(R.string.update_dialog_body, updateState.installedVersionName, release.versionName)
+                            Text(if (release.notes != null) body + "\n\n" + release.notes else body)
+                        },
+                        confirmButton = {
+                            TextButton(onClick = {
+                                updateViewModel.dismissPrompt()
+                                openDownloadPage()
+                            }) { Text(stringResource(R.string.update_dialog_download)) }
+                        },
+                        dismissButton = {
+                            TextButton(onClick = updateViewModel::dismissPrompt) { Text(stringResource(R.string.update_dialog_later)) }
+                        },
+                    )
+                }
             }
         }
         consumeCallback(intent)
@@ -453,6 +622,17 @@ class MainActivity : ComponentActivity() {
         }
     }
 
+    // TASK-066: the download page asks for its password itself, so it opens in the browser.
+    private fun openDownloadPage() {
+        try {
+            CustomTabsIntent.Builder()
+                .build()
+                .launchUrl(this, Uri.parse(AppUpdateLocations.DOWNLOAD_PAGE))
+        } catch (_: ActivityNotFoundException) {
+            Toast.makeText(this, AppUpdateLocations.DOWNLOAD_PAGE, Toast.LENGTH_LONG).show()
+        }
+    }
+
     private fun consumeCallback(intent: Intent?) {
         val callback = intent?.dataString ?: return
         setIntent(Intent(intent).setData(null))

app/src/main/java/com/ubisam/ubgitea/core/settings/AppSettingsStore.kt

@@ -1,6 +1,8 @@
 package com.ubisam.ubgitea.core.settings
 
 import android.content.Context
+import org.json.JSONArray
+import org.json.JSONException
 
 /**
  * The two user-facing toggles TASK-038 introduced, both defaulted to preserve exactly what the app
@@ -42,6 +44,16 @@ interface AppSettingsStore {
     fun isOutlineAboveFolders(): Boolean = false
     fun setOutlineAboveFolders(above: Boolean) = Unit
 
+    // The width of the viewer's side pane on a wide window, in dp, once the reader has dragged it
+    // (TASK-065); null while it is the default.
+    fun codeSidePaneWidthDp(): Int? = null
+    fun setCodeSidePaneWidthDp(widthDp: Int?) = Unit
+
+    // The files kept as tabs under the screen (TASK-065), oldest first, each as encoded by
+    // SavedCodeTab.encode. Names and paths only: never content.
+    fun savedCodeTabs(): List<String> = emptyList()
+    fun setSavedCodeTabs(tabs: List<String>) = Unit
+
     companion object {
         const val DEFAULT_CODE_FONT_SIZE_SP = 13
         val CODE_FONT_SIZES_SP = listOf(11, 12, 13, 14, 16)
@@ -99,7 +111,31 @@ class SharedPreferencesAppSettingsStore(context: Context) : AppSettingsStore {
         preferences.edit().putBoolean(KEY_OUTLINE_ABOVE_FOLDERS, above).apply()
     }
 
+    override fun codeSidePaneWidthDp(): Int? =
+        preferences.getInt(KEY_CODE_SIDE_PANE_WIDTH, 0).takeIf { it > 0 }
+
+    override fun setCodeSidePaneWidthDp(widthDp: Int?) {
+        preferences.edit().putInt(KEY_CODE_SIDE_PANE_WIDTH, widthDp ?: 0).apply()
+    }
+
+    // A JSON array keeps the order, which a string set would not.
+    override fun savedCodeTabs(): List<String> {
+        val stored = preferences.getString(KEY_SAVED_CODE_TABS, null) ?: return emptyList()
+        return try {
+            val array = JSONArray(stored)
+            List(array.length()) { array.getString(it) }
+        } catch (_: JSONException) {
+            emptyList()
+        }
+    }
+
+    override fun setSavedCodeTabs(tabs: List<String>) {
+        preferences.edit().putString(KEY_SAVED_CODE_TABS, JSONArray(tabs).toString()).apply()
+    }
+
     private companion object {
+        const val KEY_CODE_SIDE_PANE_WIDTH = "code_side_pane_width_dp"
+        const val KEY_SAVED_CODE_TABS = "saved_code_tabs"
         const val KEY_OUTLINE_ABOVE_FOLDERS = "code_outline_above_folders"
         const val KEY_HOME_SOURCE = "home_source"
         const val KEY_THEME_MODE = "theme_mode"

app/src/main/java/com/ubisam/ubgitea/core/update/AppUpdate.kt

@@ -0,0 +1,68 @@
+package com.ubisam.ubgitea.core.update
+
+import com.google.gson.JsonParser
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import java.util.concurrent.TimeUnit
+
+/**
+ * Where new builds of the app are published (TASK-066): a page that hands out the APK behind a
+ * password, and beside it a plain file naming the newest version. The app only ever reads that
+ * file; no Gitea token goes there.
+ */
+object AppUpdateLocations {
+    const val DOWNLOAD_PAGE = "https://choimy0204.github.io/ubgitea/"
+    const val LATEST_VERSION = DOWNLOAD_PAGE + "version.json"
+}
+
+/** The newest published build. */
+data class AppRelease(
+    val versionCode: Int,
+    val versionName: String,
+    val notes: String? = null,
+)
+
+/**
+ * Reads `{"versionCode": 2, "versionName": "0.2.0", "notes": "..."}`. Anything else is null, so
+ * a page that is broken or not there yet never offers an update.
+ */
+fun parseAppRelease(json: String): AppRelease? = try {
+    val root = JsonParser.parseString(json).asJsonObject
+    val code = root.get("versionCode")?.takeIf { it.isJsonPrimitive && it.asJsonPrimitive.isNumber }?.asInt
+    val name = root.get("versionName")?.takeIf { it.isJsonPrimitive }?.asString?.trim()
+    val notes = root.get("notes")?.takeIf { it.isJsonPrimitive }?.asString?.trim()?.ifEmpty { null }
+    if (code == null || code <= 0 || name.isNullOrEmpty()) null else AppRelease(code, name, notes)
+} catch (_: RuntimeException) {
+    null
+}
+
+fun interface AppReleaseSource {
+    /** The newest published build, or null when it cannot be read. */
+    suspend fun latest(): AppRelease?
+}
+
+class HttpAppReleaseSource(
+    private val url: String = AppUpdateLocations.LATEST_VERSION,
+    private val client: OkHttpClient = updateClient,
+) : AppReleaseSource {
+    override suspend fun latest(): AppRelease? = withContext(Dispatchers.IO) {
+        try {
+            // no-cache: GitHub Pages is cached for minutes, and a check by hand should see a release at once.
+            val request = Request.Builder().url(url).header("Cache-Control", "no-cache").build()
+            client.newCall(request).execute().use { response ->
+                if (!response.isSuccessful) null else parseAppRelease(response.body.string())
+            }
+        } catch (_: java.io.IOException) {
+            null
+        }
+    }
+}
+
+private val updateClient: OkHttpClient by lazy {
+    OkHttpClient.Builder()
+        .connectTimeout(10, TimeUnit.SECONDS)
+        .readTimeout(10, TimeUnit.SECONDS)
+        .build()
+}

app/src/main/java/com/ubisam/ubgitea/core/update/AppUpdateViewModel.kt

@@ -0,0 +1,74 @@
+package com.ubisam.ubgitea.core.update
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import androidx.lifecycle.viewModelScope
+import com.ubisam.ubgitea.BuildConfig
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.launch
+
+enum class UpdateCheck { IDLE, CHECKING, UP_TO_DATE, FAILED, AVAILABLE }
+
+data class AppUpdateUiState(
+    val installedVersionName: String,
+    val check: UpdateCheck = UpdateCheck.IDLE,
+    // Set when a newer build than this one is published.
+    val available: AppRelease? = null,
+    // The newer build offered on its own at launch, until it is answered.
+    val prompt: AppRelease? = null,
+)
+
+/** Whether a newer build of the app is published, checked once at launch and again on request. */
+class AppUpdateViewModel(
+    private val source: AppReleaseSource,
+    private val installedVersionCode: Int,
+    installedVersionName: String,
+) : ViewModel() {
+    private val mutableState = MutableStateFlow(AppUpdateUiState(installedVersionName))
+    val state: StateFlow<AppUpdateUiState> = mutableState.asStateFlow()
+    private var operation: Job? = null
+    private var checkedAtLaunch = false
+
+    /** The check made when the app starts: quiet unless there is something newer. */
+    fun checkAtLaunch() {
+        if (checkedAtLaunch) return
+        checkedAtLaunch = true
+        check(offer = true)
+    }
+
+    /** A check asked for by hand, as from the settings. */
+    fun checkNow() = check(offer = false)
+
+    fun dismissPrompt() = mutableState.update { it.copy(prompt = null) }
+
+    private fun check(offer: Boolean) {
+        if (operation?.isActive == true) return
+        mutableState.update { it.copy(check = UpdateCheck.CHECKING) }
+        operation = viewModelScope.launch {
+            val latest = source.latest()
+            mutableState.update { state ->
+                when {
+                    latest == null -> state.copy(check = UpdateCheck.FAILED)
+                    latest.versionCode > installedVersionCode -> state.copy(
+                        check = UpdateCheck.AVAILABLE,
+                        available = latest,
+                        prompt = if (offer) latest else state.prompt,
+                    )
+                    else -> state.copy(check = UpdateCheck.UP_TO_DATE, available = null, prompt = null)
+                }
+            }
+        }
+    }
+
+    class Factory : ViewModelProvider.Factory {
+        @Suppress("UNCHECKED_CAST")
+        override fun <T : ViewModel> create(modelClass: Class<T>): T {
+            require(modelClass.isAssignableFrom(AppUpdateViewModel::class.java))
+            return AppUpdateViewModel(HttpAppReleaseSource(), BuildConfig.VERSION_CODE, BuildConfig.VERSION_NAME) as T
+        }
+    }
+}

app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserViewModel.kt

@@ -24,6 +24,8 @@ import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.Job
+import kotlinx.coroutines.async
+import kotlinx.coroutines.coroutineScope
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
@@ -130,8 +132,46 @@ class CodeBrowserViewModel(
     private var counterpartOperation: Job? = null
     private val folderOperations = mutableMapOf<RepositoryPath, Job>()
 
+    // The last few files shown, so going back and forth between saved tabs does not fetch each again.
+    private val recentFiles = object : LinkedHashMap<Pair<CodeBrowserTarget, RepositoryPath>, CodeBrowserUiState.File>(8, 0.75f, true) {
+        override fun removeEldestEntry(eldest: MutableMap.MutableEntry<Pair<CodeBrowserTarget, RepositoryPath>, CodeBrowserUiState.File>) =
+            size > RECENT_FILES
+    }
+
     fun open(target: CodeBrowserTarget) = loadDirectory(target, RepositoryPath.Root)
 
+    /**
+     * Opens a file straight from its path, as a saved tab does, with the folder it is in listed
+     * beside it. A file seen a moment ago comes back as it was, without asking the server again.
+     */
+    fun openFile(target: CodeBrowserTarget, path: RepositoryPath) {
+        val current = mutableState.value
+        if (current is CodeBrowserUiState.File && current.target == target && current.path == path) return
+        val recent = recentFiles[target to path]
+        if (recent != null) {
+            operation?.cancel()
+            counterpartOperation?.cancel()
+            mutableState.value = recent
+            return
+        }
+        startOperation {
+            counterpartOperation?.cancel()
+            mutableState.value = CodeBrowserUiState.Loading(target, path, isFile = true)
+            try {
+                val (classification, siblingEntries) = withContext(defaultDispatcher) {
+                    coroutineScope {
+                        val listing = async { listFolderOrNothing(target, CodeBrowserNavigation.parent(path)) }
+                        val file = browser.getFile(target.repository, target.ref, path)
+                        classifier.classify(file.content, path) to listing.await()
+                    }
+                }
+                showFile(target, path, classification, siblingEntries)
+            } catch (failure: Throwable) {
+                handleFailure(target, path, failure, isFile = true)
+            }
+        }
+    }
+
     fun openEntry(entry: TreeEntry) {
         val target = currentTarget() ?: return
         when (entry.type) {
@@ -295,8 +335,22 @@ class CodeBrowserViewModel(
                 val file = browser.getFile(target.repository, target.ref, path)
                 classifier.classify(file.content, path)
             }
+            showFile(target, path, classification, siblingEntries, focusSymbol, tree)
+        } catch (failure: Throwable) {
+            handleFailure(target, path, failure, isFile = true)
+        }
+    }
+
+    private fun showFile(
+        target: CodeBrowserTarget,
+        path: RepositoryPath,
+        classification: ContentClassification,
+        siblingEntries: List<TreeEntry>,
+        focusSymbol: String? = null,
+        tree: FileTree? = null,
+    ) {
         val siblingFiles = siblingEntries.filter { it.type == TreeEntryType.FILE }.map(TreeEntry::path)
-            mutableState.value = CodeBrowserUiState.File(
+        val state = CodeBrowserUiState.File(
             target = target,
             path = path,
             content = classification,
@@ -307,9 +361,18 @@ class CodeBrowserViewModel(
             // A folder still being fetched would never hear back in the new state.
             tree = tree?.settled() ?: FileTree(CodeBrowserNavigation.parent(path), siblingEntries),
         )
-        } catch (failure: Throwable) {
+        mutableState.value = state
-            handleFailure(target, path, failure, isFile = true)
+        recentFiles[target to path] = state.copy(focusSymbol = null)
     }
+
+    // The folder a saved tab's file is in. Without it the file still opens, only with nothing beside it.
+    private suspend fun listFolderOrNothing(target: CodeBrowserTarget, folder: RepositoryPath): List<TreeEntry> = try {
+        loadAllPages { page -> browser.listTree(target.repository, target.ref, folder, page, PAGE_SIZE) }
+            .distinctBy(TreeEntry::path)
+            .sortedWith(LISTING_ORDER)
+    } catch (failure: Throwable) {
+        if (failure is CancellationException) throw failure
+        emptyList()
     }
 
     private fun handleFailure(
@@ -374,6 +437,7 @@ class CodeBrowserViewModel(
     private companion object {
         const val PAGE_SIZE = 100
         const val MAX_PAGES = 100
+        const val RECENT_FILES = 6
         val LISTING_ORDER = compareBy<TreeEntry> { it.type != TreeEntryType.DIRECTORY }.thenBy { it.name.lowercase() }
     }
 }

app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodePane.kt

@@ -1,6 +1,9 @@
 package com.ubisam.ubgitea.feature.codebrowser
 
 import androidx.compose.foundation.background
+import androidx.compose.foundation.gestures.awaitEachGesture
+import androidx.compose.foundation.gestures.awaitFirstDown
+import androidx.compose.foundation.gestures.waitForUpOrCancellation
 import androidx.compose.foundation.gestures.Orientation
 import androidx.compose.foundation.gestures.rememberScrollableState
 import androidx.compose.foundation.gestures.scrollable
@@ -33,7 +36,10 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clipToBounds
+import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.input.pointer.PointerInputScope
+import androidx.compose.ui.input.pointer.pointerInput
 import androidx.compose.ui.layout.onSizeChanged
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.text.AnnotatedString
@@ -41,6 +47,7 @@ import androidx.compose.ui.text.LinkAnnotation
 import androidx.compose.ui.text.TextLinkStyles
 import androidx.compose.ui.text.style.TextDecoration
 import androidx.compose.ui.text.SpanStyle
+import androidx.compose.ui.text.TextLayoutResult
 import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.text.buildAnnotatedString
 import androidx.compose.ui.text.font.FontFamily
@@ -60,6 +67,7 @@ import com.ubisam.ubgitea.feature.codebrowser.content.SymbolKind
 import com.ubisam.ubgitea.feature.codebrowser.content.nameRangeOf
 import com.ubisam.ubgitea.feature.codebrowser.content.rememberCodeSyntaxColors
 import com.ubisam.ubgitea.feature.codebrowser.content.syntaxLanguageForPath
+import com.ubisam.ubgitea.feature.codebrowser.content.wordAt
 import com.ubisam.ubgitea.ui.theme.UBGiteaTheme
 import kotlin.math.roundToInt
 import kotlinx.coroutines.Dispatchers
@@ -139,9 +147,14 @@ fun CodePane(
     contentPadding: PaddingValues = PaddingValues(vertical = 8.dp),
     // When given, the name of a function on the line that declares it is a link (TASK-060).
     onFunctionTapped: ((CodeSymbol) -> Unit)? = null,
+    // Every place the word the reader tapped appears, marked in its own color (TASK-065).
+    words: SearchHighlight = SearchHighlight.None,
+    // When given, a tap on a word reports it, or null for a tap on anything else.
+    onWordTapped: ((String?) -> Unit)? = null,
 ) {
     val colors = rememberCodeSyntaxColors()
     val tapped by rememberUpdatedState(onFunctionTapped)
+    val wordTapped by rememberUpdatedState(onWordTapped)
     val linked = onFunctionTapped != null
     val functionsByLine = remember(document.symbols, linked) {
         if (linked) document.symbols.filter { it.kind == SymbolKind.METHOD }.associateBy(CodeSymbol::line) else emptyMap()
@@ -162,6 +175,7 @@ fun CodePane(
     val gutterColor = MaterialTheme.colorScheme.onSurfaceVariant
     val focusColor = MaterialTheme.colorScheme.primaryContainer
     val hit = searchHitColors()
+    val wordHit = wordHitColors()
 
     var viewportWidthPx by remember { mutableIntStateOf(0) }
     val gutterWidthPx = with(density) { gutterWidth.toPx() }
@@ -179,8 +193,8 @@ fun CodePane(
             items(document.lines.size, key = { it }) { index ->
                 val line = document.highlighted.getOrElse(index) { AnnotatedString(document.lines[index]) }
                 val function = functionsByLine[index]
-                val shown = remember(line, search.byLine[index], search.current, function) {
+                val shown = remember(line, search.byLine[index], search.current, words.byLine[index], words.current, function) {
-                    val marked = withSearchHits(line, search.byLine[index], search.current, hit)
+                    val marked = withSearchHits(withSearchHits(line, words.byLine[index], words.current, wordHit), search.byLine[index], search.current, hit)
                     val name = function?.let { nameRangeOf(it, document.lines[index]) }
                     if (function == null || name == null || name.last >= marked.length) {
                         marked
@@ -199,6 +213,17 @@ fun CodePane(
                         }
                     }
                 }
+                val layout = remember { arrayOfNulls<TextLayoutResult>(1) }
+                val wordTaps = if (onWordTapped == null) {
+                    Modifier
+                } else {
+                    Modifier.pointerInput(index, document.lines) {
+                        detectQuietTap { position ->
+                            val text = layout[0] ?: return@detectQuietTap
+                            wordTapped?.invoke(wordAt(document.lines[index], text.getOffsetForPosition(position)))
+                        }
+                    }
+                }
                 Row(
                     Modifier.fillMaxWidth().background(if (index == focusedLine) focusColor else Color.Transparent),
                     verticalAlignment = Alignment.Top,
@@ -220,7 +245,8 @@ fun CodePane(
                             shown,
                             style = style.copy(textIndent = TextIndent(restLine = hanging)),
                             softWrap = true,
-                            modifier = Modifier.weight(1f).padding(end = 16.dp),
+                            onTextLayout = { layout[0] = it },
+                            modifier = Modifier.weight(1f).padding(end = 16.dp).then(wordTaps),
                         )
                     } else {
                         Box(Modifier.weight(1f).clipToBounds().scrollable(sideways, Orientation.Horizontal)) {
@@ -229,9 +255,11 @@ fun CodePane(
                                 style = style,
                                 softWrap = false,
                                 maxLines = 1,
+                                onTextLayout = { layout[0] = it },
                                 modifier = Modifier
                                     .offset { IntOffset(-offsetPx.floatValue.roundToInt(), 0) }
-                                    .wrapContentWidth(Alignment.Start, unbounded = true),
+                                    .wrapContentWidth(Alignment.Start, unbounded = true)
+                                    .then(wordTaps),
                             )
                         }
                     }
@@ -260,6 +288,33 @@ private fun searchHitColors(): SearchHitColors {
     }
 }
 
+@Composable
+private fun wordHitColors(): SearchHitColors {
+    val dark = UBGiteaTheme.isDark
+    return remember(dark) {
+        if (dark) {
+            SearchHitColors(Color(0xFF1F4D2E), Color(0xFF3FA866), Color(0xFF041A0B))
+        } else {
+            SearchHitColors(Color(0xFFC8F0D2), Color(0xFF6FD08C), Color(0xFF0E1B2C))
+        }
+    }
+}
+
+/**
+ * A tap that is only a tap: released where it went down and soon after, and not taken by anything
+ * else on the way -- a link, a scroll, a long press that starts a selection. The release is left
+ * for the others, so selecting text and following links work as before.
+ */
+private suspend fun PointerInputScope.detectQuietTap(onTap: (Offset) -> Unit) {
+    awaitEachGesture {
+        val down = awaitFirstDown(requireUnconsumed = false)
+        val up = waitForUpOrCancellation() ?: return@awaitEachGesture
+        val moved = (up.position - down.position).getDistance() > viewConfiguration.touchSlop
+        val held = up.uptimeMillis - down.uptimeMillis > viewConfiguration.longPressTimeoutMillis
+        if (!moved && !held) onTap(up.position)
+    }
+}
+
 private fun withSearchHits(
     line: AnnotatedString,
     matches: List<SearchMatch>?,

app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/CodeViewerScreen.kt

@@ -53,7 +53,8 @@ import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
-import androidx.compose.material3.VerticalDivider
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.widthIn
 import androidx.compose.material3.rememberDrawerState
 import androidx.compose.material3.rememberModalBottomSheetState
 import androidx.compose.runtime.Composable
@@ -85,6 +86,8 @@ import androidx.compose.ui.semantics.Role
 import androidx.compose.ui.semantics.contentDescription
 import androidx.compose.ui.semantics.heading
 import androidx.compose.ui.semantics.selected
+import androidx.compose.ui.semantics.LiveRegionMode
+import androidx.compose.ui.semantics.liveRegion
 import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.semantics.stateDescription
 import androidx.compose.ui.text.AnnotatedString
@@ -126,6 +129,16 @@ import com.ubisam.ubgitea.ui.components.ActivityTone
 import com.ubisam.ubgitea.ui.components.UBIcon
 import com.ubisam.ubgitea.ui.shell.WideLayoutBreakpoint
 import kotlin.math.abs
+import kotlin.math.roundToInt
+import androidx.compose.ui.hapticfeedback.HapticFeedbackType
+import androidx.compose.ui.platform.LocalHapticFeedback
+import com.ubisam.ubgitea.feature.codebrowser.content.findWordOccurrences
+import com.ubisam.ubgitea.feature.compare.CompareMenu
+import com.ubisam.ubgitea.feature.compare.CompareSide
+import com.ubisam.ubgitea.feature.compare.ComparedFile
+import com.ubisam.ubgitea.feature.compare.LocalCodeWorkbench
+import com.ubisam.ubgitea.feature.compare.PendingCompare
+import com.ubisam.ubgitea.feature.compare.SavedCodeTab
 import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.filterNotNull
 import kotlinx.coroutines.launch
@@ -202,6 +215,19 @@ fun CodeViewerScreen(
     var syncPanes by rememberSaveable { mutableStateOf(true) }
     // The share of the width the left pane of a header/source pair takes.
     var splitFraction by rememberSaveable { mutableFloatStateOf(DEFAULT_SPLIT) }
+    // The width of the side pane on a wide window, in dp, when the reader has dragged it away
+    // from the default; kept between files and launches.
+    var sidePaneDp by remember { mutableStateOf(settings.codeSidePaneWidthDp()?.toFloat()) }
+    // A word tapped in the code, marked wherever it appears, in both panes of a pair (TASK-065).
+    var selectedWord by remember(state.path) { mutableStateOf<String?>(null) }
+    val wordOccurrences = remember(document.lines, selectedWord) {
+        selectedWord?.let { findWordOccurrences(document.lines, it) }.orEmpty()
+    }
+    var currentWord by remember(wordOccurrences) { mutableIntStateOf(-1) }
+    val words = remember(wordOccurrences, currentWord) {
+        if (wordOccurrences.isEmpty()) SearchHighlight.None else SearchHighlight(wordOccurrences.groupBy { it.line }, wordOccurrences.getOrNull(currentWord))
+    }
+    val onWordTapped: (String?) -> Unit = { word -> selectedWord = if (word == null || word == selectedWord) null else word }
     val drawerState = rememberDrawerState(DrawerValue.Closed)
     // The sheet is shown from outside the layout below, where the jump is worked out.
     var jumpForSheet by remember { mutableStateOf<SymbolJump?>(null) }
@@ -212,6 +238,28 @@ fun CodeViewerScreen(
     val otherText = ((state.counterpart as? CounterpartUiState.Loaded)?.content as? ContentClassification.Text)?.renderedText
     val otherDocument = if (counterpart != null && otherText != null) rememberCodeDocument(counterpart, otherText) else null
     val otherState = remember(counterpart) { LazyListState() }
+    val otherWords = remember(otherDocument?.lines, selectedWord) {
+        val word = selectedWord
+        val occurrences = if (otherDocument == null || word == null) emptyList() else findWordOccurrences(otherDocument.lines, word)
+        if (occurrences.isEmpty()) SearchHighlight.None else SearchHighlight(occurrences.groupBy { it.line }, null)
+    }
+
+    // Keeping this file as a tab, and comparing it with another, where the activity offers them.
+    val workbench = LocalCodeWorkbench.current
+    val benchTools = workbench?.let { bench ->
+        val target = state.target
+        val tab = SavedCodeTab(target.repository.owner, target.repository.name, target.kind.name, target.ref.value, state.path.value)
+        val refLabel = if (target.kind == CodeReferenceKind.COMMIT) target.ref.value.take(SHORT_COMMIT_LENGTH) else target.ref.value
+        val file = ComparedFile(target.repository, refLabel, state.path.value, text.renderedText, text.isTruncated)
+        WorkbenchTools(
+            isSaved = tab in bench.tabs,
+            pending = bench.pending,
+            onToggleSave = { bench.onToggleTab(tab) },
+            onPin = { side -> bench.onPin(file, side) },
+            onCompare = { bench.onCompareWith(file) },
+            onClearPin = bench.onClearPin,
+        )
+    }
 
     fun goToLine(line: Int) {
         focusedLine = line
@@ -224,6 +272,12 @@ fun CodeViewerScreen(
         val match = otherDocument?.let { findSymbolNamed(it.symbols, symbol.name, symbol.kind) } ?: return
         scope.launch { otherState.scrollToItem(match.line) }
     }
+    fun goToWord(index: Int) {
+        if (wordOccurrences.isEmpty()) return
+        currentWord = index.mod(wordOccurrences.size)
+        val line = wordOccurrences[currentWord].line
+        scope.launch { listState.scrollToItem((line - SEARCH_CONTEXT_LINES).coerceAtLeast(0)) }
+    }
     fun goToMatch(index: Int) {
         if (matches.isEmpty()) return
         currentMatch = index.mod(matches.size)
@@ -245,6 +299,7 @@ fun CodeViewerScreen(
         when {
             drawerState.isOpen -> scope.launch { drawerState.close() }
             outlineOpen -> outlineOpen = false
+            selectedWord != null -> selectedWord = null
             searching -> {
                 searching = false
                 query = ""
@@ -259,7 +314,9 @@ fun CodeViewerScreen(
             maxWidth >= WideLayoutBreakpoint -> ViewerLayout.WIDE
             else -> ViewerLayout.PHONE
         }
-        val sidePaneWidth = if (maxWidth < NarrowWideBreakpoint) NarrowSidePaneWidth else SidePaneWidth
+        val defaultSidePane = if (maxWidth < NarrowWideBreakpoint) NarrowSidePaneWidth else SidePaneWidth
+        val widestSidePane = (maxWidth * MAX_SIDE_PANE_FRACTION).coerceAtLeast(MinSidePaneWidth)
+        val sidePaneWidth = (sidePaneDp?.dp ?: defaultSidePane).coerceIn(MinSidePaneWidth, widestSidePane)
         val counterpartPath = state.counterpartPath
         val showsPair = layout == ViewerLayout.WIDE && counterpartPath != null && sideBySide
         if (showsPair) LaunchedEffect(state.path, counterpartPath) { onLoadCounterpart() }
@@ -302,6 +359,7 @@ fun CodeViewerScreen(
             onToggleSideBySide = { sideBySide = !sideBySide },
             onToggleSync = { syncPanes = !syncPanes },
             text = text.renderedText,
+            workbench = benchTools,
         )
         val location = stringResource(
             R.string.codeviewer_location,
@@ -397,6 +455,9 @@ fun CodeViewerScreen(
                         counterpartPath = counterpartPath!!,
                         splitFraction = splitFraction,
                         onSplitChange = { splitFraction = it },
+                        words = words,
+                        otherWords = otherWords,
+                        onWordTapped = onWordTapped,
                         // Beside each other, a function tapped in one pane is shown in the other.
                         onFunctionTapped = { symbol ->
                             otherDocument?.let { findSymbolNamed(it.symbols, symbol.name, symbol.kind) }?.let { match ->
@@ -424,7 +485,13 @@ fun CodeViewerScreen(
                                 onSymbolSelected = { goToSymbol(it) },
                                 modifier = Modifier.width(sidePaneWidth).fillMaxHeight(),
                             )
-                            VerticalDivider(color = MaterialTheme.colorScheme.outlineVariant)
+                            SidePaneHandle(
+                                width = sidePaneWidth,
+                                defaultWidth = defaultSidePane,
+                                widest = widestSidePane,
+                                onWidthChange = { sidePaneDp = it?.value },
+                                onSettled = { settings.setCodeSidePaneWidthDp(sidePaneDp?.roundToInt()) },
+                            )
                         }
                         Box(Modifier.weight(1f).fillMaxHeight()) {
                             CodePane(
@@ -436,8 +503,10 @@ fun CodeViewerScreen(
                                 focusedLine = focusedLine,
                                 contentPadding = PaddingValues(top = 8.dp, bottom = if (counterpartPath != null) 76.dp else 8.dp),
                                 onFunctionTapped = jump?.onJump,
+                                words = words,
+                                onWordTapped = onWordTapped,
                             )
-                            if (counterpartPath != null && layout != ViewerLayout.WIDE && !searching) {
+                            if (counterpartPath != null && layout != ViewerLayout.WIDE && !searching && selectedWord == null) {
                                 val method = enclosingSymbols(document.symbols, firstVisibleLine).lastOrNull { it.kind == SymbolKind.METHOD }
                                 if (method != null) {
                                     JumpToCounterpart(
@@ -455,6 +524,16 @@ fun CodeViewerScreen(
             if (!sidePaneIsShown) {
                 EdgeTab(Modifier.align(Alignment.CenterStart)) { scope.launch { drawerState.open() } }
             }
+            selectedWord?.let { word ->
+                WordBar(
+                    word = word,
+                    count = wordOccurrences.size,
+                    onPrevious = { goToWord(if (currentWord < 0) firstMatchFrom(wordOccurrences, listState.firstVisibleItemIndex) - 1 else currentWord - 1) },
+                    onNext = { goToWord(if (currentWord < 0) firstMatchFrom(wordOccurrences, listState.firstVisibleItemIndex) else currentWord + 1) },
+                    onClear = { selectedWord = null },
+                    modifier = Modifier.align(Alignment.BottomCenter).padding(horizontal = 16.dp, vertical = 12.dp),
+                )
+            }
             }
             if (layout != ViewerLayout.LANDSCAPE) Toolbar(tools)
         }
@@ -497,6 +576,17 @@ private class ViewerTools(
     val onToggleSideBySide: () -> Unit,
     val onToggleSync: () -> Unit,
     val text: String,
+    // Null where there is nowhere to keep tabs or compare files.
+    val workbench: WorkbenchTools?,
+)
+
+private class WorkbenchTools(
+    val isSaved: Boolean,
+    val pending: PendingCompare?,
+    val onToggleSave: () -> Unit,
+    val onPin: (CompareSide) -> Unit,
+    val onCompare: () -> Unit,
+    val onClearPin: () -> Unit,
 )
 
 @Composable
@@ -521,6 +611,16 @@ private fun Toolbar(tools: ViewerTools) {
                 CopyButton(tools.text, Modifier.weight(1f)) { onCopy ->
                     ToolButton(R.drawable.ic_ub_copy, R.string.codeviewer_tool_copy, false, onClick = onCopy)
                 }
+                tools.workbench?.let { bench ->
+                    ToolButton(
+                        if (bench.isSaved) R.drawable.ic_ub_bookmark_filled else R.drawable.ic_ub_bookmark,
+                        R.string.codeviewer_tool_save_tab, bench.isSaved, Modifier.weight(1f),
+                        isToggle = true, onClick = bench.onToggleSave,
+                    )
+                    CompareMenu(bench.pending, bench.onPin, bench.onCompare, bench.onClearPin, Modifier.weight(1f)) { onOpen ->
+                        ToolButton(R.drawable.ic_ub_compare, R.string.codeviewer_tool_compare, bench.pending != null, onClick = onOpen)
+                    }
+                }
                 if (tools.canPair) {
                     ToolButton(
                         R.drawable.ic_ub_split, R.string.codeviewer_tool_side_by_side, tools.sideBySide, Modifier.weight(1f),
@@ -560,7 +660,7 @@ private fun ToolButton(
         verticalArrangement = Arrangement.spacedBy(3.dp),
     ) {
         Box(
-            Modifier.size(width = 52.dp, height = 30.dp)
+            Modifier.widthIn(max = 52.dp).fillMaxWidth().height(30.dp)
                 .clip(CircleShape)
                 .background(if (active) MaterialTheme.colorScheme.primaryContainer else MaterialTheme.colorScheme.surface),
             contentAlignment = Alignment.Center,
@@ -651,6 +751,24 @@ private fun LandscapeBar(document: CodeDocument, currentLine: Int, onBack: () ->
                 FontSizeButton(tools) { onOpen ->
                     IconButton(onClick = onOpen) { UBIcon(R.drawable.ic_ub_text_size, stringResource(R.string.codeviewer_tool_font_size)) }
                 }
+                tools.workbench?.let { bench ->
+                    IconButton(onClick = bench.onToggleSave) {
+                        UBIcon(
+                            if (bench.isSaved) R.drawable.ic_ub_bookmark_filled else R.drawable.ic_ub_bookmark,
+                            stringResource(R.string.codeviewer_tool_save_tab),
+                            tint = if (bench.isSaved) MaterialTheme.colorScheme.primary else MaterialTheme.colorScheme.onSurfaceVariant,
+                        )
+                    }
+                    CompareMenu(bench.pending, bench.onPin, bench.onCompare, bench.onClearPin) { onOpen ->
+                        IconButton(onClick = onOpen) {
+                            UBIcon(
+                                R.drawable.ic_ub_compare,
+                                stringResource(R.string.codeviewer_tool_compare),
+                                tint = if (bench.pending != null) MaterialTheme.colorScheme.primary else MaterialTheme.colorScheme.onSurfaceVariant,
+                            )
+                        }
+                    }
+                }
             }
             HorizontalDivider(color = MaterialTheme.colorScheme.outlineVariant)
         }
@@ -843,6 +961,39 @@ private fun JumpToCounterpart(counterpart: RepositoryPath, modifier: Modifier =
     }
 }
 
+/** The word tapped in the code: how often it appears, a way through those places, and a way out. */
+@Composable
+private fun WordBar(word: String, count: Int, onPrevious: () -> Unit, onNext: () -> Unit, onClear: () -> Unit, modifier: Modifier = Modifier) {
+    Surface(
+        color = MaterialTheme.colorScheme.inverseSurface,
+        contentColor = MaterialTheme.colorScheme.inverseOnSurface,
+        shape = CircleShape,
+        shadowElevation = 6.dp,
+        modifier = modifier.widthIn(max = 420.dp),
+    ) {
+        Row(Modifier.heightIn(min = 48.dp).padding(start = 18.dp, end = 4.dp), verticalAlignment = Alignment.CenterVertically) {
+            Text(
+                stringResource(R.string.codeviewer_word_count, word, count),
+                style = MaterialTheme.typography.labelLarge,
+                fontFamily = FontFamily.Monospace,
+                fontWeight = FontWeight.Bold,
+                maxLines = 1,
+                overflow = TextOverflow.Ellipsis,
+                modifier = Modifier.weight(1f, fill = false).semantics { liveRegion = LiveRegionMode.Polite },
+            )
+            IconButton(onClick = onPrevious, enabled = count > 0) {
+                UBIcon(R.drawable.ic_ub_chevron_up, stringResource(R.string.codeviewer_word_previous), size = 20.dp)
+            }
+            IconButton(onClick = onNext, enabled = count > 0) {
+                UBIcon(R.drawable.ic_ub_chevron_down, stringResource(R.string.codeviewer_word_next), size = 20.dp)
+            }
+            IconButton(onClick = onClear) {
+                UBIcon(R.drawable.ic_ub_close, stringResource(R.string.codeviewer_word_clear), size = 18.dp)
+            }
+        }
+    }
+}
+
 /**
  * A small tab on the left edge, where the side pane is drawn out from. It can be tapped as well:
  * a swipe from the edge is not available to everyone.
@@ -889,6 +1040,9 @@ private fun PairPanes(
     counterpartPath: RepositoryPath,
     splitFraction: Float,
     onSplitChange: (Float) -> Unit,
+    words: SearchHighlight,
+    otherWords: SearchHighlight,
+    onWordTapped: (String?) -> Unit,
     onFunctionTapped: (CodeSymbol) -> Unit,
     onOtherFunctionTapped: (CodeSymbol) -> Unit,
 ) {
@@ -903,6 +1057,7 @@ private fun PairPanes(
             CodePane(
                 document, listState, preferences.wordWrap, preferences.fontSizeSp,
                 search = highlight, focusedLine = focusedLine, onFunctionTapped = onFunctionTapped,
+                words = words, onWordTapped = onWordTapped,
             )
         }
     }
@@ -912,7 +1067,10 @@ private fun PairPanes(
             when {
                 otherDocument != null -> {
                     PaneHeader(name, counterpartPath, otherDocument.lines.size, enclosingSymbols(otherDocument.symbols, otherState.firstVisibleItemIndex))
-                    CodePane(otherDocument, otherState, preferences.wordWrap, preferences.fontSizeSp, onFunctionTapped = onOtherFunctionTapped)
+                    CodePane(
+                        otherDocument, otherState, preferences.wordWrap, preferences.fontSizeSp,
+                        onFunctionTapped = onOtherFunctionTapped, words = otherWords, onWordTapped = onWordTapped,
+                    )
                 }
                 else -> {
                     PaneHeader(name, counterpartPath, null, emptyList())
@@ -927,12 +1085,20 @@ private fun PairPanes(
     }
     BoxWithConstraints(Modifier.fillMaxSize()) {
         val widthPx = with(LocalDensity.current) { maxWidth.toPx() }
-        // The latest value, for a drag that outlives the composition it started in.
+        val snapPx = with(LocalDensity.current) { SnapDistance.toPx() }
-        val fraction by rememberUpdatedState(splitFraction)
+        val haptics = LocalHapticFeedback.current
+        // Where the finger has taken the split, before it is snapped to the middle.
+        var dragged by remember { mutableFloatStateOf(splitFraction) }
         Row(Modifier.fillMaxSize()) {
             (if (currentIsHeader) current else other)(Modifier.weight(splitFraction).fillMaxHeight())
             SplitHandle(
-                onDrag = { deltaPx -> onSplitChange(clampSplit(fraction + deltaPx / widthPx)) },
+                onDragStart = { dragged = splitFraction },
+                onDrag = { deltaPx ->
+                    dragged = clampSplit(dragged + deltaPx / widthPx)
+                    val snapped = snapTo(dragged, DEFAULT_SPLIT, snapPx / widthPx)
+                    if (snapped == DEFAULT_SPLIT && splitFraction != DEFAULT_SPLIT) haptics.performHapticFeedback(HapticFeedbackType.TextHandleMove)
+                    onSplitChange(snapped)
+                },
                 onReset = { onSplitChange(DEFAULT_SPLIT) },
             )
             (if (currentIsHeader) other else current)(Modifier.weight(1f - splitFraction).fillMaxHeight())
@@ -940,6 +1106,41 @@ private fun PairPanes(
     }
 }
 
+/**
+ * [value], or [target] when it is within [threshold] of it: a default that a drag sticks to like a
+ * magnet, so it is easy to find again.
+ */
+internal fun snapTo(value: Float, target: Float, threshold: Float): Float = if (abs(value - target) <= threshold) target else value
+
+/**
+ * The handle between the side pane and the code on a wide window. Dragging sets the pane's width
+ * between [MinSidePaneWidth] and [widest]; near [defaultWidth] it snaps there with a tick, and the
+ * default is reported as null. A double tap goes back to the default. [onSettled] is called when a
+ * drag ends, to keep the width.
+ */
+@Composable
+private fun SidePaneHandle(width: Dp, defaultWidth: Dp, widest: Dp, onWidthChange: (Dp?) -> Unit, onSettled: () -> Unit) {
+    val density = LocalDensity.current.density
+    val haptics = LocalHapticFeedback.current
+    var dragged by remember { mutableFloatStateOf(width.value) }
+    SplitHandle(
+        description = stringResource(R.string.codeviewer_side_pane_handle),
+        onDragStart = { dragged = width.value },
+        onDrag = { deltaPx ->
+            dragged = (dragged + deltaPx / density).coerceIn(MinSidePaneWidth.value, widest.value)
+            val snapped = snapTo(dragged, defaultWidth.value, SnapDistance.value)
+            val atDefault = snapped == defaultWidth.value
+            if (atDefault && width != defaultWidth) haptics.performHapticFeedback(HapticFeedbackType.TextHandleMove)
+            onWidthChange(if (atDefault) null else snapped.dp)
+        },
+        onDragEnd = onSettled,
+        onReset = {
+            onWidthChange(null)
+            onSettled()
+        },
+    )
+}
+
 /** Keeps either pane from being dragged down to nothing. */
 internal fun clampSplit(fraction: Float): Float = fraction.coerceIn(MIN_SPLIT, 1f - MIN_SPLIT)
 
@@ -948,20 +1149,34 @@ internal fun clampSplit(fraction: Float): Float = fraction.coerceIn(MIN_SPLIT, 1
  * middle, inside a strip a finger can land on. Dragging moves the split; a double tap evens it.
  */
 @Composable
-private fun SplitHandle(onDrag: (Float) -> Unit, onReset: () -> Unit) {
+private fun SplitHandle(
-    val description = stringResource(R.string.codeviewer_split_handle)
+    onDrag: (Float) -> Unit,
+    onReset: () -> Unit,
+    description: String = stringResource(R.string.codeviewer_split_handle),
+    onDragStart: () -> Unit = {},
+    onDragEnd: () -> Unit = {},
+) {
+    // The latest callbacks, for a gesture that outlives the composition it started in.
+    val drag by rememberUpdatedState(onDrag)
+    val reset by rememberUpdatedState(onReset)
+    val start by rememberUpdatedState(onDragStart)
+    val end by rememberUpdatedState(onDragEnd)
     Box(
         Modifier.width(SplitHandleWidth)
             .fillMaxHeight()
             .background(MaterialTheme.colorScheme.surface)
             .semantics { contentDescription = description }
             .pointerInput(Unit) {
-                detectHorizontalDragGestures { change, dragAmount ->
+                detectHorizontalDragGestures(
+                    onDragStart = { start() },
+                    onDragEnd = { end() },
+                    onDragCancel = { end() },
+                ) { change, dragAmount ->
                     change.consume()
-                    onDrag(dragAmount)
+                    drag(dragAmount)
                 }
             }
-            .pointerInput(Unit) { detectTapGestures(onDoubleTap = { onReset() }) },
+            .pointerInput(Unit) { detectTapGestures(onDoubleTap = { reset() }) },
         contentAlignment = Alignment.Center,
     ) {
         Box(Modifier.width(1.dp).fillMaxHeight().background(MaterialTheme.colorScheme.outlineVariant))
@@ -1512,6 +1727,11 @@ private fun OutlineSheet(
 
 private const val DEFAULT_SPLIT = 0.5f
 private const val MIN_SPLIT = 0.2f
+private const val MAX_SIDE_PANE_FRACTION = 0.6f
+private val MinSidePaneWidth = 160.dp
+// How near a drag has to come to a default width to stick to it.
+private val SnapDistance = 16.dp
+private const val SHORT_COMMIT_LENGTH = 7
 private const val DRAWER_WIDTH_FRACTION = 0.85f
 private val MaxDrawerWidth = 320.dp
 private val SplitHandleWidth = 24.dp

app/src/main/java/com/ubisam/ubgitea/feature/codebrowser/content/CodeSearch.kt

@@ -58,3 +58,43 @@ fun counterpartOf(path: RepositoryPath, siblings: List<RepositoryPath>): Reposit
 }
 
 private fun RepositoryPath.extension(): String = value.substringAfterLast('/').substringAfterLast('.', "").lowercase()
+
+/**
+ * The identifier at [offset] in [line], or null when the offset is not on one: a run of letters,
+ * digits and underscores that does not start with a digit. An offset just past the last character
+ * of a word still counts as on it, as a tap at a word's right edge lands there.
+ */
+fun wordAt(line: String, offset: Int): String? {
+    if (line.isEmpty()) return null
+    var at = offset.coerceIn(0, line.length)
+    if (at == line.length || !line[at].isWordCharacter()) {
+        if (at > 0 && line[at - 1].isWordCharacter()) at -= 1 else return null
+    }
+    var start = at
+    while (start > 0 && line[start - 1].isWordCharacter()) start--
+    var end = at
+    while (end < line.length && line[end].isWordCharacter()) end++
+    val word = line.substring(start, end)
+    return if (word.first().isDigit()) null else word
+}
+
+/** Every whole-word occurrence of [word] in [lines], case and all: `count` and not `counter`. */
+fun findWordOccurrences(lines: List<String>, word: String): List<SearchMatch> {
+    if (word.isEmpty()) return emptyList()
+    val occurrences = mutableListOf<SearchMatch>()
+    lines.forEachIndexed { index, line ->
+        var from = 0
+        while (true) {
+            val start = line.indexOf(word, from)
+            if (start < 0) break
+            val end = start + word.length
+            val before = start == 0 || !line[start - 1].isWordCharacter()
+            val after = end == line.length || !line[end].isWordCharacter()
+            if (before && after) occurrences += SearchMatch(index, start, end)
+            from = start + 1
+        }
+    }
+    return occurrences
+}
+
+private fun Char.isWordCharacter(): Boolean = this == '_' || isLetterOrDigit()

app/src/main/java/com/ubisam/ubgitea/feature/compare/CodeWorkbench.kt

@@ -0,0 +1,250 @@
+package com.ubisam.ubgitea.feature.compare
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.border
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.horizontalScroll
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.heightIn
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.widthIn
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material3.CircularProgressIndicator
+import androidx.compose.material3.DropdownMenu
+import androidx.compose.material3.DropdownMenuItem
+import androidx.compose.material3.HorizontalDivider
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.Stable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.runtime.staticCompositionLocalOf
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.Role
+import androidx.compose.ui.semantics.contentDescription
+import androidx.compose.ui.semantics.selected
+import androidx.compose.ui.semantics.semantics
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextOverflow
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.ubisam.ubgitea.R
+import com.ubisam.ubgitea.ui.components.UBIcon
+
+/**
+ * The saved tabs and the comparison, as the code screens use them. Handed down from the activity
+ * rather than through every screen in between; null where there is no session.
+ */
+@Stable
+class CodeWorkbench(
+    val tabs: List<SavedCodeTab>,
+    val pending: PendingCompare?,
+    val fetching: Boolean,
+    val onToggleTab: (SavedCodeTab) -> Unit,
+    val onPin: (ComparedFile, CompareSide) -> Unit,
+    val onCompareWith: (ComparedFile) -> Unit,
+    val onClearPin: () -> Unit,
+    // A file as it is at a commit: fetched, then pinned on the side given, or compared when null.
+    val onUseCommitFile: (commitId: String, shortId: String, path: String, side: CompareSide?) -> Unit,
+)
+
+val LocalCodeWorkbench = staticCompositionLocalOf<CodeWorkbench?> { null }
+
+/**
+ * Wraps a compare button in its menu. With nothing waiting, the menu puts the file on screen on
+ * the left or the right. With a file waiting, it compares with that file first, and can still put
+ * this one in its place.
+ */
+@Composable
+fun CompareMenu(
+    pending: PendingCompare?,
+    onPin: (CompareSide) -> Unit,
+    onCompare: () -> Unit,
+    onClearPin: () -> Unit,
+    modifier: Modifier = Modifier,
+    button: @Composable (onOpen: () -> Unit) -> Unit,
+) {
+    var open by remember { mutableStateOf(false) }
+    Box(modifier, contentAlignment = Alignment.Center) {
+        button { open = true }
+        DropdownMenu(expanded = open, onDismissRequest = { open = false }) {
+            if (pending != null) {
+                DropdownMenuItem(
+                    text = { Text(stringResource(R.string.compare_with_pinned, pending.file.fileName), fontWeight = FontWeight.Bold) },
+                    leadingIcon = { UBIcon(R.drawable.ic_ub_compare, null, size = 20.dp) },
+                    onClick = {
+                        open = false
+                        onCompare()
+                    },
+                )
+                HorizontalDivider(color = MaterialTheme.colorScheme.outlineVariant)
+            }
+            DropdownMenuItem(
+                text = { Text(stringResource(R.string.compare_put_left)) },
+                onClick = {
+                    open = false
+                    onPin(CompareSide.LEFT)
+                },
+            )
+            DropdownMenuItem(
+                text = { Text(stringResource(R.string.compare_put_right)) },
+                onClick = {
+                    open = false
+                    onPin(CompareSide.RIGHT)
+                },
+            )
+            if (pending != null) {
+                DropdownMenuItem(
+                    text = { Text(stringResource(R.string.compare_unpin)) },
+                    onClick = {
+                        open = false
+                        onClearPin()
+                    },
+                )
+            }
+        }
+    }
+}
+
+/**
+ * The strip between the screen and the bottom tabs: the file waiting to be compared, and the
+ * saved tabs. Nothing is drawn when there is neither.
+ */
+@Composable
+fun CodeTabStrip(
+    tabs: List<SavedCodeTab>,
+    current: SavedCodeTab?,
+    pending: PendingCompare?,
+    fetching: Boolean,
+    onOpen: (SavedCodeTab) -> Unit,
+    onClose: (SavedCodeTab) -> Unit,
+    onClearPin: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    if (tabs.isEmpty() && pending == null && !fetching) return
+    Surface(color = MaterialTheme.colorScheme.surface, modifier = modifier.fillMaxWidth()) {
+        Column {
+            HorizontalDivider(color = MaterialTheme.colorScheme.outlineVariant)
+            if (pending != null || fetching) PendingRow(pending, fetching, onClearPin)
+            if (tabs.isNotEmpty()) {
+                val label = stringResource(R.string.workbench_tabs)
+                Row(
+                    Modifier.fillMaxWidth()
+                        .semantics { contentDescription = label }
+                        .horizontalScroll(rememberScrollState())
+                        .padding(horizontal = 8.dp, vertical = 6.dp),
+                    horizontalArrangement = Arrangement.spacedBy(6.dp),
+                ) {
+                    tabs.forEach { tab -> TabChip(tab, tab == current, { onOpen(tab) }, { onClose(tab) }) }
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun PendingRow(pending: PendingCompare?, fetching: Boolean, onClearPin: () -> Unit) {
+    Row(
+        Modifier.fillMaxWidth()
+            .background(MaterialTheme.colorScheme.primaryContainer)
+            .padding(start = 12.dp, end = 4.dp)
+            .heightIn(min = 40.dp),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        if (fetching) {
+            CircularProgressIndicator(Modifier.size(16.dp), strokeWidth = 2.dp)
+            Spacer(Modifier.size(8.dp))
+        } else {
+            UBIcon(R.drawable.ic_ub_compare, null, size = 18.dp, tint = MaterialTheme.colorScheme.onPrimaryContainer)
+            Spacer(Modifier.size(8.dp))
+        }
+        Column(Modifier.weight(1f)) {
+            if (pending != null) {
+                val side = stringResource(if (pending.side == CompareSide.LEFT) R.string.compare_side_left else R.string.compare_side_right)
+                Text(
+                    stringResource(R.string.compare_pending, pending.file.fileName, side),
+                    style = MaterialTheme.typography.labelLarge,
+                    color = MaterialTheme.colorScheme.onPrimaryContainer,
+                    maxLines = 1,
+                    overflow = TextOverflow.Ellipsis,
+                )
+            }
+            Text(
+                stringResource(if (fetching) R.string.compare_fetching else R.string.compare_pending_hint),
+                fontSize = 11.sp,
+                color = MaterialTheme.colorScheme.onPrimaryContainer,
+                maxLines = 1,
+            )
+        }
+        if (pending != null) {
+            Box(
+                Modifier.size(40.dp).clip(RoundedCornerShape(20.dp)).clickable(role = Role.Button, onClick = onClearPin),
+                contentAlignment = Alignment.Center,
+            ) {
+                UBIcon(R.drawable.ic_ub_close, stringResource(R.string.compare_unpin), size = 18.dp, tint = MaterialTheme.colorScheme.onPrimaryContainer)
+            }
+        }
+    }
+}
+
+@Composable
+private fun TabChip(tab: SavedCodeTab, isCurrent: Boolean, onOpen: () -> Unit, onClose: () -> Unit) {
+    val colors = MaterialTheme.colorScheme
+    val openLabel = stringResource(R.string.workbench_tab_open, tab.fileName, tab.name)
+    val currentLabel = stringResource(R.string.workbench_tab_current)
+    Row(
+        Modifier.clip(RoundedCornerShape(10.dp))
+            .background(if (isCurrent) colors.primaryContainer else colors.surfaceVariant)
+            .border(1.dp, if (isCurrent) colors.primary else colors.outlineVariant, RoundedCornerShape(10.dp))
+            .heightIn(min = 40.dp),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        Column(
+            Modifier.clickable(role = Role.Tab, onClick = onOpen)
+                .semantics(mergeDescendants = true) {
+                    contentDescription = if (isCurrent) "$openLabel, $currentLabel" else openLabel
+                    selected = isCurrent
+                }
+                .padding(start = 10.dp, end = 2.dp, top = 3.dp, bottom = 3.dp)
+                .widthIn(max = 168.dp),
+        ) {
+            Text(
+                tab.fileName,
+                fontFamily = FontFamily.Monospace,
+                fontSize = 12.sp,
+                fontWeight = if (isCurrent) FontWeight.Bold else FontWeight.Medium,
+                color = if (isCurrent) colors.onPrimaryContainer else colors.onSurface,
+                maxLines = 1,
+                overflow = TextOverflow.Ellipsis,
+            )
+            Text(
+                "${tab.name} · ${tab.ref}",
+                fontSize = 10.sp,
+                color = if (isCurrent) colors.onPrimaryContainer else colors.onSurfaceVariant,
+                maxLines = 1,
+                overflow = TextOverflow.Ellipsis,
+            )
+        }
+        Box(
+            Modifier.size(36.dp).clip(RoundedCornerShape(18.dp)).clickable(role = Role.Button, onClick = onClose),
+            contentAlignment = Alignment.Center,
+        ) {
+            UBIcon(R.drawable.ic_ub_close, stringResource(R.string.workbench_tab_close, tab.fileName), size = 16.dp, tint = colors.onSurfaceVariant)
+        }
+    }
+}

app/src/main/java/com/ubisam/ubgitea/feature/compare/CodeWorkbenchViewModel.kt

@@ -0,0 +1,238 @@
+package com.ubisam.ubgitea.feature.compare
+
+import android.app.Application
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import androidx.lifecycle.viewModelScope
+import com.ubisam.ubgitea.core.auth.android.AuthSession
+import com.ubisam.ubgitea.core.auth.protocol.UBGiteaOAuthDefaults
+import com.ubisam.ubgitea.core.network.OkHttpTransport
+import com.ubisam.ubgitea.core.settings.AppSettingsSession
+import com.ubisam.ubgitea.core.settings.AppSettingsStore
+import com.ubisam.ubgitea.data.repositories.GiteaRepositoryBrowserApi
+import com.ubisam.ubgitea.domain.model.RepositoryCoordinates
+import com.ubisam.ubgitea.domain.model.RepositoryPath
+import com.ubisam.ubgitea.domain.model.RepositoryRef
+import com.ubisam.ubgitea.domain.repository.GiteaRepositoryBrowser
+import com.ubisam.ubgitea.feature.codebrowser.content.ContentClassification
+import com.ubisam.ubgitea.feature.codebrowser.content.SourceContentClassifier
+import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+
+/**
+ * A code file kept as a tab: where it is, never what is in it. Its fields are joined with U+001F
+ * for storage, which owner, repository, ref and path can never contain.
+ */
+data class SavedCodeTab(
+    val owner: String,
+    val name: String,
+    val refKind: String,
+    val ref: String,
+    val path: String,
+) {
+    val fileName: String get() = path.substringAfterLast('/')
+
+    fun encode(): String = listOf(owner, name, refKind, ref, path).joinToString(SEPARATOR)
+
+    companion object {
+        const val MAX_TABS = 5
+        private const val SEPARATOR = "\u001F"
+
+        fun decodeOrNull(encoded: String): SavedCodeTab? {
+            val parts = encoded.split(SEPARATOR)
+            if (parts.size != 5 || parts.any(String::isEmpty)) return null
+            return SavedCodeTab(parts[0], parts[1], parts[2], parts[3], parts[4])
+        }
+    }
+}
+
+/** One side of a comparison: a text file as it is at one ref or commit. */
+data class ComparedFile(
+    val repository: RepositoryCoordinates,
+    // The branch, tag or short commit id shown under the file's name.
+    val refLabel: String,
+    val path: String,
+    val text: String,
+    val isTruncated: Boolean = false,
+) {
+    val fileName: String get() = path.substringAfterLast('/')
+
+    fun isSameFileAs(other: ComparedFile): Boolean =
+        repository == other.repository && refLabel == other.refLabel && path == other.path
+}
+
+enum class CompareSide { LEFT, RIGHT }
+
+/** The first file chosen for a comparison, waiting for the second. */
+data class PendingCompare(val file: ComparedFile, val side: CompareSide)
+
+/** Two files and how their lines line up. */
+class CompareSession(
+    val left: ComparedFile,
+    val right: ComparedFile,
+    val leftLines: List<String>,
+    val rightLines: List<String>,
+    val rows: List<CompareRow>,
+) {
+    val differences: List<Int> = differenceStarts(rows)
+}
+
+sealed interface CompareUiState {
+    data object None : CompareUiState
+    data class Working(val left: ComparedFile, val right: ComparedFile) : CompareUiState
+    data class Ready(val session: CompareSession) : CompareUiState
+}
+
+/** Something to tell the reader once, in passing. */
+enum class WorkbenchMessage { TABS_FULL, FILE_UNAVAILABLE, FILE_NOT_TEXT, SAME_FILE }
+
+data class CodeWorkbenchState(
+    val tabs: List<SavedCodeTab> = emptyList(),
+    val pending: PendingCompare? = null,
+    // A commit's file being fetched to become one side of a comparison.
+    val fetching: Boolean = false,
+    val compare: CompareUiState = CompareUiState.None,
+    val message: WorkbenchMessage? = null,
+)
+
+/**
+ * What the code screens share across repositories: the files kept as tabs, and a comparison
+ * between two files from anywhere -- two refs, two commits, or two places in the code.
+ */
+class CodeWorkbenchViewModel(
+    private val browser: GiteaRepositoryBrowser,
+    private val settings: AppSettingsStore,
+    private val classifier: SourceContentClassifier = SourceContentClassifier(
+        maxInputBytes = 2_000_000,
+        maxRenderedCharacters = 400_000,
+        maxRenderedLines = 20_000,
+    ),
+    private val defaultDispatcher: CoroutineDispatcher = Dispatchers.Default,
+) : ViewModel() {
+    private val mutableState = MutableStateFlow(
+        CodeWorkbenchState(tabs = settings.savedCodeTabs().mapNotNull(SavedCodeTab::decodeOrNull).take(SavedCodeTab.MAX_TABS)),
+    )
+    val state: StateFlow<CodeWorkbenchState> = mutableState.asStateFlow()
+    private var fetch: Job? = null
+    private var comparing: Job? = null
+
+    /** Keeps [tab] as a tab, or lets it go if it already is one. A sixth is refused, not swapped in. */
+    fun toggleTab(tab: SavedCodeTab) {
+        val tabs = mutableState.value.tabs
+        when {
+            tab in tabs -> saveTabs(tabs - tab)
+            tabs.size >= SavedCodeTab.MAX_TABS -> mutableState.update { it.copy(message = WorkbenchMessage.TABS_FULL) }
+            else -> saveTabs(tabs + tab)
+        }
+    }
+
+    fun removeTab(tab: SavedCodeTab) = saveTabs(mutableState.value.tabs - tab)
+
+    /** Puts [file] on one side, to be compared with the next file chosen. */
+    fun pin(file: ComparedFile, side: CompareSide) {
+        mutableState.update { it.copy(pending = PendingCompare(file, side)) }
+    }
+
+    fun clearPin() {
+        fetch?.cancel()
+        mutableState.update { it.copy(pending = null, fetching = false) }
+    }
+
+    /** Compares [file] with the one waiting on the other side. */
+    fun compareWith(file: ComparedFile) {
+        val pending = mutableState.value.pending ?: return
+        if (pending.file.isSameFileAs(file)) {
+            mutableState.update { it.copy(message = WorkbenchMessage.SAME_FILE) }
+            return
+        }
+        val (left, right) = if (pending.side == CompareSide.LEFT) pending.file to file else file to pending.file
+        mutableState.update { it.copy(pending = null) }
+        start(left, right)
+    }
+
+    /** Fetches a file as it is at a commit, then pins it or compares it with the waiting one. */
+    fun useCommitFile(repository: RepositoryCoordinates, commitId: String, shortId: String, path: String, side: CompareSide?) {
+        fetch?.cancel()
+        mutableState.update { it.copy(fetching = true) }
+        fetch = viewModelScope.launch {
+            val result = try {
+                withContext(defaultDispatcher) {
+                    val repositoryPath = RepositoryPath.of(path)
+                    classifier.classify(browser.getFile(repository, RepositoryRef.of(commitId), repositoryPath).content, repositoryPath)
+                }
+            } catch (failure: Throwable) {
+                if (failure is CancellationException) throw failure
+                null
+            }
+            mutableState.update { it.copy(fetching = false) }
+            when (result) {
+                null -> mutableState.update { it.copy(message = WorkbenchMessage.FILE_UNAVAILABLE) }
+                !is ContentClassification.Text -> mutableState.update { it.copy(message = WorkbenchMessage.FILE_NOT_TEXT) }
+                else -> {
+                    val file = ComparedFile(repository, shortId, path, result.renderedText, result.isTruncated)
+                    if (side != null) pin(file, side) else compareWith(file)
+                }
+            }
+        }
+    }
+
+    fun swapSides() {
+        val session = (mutableState.value.compare as? CompareUiState.Ready)?.session ?: return
+        start(session.right, session.left)
+    }
+
+    fun closeCompare() {
+        comparing?.cancel()
+        mutableState.update { it.copy(compare = CompareUiState.None) }
+    }
+
+    fun messageShown() {
+        mutableState.update { it.copy(message = null) }
+    }
+
+    private fun start(left: ComparedFile, right: ComparedFile) {
+        comparing?.cancel()
+        mutableState.update { it.copy(compare = CompareUiState.Working(left, right)) }
+        comparing = viewModelScope.launch {
+            val session = withContext(defaultDispatcher) {
+                val leftLines = left.text.toLines()
+                val rightLines = right.text.toLines()
+                CompareSession(left, right, leftLines, rightLines, compareLines(leftLines, rightLines))
+            }
+            mutableState.update { it.copy(compare = CompareUiState.Ready(session)) }
+        }
+    }
+
+    private fun saveTabs(tabs: List<SavedCodeTab>) {
+        mutableState.update { it.copy(tabs = tabs) }
+        settings.setSavedCodeTabs(tabs.map(SavedCodeTab::encode))
+    }
+
+    class Factory(private val application: Application) : ViewModelProvider.Factory {
+        override fun <T : ViewModel> create(modelClass: Class<T>): T {
+            require(modelClass.isAssignableFrom(CodeWorkbenchViewModel::class.java))
+            val settings = AppSettingsSession.store(application)
+            @Suppress("UNCHECKED_CAST")
+            return CodeWorkbenchViewModel(
+                GiteaRepositoryBrowserApi(
+                    UBGiteaOAuthDefaults.config,
+                    OkHttpTransport(),
+                    AuthSession.tokenProvider(application),
+                    reactiveAuthRetryEnabled = { settings.isReactiveAuthRetryEnabled() },
+                ),
+                settings,
+            ) as T
+        }
+    }
+}
+
+// Lines as the code viewer splits them: a Windows "\r" is not part of a line.
+internal fun String.toLines(): List<String> = split("\n").map { it.removeSuffix("\r") }

app/src/main/java/com/ubisam/ubgitea/feature/compare/CompareScreen.kt

@@ -0,0 +1,314 @@
+package com.ubisam.ubgitea.feature.compare
+
+import androidx.activity.compose.BackHandler
+import androidx.annotation.DrawableRes
+import androidx.annotation.StringRes
+import androidx.compose.foundation.background
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.BoxWithConstraints
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.IntrinsicSize
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.heightIn
+import androidx.compose.foundation.layout.navigationBarsPadding
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.statusBarsPadding
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.LazyListState
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.text.selection.DisableSelection
+import androidx.compose.foundation.text.selection.SelectionContainer
+import androidx.compose.material3.HorizontalDivider
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
+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.LocalDensity
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.Role
+import androidx.compose.ui.semantics.contentDescription
+import androidx.compose.ui.semantics.semantics
+import androidx.compose.ui.text.AnnotatedString
+import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.rememberTextMeasurer
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.text.style.TextIndent
+import androidx.compose.ui.text.style.TextOverflow
+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.domain.model.RepositoryPath
+import com.ubisam.ubgitea.feature.codebrowser.content.SyntaxLanguage
+import com.ubisam.ubgitea.feature.codebrowser.content.highlightLine
+import com.ubisam.ubgitea.feature.codebrowser.content.rememberCodeSyntaxColors
+import com.ubisam.ubgitea.feature.codebrowser.content.syntaxLanguageForPath
+import com.ubisam.ubgitea.ui.components.CautionBanner
+import com.ubisam.ubgitea.ui.components.CenteredLoading
+import com.ubisam.ubgitea.ui.components.CenteredMessage
+import com.ubisam.ubgitea.ui.components.ScreenTopBar
+import com.ubisam.ubgitea.ui.components.UBIcon
+import com.ubisam.ubgitea.ui.shell.WideLayoutBreakpoint
+import com.ubisam.ubgitea.ui.theme.UBGiteaTheme
+import kotlinx.coroutines.launch
+
+/**
+ * Two files side by side, the way a merge tool shows them: lines that match sit level, a changed
+ * line is amber on both sides, a line only one side has is red on the left or green on the right
+ * with a gap opposite. On a narrow window the two sides are interleaved in one column instead.
+ */
+@Composable
+fun CompareScreen(
+    state: CompareUiState,
+    fontSizeSp: Int,
+    onSwap: () -> Unit,
+    onClose: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    BackHandler(onBack = onClose)
+    val (left, right) = when (state) {
+        is CompareUiState.Ready -> state.session.left to state.session.right
+        is CompareUiState.Working -> state.left to state.right
+        CompareUiState.None -> return
+    }
+    val session = (state as? CompareUiState.Ready)?.session
+    val listState = remember(session) { LazyListState() }
+    val scope = rememberCoroutineScope()
+
+    fun jump(direction: Int) {
+        val differences = session?.differences ?: return
+        val current = listState.firstVisibleItemIndex + CONTEXT_ROWS
+        val target = if (direction > 0) differences.firstOrNull { it > current } else differences.lastOrNull { it < current }
+        if (target != null) scope.launch { listState.animateScrollToItem((target - CONTEXT_ROWS).coerceAtLeast(0)) }
+    }
+
+    Column(modifier.fillMaxSize().background(MaterialTheme.colorScheme.surface).statusBarsPadding()) {
+        ScreenTopBar(
+            title = if (left.fileName == right.fileName) left.fileName else "${left.fileName} ↔ ${right.fileName}",
+            subtitle = "${left.refLabel} ↔ ${right.refLabel}",
+            monospaceTitle = true,
+            onBack = onClose,
+            actions = {
+                IconButton(onClick = onSwap, enabled = session != null) {
+                    UBIcon(R.drawable.ic_ub_compare, stringResource(R.string.compare_swap), size = 22.dp)
+                }
+            },
+        )
+        if (left.isTruncated || right.isTruncated) CautionBanner(stringResource(R.string.compare_truncated))
+        BoxWithConstraints(Modifier.weight(1f).fillMaxWidth()) {
+            val sideBySide = maxWidth >= WideLayoutBreakpoint
+            Column(Modifier.fillMaxSize()) {
+                if (sideBySide) SideHeaders(left, right)
+                when {
+                    session == null -> CenteredLoading(stringResource(R.string.compare_working))
+                    session.differences.isEmpty() -> CenteredMessage(stringResource(R.string.compare_identical))
+                    else -> CompareList(session, fontSizeSp, sideBySide, listState)
+                }
+            }
+        }
+        val position by remember(session) {
+            derivedStateOf {
+                val current = listState.firstVisibleItemIndex + CONTEXT_ROWS
+                session?.differences?.count { it <= current } ?: 0
+            }
+        }
+        CompareToolbar(
+            summary = session?.let {
+                if (it.differences.isEmpty()) null else stringResource(R.string.compare_summary, it.differences.size)
+            },
+            position = position,
+            canJump = !session?.differences.isNullOrEmpty(),
+            onPrevious = { jump(-1) },
+            onNext = { jump(1) },
+        )
+    }
+}
+
+@Composable
+private fun SideHeaders(left: ComparedFile, right: ComparedFile) {
+    Row(Modifier.fillMaxWidth().background(MaterialTheme.colorScheme.surfaceVariant).height(IntrinsicSize.Min)) {
+        SideHeader(R.string.compare_side_left, left, Modifier.weight(1f))
+        Box(Modifier.width(1.dp).fillMaxHeight().background(MaterialTheme.colorScheme.outlineVariant))
+        SideHeader(R.string.compare_side_right, right, Modifier.weight(1f))
+    }
+    HorizontalDivider(color = MaterialTheme.colorScheme.outlineVariant)
+}
+
+@Composable
+private fun SideHeader(@StringRes side: Int, file: ComparedFile, modifier: Modifier) {
+    Column(modifier.padding(horizontal = 12.dp, vertical = 6.dp)) {
+        Text(
+            stringResource(side) + " · " + file.path,
+            fontFamily = FontFamily.Monospace,
+            fontSize = 12.sp,
+            fontWeight = FontWeight.Medium,
+            maxLines = 1,
+            overflow = TextOverflow.Ellipsis,
+        )
+        Text(
+            stringResource(R.string.compare_side_label, file.repository.name, file.refLabel),
+            fontSize = 11.sp,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+            maxLines = 1,
+            overflow = TextOverflow.Ellipsis,
+        )
+    }
+}
+
+@Composable
+private fun CompareList(session: CompareSession, fontSizeSp: Int, sideBySide: Boolean, listState: LazyListState) {
+    val colors = rememberCodeSyntaxColors()
+    val language = remember(session.left.path) { languageOf(session.left.path) }
+    val style = remember(fontSizeSp, colors.text) {
+        TextStyle(fontFamily = FontFamily.Monospace, fontSize = fontSizeSp.sp, lineHeight = (fontSizeSp * 1.5f).sp, color = colors.text)
+    }
+    val measurer = rememberTextMeasurer()
+    val characterWidthPx = remember(style) { measurer.measure("0", style).size.width.toFloat() }
+    val digits = maxOf(session.leftLines.size, session.rightLines.size).toString().length
+    val numberWidth = with(LocalDensity.current) { (characterWidthPx * digits).toDp() } + 18.dp
+    val cell = CellStyle(style, characterWidthPx, numberWidth, language)
+
+    SelectionContainer {
+        LazyColumn(state = listState, modifier = Modifier.fillMaxSize(), contentPadding = PaddingValues(bottom = 8.dp)) {
+            items(session.rows.size, key = { it }) { index ->
+                val row = session.rows[index]
+                val leftText = row.left?.let(session.leftLines::get)
+                val rightText = row.right?.let(session.rightLines::get)
+                if (sideBySide) {
+                    Row(Modifier.fillMaxWidth().height(IntrinsicSize.Min)) {
+                        CompareCell(leftText, row.left, row.kind, isLeft = true, cell, Modifier.weight(1f).fillMaxHeight())
+                        Box(Modifier.width(1.dp).fillMaxHeight().background(MaterialTheme.colorScheme.outlineVariant))
+                        CompareCell(rightText, row.right, row.kind, isLeft = false, cell, Modifier.weight(1f).fillMaxHeight())
+                    }
+                } else {
+                    Column(Modifier.fillMaxWidth()) {
+                        if (row.kind == CompareRowKind.SAME) {
+                            CompareCell(leftText, row.left, row.kind, isLeft = true, cell, Modifier.fillMaxWidth())
+                        } else {
+                            if (leftText != null) CompareCell(leftText, row.left, row.kind, isLeft = true, cell, Modifier.fillMaxWidth())
+                            if (rightText != null) CompareCell(rightText, row.right, row.kind, isLeft = false, cell, Modifier.fillMaxWidth())
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+private class CellStyle(val text: TextStyle, val characterWidthPx: Float, val numberWidth: Dp, val language: SyntaxLanguage)
+
+@Composable
+private fun CompareCell(text: String?, index: Int?, kind: CompareRowKind, isLeft: Boolean, cell: CellStyle, modifier: Modifier) {
+    if (text == null || index == null) {
+        // The other side has a line this side lacks.
+        Box(modifier.background(MaterialTheme.colorScheme.surfaceVariant))
+        return
+    }
+    val syntax = rememberCodeSyntaxColors()
+    val background = when (kind) {
+        CompareRowKind.SAME -> Color.Transparent
+        CompareRowKind.CHANGED -> UBGiteaTheme.colors.warningContainer
+        CompareRowKind.LEFT_ONLY -> MaterialTheme.colorScheme.errorContainer
+        CompareRowKind.RIGHT_ONLY -> UBGiteaTheme.colors.successContainer
+    }
+    val (sign, signColor, signLabel) = when {
+        kind == CompareRowKind.SAME -> Triple("", Color.Transparent, null)
+        isLeft -> Triple("−", MaterialTheme.colorScheme.error, stringResource(R.string.compare_side_left))
+        else -> Triple("+", UBGiteaTheme.colors.success, stringResource(R.string.compare_side_right))
+    }
+    val shown: AnnotatedString = remember(text, cell.language, syntax) { highlightLine(text, cell.language, syntax) }
+    val indent = text.takeWhile { it == ' ' || it == '\t' }.sumOf { if (it == '\t') 4 else 1 }
+    val hanging = with(LocalDensity.current) { (cell.characterWidthPx * (indent + 4)).toSp() }
+    Row(modifier.background(background), verticalAlignment = Alignment.Top) {
+        DisableSelection {
+            Text(
+                (index + 1).toString(),
+                style = cell.text,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                textAlign = TextAlign.End,
+                maxLines = 1,
+                modifier = Modifier.width(cell.numberWidth).padding(end = 6.dp),
+            )
+            Text(
+                sign,
+                style = cell.text,
+                color = signColor,
+                fontWeight = FontWeight.Bold,
+                textAlign = TextAlign.Center,
+                modifier = Modifier.width(16.dp).semantics { if (signLabel != null) contentDescription = signLabel },
+            )
+        }
+        Text(
+            shown,
+            style = cell.text.copy(textIndent = TextIndent(restLine = hanging)),
+            softWrap = true,
+            modifier = Modifier.weight(1f).padding(end = 10.dp),
+        )
+    }
+}
+
+@Composable
+private fun CompareToolbar(summary: String?, position: Int, canJump: Boolean, onPrevious: () -> Unit, onNext: () -> Unit) {
+    Surface(color = MaterialTheme.colorScheme.surface) {
+        Column(Modifier.navigationBarsPadding()) {
+            HorizontalDivider(color = MaterialTheme.colorScheme.outlineVariant)
+            Row(Modifier.fillMaxWidth().padding(horizontal = 6.dp, vertical = 6.dp), verticalAlignment = Alignment.CenterVertically) {
+                CompareTool(R.drawable.ic_ub_chevron_up, R.string.compare_previous, canJump, Modifier.weight(1f), onPrevious)
+                Text(
+                    if (summary == null) "" else "$position / $summary",
+                    style = MaterialTheme.typography.labelLarge,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    textAlign = TextAlign.Center,
+                    maxLines = 1,
+                    modifier = Modifier.weight(1.4f),
+                )
+                CompareTool(R.drawable.ic_ub_chevron_down, R.string.compare_next, canJump, Modifier.weight(1f), onNext)
+            }
+        }
+    }
+}
+
+@Composable
+private fun CompareTool(@DrawableRes icon: Int, @StringRes label: Int, enabled: Boolean, modifier: Modifier, onClick: () -> Unit) {
+    val color = if (enabled) MaterialTheme.colorScheme.onSurfaceVariant else MaterialTheme.colorScheme.outline
+    Column(
+        modifier
+            .clip(RoundedCornerShape(16.dp))
+            .clickable(enabled = enabled, role = Role.Button, onClick = onClick)
+            .heightIn(min = 52.dp)
+            .padding(vertical = 4.dp),
+        horizontalAlignment = Alignment.CenterHorizontally,
+        verticalArrangement = Arrangement.spacedBy(3.dp),
+    ) {
+        Box(Modifier.height(30.dp), contentAlignment = Alignment.Center) { UBIcon(icon, null, size = 22.dp, tint = color) }
+        Text(stringResource(label), fontSize = 11.sp, fontWeight = FontWeight.Medium, color = color, maxLines = 1)
+    }
+}
+
+private fun languageOf(path: String): SyntaxLanguage =
+    try {
+        syntaxLanguageForPath(RepositoryPath.of(path))
+    } catch (_: IllegalArgumentException) {
+        SyntaxLanguage.PLAIN
+    }
+
+private const val CONTEXT_ROWS = 2

app/src/main/java/com/ubisam/ubgitea/feature/compare/LineDiff.kt

@@ -0,0 +1,144 @@
+package com.ubisam.ubgitea.feature.compare
+
+/** How one row of a two-column comparison differs between its sides. */
+enum class CompareRowKind {
+    /** The same line on both sides. */
+    SAME,
+
+    /** A line on each side, and they differ. */
+    CHANGED,
+
+    /** A line only on the left; the right is blank. */
+    LEFT_ONLY,
+
+    /** A line only on the right; the left is blank. */
+    RIGHT_ONLY,
+}
+
+/**
+ * One row of a merge-tool style comparison: the left file's line beside the right file's, or a
+ * blank on the side that has none, so the lines that match stay level. Line numbers are zero-based
+ * indexes into each side's lines, null on a blank side.
+ */
+data class CompareRow(val kind: CompareRowKind, val left: Int?, val right: Int?)
+
+/**
+ * Lines the two sides share are found with Myers' algorithm, after the common start and end are set
+ * aside. Between two shared lines, removed and added lines are paired in order into changed rows;
+ * whichever side has more keeps the rest to itself.
+ *
+ * When the files differ in more than [maxEdits] lines the search stops and the differing middle is
+ * shown as one changed block. Each step of the search keeps a copy of its frontier, so memory grows
+ * with the square of the edit count, and an unbounded search on two unrelated large files could take
+ * all of it.
+ */
+fun compareLines(left: List<String>, right: List<String>, maxEdits: Int = DEFAULT_MAX_EDITS): List<CompareRow> {
+    var prefix = 0
+    while (prefix < left.size && prefix < right.size && left[prefix] == right[prefix]) prefix++
+    var suffix = 0
+    while (
+        suffix < left.size - prefix && suffix < right.size - prefix &&
+        left[left.size - 1 - suffix] == right[right.size - 1 - suffix]
+    ) suffix++
+
+    val rows = ArrayList<CompareRow>(maxOf(left.size, right.size) + 16)
+    repeat(prefix) { rows += CompareRow(CompareRowKind.SAME, it, it) }
+    val leftMiddle = left.subList(prefix, left.size - suffix)
+    val rightMiddle = right.subList(prefix, right.size - suffix)
+    val shared = sharedLines(leftMiddle, rightMiddle, maxEdits)
+
+    var l = 0
+    var r = 0
+    for ((sharedLeft, sharedRight) in shared + (leftMiddle.size to rightMiddle.size)) {
+        addBlock(rows, prefix + l, prefix + sharedLeft, prefix + r, prefix + sharedRight)
+        if (sharedLeft < leftMiddle.size) rows += CompareRow(CompareRowKind.SAME, prefix + sharedLeft, prefix + sharedRight)
+        l = sharedLeft + 1
+        r = sharedRight + 1
+    }
+    repeat(suffix) {
+        rows += CompareRow(CompareRowKind.SAME, left.size - suffix + it, right.size - suffix + it)
+    }
+    return rows
+}
+
+/** The index of the first row of every run of differing rows: where "next difference" lands. */
+fun differenceStarts(rows: List<CompareRow>): List<Int> =
+    rows.indices.filter { rows[it].kind != CompareRowKind.SAME && (it == 0 || rows[it - 1].kind == CompareRowKind.SAME) }
+
+private fun addBlock(rows: MutableList<CompareRow>, leftFrom: Int, leftTo: Int, rightFrom: Int, rightTo: Int) {
+    val leftCount = leftTo - leftFrom
+    val rightCount = rightTo - rightFrom
+    for (i in 0 until maxOf(leftCount, rightCount)) {
+        rows += when {
+            i < leftCount && i < rightCount -> CompareRow(CompareRowKind.CHANGED, leftFrom + i, rightFrom + i)
+            i < leftCount -> CompareRow(CompareRowKind.LEFT_ONLY, leftFrom + i, null)
+            else -> CompareRow(CompareRowKind.RIGHT_ONLY, null, rightFrom + i)
+        }
+    }
+}
+
+/**
+ * The pairs (left index, right index) of lines kept in a shortest edit script from [a] to [b], in
+ * order. Empty when nothing is shared or when more than [maxEdits] edits would be needed.
+ */
+private fun sharedLines(a: List<String>, b: List<String>, maxEdits: Int): List<Pair<Int, Int>> {
+    val n = a.size
+    val m = b.size
+    if (n == 0 || m == 0) return emptyList()
+    val max = minOf(n + m, maxEdits)
+    val offset = max + 1
+    val v = IntArray(2 * max + 3)
+    // trace[d] is v for diagonals -d..d after step d.
+    val trace = ArrayList<IntArray>()
+    var found = -1
+    search@ for (d in 0..max) {
+        for (k in -d..d step 2) {
+            var x = if (k == -d || (k != d && v[offset + k - 1] < v[offset + k + 1])) {
+                v[offset + k + 1]
+            } else {
+                v[offset + k - 1] + 1
+            }
+            var y = x - k
+            while (x < n && y < m && a[x] == b[y]) {
+                x++
+                y++
+            }
+            v[offset + k] = x
+            if (x >= n && y >= m) {
+                trace += v.copyOfRange(offset - d, offset + d + 1)
+                found = d
+                break@search
+            }
+        }
+        trace += v.copyOfRange(offset - d, offset + d + 1)
+    }
+    if (found < 0) return emptyList()
+
+    val pairs = ArrayList<Pair<Int, Int>>()
+    var x = n
+    var y = m
+    for (d in found downTo 1) {
+        val previous = trace[d - 1]
+        fun at(k: Int) = previous[k + d - 1]
+        val k = x - y
+        val previousK = if (k == -d || (k != d && at(k - 1) < at(k + 1))) k + 1 else k - 1
+        val previousX = at(previousK)
+        val previousY = previousX - previousK
+        while (x > previousX && y > previousY) {
+            x--
+            y--
+            pairs += x to y
+        }
+        x = previousX
+        y = previousY
+    }
+    while (x > 0 && y > 0) {
+        x--
+        y--
+        pairs += x to y
+    }
+    pairs.reverse()
+    return pairs
+}
+
+private const val DEFAULT_MAX_EDITS = 3000

app/src/main/java/com/ubisam/ubgitea/feature/history/FileDiffScreen.kt

@@ -62,6 +62,8 @@ import com.ubisam.ubgitea.domain.model.RepositoryPath
 import com.ubisam.ubgitea.feature.codebrowser.content.highlightLine
 import com.ubisam.ubgitea.feature.codebrowser.content.rememberCodeSyntaxColors
 import com.ubisam.ubgitea.feature.codebrowser.content.syntaxLanguageForPath
+import com.ubisam.ubgitea.feature.compare.CompareMenu
+import com.ubisam.ubgitea.feature.compare.LocalCodeWorkbench
 import com.ubisam.ubgitea.ui.components.CautionBanner
 import com.ubisam.ubgitea.ui.components.CenteredMessage
 import com.ubisam.ubgitea.ui.components.ScreenTopBar
@@ -125,11 +127,28 @@ fun FileDiffScreen(
                 DiffList(entries, selected.file.path, fontSizeSp, sideBySide, listState)
             }
         }
+        // This file as it is after the commit, to compare with a file from anywhere else (TASK-065).
+        val workbench = LocalCodeWorkbench.current
+        val commit = state.commit
+        val path = selected.file.path
         DiffToolbar(
             canJump = changeStarts.isNotEmpty(),
             onPreviousChange = { jump(-1) },
             onNextChange = { jump(1) },
             onFileList = onClose,
+            compare = workbench?.let { bench ->
+                { modifier ->
+                    CompareMenu(
+                        pending = bench.pending,
+                        onPin = { side -> bench.onUseCommitFile(commit.id, commit.shortId, path, side) },
+                        onCompare = { bench.onUseCommitFile(commit.id, commit.shortId, path, null) },
+                        onClearPin = bench.onClearPin,
+                        modifier = modifier,
+                    ) { onOpen ->
+                        DiffTool(R.drawable.ic_ub_compare, R.string.codeviewer_tool_compare, true, Modifier.fillMaxWidth(), onOpen)
+                    }
+                }
+            },
         )
     }
 }
@@ -323,7 +342,13 @@ private fun DiffCell(
 }
 
 @Composable
-private fun DiffToolbar(canJump: Boolean, onPreviousChange: () -> Unit, onNextChange: () -> Unit, onFileList: () -> Unit) {
+private fun DiffToolbar(
+    canJump: Boolean,
+    onPreviousChange: () -> Unit,
+    onNextChange: () -> Unit,
+    onFileList: () -> Unit,
+    compare: (@Composable (Modifier) -> Unit)? = null,
+) {
     val label = stringResource(R.string.history_diff_tools)
     Surface(color = MaterialTheme.colorScheme.surface) {
         Column(Modifier.navigationBarsPadding()) {
@@ -331,6 +356,7 @@ private fun DiffToolbar(canJump: Boolean, onPreviousChange: () -> Unit, onNextCh
             Row(Modifier.fillMaxWidth().semantics { contentDescription = label }.padding(horizontal = 6.dp, vertical = 6.dp)) {
                 DiffTool(R.drawable.ic_ub_chevron_up, R.string.history_diff_previous_change, canJump, Modifier.weight(1f), onPreviousChange)
                 DiffTool(R.drawable.ic_ub_chevron_down, R.string.history_diff_next_change, canJump, Modifier.weight(1f), onNextChange)
+                compare?.invoke(Modifier.weight(1f))
                 DiffTool(R.drawable.ic_ub_files, R.string.history_diff_file_list, true, Modifier.weight(1f), onFileList)
             }
         }

app/src/main/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModel.kt

@@ -431,6 +431,25 @@ class RepositoryListViewModel(
         loadRowBranches(restored)
     }
 
+    /**
+     * The Repositories tab pressed again while it is showing: a repository's branches and tags go
+     * back to the list page they were chosen from, and a later page of the list goes to the first.
+     */
+    fun reselect() {
+        when (val current = mutableState.value) {
+            is RepositoryListUiState.ReferencesLoading,
+            is RepositoryListUiState.ReferencesContent,
+            is RepositoryListUiState.ReferencesError,
+            -> backToRepositories()
+            is RepositoryListUiState.Content -> {
+                if (current.page <= 1) return
+                val account = activeAccountName ?: return
+                startOperation { loadRepositoryPage(account, 1, current.mode, current.organization) }
+            }
+            else -> Unit
+        }
+    }
+
     fun cancelSignIn() {
         startOperation {
             pendingAuthStore.clear()

app/src/main/java/com/ubisam/ubgitea/feature/settings/SettingsScreen.kt

@@ -14,6 +14,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.verticalScroll
+import androidx.compose.material3.Button
 import androidx.compose.material3.FilterChip
 import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.MaterialTheme
@@ -24,12 +25,17 @@ import androidx.compose.runtime.Composable
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.LiveRegionMode
+import androidx.compose.ui.semantics.liveRegion
+import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import com.ubisam.ubgitea.R
 import com.ubisam.ubgitea.core.settings.AppSettingsStore
 import com.ubisam.ubgitea.core.settings.ThemeMode
+import com.ubisam.ubgitea.core.update.AppUpdateUiState
+import com.ubisam.ubgitea.core.update.UpdateCheck
 import com.ubisam.ubgitea.ui.components.Avatar
 import com.ubisam.ubgitea.ui.components.ListCard
 import com.ubisam.ubgitea.ui.components.ScreenTopBar
@@ -49,6 +55,9 @@ fun SettingsScreen(
     onLogout: () -> Unit,
     onBack: () -> Unit,
     modifier: Modifier = Modifier,
+    update: AppUpdateUiState? = null,
+    onCheckUpdate: () -> Unit = {},
+    onOpenDownloadPage: () -> Unit = {},
 ) {
     BackHandler(onBack = onBack)
     Column(modifier.fillMaxSize()) {
@@ -152,11 +161,53 @@ fun SettingsScreen(
                     onCheckedChange = onSetFavoritePushNotificationsEnabled,
                 )
             }
+            if (update != null) {
+                SectionTitle(stringResource(R.string.update_section), Modifier.padding(top = 8.dp))
+                ListCard(Modifier.padding(horizontal = 20.dp)) {
+                    UpdateRow(update, onCheckUpdate, onOpenDownloadPage)
+                }
+            }
             Spacer(Modifier.height(8.dp))
         }
     }
 }
 
+@Composable
+private fun UpdateRow(update: AppUpdateUiState, onCheckUpdate: () -> Unit, onOpenDownloadPage: () -> Unit) {
+    Column(Modifier.padding(16.dp), verticalArrangement = Arrangement.spacedBy(8.dp)) {
+        Text(stringResource(R.string.update_installed_version, update.installedVersionName), style = MaterialTheme.typography.titleMedium)
+        val status = when (update.check) {
+            UpdateCheck.IDLE -> null
+            UpdateCheck.CHECKING -> stringResource(R.string.update_checking)
+            UpdateCheck.UP_TO_DATE -> stringResource(R.string.update_up_to_date)
+            UpdateCheck.FAILED -> stringResource(R.string.update_failed)
+            UpdateCheck.AVAILABLE -> update.available?.let { stringResource(R.string.update_available, it.versionName) }
+        }
+        if (status != null) {
+            Text(
+                status,
+                style = MaterialTheme.typography.bodySmall,
+                color = if (update.check == UpdateCheck.AVAILABLE) MaterialTheme.colorScheme.primary else MaterialTheme.colorScheme.onSurfaceVariant,
+                modifier = Modifier.semantics { liveRegion = LiveRegionMode.Polite },
+            )
+        }
+        Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+            OutlinedButton(
+                onClick = onCheckUpdate,
+                enabled = update.check != UpdateCheck.CHECKING,
+                modifier = Modifier.heightIn(min = 48.dp),
+            ) {
+                Text(stringResource(R.string.update_check))
+            }
+            if (update.available != null) {
+                Button(onClick = onOpenDownloadPage, modifier = Modifier.heightIn(min = 48.dp)) {
+                    Text(stringResource(R.string.update_download))
+                }
+            }
+        }
+    }
+}
+
 private val ThemeMode.label: Int
     get() = when (this) {
         ThemeMode.SYSTEM -> R.string.settings_theme_system

app/src/main/java/com/ubisam/ubgitea/ui/navigation/Route.kt

@@ -18,7 +18,14 @@ sealed interface Route {
     // one branch/tag/commit ref. Each tab's own internal drill-down (a subfolder, a commit's
     // detail) is handled entirely inside that tab's existing ViewModel state machine, not by
     // pushing further routes, so this one route covers the whole branch-detail experience.
-    data class BranchDetail(val owner: String, val name: String, val refKind: String, val ref: String) : Route
+    // path is set when the screen opens straight on one file, as a saved code tab does.
+    data class BranchDetail(
+        val owner: String,
+        val name: String,
+        val refKind: String,
+        val ref: String,
+        val path: String? = null,
+    ) : Route
     // number is set when the screen opens on one issue or pull request rather than on the list.
     data class WorkItems(
         val owner: String,
@@ -28,6 +35,10 @@ sealed interface Route {
     ) : Route
     data object Settings : Route
 
+    // Two files side by side. What is compared lives only in memory, so this route is not
+    // restored after the process is gone.
+    data object Compare : Route
+
     val isTab: Boolean
         get() = this is Home || this is Repositories || this is Work || this is Notifications
 }

app/src/main/java/com/ubisam/ubgitea/ui/navigation/RouteStackSaver.kt

@@ -30,12 +30,17 @@ internal object RouteEncoding {
     private const val TYPE_WORK_ITEMS = "workItems"
     private const val TYPE_NOTIFICATIONS = "notifications"
     private const val TYPE_SETTINGS = "settings"
+    private const val TYPE_COMPARE = "compare"
 
     fun encode(route: Route): String = when (route) {
         Route.Home -> TYPE_HOME
         Route.Repositories -> TYPE_REPOSITORIES
         Route.Work -> TYPE_WORK
-        is Route.BranchDetail -> join(TYPE_BRANCH_DETAIL, route.owner, route.name, route.refKind, route.ref)
+        is Route.BranchDetail -> if (route.path == null) {
+            join(TYPE_BRANCH_DETAIL, route.owner, route.name, route.refKind, route.ref)
+        } else {
+            join(TYPE_BRANCH_DETAIL, route.owner, route.name, route.refKind, route.ref, route.path)
+        }
         is Route.WorkItems -> if (route.number == null) {
             join(TYPE_WORK_ITEMS, route.owner, route.name)
         } else {
@@ -49,6 +54,7 @@ internal object RouteEncoding {
         }
         Route.Notifications -> TYPE_NOTIFICATIONS
         Route.Settings -> TYPE_SETTINGS
+        Route.Compare -> TYPE_COMPARE
     }
 
     fun decode(encoded: String): Route = decodeOrNull(encoded) ?: Route.Home
@@ -56,8 +62,8 @@ internal object RouteEncoding {
     fun decodeOrNull(encoded: String): Route? {
         val parts = encoded.split(FIELD_SEPARATOR)
         return when (parts.first()) {
-            TYPE_BRANCH_DETAIL -> parts.takeIf { it.size == 5 }?.let {
+            TYPE_BRANCH_DETAIL -> parts.takeIf { it.size == 5 || it.size == 6 }?.let {
-                Route.BranchDetail(owner = it[1], name = it[2], refKind = it[3], ref = it[4])
+                Route.BranchDetail(owner = it[1], name = it[2], refKind = it[3], ref = it[4], path = it.getOrNull(5))
             }
             TYPE_WORK_ITEMS -> when (parts.size) {
                 3 -> Route.WorkItems(owner = parts[1], name = parts[2])
@@ -75,6 +81,8 @@ internal object RouteEncoding {
             TYPE_NOTIFICATIONS -> Route.Notifications
             TYPE_SETTINGS -> Route.Settings
             TYPE_REPOSITORIES -> Route.Repositories
+            // The files being compared are not saved with the route.
+            TYPE_COMPARE -> null
             else -> null
         }
     }

app/src/main/java/com/ubisam/ubgitea/ui/shell/AppShell.kt

@@ -4,6 +4,10 @@ import androidx.annotation.DrawableRes
 import androidx.annotation.StringRes
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.BoxWithConstraints
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.WindowInsets
+import androidx.compose.foundation.layout.navigationBars
+import androidx.compose.foundation.layout.windowInsetsPadding
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.consumeWindowInsets
 import androidx.compose.foundation.layout.fillMaxHeight
@@ -55,6 +59,9 @@ fun AppShell(
     unreadNotifications: Int?,
     onTabSelected: (AppTab) -> Unit,
     modifier: Modifier = Modifier,
+    // Drawn between the screen and the bottom tabs, or at the bottom where there are none: the
+    // saved code tabs. Null when there is nothing to show.
+    strip: (@Composable () -> Unit)? = null,
     content: @Composable (isWide: Boolean) -> Unit,
 ) {
     BoxWithConstraints(modifier.fillMaxSize()) {
@@ -62,7 +69,14 @@ fun AppShell(
         Scaffold(
             containerColor = MaterialTheme.colorScheme.background,
             bottomBar = {
-                if (showNavigation && !isWide) BottomTabs(selectedTab, unreadNotifications, onTabSelected)
+                val tabs = showNavigation && !isWide
+                Column {
+                    if (strip != null) {
+                        // The bottom tabs keep clear of the system bar themselves; alone, the strip has to.
+                        Box(if (tabs) Modifier else Modifier.windowInsetsPadding(WindowInsets.navigationBars)) { strip() }
+                    }
+                    if (tabs) BottomTabs(selectedTab, unreadNotifications, onTabSelected)
+                }
             },
         ) { padding ->
             Row(Modifier.fillMaxSize().padding(padding).consumeWindowInsets(padding)) {

app/src/main/res/drawable/ic_ub_bookmark.xml

@@ -0,0 +1,14 @@
+<?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="M6.5,3.5h11v17l-5.5,-4 -5.5,4z" />
+</vector>

app/src/main/res/drawable/ic_ub_bookmark_filled.xml

@@ -0,0 +1,13 @@
+<?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="#FF000000"
+        android:strokeColor="#FF000000"
+        android:strokeLineJoin="round"
+        android:strokeWidth="1.8"
+        android:pathData="M6.5,3.5h11v17l-5.5,-4 -5.5,4z" />
+</vector>

app/src/main/res/drawable/ic_ub_compare.xml

@@ -0,0 +1,14 @@
+<?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="M4,4.5h6v15h-6zM14,4.5h6v15h-6zM6,8.5h2M6,12h2M16,8.5h2M16,15.5h2" />
+</vector>

app/src/main/res/values/strings_compare.xml

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Saved code tabs (TASK-065) -->
+    <string name="workbench_tabs">저장한 탭</string>
+    <string name="workbench_tab_open">%1$s 열기 · %2$s</string>
+    <string name="workbench_tab_close">%1$s 탭 닫기</string>
+    <string name="workbench_tab_current">지금 보는 파일</string>
+    <string name="workbench_tabs_full">탭은 %1$d개까지 저장할 수 있습니다. 하나를 닫고 다시 저장하세요.</string>
+    <string name="codeviewer_tool_save_tab">탭 저장</string>
+    <string name="codeviewer_tool_compare">비교</string>
+
+    <!-- Comparing two files -->
+    <string name="compare_put_left">이 파일을 왼쪽에 두기</string>
+    <string name="compare_put_right">이 파일을 오른쪽에 두기</string>
+    <string name="compare_with_pinned">%1$s와 비교하기</string>
+    <string name="compare_unpin">비교 대기 취소</string>
+    <string name="compare_pending">비교 대기 · %1$s (%2$s)</string>
+    <string name="compare_pending_hint">다른 파일에서 비교를 누르세요</string>
+    <string name="compare_side_left">왼쪽</string>
+    <string name="compare_side_right">오른쪽</string>
+    <string name="compare_fetching">커밋의 파일을 불러오는 중입니다.</string>
+    <string name="compare_file_unavailable">이 커밋의 파일을 불러오지 못했습니다. 삭제된 파일은 비교할 수 없습니다.</string>
+    <string name="compare_file_not_text">텍스트 파일만 비교할 수 있습니다.</string>
+    <string name="compare_same_file">같은 파일입니다. 다른 커밋이나 다른 파일을 고르세요.</string>
+    <string name="compare_working">두 파일을 맞춰 보는 중입니다.</string>
+    <string name="compare_summary">다른 곳 %1$d군데</string>
+    <string name="compare_identical">두 파일이 같습니다.</string>
+    <string name="compare_previous">이전 차이</string>
+    <string name="compare_next">다음 차이</string>
+    <string name="compare_swap">좌우 바꾸기</string>
+    <string name="compare_truncated">파일이 길어 앞부분만 비교합니다.</string>
+    <string name="compare_side_label">%1$s · %2$s</string>
+
+    <!-- Highlighting a word in the code -->
+    <string name="codeviewer_word_count">%1$s · %2$d곳</string>
+    <string name="codeviewer_word_previous">이전 위치</string>
+    <string name="codeviewer_word_next">다음 위치</string>
+    <string name="codeviewer_word_clear">표시 지우기</string>
+
+    <!-- Side pane width -->
+    <string name="codeviewer_side_pane_handle">옆 창 너비 조절. 좌우로 끌어 조절하고, 두 번 누르면 기본 너비로 되돌립니다.</string>
+</resources>

app/src/main/res/values/strings_update.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="update_section">앱 정보</string>
+    <string name="update_installed_version">현재 버전 %1$s</string>
+    <string name="update_check">업데이트 확인</string>
+    <string name="update_checking">확인하는 중…</string>
+    <string name="update_up_to_date">최신 버전입니다.</string>
+    <string name="update_failed">새 버전을 확인하지 못했습니다. 네트워크를 확인하세요.</string>
+    <string name="update_available">새 버전 %1$s을(를) 받을 수 있습니다.</string>
+    <string name="update_download">다운로드 페이지 열기</string>
+    <string name="update_dialog_title">새 버전이 있습니다</string>
+    <string name="update_dialog_body">현재 %1$s → 새 버전 %2$s\n다운로드 페이지에서 비밀번호를 입력해 받은 뒤 설치하세요.</string>
+    <string name="update_dialog_download">다운로드</string>
+    <string name="update_dialog_later">나중에</string>
+</resources>

app/src/test/java/com/ubisam/ubgitea/core/update/AppUpdateTest.kt

@@ -0,0 +1,92 @@
+package com.ubisam.ubgitea.core.update
+
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.test.setMain
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Before
+import org.junit.Test
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class AppUpdateTest {
+    private val dispatcher = StandardTestDispatcher()
+    @Before fun setMainDispatcher() = Dispatchers.setMain(dispatcher)
+    @After fun resetMainDispatcher() = Dispatchers.resetMain()
+
+    @Test
+    fun `a version file is read`() {
+        assertEquals(
+            AppRelease(3, "0.3.0", "탭 저장"),
+            parseAppRelease("""{"versionCode": 3, "versionName": " 0.3.0 ", "notes": "탭 저장"}"""),
+        )
+        assertEquals(AppRelease(3, "0.3.0"), parseAppRelease("""{"versionCode": 3, "versionName": "0.3.0", "notes": ""}"""))
+    }
+
+    @Test
+    fun `a broken or incomplete version file is no release`() {
+        assertNull(parseAppRelease("<html>404</html>"))
+        assertNull(parseAppRelease("""{"versionName": "0.3.0"}"""))
+        assertNull(parseAppRelease("""{"versionCode": "three", "versionName": "0.3.0"}"""))
+        assertNull(parseAppRelease("""{"versionCode": 0, "versionName": "0.3.0"}"""))
+        assertNull(parseAppRelease("""{"versionCode": 3}"""))
+        assertNull(parseAppRelease("[]"))
+    }
+
+    @Test
+    fun `a newer build is offered at launch`() = runTest(dispatcher) {
+        val release = AppRelease(3, "0.3.0")
+        val viewModel = AppUpdateViewModel({ release }, installedVersionCode = 2, installedVersionName = "0.2.0")
+        viewModel.checkAtLaunch()
+        advanceUntilIdle()
+        assertEquals(UpdateCheck.AVAILABLE, viewModel.state.value.check)
+        assertEquals(release, viewModel.state.value.prompt)
+        viewModel.dismissPrompt()
+        assertNull(viewModel.state.value.prompt)
+        assertEquals(release, viewModel.state.value.available)
+    }
+
+    @Test
+    fun `the launch check runs once`() = runTest(dispatcher) {
+        var calls = 0
+        val viewModel = AppUpdateViewModel({ calls++; AppRelease(3, "0.3.0") }, 2, "0.2.0")
+        viewModel.checkAtLaunch()
+        advanceUntilIdle()
+        viewModel.dismissPrompt()
+        viewModel.checkAtLaunch()
+        advanceUntilIdle()
+        assertEquals(1, calls)
+        assertNull(viewModel.state.value.prompt)
+    }
+
+    @Test
+    fun `the same or an older build is up to date`() = runTest(dispatcher) {
+        val viewModel = AppUpdateViewModel({ AppRelease(2, "0.2.0") }, 2, "0.2.0")
+        viewModel.checkNow()
+        advanceUntilIdle()
+        assertEquals(UpdateCheck.UP_TO_DATE, viewModel.state.value.check)
+        assertNull(viewModel.state.value.available)
+    }
+
+    @Test
+    fun `a check by hand finds a newer build without the launch prompt`() = runTest(dispatcher) {
+        val viewModel = AppUpdateViewModel({ AppRelease(3, "0.3.0") }, 2, "0.2.0")
+        viewModel.checkNow()
+        advanceUntilIdle()
+        assertEquals(UpdateCheck.AVAILABLE, viewModel.state.value.check)
+        assertNull(viewModel.state.value.prompt)
+    }
+
+    @Test
+    fun `an unreadable version file is a failed check`() = runTest(dispatcher) {
+        val viewModel = AppUpdateViewModel({ null }, 2, "0.2.0")
+        viewModel.checkNow()
+        advanceUntilIdle()
+        assertEquals(UpdateCheck.FAILED, viewModel.state.value.check)
+    }
+}

app/src/test/java/com/ubisam/ubgitea/feature/codebrowser/CodeBrowserViewModelTest.kt

@@ -178,6 +178,25 @@ class CodeBrowserViewModelTest {
         assertEquals(2, browser.fileRequests)
     }
 
+    @Test
+    fun `a file opened by path lists its folder and comes back without a second fetch`() = runTest(dispatcher.scheduler) {
+        val browser = FakeBrowser()
+        val viewModel = CodeBrowserViewModel(browser, defaultDispatcher = dispatcher)
+        viewModel.openFile(target, RepositoryPath.of("src/한글.kt"))
+        advanceUntilIdle()
+        val file = viewModel.state.value as CodeBrowserUiState.File
+        assertEquals("src/한글.kt", file.path.value)
+        assertEquals(listOf("src/한글.kt"), file.siblingEntries.map { it.path.value })
+        assertEquals(1, browser.fileRequests)
+
+        viewModel.openFile(target, RepositoryPath.of("gallery/notes.txt"))
+        advanceUntilIdle()
+        viewModel.openFile(target, RepositoryPath.of("src/한글.kt"))
+        advanceUntilIdle()
+        assertEquals("src/한글.kt", (viewModel.state.value as CodeBrowserUiState.File).path.value)
+        assertEquals(2, browser.fileRequests)
+    }
+
     private class FakeBrowser(
         private val rootEntryType: TreeEntryType = TreeEntryType.DIRECTORY,
         var fileFailure: Throwable? = null,

app/src/test/java/com/ubisam/ubgitea/feature/codebrowser/SplitTest.kt

@@ -15,4 +15,16 @@ class SplitTest {
         assertEquals(0.8f, clampSplit(0.97f), 0f)
         assertEquals(0.2f, clampSplit(-1f), 0f)
     }
+
+    @Test
+    fun `a width near the default snaps onto it`() {
+        assertEquals(240f, snapTo(252f, 240f, 16f), 0f)
+        assertEquals(240f, snapTo(224f, 240f, 16f), 0f)
+    }
+
+    @Test
+    fun `a width beyond the snap distance is kept`() {
+        assertEquals(260f, snapTo(260f, 240f, 16f), 0f)
+        assertEquals(0.3f, snapTo(0.3f, 0.5f, 0.03f), 0f)
+    }
 }

app/src/test/java/com/ubisam/ubgitea/feature/codebrowser/content/CodeSearchTest.kt

@@ -164,4 +164,27 @@ class CodeSearchTest {
         val header = RepositoryPath.of("src/a/Foo.h")
         assertNull(counterpartOf(header, listOf(header)))
     }
+
+    @Test
+    fun `the word under a tap includes underscores and digits`() {
+        assertEquals("item_count2", wordAt("val item_count2 = 3", 6))
+        assertEquals("item_count2", wordAt("val item_count2 = 3", 15))
+    }
+
+    @Test
+    fun `a tap on spaces, symbols or a number is no word`() {
+        assertNull(wordAt("a = 12", 2))
+        assertNull(wordAt("a = 12", 5))
+        assertNull(wordAt("", 0))
+    }
+
+    @Test
+    fun `occurrences are whole words and case sensitive`() {
+        val lines = listOf("count = count + 1", "val counter = Count", "count")
+        val hits = findWordOccurrences(lines, "count")
+        assertEquals(
+            listOf(SearchMatch(0, 0, 5), SearchMatch(0, 8, 13), SearchMatch(2, 0, 5)),
+            hits,
+        )
+    }
 }

app/src/test/java/com/ubisam/ubgitea/feature/compare/CodeWorkbenchViewModelTest.kt

@@ -0,0 +1,150 @@
+package com.ubisam.ubgitea.feature.compare
+
+import com.ubisam.ubgitea.core.network.ApiFailure
+import com.ubisam.ubgitea.core.settings.AppSettingsStore
+import com.ubisam.ubgitea.domain.model.BranchSummary
+import com.ubisam.ubgitea.domain.model.CommitSummary
+import com.ubisam.ubgitea.domain.model.Page
+import com.ubisam.ubgitea.domain.model.RepositoryCoordinates
+import com.ubisam.ubgitea.domain.model.RepositoryPath
+import com.ubisam.ubgitea.domain.model.RepositoryRef
+import com.ubisam.ubgitea.domain.model.RepositorySummary
+import com.ubisam.ubgitea.domain.model.SourceContent
+import com.ubisam.ubgitea.domain.model.SourceFile
+import com.ubisam.ubgitea.domain.model.TagSummary
+import com.ubisam.ubgitea.domain.model.TreeEntry
+import com.ubisam.ubgitea.domain.repository.GiteaRepositoryBrowser
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.advanceUntilIdle
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.test.setMain
+import org.junit.After
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class CodeWorkbenchViewModelTest {
+    private val dispatcher = StandardTestDispatcher()
+    private val repository = RepositoryCoordinates.of("owner", "repo")
+
+    @Before fun setMainDispatcher() = Dispatchers.setMain(dispatcher)
+    @After fun resetMainDispatcher() = Dispatchers.resetMain()
+
+    @Test
+    fun `tabs are kept, toggled off, and a sixth is refused`() {
+        val settings = FakeSettings()
+        val viewModel = CodeWorkbenchViewModel(FakeBrowser(), settings, defaultDispatcher = dispatcher)
+        val tabs = (1..6).map { tab("src/F$it.kt") }
+        tabs.take(5).forEach(viewModel::toggleTab)
+        assertEquals(5, viewModel.state.value.tabs.size)
+
+        viewModel.toggleTab(tabs[5])
+        assertEquals(tabs.take(5), viewModel.state.value.tabs)
+        assertEquals(WorkbenchMessage.TABS_FULL, viewModel.state.value.message)
+
+        viewModel.toggleTab(tabs[0])
+        assertEquals(tabs.subList(1, 5), viewModel.state.value.tabs)
+        assertEquals(tabs.subList(1, 5).map(SavedCodeTab::encode), settings.tabs)
+
+        val reopened = CodeWorkbenchViewModel(FakeBrowser(), settings, defaultDispatcher = dispatcher)
+        assertEquals(tabs.subList(1, 5), reopened.state.value.tabs)
+    }
+
+    @Test
+    fun `a tab survives encoding, and damaged entries are dropped`() {
+        val tab = tab("dir/a b.kt")
+        assertEquals(tab, SavedCodeTab.decodeOrNull(tab.encode()))
+        assertNull(SavedCodeTab.decodeOrNull("only\u001Ftwo"))
+    }
+
+    @Test
+    fun `the pinned side decides which file is on the left`() = runTest(dispatcher.scheduler) {
+        val viewModel = CodeWorkbenchViewModel(FakeBrowser(), FakeSettings(), defaultDispatcher = dispatcher)
+        val mine = file("main", "a\nb")
+        val theirs = file("dev", "a\nc")
+        viewModel.pin(mine, CompareSide.RIGHT)
+        viewModel.compareWith(theirs)
+        advanceUntilIdle()
+
+        val session = (viewModel.state.value.compare as CompareUiState.Ready).session
+        assertEquals("dev", session.left.refLabel)
+        assertEquals("main", session.right.refLabel)
+        assertEquals(listOf(1), session.differences)
+        assertNull(viewModel.state.value.pending)
+
+        viewModel.swapSides()
+        advanceUntilIdle()
+        assertEquals("main", (viewModel.state.value.compare as CompareUiState.Ready).session.left.refLabel)
+    }
+
+    @Test
+    fun `comparing a file with itself is refused`() {
+        val viewModel = CodeWorkbenchViewModel(FakeBrowser(), FakeSettings(), defaultDispatcher = dispatcher)
+        viewModel.pin(file("main", "a"), CompareSide.LEFT)
+        viewModel.compareWith(file("main", "a"))
+        assertEquals(WorkbenchMessage.SAME_FILE, viewModel.state.value.message)
+        assertTrue(viewModel.state.value.compare is CompareUiState.None)
+    }
+
+    @Test
+    fun `a commit's file is fetched at that commit and compared`() = runTest(dispatcher.scheduler) {
+        val browser = FakeBrowser()
+        val viewModel = CodeWorkbenchViewModel(browser, FakeSettings(), defaultDispatcher = dispatcher)
+        viewModel.pin(file("main", "x"), CompareSide.LEFT)
+        viewModel.useCommitFile(repository, "abcdef0123", "abcdef0", "src/F.kt", side = null)
+        advanceUntilIdle()
+
+        assertEquals(listOf("abcdef0123"), browser.refs)
+        val session = (viewModel.state.value.compare as CompareUiState.Ready).session
+        assertEquals("abcdef0", session.right.refLabel)
+        assertEquals(listOf("at abcdef0123"), session.rightLines)
+    }
+
+    @Test
+    fun `a commit's file that cannot be fetched says so and keeps the pin`() = runTest(dispatcher.scheduler) {
+        val viewModel = CodeWorkbenchViewModel(FakeBrowser(failure = ApiFailure.NotFound()), FakeSettings(), defaultDispatcher = dispatcher)
+        viewModel.pin(file("main", "x"), CompareSide.LEFT)
+        viewModel.useCommitFile(repository, "abc", "abc", "src/F.kt", side = null)
+        advanceUntilIdle()
+        assertEquals(WorkbenchMessage.FILE_UNAVAILABLE, viewModel.state.value.message)
+        assertEquals("main", viewModel.state.value.pending?.file?.refLabel)
+    }
+
+    private fun tab(path: String) = SavedCodeTab("owner", "repo", "BRANCH", "main", path)
+
+    private fun file(ref: String, text: String) = ComparedFile(repository, ref, "src/F.kt", text)
+
+    private class FakeSettings : AppSettingsStore {
+        var tabs: List<String> = emptyList()
+        override fun isReactiveAuthRetryEnabled() = false
+        override fun setReactiveAuthRetryEnabled(enabled: Boolean) = Unit
+        override fun isFavoritePushNotificationsEnabled() = false
+        override fun setFavoritePushNotificationsEnabled(enabled: Boolean) = Unit
+        override fun savedCodeTabs(): List<String> = tabs
+        override fun setSavedCodeTabs(tabs: List<String>) {
+            this.tabs = tabs
+        }
+    }
+
+    private class FakeBrowser(private val failure: Throwable? = null) : GiteaRepositoryBrowser {
+        val refs = mutableListOf<String>()
+        override suspend fun listRepositories(page: Int, pageSize: Int): Page<RepositorySummary> = Page.of(emptyList(), null)
+        override suspend fun listBranches(repository: RepositoryCoordinates, page: Int, pageSize: Int): Page<BranchSummary> = Page.of(emptyList(), null)
+        override suspend fun listTags(repository: RepositoryCoordinates, page: Int, pageSize: Int): Page<TagSummary> = Page.of(emptyList(), null)
+        override suspend fun listTree(repository: RepositoryCoordinates, ref: RepositoryRef, path: RepositoryPath, page: Int, pageSize: Int): Page<TreeEntry> =
+            Page.of(emptyList(), null)
+        override suspend fun getFile(repository: RepositoryCoordinates, ref: RepositoryRef, path: RepositoryPath): SourceFile {
+            refs += ref.value
+            failure?.let { throw it }
+            return SourceFile(path, ref, SourceContent.from("at ${ref.value}".encodeToByteArray()), "text/plain")
+        }
+        override suspend fun listCommits(repository: RepositoryCoordinates, ref: RepositoryRef, path: RepositoryPath?, page: Int, pageSize: Int): Page<CommitSummary> =
+            Page.of(emptyList(), null)
+    }
+}

app/src/test/java/com/ubisam/ubgitea/feature/compare/LineDiffTest.kt

@@ -0,0 +1,93 @@
+package com.ubisam.ubgitea.feature.compare
+
+import com.ubisam.ubgitea.feature.compare.CompareRowKind.CHANGED
+import com.ubisam.ubgitea.feature.compare.CompareRowKind.LEFT_ONLY
+import com.ubisam.ubgitea.feature.compare.CompareRowKind.RIGHT_ONLY
+import com.ubisam.ubgitea.feature.compare.CompareRowKind.SAME
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class LineDiffTest {
+    @Test
+    fun identicalFilesAreAllSame() {
+        val lines = listOf("a", "b", "c")
+        assertEquals(
+            listOf(CompareRow(SAME, 0, 0), CompareRow(SAME, 1, 1), CompareRow(SAME, 2, 2)),
+            compareLines(lines, lines),
+        )
+    }
+
+    @Test
+    fun aChangedLineIsPairedWithItsReplacement() {
+        val rows = compareLines(listOf("a", "b", "c"), listOf("a", "x", "c"))
+        assertEquals(listOf(CompareRow(SAME, 0, 0), CompareRow(CHANGED, 1, 1), CompareRow(SAME, 2, 2)), rows)
+    }
+
+    @Test
+    fun anInsertedLineLeavesABlankOnTheLeft() {
+        val rows = compareLines(listOf("a", "c"), listOf("a", "b", "c"))
+        assertEquals(listOf(CompareRow(SAME, 0, 0), CompareRow(RIGHT_ONLY, null, 1), CompareRow(SAME, 1, 2)), rows)
+    }
+
+    @Test
+    fun aRemovedLineLeavesABlankOnTheRight() {
+        val rows = compareLines(listOf("a", "b", "c"), listOf("a", "c"))
+        assertEquals(listOf(CompareRow(SAME, 0, 0), CompareRow(LEFT_ONLY, 1, null), CompareRow(SAME, 2, 1)), rows)
+    }
+
+    @Test
+    fun sharedLinesInTheMiddleStayLevel() {
+        val left = listOf("1", "x", "keep", "y", "2")
+        val right = listOf("1", "keep", "z", "w", "2")
+        val rows = compareLines(left, right)
+        val keep = rows.single { it.kind == SAME && it.left == 2 }
+        assertEquals(1, keep.right)
+        assertEveryLineAppearsOnceInOrder(rows, left.size, right.size)
+    }
+
+    @Test
+    fun emptySides() {
+        assertEquals(listOf(CompareRow(RIGHT_ONLY, null, 0)), compareLines(emptyList(), listOf("a")))
+        assertEquals(listOf(CompareRow(LEFT_ONLY, 0, null)), compareLines(listOf("a"), emptyList()))
+        assertEquals(emptyList<CompareRow>(), compareLines(emptyList(), emptyList()))
+    }
+
+    @Test
+    fun tooManyEditsFallsBackToOneChangedBlock() {
+        val left = (0 until 50).map { "L$it" } + "end"
+        val right = (0 until 40).map { "R$it" } + "end"
+        val rows = compareLines(left, right, maxEdits = 10)
+        assertEquals(40, rows.count { it.kind == CHANGED })
+        assertEquals(10, rows.count { it.kind == LEFT_ONLY })
+        assertEquals(CompareRow(SAME, 50, 40), rows.last())
+    }
+
+    @Test
+    fun randomEditsKeepEveryLineInOrder() {
+        val random = java.util.Random(7)
+        repeat(200) {
+            val left = List(random.nextInt(30)) { "l${random.nextInt(6)}" }
+            val right = List(random.nextInt(30)) { "l${random.nextInt(6)}" }
+            val rows = compareLines(left, right)
+            assertEveryLineAppearsOnceInOrder(rows, left.size, right.size)
+            rows.filter { it.kind == SAME }.forEach { assertEquals(left[it.left!!], right[it.right!!]) }
+        }
+    }
+
+    @Test
+    fun differenceStartsMarksTheFirstRowOfEachRun() {
+        val rows = listOf(
+            CompareRow(SAME, 0, 0),
+            CompareRow(CHANGED, 1, 1),
+            CompareRow(LEFT_ONLY, 2, null),
+            CompareRow(SAME, 3, 2),
+            CompareRow(RIGHT_ONLY, null, 3),
+        )
+        assertEquals(listOf(1, 4), differenceStarts(rows))
+    }
+
+    private fun assertEveryLineAppearsOnceInOrder(rows: List<CompareRow>, leftSize: Int, rightSize: Int) {
+        assertEquals((0 until leftSize).toList(), rows.mapNotNull { it.left })
+        assertEquals((0 until rightSize).toList(), rows.mapNotNull { it.right })
+    }
+}

app/src/test/java/com/ubisam/ubgitea/feature/repositories/RepositoryListViewModelTest.kt

@@ -172,6 +172,36 @@ class RepositoryListViewModelTest {
         assertEquals(listOf(1 to 50, 2 to 50), browser.repositoryPageRequests)
     }
 
+    @Test
+    fun `reselecting the tab goes from a repository to its list page and from there to the first page`() = runTest(dispatcher.scheduler) {
+        val browser = FakeBrowser(
+            repositories = listOf(
+                Page.of(listOf(repo("oldest", 1_000L), repo("middle", 2_000L)), nextPage = 2),
+                Page.of(listOf(repo("newest", 3_000L), repo("newer", 2_500L), repo("older", 1_500L), repo("old", 500L)), nextPage = null),
+            ),
+        )
+        val viewModel = viewModel(browser)
+        advanceUntilIdle()
+        viewModel.nextPage()
+        advanceUntilIdle()
+        val secondPage = viewModel.state.value as RepositoryListUiState.Content
+        viewModel.selectRepository(secondPage.repositories.single())
+        advanceUntilIdle()
+        assertTrue(viewModel.state.value is RepositoryListUiState.ReferencesContent)
+
+        viewModel.reselect()
+        advanceUntilIdle()
+        assertEquals(2, (viewModel.state.value as RepositoryListUiState.Content).page)
+
+        viewModel.reselect()
+        advanceUntilIdle()
+        assertEquals(1, (viewModel.state.value as RepositoryListUiState.Content).page)
+
+        viewModel.reselect()
+        advanceUntilIdle()
+        assertEquals(1, (viewModel.state.value as RepositoryListUiState.Content).page)
+    }
+
     @Test
     fun `refresh invalidates the globally sorted repository snapshot`() = runTest(dispatcher.scheduler) {
         val browser = FakeBrowser(repositories = listOf(page1Of(repo("repo"))))

app/src/test/java/com/ubisam/ubgitea/ui/navigation/RouteEncodingTest.kt

@@ -91,4 +91,17 @@ class RouteEncodingTest {
 
         assertEquals(stack, restored)
     }
+
+    @Test
+    fun `branch detail route opened on a file round-trips`() {
+        val route = Route.BranchDetail(owner = "o", name = "r", refKind = "BRANCH", ref = "main", path = "src/a/Foo.cpp")
+        assertEquals(route, RouteEncoding.decode(RouteEncoding.encode(route)))
+    }
+
+    @Test
+    fun `a comparison is not restored`() {
+        val branch = Route.BranchDetail(owner = "o", name = "r", refKind = "BRANCH", ref = "main")
+        val saved = listOf(Route.Repositories, branch, Route.Compare).map(RouteEncoding::encode)
+        assertEquals(listOf(Route.Repositories, branch), RouteStackSaver.restore(saved))
+    }
 }

docs/development-log.md

@@ -1455,3 +1455,28 @@ This is the append-only implementation and handoff record shared by Codex and Cl
   leaves its rows unnumbered instead of numbering them from 1.
 - Verification: `compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug
   lintDebug` pass; 440 unit tests, 0 failures, three of them new. Not yet confirmed on a device.
+
+## 2026-10-07 — TASK-065: code tabs, comparing two files, and reading aids
+
+- Request: the human product owner asked for five things: up to five code files saved as tabs
+  above the bottom tabs; comparing a file with one from another commit or place, choosing which
+  side the current one goes on; a draggable side pane width on an unfolded Fold that snaps to its
+  default; every use of a tapped name marked in the code; and the Repositories tab, pressed again
+  inside a repository, going back to the list page it was opened from, then to the first page.
+- What changed: see `tasks/065-code-tabs-compare-and-reading-aids.md`. A new
+  `CodeWorkbenchViewModel` holds the saved tabs (stored as locations, never content) and the
+  comparison; `Route.Compare` is not restored after the process is gone.
+- Checks and results: the required checks pass; 461 unit tests, 0 failures; lint 0 errors.
+- Live verification: none; no device was connected.
+- Next owner: the product owner, to confirm on the device.
+
+## 2026-10-07 (continued) — TASK-066: download page and update check
+
+- Request: the human product owner asked for a password-protected web download and for the app
+  to offer the newest version.
+- What changed: see `tasks/066-download-page-and-update-check.md`. Version 0.2.0
+  (versionCode 2) is published at `https://choimy0204.github.io/ubgitea/`.
+- Checks and results: the required checks pass; 468 unit tests, 0 failures; lint 0 errors.
+- Caution: the published APK is the debug build, signed with this PC's debug key. It installs
+  over copies built on this PC; a copy built elsewhere has to be removed first.
+- Next owner: the product owner, to try the link and the install on the device.

tasks/065-code-tabs-compare-and-reading-aids.md

@@ -0,0 +1,76 @@
+# TASK-065: Saved code tabs, comparing two files, and reading aids
+
+Status: done
+Owner: Claude
+Reviewer: human product owner
+
+## Outcome
+
+Requested by the human product owner, 2026-10-07:
+
+1. Code files can be kept as tabs. Saving a tab puts a strip between the screen and the bottom
+   tabs; each saved file stays there, at most five, and tapping one goes back to it.
+2. Two files can be compared side by side like a merge tool: the current file is placed on the
+   left or right, then another file (from another commit or another place) is opened and the
+   same button pressed again to compare the two.
+3. On the unfolded screen the side pane beside the code can be resized by dragging; near its
+   default width it snaps to the default like a magnet.
+4. Tapping a word in the code marks every occurrence of the same name.
+5. Pressing the Repositories tab again while inside a repository returns to the repository list
+   page that was being viewed; pressing it again there goes to the first page.
+
+## Scope
+
+- Included: the five items above.
+- Excluded: editing or merging files; comparing directories; three-way comparison.
+
+## Writable paths
+
+- `app/src/main/java/com/ubisam/ubgitea/`
+- `app/src/main/res/values/`
+- `app/src/test/java/com/ubisam/ubgitea/`
+- `tasks/`, `docs/`
+
+## Acceptance criteria
+
+- [ ] The code viewer has a "save tab" button; a saved file shows as a chip in a strip above the
+      bottom tabs (and above the viewer's toolbar when reading full screen). Tapping a chip opens
+      that file in its repository and ref; its close mark removes it. Tabs survive a restart.
+- [ ] A sixth tab is refused with a message; nothing is evicted silently.
+- [ ] The compare button asks whether the current file goes left or right, then a banner shows
+      the waiting file. Pressing compare on another file (in the code viewer or a commit's file
+      diff) opens a two-column view where matching lines stay level, differing lines are
+      coloured, and there are next/previous difference and swap-sides actions.
+- [ ] The line comparison is a pure function with unit tests, and gives up gracefully on files
+      that differ too much.
+- [ ] The side pane width is dragged with a handle, kept between launches, snaps to the default
+      within 16dp, and resets on double tap.
+- [ ] Tapping an identifier highlights all whole-word occurrences in a colour distinct from
+      search hits; tapping it again or tapping a non-word clears it.
+- [ ] Repositories tab reselect: inside a repository → the list page last viewed; on the list
+      with page > 1 → page 1. Other tabs behave as before.
+- [ ] All new text is in string resources; new controls have spoken labels.
+
+## Security and privacy
+
+No additional concerns. Saved tabs hold only owner, repository name, ref and path; no tokens.
+
+## Required checks
+
+```text
+./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug
+```
+
+## Evidence
+
+- 2026-10-07: the required checks pass; 461 unit tests, 0 failures; lint 0 errors.
+- New tests: `LineDiffTest`, `CodeWorkbenchViewModelTest`, `openFile` in
+  `CodeBrowserViewModelTest`, `reselect` in `RepositoryListViewModelTest`, `snapTo` in
+  `SplitTest`, `wordAt` and `findWordOccurrences` in `CodeSearchTest`, and a file route and an
+  unrestored comparison in `RouteEncodingTest`.
+- Live verification: none. No device was connected; the tab strip, the compare screen, the
+  drag handle's snap and the word marks were not seen on a screen by the implementer.
+
+## Review findings
+
+None yet.

tasks/066-download-page-and-update-check.md

@@ -0,0 +1,51 @@
+# TASK-066: download page and in-app update check
+
+Status: done
+Owner: Claude
+Reviewer: human product owner
+
+## Request
+
+The human product owner asked for a web link to download the app, protected by a download
+password they chose, and for the app to offer the newest version when it is not on it. They chose
+to host it in a folder of the existing `choimy0204.github.io` site.
+
+## Acceptance criteria
+
+- `https://choimy0204.github.io/ubgitea/` serves a page that asks for the password and only then
+  gives the APK. The APK on the host is encrypted (AES-256-GCM, key from PBKDF2-SHA256), so its
+  address alone gives nothing. The password is not in this repository.
+- `version.json` beside it names the newest versionCode, versionName and notes.
+- The app reads it once at launch; when it is newer than the installed build, a dialog offers the
+  download page. Settings shows the installed version, a check button, and the download page when
+  something newer is out. No Gitea token is sent to that host.
+- `tools/publish-download.py` builds the page from an APK; versionCode is raised for every build
+  published.
+
+## Writable paths
+
+`app/build.gradle.kts`, `app/src/main/java/com/ubisam/ubgitea/core/update/`, `MainActivity.kt`,
+`feature/settings/SettingsScreen.kt`, `res/values/strings_update.xml`, `app/src/test/.../core/update/`,
+`tools/publish-download.py`, `docs/development-log.md`, this file.
+
+## Checks
+
+```text
+./gradlew compileDebugKotlin compileDebugUnitTestKotlin testDebugUnitTest assembleDebug lintDebug
+```
+
+## Evidence
+
+- 2026-10-07: the required checks pass; 468 unit tests, 0 failures; lint 0 errors.
+- The page's decryption was run with Node's WebCrypto (the browser's API): the right password
+  gives a file byte-identical to `app-debug.apk`, a wrong one is refused.
+- Published version 0.2.0 (versionCode 2), the debug build, to `choimy0204.github.io/ubgitea/`.
+- Not seen: the page opened on a phone, the install over an existing copy, the in-app dialog.
+
+## Review findings
+
+- 2026-10-07, product owner: a wrong password still downloaded. In a desktop browser a wrong
+  password got nothing, but the page fetched the encrypted APK before checking the password,
+  and a phone browser can keep that fetch as a download (still encrypted, not installable). The
+  page now opens a small sealed check with the password first and fetches nothing when it is
+  wrong; tried in the browser: a wrong password made no request, the right one downloaded.

tools/publish-download.py

@@ -0,0 +1,187 @@
+"""Builds the password-protected download page for one APK (TASK-066).
+
+The APK is encrypted with AES-256-GCM under a key derived from the password with PBKDF2-SHA256,
+so the files can sit on a public static host: the page asks for the password and decrypts in the
+browser with WebCrypto. version.json beside it is plain; the app reads it to know a newer build
+is out.
+
+    python tools/publish-download.py <apk> <out-dir> --notes "what changed"
+
+The password is read from UBGITEA_DOWNLOAD_PASSWORD, or asked for. It is never written anywhere.
+versionCode and versionName are read from app/build.gradle.kts.
+"""
+import argparse
+import base64
+import getpass
+import hashlib
+import html
+import json
+import os
+import re
+import sys
+from pathlib import Path
+
+from cryptography.hazmat.primitives.ciphers.aead import AESGCM
+
+ITERATIONS = 310_000
+ENCRYPTED_NAME = "ubgitea.apk.enc"
+CHECK_TEXT = b"UBGitea"
+
+
+def gradle_version(root: Path):
+    text = (root / "app" / "build.gradle.kts").read_text(encoding="utf-8")
+    code = re.search(r"versionCode\s*=\s*(\d+)", text)
+    name = re.search(r'versionName\s*=\s*"([^"]+)"', text)
+    if not code or not name:
+        sys.exit("versionCode / versionName not found in app/build.gradle.kts")
+    return int(code.group(1)), name.group(1)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("apk", type=Path)
+    parser.add_argument("out", type=Path)
+    parser.add_argument("--notes", default="")
+    args = parser.parse_args()
+
+    password = os.environ.get("UBGITEA_DOWNLOAD_PASSWORD") or getpass.getpass("Download password: ")
+    if not password:
+        sys.exit("A password is required.")
+    code, name = gradle_version(Path(__file__).resolve().parent.parent)
+
+    data = args.apk.read_bytes()
+    salt = os.urandom(16)
+    iv = os.urandom(12)
+    key = hashlib.pbkdf2_hmac("sha256", password.encode("utf-8"), salt, ITERATIONS, 32)
+    sealed = AESGCM(key).encrypt(iv, data, None)
+    # A few sealed bytes the page opens first: a wrong password is refused before the APK is
+    # fetched at all, so nothing is downloaded with it.
+    check_iv = os.urandom(12)
+    check = AESGCM(key).encrypt(check_iv, CHECK_TEXT, None)
+
+    args.out.mkdir(parents=True, exist_ok=True)
+    (args.out / ENCRYPTED_NAME).write_bytes(sealed)
+    release = {"versionCode": code, "versionName": name, "notes": args.notes}
+    (args.out / "version.json").write_text(json.dumps(release, ensure_ascii=False, indent=2) + "\n", encoding="utf-8")
+    meta = {
+        "salt": base64.b64encode(salt).decode(),
+        "iv": base64.b64encode(iv).decode(),
+        "iterations": ITERATIONS,
+        "check": base64.b64encode(check).decode(),
+        "checkIv": base64.b64encode(check_iv).decode(),
+        "file": ENCRYPTED_NAME,
+        "fileName": f"UBGitea-{name}.apk",
+        "size": len(data),
+    }
+    page = PAGE.replace("{{META}}", json.dumps(meta)) \
+        .replace("{{VERSION}}", html.escape(name)) \
+        .replace("{{NOTES}}", html.escape(args.notes)) \
+        .replace("{{SIZE}}", f"{len(data) / 1024 / 1024:.1f} MB")
+    (args.out / "index.html").write_text(page, encoding="utf-8")
+    print(f"UBGitea {name} (versionCode {code}) -> {args.out}")
+
+
+PAGE = """<!doctype html>
+<html lang="ko">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
+<meta name="robots" content="noindex">
+<title>UBGitea 다운로드</title>
+<style>
+  :root { --bg: #f4f7fc; --card: #ffffff; --ink: #14213d; --muted: #5b6b86; --line: #d8e1f0;
+          --blue: #1f5fd6; --blue-ink: #ffffff; --bad: #c62828; }
+  @media (prefers-color-scheme: dark) {
+    :root { --bg: #0d1524; --card: #16213a; --ink: #e8eefb; --muted: #9fb0cf; --line: #2a3a5c;
+            --blue: #6d9cff; --blue-ink: #0d1524; --bad: #ff8a80; }
+  }
+  * { box-sizing: border-box; }
+  body { margin: 0; min-height: 100vh; background: var(--bg); color: var(--ink);
+         font-family: system-ui, -apple-system, "Segoe UI", "Malgun Gothic", sans-serif;
+         display: flex; align-items: center; justify-content: center; padding: 16px; }
+  main { width: 100%; max-width: 420px; background: var(--card); border: 1px solid var(--line);
+         border-radius: 20px; padding: 28px 24px; }
+  h1 { margin: 0 0 4px; font-size: 24px; }
+  .version { color: var(--blue); font-weight: 600; }
+  p { color: var(--muted); line-height: 1.5; margin: 8px 0; }
+  .notes { white-space: pre-line; color: var(--ink); background: var(--bg); border-radius: 12px;
+           padding: 12px 14px; margin: 16px 0; }
+  .notes:empty { display: none; }
+  label { display: block; font-weight: 600; margin: 20px 0 8px; }
+  input { width: 100%; font-size: 17px; padding: 14px; border-radius: 12px; border: 1px solid var(--line);
+          background: var(--card); color: var(--ink); }
+  button { width: 100%; margin-top: 12px; font-size: 17px; font-weight: 600; padding: 14px; border: 0;
+           border-radius: 12px; background: var(--blue); color: var(--blue-ink); cursor: pointer; }
+  button:disabled { opacity: .6; cursor: default; }
+  #status { min-height: 1.5em; margin-top: 12px; }
+  #status.bad { color: var(--bad); }
+  ol { color: var(--muted); padding-left: 20px; line-height: 1.6; margin: 20px 0 0; }
+</style>
+</head>
+<body>
+<main>
+  <h1>UBGitea</h1>
+  <div class="version">버전 {{VERSION}} · {{SIZE}}</div>
+  <div class="notes">{{NOTES}}</div>
+  <form id="form">
+    <label for="password">다운로드 비밀번호</label>
+    <input id="password" type="password" autocomplete="off" required>
+    <button id="go" type="submit">APK 다운로드</button>
+  </form>
+  <p id="status" role="status" aria-live="polite"></p>
+  <ol>
+    <li>받은 APK 파일을 엽니다.</li>
+    <li>"출처를 알 수 없는 앱" 설치를 이 브라우저에 허용합니다.</li>
+    <li>설치(업데이트)를 누릅니다. 로그인과 설정은 그대로 남습니다.</li>
+  </ol>
+</main>
+<script>
+const META = {{META}};
+const status = document.getElementById("status");
+const go = document.getElementById("go");
+const b64 = s => Uint8Array.from(atob(s), c => c.charCodeAt(0));
+function say(text, bad) { status.textContent = text; status.className = bad ? "bad" : ""; }
+document.getElementById("form").addEventListener("submit", async event => {
+  event.preventDefault();
+  go.disabled = true;
+  try {
+    say("비밀번호 확인 중…");
+    const password = new TextEncoder().encode(document.getElementById("password").value);
+    const base = await crypto.subtle.importKey("raw", password, "PBKDF2", false, ["deriveKey"]);
+    const key = await crypto.subtle.deriveKey(
+      { name: "PBKDF2", salt: b64(META.salt), iterations: META.iterations, hash: "SHA-256" },
+      base, { name: "AES-GCM", length: 256 }, false, ["decrypt"]);
+    try {
+      await crypto.subtle.decrypt({ name: "AES-GCM", iv: b64(META.checkIv) }, key, b64(META.check));
+    } catch (e) {
+      say("비밀번호가 맞지 않습니다.", true);
+      return;
+    }
+    say("파일을 받는 중…");
+    const response = await fetch(META.file, { cache: "no-store" });
+    if (!response.ok) throw new Error("fetch");
+    const sealed = await response.arrayBuffer();
+    say("여는 중…");
+    const apk = await crypto.subtle.decrypt({ name: "AES-GCM", iv: b64(META.iv) }, key, sealed);
+    const url = URL.createObjectURL(new Blob([apk], { type: "application/vnd.android.package-archive" }));
+    const link = document.createElement("a");
+    link.href = url;
+    link.download = META.fileName;
+    document.body.appendChild(link);
+    link.click();
+    link.remove();
+    setTimeout(() => URL.revokeObjectURL(url), 60000);
+    say("다운로드를 시작했습니다. 받은 파일을 열어 설치하세요.");
+  } catch (e) {
+    say("파일을 받지 못했습니다. 잠시 뒤 다시 시도하세요.", true);
+  } finally {
+    go.disabled = false;
+  }
+});
+</script>
+</body>
+</html>
+"""
+
+if __name__ == "__main__":
+    main()