Add device sync: mirror folders/files locally, background WorkManager engine

- New native sync engine (SyncEngine/SyncWorker/ConflictResolveWorker,
  WorkManager-based) that mirrors selected Nextcloud folders or files to
  app-private local storage, periodically and on-demand ("Sync now"),
  with never-auto-resolved conflict notifications.
- Single files (not just folders) can now be marked "Sync to device".
- Live sync status (syncing/synced/conflicts) pushes from native to Dart
  over a new EventChannel; the persistent header chip/panel now reflects
  device-sync status instead of the WebDAV-refresh loading state, with a
  cloud_off/cloud_sync/cloud_done/cloud_alert icon set and an expandable
  conflicts list with in-app "Keep local"/"Use server" resolution.
  Per-item cloud_done/sync badges show on Files tiles.
- Share/Download short-circuit to the local copy for already-synced
  files instead of a fresh network fetch.
- Settings gained a Device Sync section (per-folder list, "Sync
  everything", Wi-Fi-only toggle, manual "Sync now").
- Fixed two release-only bugs found via on-device testing: Android's
  HttpURLConnection silently rejects the PROPFIND method (switched to
  OkHttp), and R8 was stripping WorkManager's reflection-instantiated
  internals (broadened proguard-rules.pro to keep androidx.work.**
  wholesale rather than chasing individual classes).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.claude/context/architecture.md

@@ -54,10 +54,10 @@ There is exactly one `ChangeNotifier`: [`ServerProvider`](../../lib/providers/se
 - UI settings that persist across launches — split into **global** (theme
   mode, seed color, dynamic-color toggle, bottom-bar opacity/blur,
   tap-tab-to-scroll-top, seek bar style, tab order/visibility/default, swipe
-  actions, login lock — see below) and **per-account** (grid/list view,
-  favorites-only, show-hidden, storage scope, Photos sort, Files'
-  per-folder sort map, cache policy) — see `server.md` for exactly which is
-  which and why
+  actions, login lock, sync-on-cellular — see below) and **per-account**
+  (grid/list view, favorites-only, show-hidden, storage scope, Photos sort,
+  Files' per-folder sort map, cache policy, synced folders) — see
+  `server.md` for exactly which is which and why
 - **Login lock** (`loginLockEnabled`/`lockAccountSwitching`/
   `lockHiddenFiles`/`needsUnlock`): an app-wide PIN/biometric gate via
   `AppLockService` (a thin wrapper over `local_auth` — this app never

.claude/context/server.md

@@ -157,12 +157,12 @@ rather than needing a rewrite for multi-account support.
   (`views/move_copy_destination_picker.dart`) is covered in
   `architecture.md`, including why it can't reuse the Files tab's shared
   navigation state the way `ShareUploadView` does.
-- **Uploads** (`uploadFileFromPath(folderPath, fileName, localFilePath,
-  {onProgress})`) stream the local file via `Dio().put()` with an explicit
-  `Content-Length` and `onSendProgress`, mirroring the download path. The
-  `ServerProvider` wrapper always uploads into `_currentFolderPath` — the
-  share-to-upload flow (`ShareUploadView`) gets a caller-chosen destination
-  by navigating there first (`navigateToAbsoluteFolder`), then uploading.
+- **Uploads**: there's no more in-app-only upload path - `NextcloudService`/
+  `ServerProvider.uploadFileFromPath` were removed once the Files tab's "+"
+  → "Upload File" was unified with the share-to-upload flow (below). Every
+  upload, however it's triggered, now goes through `ShareUploadView`
+  (caller-chosen destination via `navigateToAbsoluteFolder`, then
+  `UploadService`/`ShareUploadService.kt`).
 - **Receiving a shared file from another app**: hand-rolled in
   `MainActivity.kt` (Android `ACTION_SEND`/`ACTION_SEND_MULTIPLE`,
   `android:launchMode` `singleTask` in the manifest so a second share while
@@ -246,6 +246,151 @@ Google Drive/Instagram's "choose a file" flow), the reverse direction of
   backing out (system back while picking, or a picked-item mismatch) with
   `RESULT_CANCELED` instead.
 
+## Device sync
+
+Mirrors selected folders to app-private local storage
+(`getExternalFilesDir(null)/sync/<accountId>/...` - wiped on uninstall, no
+extra storage permission needed) and keeps them updated in the background,
+even with the app fully closed. Same rationale as the upload/download
+services for going native instead of a Dart background-task plugin (see
+above): a periodic job has to run without the Flutter engine loaded, and a
+notification action has to resolve without launching the UI. Rather than
+add `workmanager` (whose Dart `callbackDispatcher` spins up a second,
+minimal Flutter engine that has to re-register every plugin it touches),
+the whole engine is plain Kotlin using Android's WorkManager directly.
+
+- [`SyncEngine.kt`](../../android/app/src/main/kotlin/dev/ayushya/noo/SyncEngine.kt)
+  holds the shared primitives, reused by both workers below: a Depth-1 (or
+  Depth-0, for refreshing one item) PROPFIND (`propfindChildren`/
+  `propfindSelf`) requesting `d:getetag` alongside the usual props - unlike
+  every PROPFIND in `nextcloud_service.dart`, which never requests it
+  (`etag` is a dead field on `NextcloudItem` today); plain
+  `HttpURLConnection` GET/PUT (`downloadFile`/`uploadFile`, same style as
+  `DownloadService.kt`/`ShareUploadService.kt`); and `diffFolder`, which
+  compares one folder's freshly-walked manifest against the persisted
+  per-account sync-state map (native `SharedPreferences`, JSON keyed by
+  `oc:fileid` - stable across renames/moves, unlike `path`) to decide, per
+  file: download (new, or server `etag` changed), upload (local file's
+  mtime/size changed and the server didn't), delete locally (missing
+  server-side, unchanged locally), respect a local deletion (file's gone
+  and the server didn't change either - don't recreate it), or flag a
+  **conflict** (both changed since the last recorded state).
+- [`SyncWorker.kt`](../../android/app/src/main/kotlin/dev/ayushya/noo/SyncWorker.kt)
+  (`CoroutineWorker`) is both the periodic job and the one-off "Sync now":
+  for each configured path, `propfindSelf`s it first to check whether it's
+  a file or a folder - a folder gets the full recursive
+  `walkRemoteTree`, a file is diffed directly as a one-item list (nothing
+  else about `diffFolder`/download/upload/delete cares whether its entries
+  came from a walk or a single lookup, so single-file sync needed no engine
+  changes, just this one branch) - applies `diffFolder`'s decisions, then
+  posts a summary notification (files updated/uploaded/removed) and, for
+  any conflicts, one notification per file with two actions.
+- **Live status reaches Dart via a push channel, not polling** -
+  [`SyncStatusBus.kt`](../../android/app/src/main/kotlin/dev/ayushya/noo/SyncStatusBus.kt)
+  is a plain in-process pub/sub (no IPC needed - the workers and
+  `MainActivity` share one process) that `SyncWorker`/`ConflictResolveWorker`
+  publish into (syncing started/stopped, which `fileId`s are mid-transfer
+  right now, new/resolved conflicts) and `MainActivity.kt`'s
+  `dev.ayushya.noo/sync_service/status` `EventChannel` forwards to Dart,
+  same pattern as the share/pick-intent channels. It deliberately does
+  *not* track "which files are already synced" itself - that's read fresh
+  from `SyncEngine`'s durable per-account state map
+  (`SyncEngine.loadState(accountId).keys`) each time a snapshot is built,
+  so there's one source of truth for "synced" instead of two that could
+  drift. `SyncService.getStatus()` (one-shot, seeds `ServerProvider` right
+  after login/account-switch) and `SyncService.statusStream` (live) both
+  return the same snapshot shape. `ServerProvider.syncHeaderStatus`
+  (off/syncing/done/alert - drives `SyncedHeaderScaffold`'s persistent
+  chip/panel, replacing what used to be the WebDAV-refresh-loading
+  indicator there) and `syncStatusFor(item)` (none/syncing/synced/conflict
+  - drives the small corner badge on Files' tiles, `SyncStatusBadge`) are
+  both computed from this state, not fetched per-item.
+- **In-app conflict resolution reuses the exact same enqueue path as the
+  notification actions** - `ConflictResolveWorker.enqueue(...)` is a
+  shared companion function; `SyncConflictReceiver` (the notification
+  action) and `MainActivity.kt`'s `resolveConflict` MethodChannel method
+  (the sync header's "Keep local"/"Use server" buttons,
+  `ServerProvider.resolveSyncConflict`) both just call it, so there's one
+  resolution code path regardless of which surface triggered it.
+- **Conflicts are never auto-resolved.** The notification's "Keep local"/
+  "Use server" actions are `PendingIntent.getBroadcast`s (same shape as the
+  Cancel action on upload/download notifications, just broadcast instead of
+  service-targeted) to
+  [`SyncConflictReceiver`](../../android/app/src/main/kotlin/dev/ayushya/noo/SyncConflictReceiver.kt)
+  - a manifest-registered `BroadcastReceiver` (works even with the app
+  process dead) that can't itself block on network, so it just dismisses
+  the notification and enqueues a one-shot
+  [`ConflictResolveWorker`](../../android/app/src/main/kotlin/dev/ayushya/noo/ConflictResolveWorker.kt)
+  to actually push the local copy up or pull the server copy down and
+  refresh that file's recorded state.
+- `MainActivity.kt`'s `dev.ayushya.noo/sync_service` channel
+  (`reschedule`/`cancel`/`syncNow`) is the only bridge from Dart: a periodic
+  `WorkRequest`'s input `Data` and `Constraints` are fixed at enqueue time,
+  so changing the synced-folder list, the active account, or the Wi-Fi-only
+  setting means cancelling and re-enqueueing, not updating in place.
+  [`SyncService`](../../lib/services/sync_service.dart) (Dart) wraps this -
+  `ServerProvider` calls `reschedule` after every successful login/account
+  switch and every synced-folder/`syncOnCellular` change, and `cancel` on
+  logout/last-account-removed. The network constraint is
+  `NetworkType.UNMETERED` by default (`!syncOnCellular`, Wi-Fi only) or
+  `NetworkType.CONNECTED` if the user's opted into cellular sync.
+- Synced-path list (`ServerProvider.syncedPaths` - files or folders, not
+  just folders despite the name of the underlying pref/native `Data` key,
+  which stayed `ui_synced_folders`/`folders` to avoid a storage-key
+  migration for a rename) follows the standard per-account-pref pattern
+  (JSON-encoded string list, in `AccountStore.perAccountPrefKeys`); so does
+  `syncEverything` (`ui_sync_everything`, per account) - when on,
+  `SyncService` sends `['/']` as the path list instead of `syncedPaths`,
+  mirroring the whole account rather than requiring per-item opt-in.
+  `syncOnCellular` is a plain global pref. All three are managed from
+  Settings → Device Sync (a "Sync everything" switch, the path list with
+  remove buttons - hidden while "Sync everything" is on - the cellular
+  toggle, and a manual "Sync now"); individual files or folders are
+  additionally toggled from Files' selection toolbar ("Sync to device",
+  single-selection, either item type).
+- **`android/app/proguard-rules.pro` exists specifically for this feature,
+  and keeps `androidx.work.**` wholesale rather than naming individual
+  classes.** Flutter's own Gradle plugin auto-enables R8 minification for
+  release builds (`FlutterPlugin.kt` sets `isMinifyEnabled = true`
+  unconditionally for the `release` build type, and auto-wires this exact
+  file if it exists - nothing in this project's own `build.gradle.kts`
+  opts into it), which broke device sync on real-device testing **twice**
+  in a row: first `WorkDatabase` (WorkManager locates its bundled Room
+  database by reflecting off the abstract database class's own,
+  possibly-renamed, name), then - after narrowly keeping just that class -
+  `OverwritingInputMerger` (WorkManager's default input merger, also
+  reflection-instantiated) broke the exact same way and silently ate every
+  `enqueueUniqueWork` call, including "Sync now", with zero indication
+  beyond a `WM-InputMerger` `NoSuchMethodException` in logcat - no crash,
+  no Dart-visible error, just a folder that stayed empty. R8's member-level
+  shrinking strips whatever a class's *reflection-only* callers don't
+  reference directly, even when the class itself survives a plain `-keep
+  class` with no wildcard, and WorkManager reflects into more of its own
+  internals than any one test pass is likely to exercise - hence the
+  wholesale keep instead of chasing individual classes one crash at a
+  time. If adding another native background component reached only via
+  reflection (not a manifest-declared component, which AGP already keeps
+  automatically), don't assume default AndroidX consumer rules cover it -
+  verify on an actual release build, not just `flutter analyze`/a debug
+  build, since minification only applies to release.
+- **Files land under `Android/data/<package>/files/sync/...`
+  (`getExternalFilesDir`), which no third-party file manager can browse
+  without root** - Android's scoped storage sandboxes that whole directory
+  tree from other apps by design, same as any app-private storage. This
+  surprised real-device testing (a file manager app logged "Can't read
+  directory ... trying su" and came up empty even though the sync had
+  actually worked) - it's expected, not a bug. Confirm synced files
+  landed via `adb shell run-as`/a rooted shell, not a regular file
+  manager UI.
+- **Already-synced files skip the network** in two places:
+  `ServerProvider.localSyncedFilePath(item)` is a pure function of the
+  remote path (mirrors `SyncEngine.kt`'s `syncRoot` layout exactly, so Dart
+  never needs to read the native sync-state `SharedPreferences`) that
+  returns the local mirror path if it exists on disk. `ShareSheet`'s "Share
+  file directly" and `FilesView._downloadSelected` (only when *every*
+  selected file is already synced - a mixed selection still goes through
+  the normal `DownloadService` batch) both check it first.
+
 ## Multi-account storage & session persistence
 
 [`AccountStore`](../../lib/services/account_store.dart) owns everything

.claude/context/styling.md

@@ -63,7 +63,17 @@ widgets. Key points:
 - [`SyncedHeaderScaffold`](../../lib/widgets/synced_header_scaffold.dart) —
   the pull-to-sync `CustomScrollView` header shared by 5 of the 6 tabs (see
   `architecture.md`); also where the pull-to-refresh gesture thresholds and
-  the classic Material refresh spinner live.
+  the classic Material refresh spinner live. Its persistent chip/panel
+  (icon + "Sync off"/"Syncing…"/"Synced"/"Sync issue") reflects device-sync
+  status (`ServerProvider.syncHeaderStatus`), not the WebDAV-refresh
+  loading state the pull gesture itself triggers - that has its own,
+  separate floating spinner bubble, so nothing was lost by handing the
+  persistent text/icon over.
+- [`SyncStatusBadge`](../../lib/widgets/sync_status_badge.dart) — the small
+  corner badge over a thumbnail showing per-item device-sync status
+  (`cloud_done`/`sync`, nothing for not-synced/conflict); used in Files'
+  list and grid tiles today. Reuse this rather than a new ad hoc badge if
+  another view starts showing sync status per item.
 - [`SeekBarPainter`/`SeekBarPreview`](../../lib/widgets/seek_bar_painter.dart)
   — the four `MediaProgressBarStyle` presets (Default/Wavy/Slim/Squiggly)
   for the video player's seek bar, plus a perpetually-animated

android/app/build.gradle.kts

@@ -84,6 +84,18 @@ kotlin {
     }
 }
 
+dependencies {
+    // Device sync's periodic/one-off background jobs (SyncWorker,
+    // ConflictResolveWorker) - see their doc comments for why this is
+    // plain WorkManager rather than a Dart-side background-task plugin.
+    implementation("androidx.work:work-runtime-ktx:2.9.1")
+    // PROPFIND (WebDAV directory listing) - Android's HttpURLConnection
+    // hard-rejects any method outside {OPTIONS,GET,HEAD,POST,PUT,DELETE,
+    // TRACE,PATCH} (ProtocolException), unlike plain OpenJDK. OkHttp has
+    // no such whitelist. See SyncEngine.kt.
+    implementation("com.squareup.okhttp3:okhttp:4.12.0")
+}
+
 flutter {
     source = "../.."
 }

android/app/proguard-rules.pro

@@ -0,0 +1,18 @@
+# Device sync (SyncWorker/ConflictResolveWorker) - WorkManager instantiates
+# a lot of its own internals via reflection (Workers by class name recorded
+# at enqueue time, its bundled Room database's *_Impl class off the
+# abstract database class's own name, its default InputMerger, etc). R8's
+# member-level shrinking silently breaks any of these - e.g. stripping an
+# "unused" no-arg constructor - even when the class itself survives a
+# plain `-keep class` with no wildcard, and narrowly keeping only the
+# classes hit by one test pass just means the next reflection path (a
+# different WorkManager-internal class) breaks instead. Two separate
+# instances of this already bit real testing (WorkDatabase, then
+# OverwritingInputMerger) before landing on this broad keep - see
+# android/app/build.gradle.kts (androidx.work dependency) and
+# .claude/context/server.md's "Device sync" section.
+-keep class androidx.work.** { *; }
+-keep class * extends androidx.room.RoomDatabase { *; }
+-keep class dev.ayushya.noo.SyncWorker { *; }
+-keep class dev.ayushya.noo.ConflictResolveWorker { *; }
+-keep class dev.ayushya.noo.SyncConflictReceiver { *; }

android/app/src/main/AndroidManifest.xml

@@ -76,6 +76,13 @@
             android:name=".DownloadService"
             android:exported="false"
             android:foregroundServiceType="dataSync"/>
+        <!-- The "Keep local"/"Use server" actions on a sync-conflict
+             notification (SyncWorker/SyncEngine) - must be a manifest-
+             registered receiver, not a runtime-registered one, since it
+             needs to work even when the app process isn't running. -->
+        <receiver
+            android:name=".SyncConflictReceiver"
+            android:exported="false"/>
         <!-- Hands back the file(s) a caller picked via the GET_CONTENT filter
              above - only the app's own cache/picker/ subfolder is exposed,
              see file_paths.xml. -->

android/app/src/main/kotlin/dev/ayushya/noo/ConflictResolveWorker.kt

@@ -0,0 +1,101 @@
+package dev.ayushya.noo
+
+import android.content.Context
+import androidx.work.CoroutineWorker
+import androidx.work.OneTimeWorkRequestBuilder
+import androidx.work.WorkManager
+import androidx.work.WorkerParameters
+import androidx.work.workDataOf
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import java.io.File
+
+/**
+ * Resolves one sync conflict, triggered either by [SyncConflictReceiver]
+ * (a notification action) or directly from Dart (in-app resolution via the
+ * `dev.ayushya.noo/sync_service` MethodChannel's `resolveConflict`, see
+ * `MainActivity.kt`) - "local" pushes the on-device copy up (overwriting
+ * the server), "server" pulls the server copy down (overwriting the local
+ * mirror). Either way, the sync-state entry for this file is refreshed
+ * afterward so the next [SyncWorker] pass doesn't immediately re-flag it.
+ */
+class ConflictResolveWorker(appContext: Context, params: WorkerParameters) :
+    CoroutineWorker(appContext, params) {
+
+    companion object {
+        const val KEY_ACCOUNT_ID = "accountId"
+        const val KEY_SERVER_URL = "serverUrl"
+        const val KEY_USERNAME = "username"
+        const val KEY_AUTH_HEADER = "authHeader"
+        const val KEY_FILE_ID = "fileId"
+        const val KEY_REMOTE_PATH = "remotePath"
+        const val KEY_REL_PATH = "relPath"
+        const val KEY_RESOLUTION = "resolution"
+
+        /** The one place a resolution gets enqueued - both callers above share it. */
+        fun enqueue(
+            context: Context,
+            accountId: String?,
+            serverUrl: String?,
+            username: String?,
+            authHeader: String?,
+            fileId: String?,
+            remotePath: String?,
+            relPath: String?,
+            resolution: String?,
+        ) {
+            val data = workDataOf(
+                KEY_ACCOUNT_ID to accountId,
+                KEY_SERVER_URL to serverUrl,
+                KEY_USERNAME to username,
+                KEY_AUTH_HEADER to authHeader,
+                KEY_FILE_ID to fileId,
+                KEY_REMOTE_PATH to remotePath,
+                KEY_REL_PATH to relPath,
+                KEY_RESOLUTION to resolution,
+            )
+            val request = OneTimeWorkRequestBuilder<ConflictResolveWorker>()
+                .setInputData(data)
+                .build()
+            WorkManager.getInstance(context).enqueue(request)
+        }
+    }
+
+    override suspend fun doWork(): Result = withContext(Dispatchers.IO) {
+        val accountId = inputData.getString(KEY_ACCOUNT_ID) ?: return@withContext Result.failure()
+        val serverUrl = inputData.getString(KEY_SERVER_URL) ?: return@withContext Result.failure()
+        val username = inputData.getString(KEY_USERNAME) ?: return@withContext Result.failure()
+        val authHeader = inputData.getString(KEY_AUTH_HEADER) ?: return@withContext Result.failure()
+        val fileId = inputData.getString(KEY_FILE_ID) ?: return@withContext Result.failure()
+        val remotePath = inputData.getString(KEY_REMOTE_PATH) ?: return@withContext Result.failure()
+        val relPath = inputData.getString(KEY_REL_PATH) ?: return@withContext Result.failure()
+        val resolution = inputData.getString(KEY_RESOLUTION) ?: return@withContext Result.failure()
+
+        val syncRoot = SyncEngine.syncRoot(applicationContext, accountId)
+        val localFile = File(syncRoot, relPath)
+        val ok = when (resolution) {
+            "local" -> localFile.exists() &&
+                SyncEngine.uploadFile(serverUrl, username, authHeader, remotePath, localFile)
+            "server" -> SyncEngine.downloadFile(serverUrl, username, authHeader, remotePath, localFile)
+            else -> false
+        }
+        if (!ok) return@withContext Result.retry()
+
+        // Refresh the recorded state from the server's post-resolution
+        // etag, so this file isn't immediately re-flagged as a conflict on
+        // the next sync pass.
+        val fresh = SyncEngine.propfindSelf(serverUrl, username, authHeader, remotePath)
+        val state = SyncEngine.loadState(applicationContext, accountId).toMutableMap()
+        state[fileId] = SyncEngine.FileState(
+            relPath = relPath,
+            etag = fresh?.etag ?: "",
+            lastModified = fresh?.lastModified ?: 0L,
+            size = localFile.length(),
+            localMTime = localFile.lastModified(),
+        )
+        SyncEngine.saveState(applicationContext, accountId, state)
+        SyncStatusBus.removeConflict(accountId, fileId)
+
+        Result.success()
+    }
+}

android/app/src/main/kotlin/dev/ayushya/noo/MainActivity.kt

@@ -12,12 +12,22 @@ import android.provider.OpenableColumns
 import androidx.core.app.ActivityCompat
 import androidx.core.content.ContextCompat
 import androidx.core.content.FileProvider
+import androidx.work.Constraints
+import androidx.work.ExistingPeriodicWorkPolicy
+import androidx.work.ExistingWorkPolicy
+import androidx.work.NetworkType
+import androidx.work.OneTimeWorkRequestBuilder
+import androidx.work.PeriodicWorkRequestBuilder
+import androidx.work.WorkManager
+import androidx.work.workDataOf
 import io.flutter.embedding.android.FlutterFragmentActivity
 import io.flutter.embedding.engine.FlutterEngine
 import io.flutter.plugin.common.EventChannel
 import io.flutter.plugin.common.MethodCall
 import io.flutter.plugin.common.MethodChannel
+import org.json.JSONArray
 import java.io.File
+import java.util.concurrent.TimeUnit
 
 // FlutterFragmentActivity (not the default FlutterActivity) is required by
 // local_auth's Android implementation, which hosts its biometric/device
@@ -44,6 +54,8 @@ class MainActivity : FlutterFragmentActivity() {
     private val downloadServiceChannelName = "dev.ayushya.noo/download_service"
     private val pickIntentChannelName = "dev.ayushya.noo/pick_intent"
     private val newPickChannelName = "dev.ayushya.noo/pick_intent/new"
+    private val syncServiceChannelName = "dev.ayushya.noo/sync_service"
+    private val syncStatusChannelName = "dev.ayushya.noo/sync_service/status"
     private val notificationPermissionRequestCode = 4202
     // Lazy, not a field initializer - `packageName` reads through the
     // Activity's base Context, which isn't attached yet while this class's
@@ -53,6 +65,7 @@ class MainActivity : FlutterFragmentActivity() {
     private val mainHandler = Handler(Looper.getMainLooper())
     private var newShareSink: EventChannel.EventSink? = null
     private var newPickSink: EventChannel.EventSink? = null
+    private var syncStatusListener: ((SyncStatusBus.Status) -> Unit)? = null
 
     override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
         super.configureFlutterEngine(flutterEngine)
@@ -114,6 +127,74 @@ class MainActivity : FlutterFragmentActivity() {
                     newPickSink = null
                 }
             })
+
+        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, syncServiceChannelName)
+            .setMethodCallHandler { call, result ->
+                when (call.method) {
+                    "reschedule" -> rescheduleSyncWork(call, result)
+                    "cancel" -> cancelSyncWork(result)
+                    "syncNow" -> syncNow(call, result)
+                    "getSyncStatus" -> result.success(syncStatusMap(SyncStatusBus.snapshot()))
+                    "resolveConflict" -> resolveConflict(call, result)
+                    else -> result.notImplemented()
+                }
+            }
+
+        EventChannel(flutterEngine.dartExecutor.binaryMessenger, syncStatusChannelName)
+            .setStreamHandler(object : EventChannel.StreamHandler {
+                override fun onListen(arguments: Any?, events: EventChannel.EventSink) {
+                    val listener: (SyncStatusBus.Status) -> Unit = { status ->
+                        mainHandler.post { events.success(syncStatusMap(status)) }
+                    }
+                    syncStatusListener = listener
+                    SyncStatusBus.subscribe(listener)
+                }
+                override fun onCancel(arguments: Any?) {
+                    syncStatusListener?.let { SyncStatusBus.unsubscribe(it) }
+                    syncStatusListener = null
+                }
+            })
+    }
+
+    private fun syncStatusMap(status: SyncStatusBus.Status): Map<String, Any?> {
+        val syncedFileIds = status.accountId?.let {
+            SyncEngine.loadState(applicationContext, it).keys.toList()
+        } ?: emptyList()
+        return mapOf(
+            "accountId" to status.accountId,
+            "syncing" to status.syncing,
+            "syncingFileIds" to status.syncingFileIds.toList(),
+            "syncedFileIds" to syncedFileIds,
+            "conflicts" to status.conflicts.map {
+                mapOf(
+                    "accountId" to it.accountId,
+                    "fileId" to it.fileId,
+                    "remotePath" to it.remotePath,
+                    "relPath" to it.relPath,
+                    "name" to it.name,
+                )
+            },
+        )
+    }
+
+    /// In-app conflict resolution (the header's "Keep local"/"Use server"
+    /// buttons) - shares [ConflictResolveWorker.enqueue] with
+    /// [SyncConflictReceiver], the only other caller, so there's one
+    /// resolution code path regardless of whether it's triggered from a
+    /// notification or from inside the app.
+    private fun resolveConflict(call: MethodCall, result: MethodChannel.Result) {
+        ConflictResolveWorker.enqueue(
+            this,
+            accountId = call.argument<String>("accountId"),
+            serverUrl = call.argument<String>("serverUrl"),
+            username = call.argument<String>("username"),
+            authHeader = call.argument<String>("authHeader"),
+            fileId = call.argument<String>("fileId"),
+            remotePath = call.argument<String>("remotePath"),
+            relPath = call.argument<String>("relPath"),
+            resolution = call.argument<String>("resolution"),
+        )
+        result.success(null)
     }
 
     override fun onNewIntent(intent: Intent) {
@@ -262,6 +343,85 @@ class MainActivity : FlutterFragmentActivity() {
         result.success(null)
     }
 
+    /// Shared arg-parsing for `reschedule`/`syncNow` - both need the same
+    /// account/credentials/folder-list shape, just enqueue differently.
+    private fun syncWorkData(call: MethodCall): androidx.work.Data? {
+        val accountId = call.argument<String>("accountId")
+        val serverUrl = call.argument<String>("serverUrl")
+        val username = call.argument<String>("username")
+        val authHeader = call.argument<String>("authHeader")
+        val foldersJson = call.argument<String>("folders")
+        if (accountId == null || serverUrl == null || username == null ||
+            authHeader == null || foldersJson == null
+        ) {
+            return null
+        }
+        return workDataOf(
+            SyncWorker.KEY_ACCOUNT_ID to accountId,
+            SyncWorker.KEY_SERVER_URL to serverUrl,
+            SyncWorker.KEY_USERNAME to username,
+            SyncWorker.KEY_AUTH_HEADER to authHeader,
+            SyncWorker.KEY_FOLDERS to foldersJson,
+        )
+    }
+
+    /// Re-enqueues (or cancels, if the folder list is now empty) the
+    /// periodic device-sync job - called from Dart whenever the synced-
+    /// folder list, active account, or Wi-Fi-only setting changes, since a
+    /// periodic WorkRequest's input Data/constraints are fixed at enqueue
+    /// time and can only be changed by cancelling and re-enqueueing.
+    private fun rescheduleSyncWork(call: MethodCall, result: MethodChannel.Result) {
+        val data = syncWorkData(call)
+        val foldersJson = call.argument<String>("folders")
+        val wifiOnly = call.argument<Boolean>("wifiOnly") ?: true
+        val workManager = WorkManager.getInstance(this)
+
+        if (data == null || foldersJson == null || JSONArray(foldersJson).length() == 0) {
+            workManager.cancelUniqueWork(SyncWorker.UNIQUE_PERIODIC_NAME)
+            result.success(null)
+            return
+        }
+
+        val constraints = Constraints.Builder()
+            .setRequiredNetworkType(if (wifiOnly) NetworkType.UNMETERED else NetworkType.CONNECTED)
+            .build()
+        // 1 hour is WorkManager's own practical floor for a "battery-
+        // friendly" cadence well above its hard 15-minute minimum; there's
+        // no per-user interval setting for this in v1.
+        val request = PeriodicWorkRequestBuilder<SyncWorker>(1, TimeUnit.HOURS)
+            .setInputData(data)
+            .setConstraints(constraints)
+            .build()
+        workManager.enqueueUniquePeriodicWork(
+            SyncWorker.UNIQUE_PERIODIC_NAME,
+            ExistingPeriodicWorkPolicy.UPDATE,
+            request,
+        )
+        result.success(null)
+    }
+
+    private fun cancelSyncWork(result: MethodChannel.Result) {
+        WorkManager.getInstance(this).cancelUniqueWork(SyncWorker.UNIQUE_PERIODIC_NAME)
+        result.success(null)
+    }
+
+    /// One-off immediate run (Settings' "Sync now"), independent of the
+    /// periodic schedule.
+    private fun syncNow(call: MethodCall, result: MethodChannel.Result) {
+        val data = syncWorkData(call)
+        if (data == null) {
+            result.error("bad_args", "Missing required sync arguments", null)
+            return
+        }
+        val request = OneTimeWorkRequestBuilder<SyncWorker>().setInputData(data).build()
+        WorkManager.getInstance(this).enqueueUniqueWork(
+            SyncWorker.UNIQUE_ONE_OFF_NAME,
+            ExistingWorkPolicy.REPLACE,
+            request,
+        )
+        result.success(null)
+    }
+
     /// Non-null only when this Activity was launched (or re-delivered a new
     /// Intent) as another app's GET_CONTENT picker - the mimeType filter and
     /// multi-select flag the caller asked for, plus a best-effort display

android/app/src/main/kotlin/dev/ayushya/noo/SyncConflictReceiver.kt

@@ -0,0 +1,49 @@
+package dev.ayushya.noo
+
+import android.content.BroadcastReceiver
+import android.content.Context
+import android.content.Intent
+import androidx.core.app.NotificationManagerCompat
+
+/**
+ * Handles the "Keep local" / "Use server" actions on a sync-conflict
+ * notification (see `SyncWorker.notifyConflicts`). A `BroadcastReceiver`
+ * can't block on network itself (~10s execution budget), so this only
+ * dismisses the notification and hands off to a one-shot
+ * [ConflictResolveWorker] for the actual upload/download.
+ */
+class SyncConflictReceiver : BroadcastReceiver() {
+    companion object {
+        const val ACTION_RESOLVE = "dev.ayushya.noo.action.RESOLVE_SYNC_CONFLICT"
+        const val EXTRA_ACCOUNT_ID = "accountId"
+        const val EXTRA_SERVER_URL = "serverUrl"
+        const val EXTRA_USERNAME = "username"
+        const val EXTRA_AUTH_HEADER = "authHeader"
+        const val EXTRA_FILE_ID = "fileId"
+        const val EXTRA_REMOTE_PATH = "remotePath"
+        const val EXTRA_REL_PATH = "relPath"
+        const val EXTRA_RESOLUTION = "resolution" // "local" | "server"
+        const val EXTRA_NOTIFICATION_ID = "notificationId"
+    }
+
+    override fun onReceive(context: Context, intent: Intent) {
+        if (intent.action != ACTION_RESOLVE) return
+
+        val notificationId = intent.getIntExtra(EXTRA_NOTIFICATION_ID, -1)
+        if (notificationId != -1) {
+            NotificationManagerCompat.from(context).cancel(notificationId)
+        }
+
+        ConflictResolveWorker.enqueue(
+            context,
+            accountId = intent.getStringExtra(EXTRA_ACCOUNT_ID),
+            serverUrl = intent.getStringExtra(EXTRA_SERVER_URL),
+            username = intent.getStringExtra(EXTRA_USERNAME),
+            authHeader = intent.getStringExtra(EXTRA_AUTH_HEADER),
+            fileId = intent.getStringExtra(EXTRA_FILE_ID),
+            remotePath = intent.getStringExtra(EXTRA_REMOTE_PATH),
+            relPath = intent.getStringExtra(EXTRA_REL_PATH),
+            resolution = intent.getStringExtra(EXTRA_RESOLUTION),
+        )
+    }
+}

android/app/src/main/kotlin/dev/ayushya/noo/SyncEngine.kt

@@ -0,0 +1,399 @@
+package dev.ayushya.noo
+
+import android.content.Context
+import android.net.Uri
+import android.util.Log
+import okhttp3.MediaType.Companion.toMediaType
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.RequestBody.Companion.toRequestBody
+import org.json.JSONArray
+import org.json.JSONObject
+import java.io.File
+import java.net.HttpURLConnection
+import java.net.URL
+import java.text.SimpleDateFormat
+import java.util.Locale
+import java.util.concurrent.TimeUnit
+import javax.xml.parsers.DocumentBuilderFactory
+import org.w3c.dom.Element
+
+/**
+ * The actual WebDAV walk/diff/GET/PUT engine for device sync - shared by
+ * [SyncWorker] (periodic/manual full-folder sync) and
+ * [ConflictResolveWorker] (single-file resolution from a notification
+ * action), since both need the same PROPFIND/GET/PUT primitives and the
+ * same on-disk sync-state bookkeeping.
+ *
+ * Deliberately plain Kotlin over `HttpURLConnection`, not
+ * `NextcloudService`'s Dart/Dio code - this has to run from a
+ * [androidx.work.CoroutineWorker], independent of the Flutter engine even
+ * being loaded, the same reason `DownloadService.kt`/`ShareUploadService.kt`
+ * re-implement GET/PUT natively instead of calling back into Dart.
+ */
+object SyncEngine {
+    data class RemoteEntry(
+        val path: String,
+        val fileId: String,
+        val etag: String,
+        val lastModified: Long,
+        val size: Long,
+        val isFolder: Boolean,
+    )
+
+    data class FileState(
+        val relPath: String,
+        val etag: String,
+        val lastModified: Long,
+        val size: Long,
+        val localMTime: Long,
+    )
+
+    sealed class SyncAction {
+        data class Download(val entry: RemoteEntry) : SyncAction()
+        data class Upload(val relPath: String, val fileId: String) : SyncAction()
+        data class Delete(val relPath: String, val fileId: String) : SyncAction()
+        data class Conflict(val entry: RemoteEntry, val relPath: String) : SyncAction()
+    }
+
+    private const val TAG = "NooSync"
+    private const val STATE_PREFS = "noo_sync_state"
+    private val rfc1123 =
+        SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz", Locale.US)
+
+    // Only used for PROPFIND - unlike HttpURLConnection, OkHttp doesn't
+    // reject non-standard HTTP methods.
+    private val httpClient = OkHttpClient.Builder()
+        .connectTimeout(15, TimeUnit.SECONDS)
+        .readTimeout(30, TimeUnit.SECONDS)
+        .build()
+
+    fun syncRoot(context: Context, accountId: String): File {
+        val base = context.getExternalFilesDir(null) ?: context.filesDir
+        return File(base, "sync/$accountId").apply { mkdirs() }
+    }
+
+    private fun stateKey(accountId: String) = "state_$accountId"
+
+    fun loadState(context: Context, accountId: String): MutableMap<String, FileState> {
+        val prefs = context.getSharedPreferences(STATE_PREFS, Context.MODE_PRIVATE)
+        val json = prefs.getString(stateKey(accountId), null) ?: return mutableMapOf()
+        val obj = JSONObject(json)
+        val result = mutableMapOf<String, FileState>()
+        for (fileId in obj.keys()) {
+            val entry = obj.getJSONObject(fileId)
+            result[fileId] = FileState(
+                relPath = entry.getString("relPath"),
+                etag = entry.getString("etag"),
+                lastModified = entry.getLong("lastModified"),
+                size = entry.getLong("size"),
+                localMTime = entry.getLong("localMTime"),
+            )
+        }
+        return result
+    }
+
+    fun saveState(context: Context, accountId: String, state: Map<String, FileState>) {
+        val obj = JSONObject()
+        for ((fileId, s) in state) {
+            obj.put(
+                fileId,
+                JSONObject().apply {
+                    put("relPath", s.relPath)
+                    put("etag", s.etag)
+                    put("lastModified", s.lastModified)
+                    put("size", s.size)
+                    put("localMTime", s.localMTime)
+                },
+            )
+        }
+        val prefs = context.getSharedPreferences(STATE_PREFS, Context.MODE_PRIVATE)
+        prefs.edit().putString(stateKey(accountId), obj.toString()).apply()
+    }
+
+    /** Depth-1 PROPFIND of [remotePath], returning its direct children only. */
+    fun propfindChildren(
+        serverUrl: String,
+        username: String,
+        authHeader: String,
+        remotePath: String,
+    ): List<RemoteEntry> = propfind(serverUrl, username, authHeader, remotePath, depth = "1", skipSelf = true)
+
+    /** Depth-0 PROPFIND of [remotePath] itself (e.g. to refresh its etag after a PUT/GET). */
+    fun propfindSelf(
+        serverUrl: String,
+        username: String,
+        authHeader: String,
+        remotePath: String,
+    ): RemoteEntry? = propfind(serverUrl, username, authHeader, remotePath, depth = "0", skipSelf = false).firstOrNull()
+
+    private fun propfind(
+        serverUrl: String,
+        username: String,
+        authHeader: String,
+        remotePath: String,
+        depth: String,
+        skipSelf: Boolean,
+    ): List<RemoteEntry> {
+        var cleanPath = remotePath.trim()
+        if (!cleanPath.startsWith("/")) cleanPath = "/$cleanPath"
+        if (depth == "1" && !cleanPath.endsWith("/")) cleanPath = "$cleanPath/"
+        val encodedPath = cleanPath.split("/").joinToString("/") { Uri.encode(it) }
+        val cleanServer = serverUrl.trimEnd('/')
+        val url = "$cleanServer/remote.php/dav/files/$username$encodedPath"
+
+        val body = """<?xml version="1.0" encoding="utf-8" ?>
+<d:propfind xmlns:d="DAV:" xmlns:oc="http://owncloud.org/ns">
+  <d:prop>
+    <d:getlastmodified/>
+    <d:getcontentlength/>
+    <d:resourcetype/>
+    <d:getetag/>
+    <oc:fileid/>
+  </d:prop>
+</d:propfind>"""
+        val request = Request.Builder()
+            .url(url)
+            .method("PROPFIND", body.toRequestBody("application/xml".toMediaType()))
+            .header("Authorization", authHeader)
+            .header("Depth", depth)
+            .build()
+
+        return try {
+            httpClient.newCall(request).execute().use { response ->
+                Log.d(TAG, "PROPFIND $url -> ${response.code}")
+                if (!response.isSuccessful) {
+                    Log.w(TAG, "PROPFIND $url failed: ${response.code} ${response.body?.string()}")
+                    return emptyList()
+                }
+
+                val doc = DocumentBuilderFactory.newInstance()
+                    .apply { isNamespaceAware = true }
+                    .newDocumentBuilder()
+                    .parse(response.body!!.byteStream())
+
+                parsePropfindResponse(doc, username, cleanPath, skipSelf)
+            }
+        } catch (e: Exception) {
+            Log.e(TAG, "PROPFIND $url threw", e)
+            emptyList()
+        }
+    }
+
+    private fun parsePropfindResponse(
+        doc: org.w3c.dom.Document,
+        username: String,
+        cleanPath: String,
+        skipSelf: Boolean,
+    ): List<RemoteEntry> {
+            val marker = "/remote.php/dav/files/$username"
+            val selfPath = cleanPath.trimEnd('/')
+            val responses = doc.getElementsByTagNameNS("DAV:", "response")
+            val entries = mutableListOf<RemoteEntry>()
+            for (i in 0 until responses.length) {
+                val responseEl = responses.item(i) as? Element ?: continue
+                val hrefRaw = responseEl.getElementsByTagNameNS("DAV:", "href")
+                    .item(0)?.textContent ?: continue
+                val decodedHref = Uri.decode(hrefRaw)
+                val idx = decodedHref.indexOf(marker)
+                val hrefPath = if (idx >= 0) decodedHref.substring(idx + marker.length) else decodedHref
+                val hrefPathNorm = (if (hrefPath.isEmpty()) "/" else hrefPath).trimEnd('/')
+                if (skipSelf && hrefPathNorm == selfPath) continue // self entry, not a child
+
+                val propEl = responseEl.getElementsByTagNameNS("DAV:", "prop").item(0) as? Element
+                    ?: continue
+                val resourceTypeEl =
+                    propEl.getElementsByTagNameNS("DAV:", "resourcetype").item(0) as? Element
+                val isFolder =
+                    (resourceTypeEl?.getElementsByTagNameNS("DAV:", "collection")?.length ?: 0) > 0
+                val etag = propEl.getElementsByTagNameNS("DAV:", "getetag")
+                    .item(0)?.textContent?.trim('"') ?: ""
+                val lastModStr =
+                    propEl.getElementsByTagNameNS("DAV:", "getlastmodified").item(0)?.textContent
+                val sizeStr =
+                    propEl.getElementsByTagNameNS("DAV:", "getcontentlength").item(0)?.textContent
+                val fileId = propEl.getElementsByTagNameNS("http://owncloud.org/ns", "fileid")
+                    .item(0)?.textContent ?: hrefPathNorm
+
+                entries.add(
+                    RemoteEntry(
+                        path = hrefPathNorm,
+                        fileId = fileId,
+                        etag = etag,
+                        lastModified = lastModStr?.let { runCatching { rfc1123.parse(it)?.time }.getOrNull() } ?: 0L,
+                        size = sizeStr?.toLongOrNull() ?: 0L,
+                        isFolder = isFolder,
+                    ),
+                )
+            }
+            Log.d(TAG, "PROPFIND $cleanPath -> ${entries.size} entries")
+            return entries
+    }
+
+    /** Recursively walks [rootPath] (Depth-1 PROPFINDs, breadth-first) into a flat manifest. */
+    fun walkRemoteTree(
+        serverUrl: String,
+        username: String,
+        authHeader: String,
+        rootPath: String,
+    ): List<RemoteEntry> {
+        val result = mutableListOf<RemoteEntry>()
+        val queue = ArrayDeque<String>()
+        queue.add(rootPath)
+        while (queue.isNotEmpty()) {
+            val current = queue.removeFirst()
+            val children = propfindChildren(serverUrl, username, authHeader, current)
+            for (child in children) {
+                result.add(child)
+                if (child.isFolder) queue.add(child.path)
+            }
+        }
+        return result
+    }
+
+    fun downloadFile(
+        serverUrl: String,
+        username: String,
+        authHeader: String,
+        remotePath: String,
+        destination: File,
+    ): Boolean {
+        val encodedPath = remotePath.split("/").joinToString("/") { Uri.encode(it) }
+        val url = URL("${serverUrl.trimEnd('/')}/remote.php/dav/files/$username$encodedPath")
+        val connection = url.openConnection() as HttpURLConnection
+        return try {
+            connection.requestMethod = "GET"
+            connection.setRequestProperty("Authorization", authHeader)
+            connection.connectTimeout = 15000
+            connection.readTimeout = 30000
+            connection.connect()
+            val code = connection.responseCode
+            if (code !in 200..299) {
+                Log.w(TAG, "GET $url failed: $code")
+                return false
+            }
+
+            destination.parentFile?.mkdirs()
+            connection.inputStream.use { input ->
+                destination.outputStream().use { output -> input.copyTo(output) }
+            }
+            Log.d(TAG, "GET $url -> saved to ${destination.absolutePath} (${destination.length()} bytes)")
+            true
+        } catch (e: Exception) {
+            Log.e(TAG, "GET $url threw", e)
+            false
+        } finally {
+            connection.disconnect()
+        }
+    }
+
+    fun uploadFile(
+        serverUrl: String,
+        username: String,
+        authHeader: String,
+        remotePath: String,
+        source: File,
+    ): Boolean {
+        val encodedPath = remotePath.split("/").joinToString("/") { Uri.encode(it) }
+        val url = URL("${serverUrl.trimEnd('/')}/remote.php/dav/files/$username$encodedPath")
+        val connection = url.openConnection() as HttpURLConnection
+        return try {
+            connection.requestMethod = "PUT"
+            connection.setRequestProperty("Authorization", authHeader)
+            connection.setFixedLengthStreamingMode(source.length())
+            connection.doOutput = true
+            connection.connectTimeout = 15000
+            connection.readTimeout = 60000
+            connection.connect()
+            source.inputStream().use { input ->
+                connection.outputStream.use { output -> input.copyTo(output) }
+            }
+            connection.responseCode in 200..299
+        } catch (e: Exception) {
+            false
+        } finally {
+            connection.disconnect()
+        }
+    }
+
+    /**
+     * Diffs one synced folder's remote manifest against the persisted
+     * state, returning what to do for each item - callers own actually
+     * doing the GET/PUT/delete and updating state afterward, so this stays
+     * pure/testable-in-principle. Also returns entries no longer present
+     * remotely (deleted server-side, relative to the [priorFolderRelPaths]
+     * this folder previously produced) as [SyncAction.Delete].
+     */
+    fun diffFolder(
+        entries: List<RemoteEntry>,
+        state: Map<String, FileState>,
+        priorFolderFileIds: Set<String>,
+        syncRoot: File,
+    ): List<SyncAction> {
+        val actions = mutableListOf<SyncAction>()
+        val seenFileIds = mutableSetOf<String>()
+
+        for (entry in entries) {
+            if (entry.isFolder) continue
+            seenFileIds.add(entry.fileId)
+            val relPath = entry.path.removePrefix("/")
+            val localFile = File(syncRoot, relPath)
+            val prior = state[entry.fileId]
+
+            if (prior == null) {
+                // First time this folder's been walked with sync enabled -
+                // nothing locally recorded yet to protect, so just pull it.
+                actions.add(SyncAction.Download(entry))
+                continue
+            }
+
+            val serverChanged = entry.etag != prior.etag
+            val localExists = localFile.exists()
+            val localChanged = localExists &&
+                (localFile.lastModified() != prior.localMTime || localFile.length() != prior.size)
+
+            when {
+                !localExists && !serverChanged -> {
+                    // User deleted the local mirror copy themselves and the
+                    // server hasn't changed - respect that deletion rather
+                    // than silently re-creating it.
+                    actions.add(SyncAction.Delete(relPath, entry.fileId))
+                }
+                serverChanged && localChanged -> actions.add(SyncAction.Conflict(entry, relPath))
+                serverChanged -> actions.add(SyncAction.Download(entry))
+                localChanged -> actions.add(SyncAction.Upload(relPath, entry.fileId))
+                else -> {} // unchanged, nothing to do
+            }
+        }
+
+        // Anything this folder had state for last time but that didn't show
+        // up in this walk at all was deleted server-side.
+        for (fileId in priorFolderFileIds) {
+            if (fileId !in seenFileIds) {
+                val prior = state[fileId] ?: continue
+                actions.add(SyncAction.Delete(prior.relPath, fileId))
+            }
+        }
+
+        Log.d(
+            TAG,
+            "diffFolder: ${entries.size} entries -> " +
+                "${actions.count { it is SyncAction.Download }} downloads, " +
+                "${actions.count { it is SyncAction.Upload }} uploads, " +
+                "${actions.count { it is SyncAction.Delete }} deletes, " +
+                "${actions.count { it is SyncAction.Conflict }} conflicts",
+        )
+        return actions
+    }
+
+    fun folderIsSyncedUnder(itemPath: String, syncedFolders: List<String>): String? {
+        val normalizedItem = itemPath.trimEnd('/')
+        for (folder in syncedFolders) {
+            val normalizedFolder = folder.trimEnd('/')
+            if (normalizedItem == normalizedFolder || normalizedItem.startsWith("$normalizedFolder/")) {
+                return folder
+            }
+        }
+        return null
+    }
+}

android/app/src/main/kotlin/dev/ayushya/noo/SyncStatusBus.kt

@@ -0,0 +1,80 @@
+package dev.ayushya.noo
+
+/**
+ * In-memory, in-process pub/sub for live device-sync status -
+ * [SyncWorker]/[ConflictResolveWorker] publish into this, `MainActivity`'s
+ * `dev.ayushya.noo/sync_service/status` EventChannel forwards it to Dart.
+ * Plain in-memory state is enough (no IPC/persistence needed) since the
+ * workers and the Activity always run in the same process; contrast with
+ * [SyncEngine]'s on-disk per-account state map, which *is* durable and is
+ * what actually answers "is this file synced" (this bus only ever tracks
+ * the transient "syncing right now" / "unresolved conflict" parts of that
+ * picture).
+ */
+object SyncStatusBus {
+    data class Conflict(
+        val accountId: String,
+        val fileId: String,
+        val remotePath: String,
+        val relPath: String,
+        val name: String,
+    )
+
+    data class Status(
+        val accountId: String?,
+        val syncing: Boolean,
+        val syncingFileIds: Set<String>,
+        val conflicts: List<Conflict>,
+    )
+
+    @Volatile
+    private var current = Status(accountId = null, syncing = false, syncingFileIds = emptySet(), conflicts = emptyList())
+    private val listeners = mutableListOf<(Status) -> Unit>()
+
+    @Synchronized
+    fun subscribe(listener: (Status) -> Unit) {
+        listeners.add(listener)
+        listener(current)
+    }
+
+    @Synchronized
+    fun unsubscribe(listener: (Status) -> Unit) {
+        listeners.remove(listener)
+    }
+
+    fun snapshot(): Status = current
+
+    @Synchronized
+    fun setSyncing(accountId: String, syncing: Boolean) {
+        current = current.copy(accountId = accountId, syncing = syncing)
+        if (!syncing) current = current.copy(syncingFileIds = emptySet())
+        publish()
+    }
+
+    @Synchronized
+    fun markFileSyncing(accountId: String, fileId: String, syncing: Boolean) {
+        val ids = current.syncingFileIds.toMutableSet()
+        if (syncing) ids.add(fileId) else ids.remove(fileId)
+        current = current.copy(accountId = accountId, syncingFileIds = ids)
+        publish()
+    }
+
+    @Synchronized
+    fun addConflicts(accountId: String, newConflicts: List<Conflict>) {
+        if (newConflicts.isEmpty()) return
+        val existingIds = current.conflicts.map { it.fileId }.toSet()
+        val merged = current.conflicts + newConflicts.filter { it.fileId !in existingIds }
+        current = current.copy(accountId = accountId, conflicts = merged)
+        publish()
+    }
+
+    @Synchronized
+    fun removeConflict(accountId: String, fileId: String) {
+        current = current.copy(accountId = accountId, conflicts = current.conflicts.filter { it.fileId != fileId })
+        publish()
+    }
+
+    private fun publish() {
+        listeners.toList().forEach { it(current) }
+    }
+}

android/app/src/main/kotlin/dev/ayushya/noo/SyncWorker.kt

@@ -0,0 +1,272 @@
+package dev.ayushya.noo
+
+import android.app.Notification
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.app.PendingIntent
+import android.content.Context
+import android.content.Intent
+import android.os.Build
+import android.util.Log
+import androidx.core.app.NotificationCompat
+import androidx.work.CoroutineWorker
+import androidx.work.WorkerParameters
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import org.json.JSONArray
+import java.io.File
+
+/**
+ * The periodic (and manual "Sync now") device-sync job. Runs entirely
+ * independent of the Flutter engine (see [SyncEngine]'s doc comment) -
+ * enqueued/re-enqueued from `MainActivity.kt`'s
+ * `dev.ayushya.noo/sync_service` MethodChannel whenever the synced-folder
+ * list, account, or network setting changes, since a periodic
+ * `WorkRequest`'s input `Data` is fixed at enqueue time.
+ */
+class SyncWorker(appContext: Context, params: WorkerParameters) :
+    CoroutineWorker(appContext, params) {
+
+    companion object {
+        const val KEY_ACCOUNT_ID = "accountId"
+        const val KEY_SERVER_URL = "serverUrl"
+        const val KEY_USERNAME = "username"
+        const val KEY_AUTH_HEADER = "authHeader"
+        const val KEY_FOLDERS = "folders" // JSON array of remote file/folder paths
+
+        const val UNIQUE_PERIODIC_NAME = "noo_sync_periodic"
+        const val UNIQUE_ONE_OFF_NAME = "noo_sync_now"
+
+        private const val CHANNEL_ID = "device_sync"
+        private const val SUMMARY_NOTIFICATION_ID = 4401
+        private const val CONFLICT_NOTIFICATION_ID_BASE = 4500
+        private const val TAG = "NooSync"
+    }
+
+    override suspend fun doWork(): Result = withContext(Dispatchers.IO) {
+        val accountId = inputData.getString(KEY_ACCOUNT_ID) ?: return@withContext Result.failure()
+        val serverUrl = inputData.getString(KEY_SERVER_URL) ?: return@withContext Result.failure()
+        val username = inputData.getString(KEY_USERNAME) ?: return@withContext Result.failure()
+        val authHeader = inputData.getString(KEY_AUTH_HEADER) ?: return@withContext Result.failure()
+        val foldersJson = inputData.getString(KEY_FOLDERS) ?: "[]"
+        val folders = (0 until JSONArray(foldersJson).length()).map { JSONArray(foldersJson).getString(it) }
+        Log.d(TAG, "doWork: account=$accountId server=$serverUrl user=$username folders=$folders")
+        if (folders.isEmpty()) return@withContext Result.success()
+
+        val syncRoot = SyncEngine.syncRoot(applicationContext, accountId)
+        val state = SyncEngine.loadState(applicationContext, accountId).toMutableMap()
+
+        var downloaded = 0
+        var uploaded = 0
+        var deleted = 0
+        val conflicts = mutableListOf<Pair<SyncEngine.RemoteEntry, String>>()
+
+        SyncStatusBus.setSyncing(accountId, true)
+        try {
+            for (path in folders) {
+                // A configured path can be a file or a folder now - check
+                // which before deciding whether to walk it recursively or
+                // just diff the single item.
+                val self = SyncEngine.propfindSelf(serverUrl, username, authHeader, path)
+                val entries = when {
+                    self == null -> emptyList()
+                    self.isFolder -> SyncEngine.walkRemoteTree(serverUrl, username, authHeader, path)
+                    else -> listOf(self)
+                }
+                val pathPrefix = path.trimEnd('/') + "/"
+                val priorFileIdsForPath = state.filterValues {
+                    it.relPath == path.trimStart('/') || it.relPath.startsWith(pathPrefix.trimStart('/'))
+                }.keys
+
+                val actions = SyncEngine.diffFolder(entries, state, priorFileIdsForPath, syncRoot)
+                for (action in actions) {
+                    when (action) {
+                        is SyncEngine.SyncAction.Download -> {
+                            SyncStatusBus.markFileSyncing(accountId, action.entry.fileId, true)
+                            val relPath = action.entry.path.removePrefix("/")
+                            val dest = File(syncRoot, relPath)
+                            if (SyncEngine.downloadFile(serverUrl, username, authHeader, action.entry.path, dest)) {
+                                state[action.entry.fileId] = SyncEngine.FileState(
+                                    relPath = relPath,
+                                    etag = action.entry.etag,
+                                    lastModified = action.entry.lastModified,
+                                    size = action.entry.size,
+                                    localMTime = dest.lastModified(),
+                                )
+                                downloaded++
+                            }
+                            SyncStatusBus.markFileSyncing(accountId, action.entry.fileId, false)
+                        }
+                        is SyncEngine.SyncAction.Upload -> {
+                            SyncStatusBus.markFileSyncing(accountId, action.fileId, true)
+                            val localFile = File(syncRoot, action.relPath)
+                            val remotePath = "/${action.relPath}"
+                            if (localFile.exists() &&
+                                SyncEngine.uploadFile(serverUrl, username, authHeader, remotePath, localFile)
+                            ) {
+                                val prior = state[action.fileId]
+                                state[action.fileId] = SyncEngine.FileState(
+                                    relPath = action.relPath,
+                                    etag = prior?.etag ?: "",
+                                    lastModified = localFile.lastModified(),
+                                    size = localFile.length(),
+                                    localMTime = localFile.lastModified(),
+                                )
+                                uploaded++
+                            }
+                            SyncStatusBus.markFileSyncing(accountId, action.fileId, false)
+                        }
+                        is SyncEngine.SyncAction.Delete -> {
+                            File(syncRoot, action.relPath).delete()
+                            state.remove(action.fileId)
+                            deleted++
+                        }
+                        is SyncEngine.SyncAction.Conflict -> conflicts.add(action.entry to action.relPath)
+                    }
+                }
+            }
+        } finally {
+            SyncStatusBus.setSyncing(accountId, false)
+        }
+
+        SyncEngine.saveState(applicationContext, accountId, state)
+        Log.d(
+            TAG,
+            "doWork done: downloaded=$downloaded uploaded=$uploaded deleted=$deleted conflicts=${conflicts.size}",
+        )
+
+        if (downloaded > 0 || uploaded > 0 || deleted > 0) {
+            notifySummary(downloaded, uploaded, deleted)
+        }
+        if (conflicts.isNotEmpty()) {
+            SyncStatusBus.addConflicts(
+                accountId,
+                conflicts.map { (entry, relPath) ->
+                    SyncStatusBus.Conflict(
+                        accountId = accountId,
+                        fileId = entry.fileId,
+                        remotePath = entry.path,
+                        relPath = relPath,
+                        name = relPath.substringAfterLast('/'),
+                    )
+                },
+            )
+            notifyConflicts(accountId, serverUrl, username, authHeader, conflicts)
+        }
+
+        Result.success()
+    }
+
+    private fun notifySummary(downloaded: Int, uploaded: Int, deleted: Int) {
+        createChannel()
+        val parts = mutableListOf<String>()
+        if (downloaded > 0) parts.add("$downloaded updated")
+        if (uploaded > 0) parts.add("$uploaded uploaded")
+        if (deleted > 0) parts.add("$deleted removed")
+        val text = parts.joinToString(", ")
+
+        val notification = NotificationCompat.Builder(applicationContext, CHANNEL_ID)
+            .setSmallIcon(android.R.drawable.stat_notify_sync)
+            .setContentTitle("Noo sync")
+            .setContentText(text)
+            .setAutoCancel(true)
+            .build()
+        manager().notify(SUMMARY_NOTIFICATION_ID, notification)
+    }
+
+    private fun notifyConflicts(
+        accountId: String,
+        serverUrl: String,
+        username: String,
+        authHeader: String,
+        conflicts: List<Pair<SyncEngine.RemoteEntry, String>>,
+    ) {
+        createChannel()
+        for ((index, conflict) in conflicts.withIndex()) {
+            val (entry, relPath) = conflict
+            val fileName = relPath.substringAfterLast('/')
+            val notificationId = CONFLICT_NOTIFICATION_ID_BASE + (relPath.hashCode() and 0xFFFF)
+
+            val useLocalIntent = conflictActionIntent(
+                accountId,
+                serverUrl,
+                username,
+                authHeader,
+                entry.fileId,
+                entry.path,
+                relPath,
+                "local",
+                notificationId,
+            )
+            val useServerIntent = conflictActionIntent(
+                accountId,
+                serverUrl,
+                username,
+                authHeader,
+                entry.fileId,
+                entry.path,
+                relPath,
+                "server",
+                notificationId,
+            )
+
+            val notification = NotificationCompat.Builder(applicationContext, CHANNEL_ID)
+                .setSmallIcon(android.R.drawable.stat_notify_error)
+                .setContentTitle("Sync conflict: $fileName")
+                .setContentText("Changed both on this device and on the server.")
+                .setAutoCancel(true)
+                .addAction(0, "Keep local", useLocalIntent)
+                .addAction(0, "Use server", useServerIntent)
+                .build()
+            manager().notify(notificationId, notification)
+        }
+    }
+
+    private fun conflictActionIntent(
+        accountId: String,
+        serverUrl: String,
+        username: String,
+        authHeader: String,
+        fileId: String,
+        remotePath: String,
+        relPath: String,
+        resolution: String,
+        notificationId: Int,
+    ): PendingIntent {
+        val intent = Intent(applicationContext, SyncConflictReceiver::class.java).apply {
+            action = SyncConflictReceiver.ACTION_RESOLVE
+            putExtra(SyncConflictReceiver.EXTRA_ACCOUNT_ID, accountId)
+            putExtra(SyncConflictReceiver.EXTRA_SERVER_URL, serverUrl)
+            putExtra(SyncConflictReceiver.EXTRA_USERNAME, username)
+            putExtra(SyncConflictReceiver.EXTRA_AUTH_HEADER, authHeader)
+            putExtra(SyncConflictReceiver.EXTRA_FILE_ID, fileId)
+            putExtra(SyncConflictReceiver.EXTRA_REMOTE_PATH, remotePath)
+            putExtra(SyncConflictReceiver.EXTRA_REL_PATH, relPath)
+            putExtra(SyncConflictReceiver.EXTRA_RESOLUTION, resolution)
+            putExtra(SyncConflictReceiver.EXTRA_NOTIFICATION_ID, notificationId)
+        }
+        // Request code must be unique per (file, resolution) pair, else the
+        // two actions' PendingIntents collide and only one survives.
+        val requestCode = (relPath + resolution).hashCode()
+        return PendingIntent.getBroadcast(
+            applicationContext,
+            requestCode,
+            intent,
+            PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE,
+        )
+    }
+
+    private fun manager() =
+        applicationContext.getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
+
+    private fun createChannel() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            val channel = NotificationChannel(
+                CHANNEL_ID,
+                "Device sync",
+                NotificationManager.IMPORTANCE_DEFAULT,
+            ).apply { description = "Updates and conflicts for folders synced to this device" }
+            manager().createNotificationChannel(channel)
+        }
+    }
+}

lib/models/sync_status.dart

@@ -0,0 +1,38 @@
+/// A pending device-sync conflict (a file changed both locally and on the
+/// server since the last sync) - mirrors `SyncStatusBus.Conflict` on the
+/// native side exactly, see `SyncEngine.kt`/`server.md`'s "Device sync"
+/// section.
+class SyncConflictInfo {
+  final String accountId;
+  final String fileId;
+  final String remotePath;
+  final String relPath;
+  final String name;
+
+  const SyncConflictInfo({
+    required this.accountId,
+    required this.fileId,
+    required this.remotePath,
+    required this.relPath,
+    required this.name,
+  });
+
+  factory SyncConflictInfo.fromMap(Map<dynamic, dynamic> map) {
+    return SyncConflictInfo(
+      accountId: map['accountId'] as String? ?? '',
+      fileId: map['fileId'] as String? ?? '',
+      remotePath: map['remotePath'] as String? ?? '',
+      relPath: map['relPath'] as String? ?? '',
+      name: map['name'] as String? ?? '',
+    );
+  }
+}
+
+/// A single item's device-sync status, used to badge its tile in the
+/// Files view.
+enum SyncItemStatus { none, syncing, synced, conflict }
+
+/// The persistent header chip/panel's overall status (account-wide, not
+/// scoped to whatever folder is currently browsed) - see
+/// `ServerProvider.syncHeaderStatus`.
+enum SyncHeaderStatus { off, syncing, done, alert }

lib/providers/server_provider.dart

@@ -14,11 +14,13 @@ import '../models/nextcloud_share.dart';
 import '../models/nextcloud_sharee.dart';
 import '../models/pick_request.dart';
 import '../models/saved_account.dart';
+import '../models/sync_status.dart';
 import '../services/account_store.dart';
 import '../services/app_lock_service.dart';
 import '../services/login_flow_service.dart';
 import '../services/nextcloud_service.dart';
 import '../services/pick_intent_service.dart';
+import '../services/sync_service.dart';
 import '../theme/app_theme.dart';
 
 enum LoginFlowStatus { idle, initiating, awaitingBrowser, error }
@@ -97,6 +99,9 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
   static const _prefLoginLockEnabled = 'ui_login_lock_enabled';
   static const _prefLockAccountSwitching = 'ui_lock_account_switching';
   static const _prefLockHiddenFiles = 'ui_lock_hidden_files';
+  static const _prefSyncedFolders = 'ui_synced_folders';
+  static const _prefSyncEverything = 'ui_sync_everything';
+  static const _prefSyncOnCellular = 'ui_sync_on_cellular';
 
   final Future<SharedPreferences> _prefsFuture =
       SharedPreferences.getInstance();
@@ -127,6 +132,23 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
   double _bottomBarBlur = 28;
   bool _tapTabToScrollTop = true;
 
+  // Device sync - which remote paths (files or folders, per account) get
+  // mirrored locally by the native SyncWorker, and whether its periodic
+  // background runs are allowed on cellular (default Wi-Fi-only). See
+  // SyncEngine.kt/server.md.
+  List<String> _syncedPaths = [];
+  bool _syncEverything = false;
+  bool _syncOnCellular = false;
+
+  // Live device-sync status, pushed from SyncStatusBus.kt via
+  // SyncService.statusStream (see _subscribeToSyncStatus) - account-wide,
+  // not scoped to whatever folder is currently browsed.
+  bool _isSyncingNow = false;
+  Set<String> _syncingFileIds = {};
+  Set<String> _syncedFileIds = {};
+  List<SyncConflictInfo> _syncConflicts = [];
+  StreamSubscription<SyncStatusSnapshot>? _syncStatusSub;
+
   // App lock (PIN/biometric via the device's own credential, not our own
   // storage - see AppLockService). Global, not per-account: it guards
   // access to the app/its accounts, not any one account's content.
@@ -255,6 +277,7 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
   ServerProvider() {
     WidgetsBinding.instance.addObserver(this);
     _init();
+    _subscribeToSyncStatus();
   }
 
   Future<void> _init() async {
@@ -265,6 +288,29 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
     await Future.wait([_loadPreferences(), _restoreSession()]);
   }
 
+  /// Live device-sync status for the rest of the app's lifetime (not
+  /// re-subscribed per account switch - each event carries its own
+  /// `accountId`, so events for an account that isn't currently active are
+  /// just ignored below). Seeded once via a one-shot snapshot right after
+  /// every successful login/account-switch instead (see
+  /// `_applyCredentialsForAccount`), since events only arrive on change.
+  void _subscribeToSyncStatus() {
+    _syncStatusSub = SyncService.statusStream.listen((snapshot) {
+      _applySyncStatus(snapshot);
+    });
+  }
+
+  void _applySyncStatus(SyncStatusSnapshot snapshot) {
+    if (snapshot.accountId != null && snapshot.accountId != _activeAccountId) {
+      return;
+    }
+    _isSyncingNow = snapshot.syncing;
+    _syncingFileIds = snapshot.syncingFileIds;
+    _syncedFileIds = snapshot.syncedFileIds;
+    _syncConflicts = snapshot.conflicts;
+    notifyListeners();
+  }
+
   /// Starts/stops the periodic folder-listing refresh as the app leaves and
   /// returns to the foreground - only relevant under [CachePolicy.interval].
   /// Also re-locks the app on backgrounding when login lock is set up - a
@@ -323,6 +369,29 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
   bool get lockHiddenFiles => _lockHiddenFiles;
   bool get needsUnlock => _loginLockEnabled && !_isUnlocked;
 
+  List<String> get syncedPaths => List.unmodifiable(_syncedPaths);
+  bool get syncEverything => _syncEverything;
+  bool get syncOnCellular => _syncOnCellular;
+
+  bool get isSyncingNow => _isSyncingNow;
+  List<SyncConflictInfo> get syncConflicts => List.unmodifiable(_syncConflicts);
+
+  SyncHeaderStatus get syncHeaderStatus {
+    if (_syncConflicts.isNotEmpty) return SyncHeaderStatus.alert;
+    if (_isSyncingNow) return SyncHeaderStatus.syncing;
+    if (!_syncEverything && _syncedPaths.isEmpty) return SyncHeaderStatus.off;
+    return SyncHeaderStatus.done;
+  }
+
+  SyncItemStatus syncStatusFor(NextcloudItem item) {
+    if (_syncingFileIds.contains(item.id)) return SyncItemStatus.syncing;
+    if (_syncConflicts.any((c) => c.fileId == item.id)) {
+      return SyncItemStatus.conflict;
+    }
+    if (_syncedFileIds.contains(item.id)) return SyncItemStatus.synced;
+    return SyncItemStatus.none;
+  }
+
   String get currentFolderPath => _currentFolderPath;
   AppTab? get requestedTab => _requestedTab;
 
@@ -621,6 +690,7 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
           prefs.getBool(_prefLockAccountSwitching) ?? _lockAccountSwitching;
       _lockHiddenFiles =
           prefs.getBool(_prefLockHiddenFiles) ?? _lockHiddenFiles;
+      _syncOnCellular = prefs.getBool(_prefSyncOnCellular) ?? _syncOnCellular;
       _applyAccountPrefs(prefs, _activeAccountId);
 
       final savedOrderNames = prefs.getStringList(_prefTabOrder);
@@ -709,6 +779,8 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
       _photosSortAscending = true;
       _cachePolicy = CachePolicy.never;
       _cacheIntervalMinutes = 5;
+      _syncedPaths = [];
+      _syncEverything = false;
       return;
     }
 
@@ -767,6 +839,19 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
       orElse: () => CachePolicy.never,
     );
     _cacheIntervalMinutes = prefs.getInt(k(_prefCacheIntervalMinutes)) ?? 5;
+
+    final syncedFoldersJson = prefs.getString(k(_prefSyncedFolders));
+    if (syncedFoldersJson != null) {
+      try {
+        _syncedPaths = (jsonDecode(syncedFoldersJson) as List).cast<String>();
+      } catch (e) {
+        debugPrint('[ServerProvider] Synced folders restore failed: $e');
+        _syncedPaths = [];
+      }
+    } else {
+      _syncedPaths = [];
+    }
+    _syncEverything = prefs.getBool(k(_prefSyncEverything)) ?? false;
   }
 
   /// Verifies [appPassword] for [account] and, on success, makes it the
@@ -806,6 +891,8 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
         if (gen != _sessionGeneration) return false;
         _isLoading = false;
         notifyListeners();
+        unawaited(SyncService.reschedule(this));
+        unawaited(SyncService.getStatus().then(_applySyncStatus));
         return true;
       }
     } catch (e) {
@@ -1131,7 +1218,12 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
     final prefs = await _prefsFuture;
     await _accountStore.saveActiveAccountId(prefs, null);
     _applyAccountPrefs(prefs, null);
+    _isSyncingNow = false;
+    _syncingFileIds = {};
+    _syncedFileIds = {};
+    _syncConflicts = [];
     notifyListeners();
+    unawaited(SyncService.cancel());
   }
 
   /// Ends the active session but keeps this account saved - unlike
@@ -1473,6 +1565,93 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
     _persistFolderSort();
   }
 
+  void _persistSyncedPaths() {
+    _persistAccountPref(
+      _prefSyncedFolders,
+      (p, key) => p.setString(key, jsonEncode(_syncedPaths)),
+    );
+  }
+
+  bool isPathSynced(String path) => _syncedPaths.contains(path);
+
+  void addSyncedPath(String path) {
+    if (_syncedPaths.contains(path)) return;
+    _syncedPaths = [..._syncedPaths, path];
+    notifyListeners();
+    _persistSyncedPaths();
+    unawaited(SyncService.reschedule(this));
+  }
+
+  void removeSyncedPath(String path) {
+    if (!_syncedPaths.contains(path)) return;
+    _syncedPaths = _syncedPaths.where((f) => f != path).toList();
+    notifyListeners();
+    _persistSyncedPaths();
+    unawaited(SyncService.reschedule(this));
+  }
+
+  void setSyncEverything(bool value) {
+    if (_syncEverything == value) return;
+    _syncEverything = value;
+    notifyListeners();
+    _persistAccountPref(_prefSyncEverything, (p, key) => p.setBool(key, value));
+    unawaited(SyncService.reschedule(this));
+  }
+
+  void setSyncOnCellular(bool value) {
+    if (_syncOnCellular == value) return;
+    _syncOnCellular = value;
+    notifyListeners();
+    _prefsFuture.then((p) => p.setBool(_prefSyncOnCellular, value));
+    unawaited(SyncService.reschedule(this));
+  }
+
+  /// In-app conflict resolution (the sync header's "Keep local"/"Use
+  /// server" buttons) - see `SyncService.resolveConflict`'s doc comment
+  /// for why this shares the exact same native path the notification
+  /// actions use.
+  Future<void> resolveSyncConflict(
+    SyncConflictInfo conflict, {
+    required bool useLocal,
+  }) {
+    return SyncService.resolveConflict(
+      this,
+      conflict,
+      useLocal ? 'local' : 'server',
+    );
+  }
+
+  /// The local mirror path for [item] if it falls under a synced folder
+  /// *and* has actually been synced down already - a pure function of the
+  /// remote path once a folder's marked synced (mirrors
+  /// `SyncEngine.kt#syncRoot`'s `<externalFilesDir>/sync/<accountId>/...`
+  /// layout exactly), so this never needs to read the native sync-state
+  /// SharedPreferences from Dart. Callers (Share/Download) use this to
+  /// skip a fresh WebDAV fetch when a local copy already exists.
+  Future<String?> localSyncedFilePath(NextcloudItem item) async {
+    final id = activeAccountId;
+    if (id == null) return null;
+    final itemPath = item.path.endsWith('/')
+        ? item.path.substring(0, item.path.length - 1)
+        : item.path;
+    final isSynced =
+        _syncEverything ||
+        _syncedPaths.any((folder) {
+          final f = folder.endsWith('/')
+              ? folder.substring(0, folder.length - 1)
+              : folder;
+          return itemPath == f || itemPath.startsWith('$f/');
+        });
+    if (!isSynced) return null;
+    final base = await getExternalStorageDirectory();
+    if (base == null) return null;
+    final relPath = item.path.startsWith('/')
+        ? item.path.substring(1)
+        : item.path;
+    final file = File(p.join(base.path, 'sync', id, relPath));
+    return file.existsSync() ? file.path : null;
+  }
+
   void setTabOrder(List<AppTab> order) {
     _tabOrder = order;
     notifyListeners();
@@ -2154,6 +2333,7 @@ class ServerProvider extends ChangeNotifier with WidgetsBindingObserver {
     _pollTimer?.cancel();
     _pollTimeoutTimer?.cancel();
     _cacheRefreshTimer?.cancel();
+    _syncStatusSub?.cancel();
     super.dispose();
   }
 }

lib/services/account_store.dart

@@ -37,6 +37,8 @@ class AccountStore {
     'ui_files_type_filter',
     'ui_cache_policy',
     'ui_cache_interval_minutes',
+    'ui_synced_folders',
+    'ui_sync_everything',
   ];
 
   String accountPrefKey(String accountId, String baseKey) =>

lib/services/sync_service.dart

@@ -0,0 +1,144 @@
+import 'dart:convert';
+import 'package:flutter/services.dart';
+import '../models/sync_status.dart';
+import '../providers/server_provider.dart';
+
+/// A snapshot of native device-sync status - see `SyncStatusBus.kt` (the
+/// in-process pub/sub it mirrors) and `MainActivity.kt`'s `syncStatusMap`.
+class SyncStatusSnapshot {
+  final String? accountId;
+  final bool syncing;
+  final Set<String> syncingFileIds;
+  final Set<String> syncedFileIds;
+  final List<SyncConflictInfo> conflicts;
+
+  const SyncStatusSnapshot({
+    required this.accountId,
+    required this.syncing,
+    required this.syncingFileIds,
+    required this.syncedFileIds,
+    required this.conflicts,
+  });
+
+  factory SyncStatusSnapshot.fromMap(Map<dynamic, dynamic> map) {
+    return SyncStatusSnapshot(
+      accountId: map['accountId'] as String?,
+      syncing: map['syncing'] as bool? ?? false,
+      syncingFileIds: ((map['syncingFileIds'] as List?) ?? const [])
+          .cast<String>()
+          .toSet(),
+      syncedFileIds: ((map['syncedFileIds'] as List?) ?? const [])
+          .cast<String>()
+          .toSet(),
+      conflicts: ((map['conflicts'] as List?) ?? const [])
+          .cast<Map<dynamic, dynamic>>()
+          .map(SyncConflictInfo.fromMap)
+          .toList(),
+    );
+  }
+}
+
+/// Talks to `SyncWorker`/`SyncEngine.kt`'s Android WorkManager-based device
+/// sync (see `server.md`'s "Device sync" section for the full design) -
+/// Dart's job here is only to gather what the native side needs, push a
+/// fresh config whenever it changes, and listen for live status; the actual
+/// PROPFIND-walk/diff/GET/PUT engine runs entirely in Kotlin, independent
+/// of the Flutter engine.
+class SyncService {
+  static const _channel = MethodChannel('dev.ayushya.noo/sync_service');
+  static const _statusChannel = EventChannel(
+    'dev.ayushya.noo/sync_service/status',
+  );
+
+  /// Cancels (if [ServerProvider.syncedPaths] is now empty) or re-enqueues
+  /// the periodic sync job with fresh account/credentials/path-list/
+  /// network-constraint data - call this any time one of those changes,
+  /// since a periodic `WorkRequest`'s input is fixed at enqueue time and
+  /// can only be updated by re-enqueueing.
+  static Future<void> reschedule(ServerProvider provider) async {
+    final accountId = provider.activeAccountId;
+    final service = provider.service;
+    final authHeader = service?.authHeaders['Authorization'];
+    if (accountId == null || service == null || authHeader == null) {
+      return cancel();
+    }
+
+    final paths = provider.syncEverything ? ['/'] : provider.syncedPaths;
+    await _channel.invokeMethod('reschedule', {
+      'accountId': accountId,
+      'serverUrl': provider.serverUrl,
+      'username': provider.username,
+      'authHeader': authHeader,
+      'folders': jsonEncode(paths),
+      'wifiOnly': !provider.syncOnCellular,
+    });
+  }
+
+  static Future<void> cancel() async {
+    await _channel.invokeMethod('cancel');
+  }
+
+  /// Runs a one-off sync pass immediately (Settings' "Sync now"),
+  /// independent of the periodic schedule.
+  static Future<void> syncNow(ServerProvider provider) async {
+    final accountId = provider.activeAccountId;
+    final service = provider.service;
+    final authHeader = service?.authHeaders['Authorization'];
+    if (accountId == null || service == null || authHeader == null) {
+      throw Exception('Not logged in.');
+    }
+
+    final paths = provider.syncEverything ? ['/'] : provider.syncedPaths;
+    await _channel.invokeMethod('syncNow', {
+      'accountId': accountId,
+      'serverUrl': provider.serverUrl,
+      'username': provider.username,
+      'authHeader': authHeader,
+      'folders': jsonEncode(paths),
+    });
+  }
+
+  /// One-shot status snapshot - used to seed [ServerProvider]'s state right
+  /// after login/account-switch, before the first [statusStream] event
+  /// arrives.
+  static Future<SyncStatusSnapshot> getStatus() async {
+    final result = await _channel.invokeMethod<Map<dynamic, dynamic>>(
+      'getSyncStatus',
+    );
+    return SyncStatusSnapshot.fromMap(result ?? const {});
+  }
+
+  /// Live status updates pushed from `SyncStatusBus` (Kotlin) - syncing
+  /// started/stopped, per-file progress, new/resolved conflicts.
+  static Stream<SyncStatusSnapshot> get statusStream {
+    return _statusChannel.receiveBroadcastStream().map(
+      (event) => SyncStatusSnapshot.fromMap(event as Map<dynamic, dynamic>),
+    );
+  }
+
+  /// In-app conflict resolution (the header's "Keep local"/"Use server"
+  /// buttons) - shares the exact same native `ConflictResolveWorker`
+  /// enqueue path the notification actions use, just triggered from Dart
+  /// instead of a `PendingIntent`.
+  static Future<void> resolveConflict(
+    ServerProvider provider,
+    SyncConflictInfo conflict,
+    String resolution,
+  ) async {
+    final service = provider.service;
+    final authHeader = service?.authHeaders['Authorization'];
+    if (service == null || authHeader == null) {
+      throw Exception('Not logged in.');
+    }
+    await _channel.invokeMethod('resolveConflict', {
+      'accountId': conflict.accountId,
+      'serverUrl': provider.serverUrl,
+      'username': provider.username,
+      'authHeader': authHeader,
+      'fileId': conflict.fileId,
+      'remotePath': conflict.remotePath,
+      'relPath': conflict.relPath,
+      'resolution': resolution,
+    });
+  }
+}

lib/views/account_view.dart

@@ -3,6 +3,7 @@ import 'package:provider/provider.dart';
 import '../models/app_tab.dart';
 import '../models/saved_account.dart';
 import '../providers/server_provider.dart';
+import '../services/sync_service.dart';
 import '../theme/app_theme.dart';
 import '../widgets/frosted_glass_container.dart';
 import '../widgets/seek_bar_painter.dart';
@@ -237,6 +238,17 @@ class AccountView extends StatelessWidget {
             const _SecurityCard(),
             const SizedBox(height: 24),
 
+            // Device Sync Section
+            Text(
+              'Device Sync',
+              style: theme.textTheme.titleMedium?.copyWith(
+                fontWeight: FontWeight.w700,
+              ),
+            ),
+            const SizedBox(height: 10),
+            const _DeviceSyncCard(),
+            const SizedBox(height: 24),
+
             // Material You Design Settings
             Text(
               'Material You Aesthetics',
@@ -722,6 +734,120 @@ class _SecurityCard extends StatelessWidget {
   }
 }
 
+class _DeviceSyncCard extends StatefulWidget {
+  const _DeviceSyncCard();
+
+  @override
+  State<_DeviceSyncCard> createState() => _DeviceSyncCardState();
+}
+
+class _DeviceSyncCardState extends State<_DeviceSyncCard> {
+  bool _syncingNow = false;
+
+  Future<void> _syncNow(ServerProvider provider) async {
+    setState(() => _syncingNow = true);
+    try {
+      await SyncService.syncNow(provider);
+    } catch (e) {
+      if (mounted) {
+        ScaffoldMessenger.of(context).showSnackBar(
+          SnackBar(
+            content: Text('Could not start sync: $e'),
+            behavior: SnackBarBehavior.floating,
+          ),
+        );
+      }
+    } finally {
+      if (mounted) setState(() => _syncingNow = false);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final colorScheme = theme.colorScheme;
+    final provider = context.watch<ServerProvider>();
+    final folders = provider.syncedPaths;
+    final everything = provider.syncEverything;
+
+    return Card(
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          SwitchListTile(
+            secondary: const Icon(Icons.cloud_sync_rounded),
+            title: const Text('Sync everything'),
+            subtitle: const Text(
+              'Mirror the whole account instead of picking folders',
+            ),
+            value: everything,
+            onChanged: provider.setSyncEverything,
+          ),
+          const Divider(height: 1, indent: 16, endIndent: 16),
+          if (everything)
+            Padding(
+              padding: const EdgeInsets.fromLTRB(16, 16, 16, 4),
+              child: Text(
+                'Every folder in this account is being synced to this '
+                'device.',
+                style: theme.textTheme.bodySmall?.copyWith(
+                  color: colorScheme.onSurfaceVariant,
+                ),
+              ),
+            )
+          else if (folders.isEmpty)
+            Padding(
+              padding: const EdgeInsets.fromLTRB(16, 16, 16, 4),
+              child: Text(
+                'No folders synced yet - select a folder in Files and use '
+                '"Sync to device" to mirror it here for offline access.',
+                style: theme.textTheme.bodySmall?.copyWith(
+                  color: colorScheme.onSurfaceVariant,
+                ),
+              ),
+            )
+          else
+            for (final folder in folders) ...[
+              ListTile(
+                leading: const Icon(Icons.sync_rounded),
+                title: Text(folder),
+                trailing: IconButton(
+                  icon: const Icon(Icons.close_rounded),
+                  tooltip: 'Stop syncing',
+                  onPressed: () => provider.removeSyncedPath(folder),
+                ),
+              ),
+              const Divider(height: 1, indent: 16, endIndent: 16),
+            ],
+          SwitchListTile(
+            secondary: const Icon(Icons.signal_cellular_alt_rounded),
+            title: const Text('Sync on cellular'),
+            subtitle: const Text('Off = background sync only runs on Wi-Fi'),
+            value: provider.syncOnCellular,
+            onChanged: provider.setSyncOnCellular,
+          ),
+          const Divider(height: 1, indent: 16, endIndent: 16),
+          ListTile(
+            leading: _syncingNow
+                ? const Padding(
+                    padding: EdgeInsets.all(2),
+                    child: SizedBox(
+                      width: 20,
+                      height: 20,
+                      child: CircularProgressIndicator(strokeWidth: 2),
+                    ),
+                  )
+                : const Icon(Icons.sync_rounded),
+            title: const Text('Sync now'),
+            enabled: (everything || folders.isNotEmpty) && !_syncingNow,
+            onTap: () => _syncNow(provider),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
 class _BottomBarAppearanceCard extends StatefulWidget {
   const _BottomBarAppearanceCard();
 

lib/views/files_view.dart

@@ -1,8 +1,10 @@
 import 'package:file_picker/file_picker.dart';
+import 'package:file_saver/file_saver.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:intl/intl.dart';
 import 'package:material_symbols_icons/symbols.dart';
+import 'package:path/path.dart' as p;
 import 'package:provider/provider.dart';
 import 'package:share_plus/share_plus.dart';
 import '../models/nextcloud_item.dart';
@@ -21,6 +23,7 @@ import '../widgets/share_sheet.dart';
 import '../widgets/sort_menu_button.dart';
 import '../widgets/sticky_header_delegate.dart';
 import '../widgets/swipeable_item.dart';
+import '../widgets/sync_status_badge.dart';
 import '../widgets/synced_header_scaffold.dart';
 import 'file_viewer_screen.dart';
 import 'move_copy_destination_picker.dart';
@@ -284,6 +287,18 @@ class _FilesViewState extends State<FilesView>
           label: 'Rename',
           onTap: () => _renameItem(provider, selected.single),
         ),
+      if (selected.length == 1)
+        SelectionAction(
+          icon: provider.isPathSynced(selected.single.path)
+              ? Icons.sync_rounded
+              : Icons.sync_outlined,
+          label: provider.isPathSynced(selected.single.path)
+              ? 'Stop syncing to device'
+              : 'Sync to device',
+          onTap: () => provider.isPathSynced(selected.single.path)
+              ? provider.removeSyncedPath(selected.single.path)
+              : provider.addSyncedPath(selected.single.path),
+        ),
       if (selected.length == 1)
         SelectionAction(
           icon: Icons.info_outline_rounded,
@@ -803,6 +818,46 @@ class _FilesViewState extends State<FilesView>
     if (files.isEmpty) return;
 
     final messenger = ScaffoldMessenger.of(context);
+
+    // Already mirrored locally by device sync (every selected file, not
+    // just some)? Save straight from the local copy instead of a fresh
+    // network fetch through DownloadService - see
+    // ServerProvider.localSyncedFilePath.
+    final localPaths = await Future.wait(
+      files.map(provider.localSyncedFilePath),
+    );
+    if (localPaths.every((path) => path != null)) {
+      try {
+        for (var i = 0; i < files.length; i++) {
+          final ext = p.extension(files[i].name).replaceFirst('.', '');
+          final baseName = p.basenameWithoutExtension(files[i].name);
+          await FileSaver.instance.saveFile(
+            name: baseName,
+            filePath: localPaths[i]!,
+            ext: ext,
+          );
+        }
+        messenger.showSnackBar(
+          SnackBar(
+            content: Text(
+              files.length == 1
+                  ? 'Downloaded ${files.first.name}'
+                  : 'Downloaded ${files.length} files',
+            ),
+            behavior: SnackBarBehavior.floating,
+          ),
+        );
+      } catch (e) {
+        messenger.showSnackBar(
+          SnackBar(
+            content: Text('Could not save file(s): $e'),
+            behavior: SnackBarBehavior.floating,
+          ),
+        );
+      }
+      return;
+    }
+
     try {
       await DownloadService.startDownload(provider, files);
       messenger.showSnackBar(
@@ -930,17 +985,29 @@ class _FilesViewState extends State<FilesView>
           padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 12),
           child: Row(
             children: [
-              SelectableThumbnail(
-                isSelected: isSelected,
-                size: 44,
-                checkmarkSize: 24,
-                child: ItemThumbnail(
-                  item: item,
-                  provider: provider,
-                  size: 44,
-                  borderRadius: 12,
-                  iconSize: 22,
-                ),
+              Stack(
+                clipBehavior: Clip.none,
+                children: [
+                  SelectableThumbnail(
+                    isSelected: isSelected,
+                    size: 44,
+                    checkmarkSize: 24,
+                    child: ItemThumbnail(
+                      item: item,
+                      provider: provider,
+                      size: 44,
+                      borderRadius: 12,
+                      iconSize: 22,
+                    ),
+                  ),
+                  Positioned(
+                    right: -2,
+                    bottom: -2,
+                    child: SyncStatusBadge(
+                      status: provider.syncStatusFor(item),
+                    ),
+                  ),
+                ],
               ),
               const SizedBox(width: 14),
               Expanded(
@@ -1036,12 +1103,21 @@ class _FilesViewState extends State<FilesView>
         onLongPress: provider.isPicking && !provider.pickRequest!.allowMultiple
             ? null
             : () => _toggleSelection(item),
-        child: SelectableThumbnail(
-          isSelected: isSelected,
-          checkmarkSize: 32,
-          child: isMedia
-              ? _buildMediaGridContent(context, item, provider)
-              : _buildPlainGridContent(context, item),
+        child: Stack(
+          children: [
+            SelectableThumbnail(
+              isSelected: isSelected,
+              checkmarkSize: 32,
+              child: isMedia
+                  ? _buildMediaGridContent(context, item, provider)
+                  : _buildPlainGridContent(context, item),
+            ),
+            Positioned(
+              right: 6,
+              bottom: 6,
+              child: SyncStatusBadge(status: provider.syncStatusFor(item)),
+            ),
+          ],
         ),
       ),
     );

lib/widgets/share_sheet.dart

@@ -236,9 +236,17 @@ class _ShareSheetState extends State<ShareSheet> {
     setState(() => _isSharingFile = true);
     final messenger = ScaffoldMessenger.of(context);
     try {
-      final tempDir = await getTemporaryDirectory();
-      final tempPath = p.join(tempDir.path, widget.item.name);
-      await provider.service!.downloadToFile(widget.item.path, tempPath);
+      // Already mirrored locally by device sync? Share that copy straight
+      // away instead of a fresh WebDAV fetch - see
+      // ServerProvider.localSyncedFilePath.
+      final tempPath =
+          await provider.localSyncedFilePath(widget.item) ??
+          await () async {
+            final tempDir = await getTemporaryDirectory();
+            final path = p.join(tempDir.path, widget.item.name);
+            await provider.service!.downloadToFile(widget.item.path, path);
+            return path;
+          }();
       if (!mounted) return;
       await SharePlus.instance.share(
         ShareParams(

lib/widgets/sync_status_badge.dart

@@ -0,0 +1,34 @@
+import 'package:flutter/material.dart';
+import '../models/sync_status.dart';
+
+/// A small corner badge over a thumbnail showing device-sync status - a
+/// `cloud_done` badge once a file's mirrored locally, `sync` while it's
+/// actively being transferred. Nothing is drawn for `none`/`conflict`
+/// (conflicts surface in the sync header, not as per-tile noise).
+class SyncStatusBadge extends StatelessWidget {
+  final SyncItemStatus status;
+
+  const SyncStatusBadge({super.key, required this.status});
+
+  @override
+  Widget build(BuildContext context) {
+    if (status != SyncItemStatus.syncing && status != SyncItemStatus.synced) {
+      return const SizedBox.shrink();
+    }
+    final colorScheme = Theme.of(context).colorScheme;
+    final icon = status == SyncItemStatus.syncing
+        ? Icons.sync_rounded
+        : Icons.cloud_done_rounded;
+
+    return Container(
+      width: 18,
+      height: 18,
+      decoration: BoxDecoration(
+        color: colorScheme.surface,
+        shape: BoxShape.circle,
+        border: Border.all(color: colorScheme.surface, width: 1.5),
+      ),
+      child: Icon(icon, size: 13, color: colorScheme.primary),
+    );
+  }
+}

lib/widgets/synced_header_scaffold.dart

@@ -1,7 +1,23 @@
 import 'package:flutter/material.dart';
+import 'package:material_symbols_icons/symbols.dart';
 import '../models/nextcloud_item.dart';
+import '../models/sync_status.dart';
 import '../providers/server_provider.dart';
 
+/// Icon/label for the persistent header chip/panel - reflects device-sync
+/// status (see `ServerProvider.syncHeaderStatus`), not the WebDAV
+/// directory-listing refresh the pull gesture itself triggers (that has
+/// its own, separate floating spinner bubble - see
+/// `_SyncedHeaderScaffoldState`'s `_isRefreshing`).
+(IconData, String) _syncHeaderDisplay(SyncHeaderStatus status) {
+  return switch (status) {
+    SyncHeaderStatus.off => (Icons.cloud_off_rounded, 'Sync off'),
+    SyncHeaderStatus.syncing => (Icons.cloud_sync_rounded, 'Syncing…'),
+    SyncHeaderStatus.done => (Icons.cloud_done_rounded, 'Synced'),
+    SyncHeaderStatus.alert => (Symbols.cloud_alert_rounded, 'Sync issue'),
+  };
+}
+
 String formatBytes(int bytes) {
   if (bytes <= 0) return '0 B';
   if (bytes < 1024) return '$bytes B';
@@ -188,7 +204,9 @@ class _SyncedHeaderScaffoldState extends State<SyncedHeaderScaffold> {
                   stretch: widget.selectionBar == null,
                   expandedHeight: widget.selectionBar != null
                       ? kToolbarHeight
-                      : (_headerLocked ? 190 : kToolbarHeight),
+                      : (_headerLocked
+                            ? 190.0 + provider.syncConflicts.length * 52.0
+                            : kToolbarHeight),
                   collapsedHeight: kToolbarHeight,
                   backgroundColor: colorScheme.surfaceContainer,
                   surfaceTintColor: colorScheme.surfaceContainer,
@@ -278,7 +296,11 @@ class _SyncStatusChip extends StatelessWidget {
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
     final colorScheme = theme.colorScheme;
-    final quota = provider.quota;
+    final status = provider.syncHeaderStatus;
+    final (icon, label) = _syncHeaderDisplay(status);
+    final iconColor = status == SyncHeaderStatus.alert
+        ? colorScheme.error
+        : colorScheme.primary;
 
     return Padding(
       padding: const EdgeInsets.only(left: 12),
@@ -293,16 +315,10 @@ class _SyncStatusChip extends StatelessWidget {
             child: Row(
               mainAxisSize: MainAxisSize.min,
               children: [
-                Icon(
-                  provider.isLoading
-                      ? Icons.cloud_sync_rounded
-                      : Icons.cloud_done_outlined,
-                  color: colorScheme.primary,
-                  size: 18,
-                ),
+                Icon(icon, color: iconColor, size: 18),
                 const SizedBox(width: 6),
                 Text(
-                  quota != null ? formatQuota(quota) : 'Sync',
+                  label,
                   style: theme.textTheme.labelMedium?.copyWith(
                     fontWeight: FontWeight.w700,
                   ),
@@ -348,6 +364,9 @@ class _SyncedStretchPanel extends StatelessWidget {
         // before the 100px lock threshold.
         final progress = forceVisible ? 1.0 : (stretch / 50).clamp(0.0, 1.0);
         final quota = provider.quota;
+        final status = provider.syncHeaderStatus;
+        final (_, statusLabel) = _syncHeaderDisplay(status);
+        final conflicts = provider.syncConflicts;
 
         return Stack(
           children: [
@@ -365,7 +384,7 @@ class _SyncedStretchPanel extends StatelessWidget {
                     crossAxisAlignment: CrossAxisAlignment.start,
                     children: [
                       Text(
-                        provider.isLoading ? 'Syncing…' : 'Synced',
+                        statusLabel,
                         style: theme.textTheme.titleLarge?.copyWith(
                           fontWeight: FontWeight.w700,
                         ),
@@ -414,6 +433,17 @@ class _SyncedStretchPanel extends StatelessWidget {
                           ],
                         ),
                       ),
+                      if (conflicts.isNotEmpty) ...[
+                        const SizedBox(height: 10),
+                        for (final conflict in conflicts)
+                          Padding(
+                            padding: const EdgeInsets.only(bottom: 8),
+                            child: _SyncConflictRow(
+                              conflict: conflict,
+                              provider: provider,
+                            ),
+                          ),
+                      ],
                     ],
                   ),
                 ),
@@ -424,3 +454,93 @@ class _SyncedStretchPanel extends StatelessWidget {
     );
   }
 }
+
+/// One row in the locked-open panel's conflicts section - a file that
+/// changed both locally and on the server since the last sync, with the
+/// same two resolutions the sync-conflict notification offers (see
+/// `SyncWorker.notifyConflicts`/`ConflictResolveWorker` on the native
+/// side), just triggered in-app instead.
+class _SyncConflictRow extends StatefulWidget {
+  final SyncConflictInfo conflict;
+  final ServerProvider provider;
+
+  const _SyncConflictRow({required this.conflict, required this.provider});
+
+  @override
+  State<_SyncConflictRow> createState() => _SyncConflictRowState();
+}
+
+class _SyncConflictRowState extends State<_SyncConflictRow> {
+  bool _resolving = false;
+
+  Future<void> _resolve(bool useLocal) async {
+    setState(() => _resolving = true);
+    try {
+      await widget.provider.resolveSyncConflict(
+        widget.conflict,
+        useLocal: useLocal,
+      );
+    } catch (_) {
+      if (mounted) setState(() => _resolving = false);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final colorScheme = theme.colorScheme;
+
+    return Container(
+      padding: const EdgeInsets.symmetric(horizontal: 14, vertical: 10),
+      decoration: BoxDecoration(
+        color: colorScheme.errorContainer.withValues(alpha: 0.4),
+        borderRadius: BorderRadius.circular(16),
+      ),
+      child: Row(
+        children: [
+          Icon(Symbols.cloud_alert_rounded, color: colorScheme.error, size: 18),
+          const SizedBox(width: 10),
+          Expanded(
+            child: Text(
+              widget.conflict.name,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              style: theme.textTheme.bodyMedium?.copyWith(
+                fontWeight: FontWeight.w600,
+              ),
+            ),
+          ),
+          if (_resolving)
+            const Padding(
+              padding: EdgeInsets.symmetric(horizontal: 8),
+              child: SizedBox(
+                width: 16,
+                height: 16,
+                child: CircularProgressIndicator(strokeWidth: 2),
+              ),
+            )
+          else ...[
+            TextButton(
+              style: TextButton.styleFrom(
+                padding: const EdgeInsets.symmetric(horizontal: 8),
+                minimumSize: Size.zero,
+                tapTargetSize: MaterialTapTargetSize.shrinkWrap,
+              ),
+              onPressed: () => _resolve(true),
+              child: const Text('Keep local'),
+            ),
+            TextButton(
+              style: TextButton.styleFrom(
+                padding: const EdgeInsets.symmetric(horizontal: 8),
+                minimumSize: Size.zero,
+                tapTargetSize: MaterialTapTargetSize.shrinkWrap,
+              ),
+              onPressed: () => _resolve(false),
+              child: const Text('Use server'),
+            ),
+          ],
+        ],
+      ),
+    );
+  }
+}