feat(core,fuse,gui,cli): list and resolve sync conflicts (phase 3)

Conflict copies under My Files are paired with their original and listed
over the control socket. The Sync page shows them with a resolve dialog
(keep original, keep copy, keep both under a new name), and the CLI gains
`pdfs conflicts` and `pdfs conflicts resolve`. Every resolution goes
through the Proton trash, and files that are open, being written or still
owed an upload are refused.

crates/pdfs-cli/src/main.rs

@@ -13,8 +13,9 @@ use pdfs_core::auth;
 use pdfs_core::cache::ContentCache;
 use pdfs_core::config::AppDirs;
 use pdfs_core::control::{
-    ErrorKind, MountKind, RefreshScope, Request as CtlRequest, Response as CtlResponse,
-    RestoreItem as CtlRestoreItem, ShareEntryKind, SyncPhase, pending_summary,
+    ConflictKeep, ErrorKind, MountKind, RefreshScope, Request as CtlRequest,
+    Response as CtlResponse, RestoreItem as CtlRestoreItem, ShareEntryKind, SyncPhase,
+    pending_summary,
 };
 use pdfs_core::db::Db;
 use pdfs_core::service;
@@ -327,6 +328,11 @@ enum Command {
         #[command(subcommand)]
         action: SyncCmd,
     },
+    /// List `(sync-conflict …)` copies, or resolve one.
+    Conflicts {
+        #[command(subcommand)]
+        action: Option<ConflictCmd>,
+    },
     /// Share a file or folder with Proton and/or external email addresses.
     Share {
         /// File/folder path, inside the mountpoint or relative to it.
@@ -521,6 +527,22 @@ enum DeviceCmd {
     },
 }
 
+#[derive(Subcommand)]
+enum ConflictCmd {
+    /// Decide which side of a conflict to keep. Whatever is removed goes to Trash.
+    Resolve {
+        /// The conflict copy, absolute or relative to the mountpoint.
+        path: PathBuf,
+        /// `original` trashes the copy; `copy` trashes the original and gives the
+        /// copy its name; `both` renames the copy to `--name`.
+        #[arg(long, value_parser = ["original", "copy", "both"])]
+        keep: String,
+        /// New name for the copy with `--keep both`.
+        #[arg(long, required_if_eq("keep", "both"))]
+        name: Option<String>,
+    },
+}
+
 #[derive(Subcommand)]
 enum SyncCmd {
     /// Add a local folder to this machine's device and upload its contents.
@@ -707,6 +729,7 @@ fn main() -> Result<()> {
         Command::Refresh { target, full } => cmd_refresh(target, full),
         Command::Devices { action } => cmd_devices(action),
         Command::Sync { action } => cmd_sync(action),
+        Command::Conflicts { action } => cmd_conflicts(action),
         Command::Share {
             path,
             emails,
@@ -871,6 +894,47 @@ fn cmd_sync(action: SyncCmd) -> Result<()> {
     Ok(())
 }
 
+/// `pdfs conflicts`: list conflict copies, or resolve one.
+fn cmd_conflicts(action: Option<ConflictCmd>) -> Result<()> {
+    if let Some(ConflictCmd::Resolve { path, keep, name }) = action {
+        let keep = match keep.as_str() {
+            "original" => ConflictKeep::Original,
+            "copy" => ConflictKeep::Copy,
+            _ => ConflictKeep::Both {
+                name: name.unwrap_or_default(),
+            },
+        };
+        let path = path_arg(&path)?;
+        return ok_or_bail(control_request(CtlRequest::ResolveConflict { path, keep })?);
+    }
+    let response = control_request(CtlRequest::ListConflicts)?;
+    if emit_json(&response)? {
+        return Ok(());
+    }
+    match response {
+        CtlResponse::Conflicts { items } if items.is_empty() => println!("No conflicts."),
+        CtlResponse::Conflicts { items } => {
+            for c in items {
+                println!("{}", c.path);
+                let verdict = match (c.original_exists, c.identical) {
+                    (false, _) => "original is gone".to_string(),
+                    (true, true) => format!("identical to {}", c.original_path),
+                    (true, false) => format!(
+                        "differs from {} ({} vs {})",
+                        c.original_path,
+                        human_bytes(c.size),
+                        human_bytes(c.original_size.unwrap_or_default()),
+                    ),
+                };
+                println!("      {verdict}");
+            }
+        }
+        CtlResponse::Error { message, kind } => bail!("{}", cli_error(kind, &message)),
+        other => bail!("unexpected response: {other:?}"),
+    }
+    Ok(())
+}
+
 /// `pdfs sync queue`: what has not reached Proton Drive yet, and why.
 fn cmd_sync_queue() -> Result<()> {
     let response = control_request(CtlRequest::ListPendingOps)?;

crates/pdfs-core/src/control.rs

@@ -396,6 +396,13 @@ pub enum Request {
     /// Retry a backed-off queued op now instead of waiting out its backoff;
     /// every failed op when `id` is `None`. Replies with [`Response::Ok`].
     RetryPendingOp { id: Option<i64> },
+    /// List the `(sync-conflict …)` copies under My Files. Replies with
+    /// [`Response::Conflicts`].
+    ListConflicts,
+    /// Resolve one conflict copy (`path` mountpoint-relative or absolute).
+    /// Everything removed goes to the Proton trash. Replies with
+    /// [`Response::Ok`].
+    ResolveConflict { path: String, keep: ConflictKeep },
     /// List the folders under this machine's device that can be synced here,
     /// each with a proposed local path (features.md 5.2). Replies with
     /// [`Response::RestorableFolders`].
@@ -638,6 +645,36 @@ pub struct DeviceInfo {
     pub adopted: bool,
 }
 
+/// One `(sync-conflict …)` copy and the file it is a copy of (in
+/// [`Response::Conflicts`]).
+#[derive(Serialize, Deserialize, Debug, Clone)]
+pub struct ConflictInfo {
+    /// Mountpoint-relative path of the copy.
+    pub path: String,
+    /// Mountpoint-relative path of the file it is a copy of.
+    pub original_path: String,
+    /// False when the original is gone and only the copy is left.
+    pub original_exists: bool,
+    pub size: u64,
+    /// Unix seconds.
+    pub modified: i64,
+    pub original_size: Option<u64>,
+    pub original_modified: Option<i64>,
+    /// Same size and content hash as the original: keeping either loses nothing.
+    pub identical: bool,
+}
+
+/// Which side of a conflict to keep (in [`Request::ResolveConflict`]).
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
+pub enum ConflictKeep {
+    /// Keep the original; the copy goes to Trash.
+    Original,
+    /// Keep the copy under the original's name; the original goes to Trash.
+    Copy,
+    /// Keep both; the copy is renamed to `name`.
+    Both { name: String },
+}
+
 /// One queued upload or change (in [`Response::PendingOps`]).
 #[derive(Serialize, Deserialize, Debug, Clone)]
 pub struct PendingOpInfo {
@@ -1736,6 +1773,8 @@ pub enum Response {
     SyncFolders { items: Vec<SyncFolderInfo> },
     /// The upload/change queue (reply to [`Request::ListPendingOps`]).
     PendingOps { items: Vec<PendingOpInfo> },
+    /// Conflict copies (reply to [`Request::ListConflicts`]).
+    Conflicts { items: Vec<ConflictInfo> },
     /// Folders offered for restore (reply to [`Request::ListRestorableFolders`]).
     RestorableFolders { items: Vec<RestorableFolder> },
     /// A node's share: members + pending invitations, and its public link if any

crates/pdfs-fuse/src/conflicts.rs

@@ -0,0 +1,156 @@
+//! Listing and resolving `(sync-conflict …)` copies for the user.
+//!
+//! The sweep ([`crate::sweep`]) removes copies it can prove identical and flags
+//! the rest once in the activity feed. That leaves divergent copies sitting in
+//! folders with nothing but a name to find them by. This module lists them with
+//! the file they are a copy of, and resolves one the way the user chooses:
+//!
+//! - **Keep the original**: trash the copy.
+//! - **Keep the copy**: trash the original, then give the copy its name.
+//! - **Keep both**: rename the copy to a name of the user's choosing.
+//!
+//! Every resolution goes through the Proton trash, never a delete, so a wrong
+//! choice is undone by restoring from Trash. Resolution refuses to touch a file
+//! that is open, being written, or still owed an upload, for the same reason the
+//! sweep does: the node is about to change under the decision.
+//!
+//! Only copies under My Files are handled here. A copy inside a mirror folder is
+//! a local file first; the sync engine owns it.
+
+use super::*;
+use pdfs_core::control::{ConflictInfo, ConflictKeep};
+use sweep::conflict_base_name;
+
+impl Core {
+    /// Every conflict copy under My Files, with the file it is a copy of.
+    pub(crate) fn list_conflicts(&self) -> CoreResult<Vec<ConflictInfo>> {
+        let stored = self
+            .db
+            .load_all()
+            .map_err(|e| CoreError::internal(format!("listing conflicts: {e:?}")))?;
+        let nodes: Vec<Node> = stored
+            .into_iter()
+            .map(|stored| stored.node)
+            .filter(|node| !node.trashed && !node.is_folder() && self.is_own_or_virtual(&node.uid))
+            .collect();
+        let mut by_parent_name: HashMap<(Option<&NodeUid>, &str), &Node> = HashMap::new();
+        for node in &nodes {
+            by_parent_name.insert((node.parent_uid.as_ref(), node.name.as_str()), node);
+        }
+        let root = self.primary_root_uid.to_string();
+        let mut items = Vec::new();
+        for node in &nodes {
+            let Some(base) = conflict_base_name(&node.name) else {
+                continue;
+            };
+            let Ok(Some(path)) = self.db.path_relative_to(&root, &node.uid.to_string()) else {
+                continue;
+            };
+            let original = by_parent_name
+                .get(&(node.parent_uid.as_ref(), base.as_str()))
+                .copied();
+            items.push(ConflictInfo {
+                original_path: sibling_path(&path, &base),
+                original_exists: original.is_some(),
+                size: node_size(node),
+                modified: node.modification_time,
+                original_size: original.map(node_size),
+                original_modified: original.map(|o| o.modification_time),
+                identical: original.is_some_and(|o| {
+                    node_size(o) == node_size(node)
+                        && node_content_sha1(node)
+                            .is_some_and(|sha| node_content_sha1(o).as_deref() == Some(&sha))
+                }),
+                path,
+            });
+        }
+        items.sort_by(|a, b| a.path.cmp(&b.path));
+        Ok(items)
+    }
+
+    /// Resolve the conflict copy at mountpoint-relative `copy`. Returns a line
+    /// for the user saying what happened.
+    pub(crate) fn resolve_conflict(&self, copy: &Path, keep: &ConflictKeep) -> CoreResult<String> {
+        let copy_name = copy
+            .file_name()
+            .and_then(|n| n.to_str())
+            .ok_or_else(|| CoreError::invalid("the conflict copy has no file name"))?;
+        let base = conflict_base_name(copy_name)
+            .ok_or_else(|| CoreError::invalid(format!("{copy_name} is not a conflict copy")))?;
+        let original = copy.with_file_name(&base);
+        self.require_settled(copy)?;
+        let message = match keep {
+            ConflictKeep::Original => {
+                self.delete(copy)?;
+                self.log_activity(ActivityKind::Trash, copy_name, format!("kept {base}"), true);
+                format!("kept {base}; the copy is in Trash")
+            }
+            ConflictKeep::Copy => {
+                self.require_settled(&original)?;
+                self.delete(&original)?;
+                // The original is already in Trash. A failed rename leaves the
+                // copy under its conflict name, which loses nothing — say so
+                // rather than leave the user guessing where their file went.
+                self.rename(copy, &base).map_err(|e| {
+                    e.context(&format!(
+                        "{base} was moved to Trash, but the copy kept its conflict name"
+                    ))
+                })?;
+                self.log_activity(
+                    ActivityKind::Rename,
+                    &base,
+                    format!("kept the conflict copy {copy_name}"),
+                    true,
+                );
+                format!("kept the copy as {base}; the previous version is in Trash")
+            }
+            ConflictKeep::Both { name } => {
+                let name = name.trim();
+                if name == base || name == copy_name {
+                    return Err(CoreError::invalid("choose a name that no other file has"));
+                }
+                self.rename(copy, name)?;
+                self.log_activity(ActivityKind::Rename, name, format!("was {copy_name}"), true);
+                format!("kept both; the copy is now {name}")
+            }
+        };
+        Ok(message)
+    }
+
+    /// Refuse to resolve around a file that is open, being written, or still
+    /// owed an upload: the decision would be about content that is changing.
+    fn require_settled(&self, rel: &Path) -> CoreResult<()> {
+        let (_, uid) = self.resolve(rel)?;
+        let queued = self.db.has_any_op(&uid.to_string()).unwrap_or(true);
+        if queued || self.is_busy(&uid) {
+            return Err(CoreError::conflict(format!(
+                "{} is still being written or uploaded; try again once it has synced",
+                rel.display()
+            )));
+        }
+        self.conflict_notified.lock().remove(&uid);
+        Ok(())
+    }
+}
+
+/// The path of `name` next to the file at `path`.
+fn sibling_path(path: &str, name: &str) -> String {
+    match path.rsplit_once('/') {
+        Some((dir, _)) => format!("{dir}/{name}"),
+        None => name.to_string(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn the_original_sits_next_to_its_copy() {
+        assert_eq!(
+            sibling_path("a/b/f (sync-conflict 1).txt", "f.txt"),
+            "a/b/f.txt"
+        );
+        assert_eq!(sibling_path("f (sync-conflict 1).txt", "f.txt"), "f.txt");
+    }
+}

crates/pdfs-fuse/src/control.rs

@@ -1003,6 +1003,17 @@ fn handle_control_conn(core: &Core, username: &str, mountpoint: &Path, stream: U
                 Err(e) => CtlResponse::error(e),
             }
         }
+        Ok(CtlRequest::ListConflicts) => match core.list_conflicts() {
+            Ok(items) => CtlResponse::Conflicts { items },
+            Err(e) => CtlResponse::error(e),
+        },
+        Ok(CtlRequest::ResolveConflict { path, keep }) => match rel_to_mount(mountpoint, &path) {
+            Ok(rel) => match core.resolve_conflict(&rel, &keep) {
+                Ok(message) => CtlResponse::Ok { message },
+                Err(e) => CtlResponse::error(e),
+            },
+            Err(e) => CtlResponse::error(e),
+        },
         Ok(CtlRequest::ListPendingOps) => match core.pending_op_infos() {
             Ok(items) => CtlResponse::PendingOps { items },
             Err(e) => CtlResponse::error(e),

crates/pdfs-fuse/src/lib.rs

@@ -80,6 +80,7 @@ use proton_drive_rs::{
 
 mod albums;
 mod background;
+mod conflicts;
 mod control;
 use control::run_control_socket;
 mod devices;

crates/pdfs-fuse/src/sweep.rs

@@ -261,7 +261,7 @@ impl Core {
     /// is tracked in that fork's `State` — so consulting `self.state` alone
     /// answered "idle" for every such file and let the sweep delete one with a
     /// writer attached (`docs/BUGS.md` B74). Busy anywhere means busy.
-    fn is_busy(&self, uid: &NodeUid) -> bool {
+    pub(crate) fn is_busy(&self, uid: &NodeUid) -> bool {
         let mut busy = false;
         self.for_each_state(|st| {
             let Some(&ino) = st.by_uid.get(uid) else {

crates/pdfs-gui/src/app/main.rs

@@ -47,11 +47,11 @@ use pdfs_core::auth;
 use pdfs_core::config::AppDirs;
 
 use pdfs_core::control::{
-    ActivityEntry, ActivityKind, AlbumInfo, BookmarkInfo, DeviceInfo, DirEntry, ErrorKind,
-    ImportSummary, InvitationInfo, JobItem, PendingOpInfo, PhotoItem, PhotoKind, PublicLinkInfo,
-    RefreshScope, Request, Response, RestorableFolder, RestoreItem, SearchHit, ShareEntry,
-    ShareEntryKind, SharedItem, SyncFolderInfo, SyncPhase, SyncProgress, ThumbnailBuildStatus,
-    TransferDirection, TransferItem, pending_summary, send,
+    ActivityEntry, ActivityKind, AlbumInfo, BookmarkInfo, ConflictInfo, ConflictKeep, DeviceInfo,
+    DirEntry, ErrorKind, ImportSummary, InvitationInfo, JobItem, PendingOpInfo, PhotoItem,
+    PhotoKind, PublicLinkInfo, RefreshScope, Request, Response, RestorableFolder, RestoreItem,
+    SearchHit, ShareEntry, ShareEntryKind, SharedItem, SyncFolderInfo, SyncPhase, SyncProgress,
+    ThumbnailBuildStatus, TransferDirection, TransferItem, pending_summary, send,
 };
 
 use pdfs_core::mounts::{MountAccess, MountKind, MountMode, MountSpec};
@@ -555,6 +555,13 @@ fn build_window(app: &adw::Application) {
                 painted: RefCell::new(Vec::new()),
                 inflight: Cell::new(false),
             },
+            conflicts: ConflictsState {
+                group: locations_widgets.conflicts_group.clone(),
+                rows: RefCell::new(Vec::new()),
+                painted: RefCell::new(Vec::new()),
+                inflight: Cell::new(false),
+                fetched_at: Cell::new(None),
+            },
         },
         activity: ActivityState {
             content: activity_widgets.content.clone(),
@@ -666,8 +673,12 @@ fn build_window(app: &adw::Application) {
             Some("shared") => load_shared(&ui_nav),
             Some("devices") if page_fresh(&ui_nav.devices.loaded_at) => {}
             Some("devices") => load_devices(&ui_nav),
-            Some("locations") if page_fresh(&ui_nav.locations.loaded_at) => {}
-            Some("locations") => load_locations(&ui_nav),
+            Some("locations") => {
+                refresh_conflicts(&ui_nav, true);
+                if !page_fresh(&ui_nav.locations.loaded_at) {
+                    load_locations(&ui_nav);
+                }
+            }
             // Activity is intentionally not TTL-cached: it changes out from under
             // the page as background uploads and edits complete, so it reloads on
             // every visit to stay live.

crates/pdfs-gui/src/app/pages/locations.rs

@@ -24,6 +24,7 @@ pub(crate) struct LocationsState {
     pub(crate) loaded_at: Cell<Option<Instant>>,
     pub(crate) card: SyncCard,
     pub(crate) queue: QueueState,
+    pub(crate) conflicts: ConflictsState,
 }
 
 /// The status card heading the Sync page: what sync is doing, and Pause/Resume.
@@ -49,6 +50,20 @@ pub(crate) struct QueueState {
     pub(crate) inflight: Cell<bool>,
 }
 
+/// What a conflict row shows that can change: path, both sizes, both times.
+pub(crate) type ConflictKey = (String, u64, i64, Option<u64>, Option<i64>);
+
+/// The "Conflicts" list: `(sync-conflict …)` copies waiting for a decision.
+pub(crate) struct ConflictsState {
+    pub(crate) group: adw::PreferencesGroup,
+    pub(crate) rows: RefCell<Vec<adw::ActionRow>>,
+    pub(crate) painted: RefCell<Vec<ConflictKey>>,
+    pub(crate) inflight: Cell<bool>,
+    /// When the list was last fetched. Listing walks every node the daemon
+    /// knows, so the tick asks far less often than it does for the queue.
+    pub(crate) fetched_at: Cell<Option<Instant>>,
+}
+
 /// Widgets the Locations page's load/repaint touch.
 pub(crate) struct LocationsWidgets {
     pub(crate) content: gtk4::Stack,
@@ -64,6 +79,7 @@ pub(crate) struct LocationsWidgets {
     pub(crate) pause: adw::SplitButton,
     pub(crate) queue_group: adw::PreferencesGroup,
     pub(crate) retry_all: gtk4::Button,
+    pub(crate) conflicts_group: adw::PreferencesGroup,
 }
 
 pub(crate) fn build_locations_page() -> (gtk4::Widget, LocationsWidgets) {
@@ -80,6 +96,14 @@ pub(crate) fn build_locations_page() -> (gtk4::Widget, LocationsWidgets) {
     let transfers_group = build_transfers_group();
     let (card, card_icon, card_row, pause) = build_sync_card();
     let (queue_group, retry_all) = build_queue_group();
+    let conflicts_group = adw::PreferencesGroup::builder()
+        .title("Conflicts")
+        .description(
+            "Files changed in two places at once. Both versions were kept; choose which \
+             one stays.",
+        )
+        .visible(false)
+        .build();
 
     // Same warning the Computers page carried, for the same reason: the
     // on-demand switch removes the local copy, which is not a thing to discover
@@ -95,6 +119,7 @@ pub(crate) fn build_locations_page() -> (gtk4::Widget, LocationsWidgets) {
 
     let groups = gtk4::Box::new(gtk4::Orientation::Vertical, 18);
     groups.append(&card);
+    groups.append(&conflicts_group);
     groups.append(&queue_group);
     groups.append(&transfers_group);
     groups.append(&group);
@@ -157,6 +182,7 @@ pub(crate) fn build_locations_page() -> (gtk4::Widget, LocationsWidgets) {
         pause,
         queue_group,
         retry_all,
+        conflicts_group,
     };
     (frame.upcast(), widgets)
 }
@@ -474,6 +500,218 @@ fn retry_queued(ui: &Rc<Ui>, id: Option<i64>) {
     });
 }
 
+/// How long a conflict listing stays fresh on the refresh tick.
+const CONFLICTS_TTL: Duration = Duration::from_secs(30);
+
+/// Poll the conflict list while the Sync page is on screen. `force` skips the
+/// TTL, for navigation and right after a resolution.
+pub(crate) fn refresh_conflicts(ui: &Rc<Ui>, force: bool) {
+    let conflicts = &ui.locations.conflicts;
+    if conflicts.inflight.get()
+        || (!force
+            && conflicts
+                .fetched_at
+                .get()
+                .is_some_and(|at| at.elapsed() < CONFLICTS_TTL))
+    {
+        return;
+    }
+    conflicts.inflight.set(true);
+    let rx = spawn_request(ui.dirs.control_socket(), Request::ListConflicts);
+    let ui = ui.clone();
+    glib::spawn_future_local(async move {
+        let result = rx.recv().await;
+        let conflicts = &ui.locations.conflicts;
+        conflicts.inflight.set(false);
+        conflicts.fetched_at.set(Some(Instant::now()));
+        match result {
+            Ok(Ok(Response::Conflicts { items })) => repaint_conflicts(&ui, &items),
+            // Same as the queue: an older daemon, or none, shows nothing.
+            _ => repaint_conflicts(&ui, &[]),
+        }
+    });
+}
+
+fn repaint_conflicts(ui: &Rc<Ui>, items: &[ConflictInfo]) {
+    let conflicts = &ui.locations.conflicts;
+    let key: Vec<ConflictKey> = items
+        .iter()
+        .map(|c| {
+            (
+                c.path.clone(),
+                c.size,
+                c.modified,
+                c.original_size,
+                c.original_modified,
+            )
+        })
+        .collect();
+    if *conflicts.painted.borrow() == key {
+        return;
+    }
+    *conflicts.painted.borrow_mut() = key;
+
+    for row in conflicts.rows.borrow_mut().drain(..) {
+        conflicts.group.remove(&row);
+    }
+    conflicts.group.set_visible(!items.is_empty());
+    let mut rows = conflicts.rows.borrow_mut();
+    for conflict in items {
+        let row = conflict_row(ui, conflict);
+        conflicts.group.add(&row);
+        rows.push(row);
+    }
+}
+
+/// "12.3 MB, changed at 14:30": one side of a conflict.
+fn conflict_side(size: u64, modified: i64) -> String {
+    format!(
+        "{}, changed {}",
+        glib::format_size(size),
+        clock_time(modified)
+    )
+}
+
+fn conflict_row(ui: &Rc<Ui>, conflict: &ConflictInfo) -> adw::ActionRow {
+    let verdict = if !conflict.original_exists {
+        "The original is gone; only this copy is left".to_string()
+    } else if conflict.identical {
+        "Same content as the original".to_string()
+    } else {
+        format!("Differs from {}", file_name(&conflict.original_path))
+    };
+    let row = adw::ActionRow::builder()
+        .title(glib::markup_escape_text(&conflict.path).as_str())
+        .subtitle(glib::markup_escape_text(&verdict).as_str())
+        .title_lines(1)
+        .tooltip_text(&conflict.path)
+        .activatable(true)
+        .build();
+    let image = gtk4::Image::from_icon_name("dialog-warning-symbolic");
+    image.add_css_class("warning");
+    row.add_prefix(&image);
+    row.add_suffix(&gtk4::Image::from_icon_name("go-next-symbolic"));
+    let ui = ui.clone();
+    let conflict = conflict.clone();
+    row.connect_activated(move |_| prompt_resolve_conflict(&ui, &conflict));
+    row
+}
+
+/// The last component of a mount-relative path.
+fn file_name(path: &str) -> &str {
+    path.rsplit('/').next().unwrap_or(path)
+}
+
+/// Ask which version of a conflicted file to keep.
+fn prompt_resolve_conflict(ui: &Rc<Ui>, conflict: &ConflictInfo) {
+    let win = ui_window(ui);
+    let copy_name = file_name(&conflict.path).to_string();
+    let original_name = file_name(&conflict.original_path).to_string();
+    let body = match (conflict.original_size, conflict.original_modified) {
+        (Some(size), Some(modified)) if conflict.original_exists => format!(
+            "“{original_name}” was changed here and elsewhere at the same time.\n\n\
+             Original: {}\nCopy: {}\n\n\
+             Whatever is not kept goes to Trash, where it can be restored.",
+            conflict_side(size, modified),
+            conflict_side(conflict.size, conflict.modified),
+        ),
+        _ => format!(
+            "The original “{original_name}” no longer exists; only the copy is left \
+             ({}).\n\nKeep the copy to give it the original name back.",
+            conflict_side(conflict.size, conflict.modified),
+        ),
+    };
+    let dialog = adw::AlertDialog::builder()
+        .heading("Resolve conflict")
+        .body(body)
+        .build();
+    let group = adw::PreferencesGroup::new();
+    let name_row = adw::EntryRow::builder()
+        .title("Name for the copy, if keeping both")
+        .build();
+    name_row.set_text(&copy_name);
+    group.add(&name_row);
+    dialog.set_extra_child(Some(&group));
+    dialog.add_response("cancel", "Cancel");
+    if conflict.original_exists {
+        dialog.add_response("original", "Keep Original");
+        dialog.add_response("both", "Keep Both");
+    }
+    dialog.add_response("copy", "Keep Copy");
+    dialog.set_default_response(Some("cancel"));
+    dialog.set_close_response("cancel");
+    // Keeping both is a rename, so it needs a name that is neither side's.
+    let update_both = {
+        let dialog = dialog.clone();
+        let copy_name = copy_name.clone();
+        move |row: &adw::EntryRow| {
+            let name = row.text();
+            let name = name.trim();
+            dialog.set_response_enabled(
+                "both",
+                !name.is_empty()
+                    && name != copy_name
+                    && name != original_name
+                    && !name.contains('/'),
+            );
+        }
+    };
+    if conflict.original_exists {
+        update_both(&name_row);
+        name_row.connect_changed(update_both);
+    }
+    let ui = ui.clone();
+    let path = conflict.path.clone();
+    dialog.connect_response(None, move |_, resp| {
+        let keep = match resp {
+            "original" => ConflictKeep::Original,
+            "copy" => ConflictKeep::Copy,
+            "both" => ConflictKeep::Both {
+                name: name_row.text().trim().to_string(),
+            },
+            _ => return,
+        };
+        resolve_conflict(&ui, path.clone(), keep);
+    });
+    dialog.present(win.as_ref());
+}
+
+fn resolve_conflict(ui: &Rc<Ui>, path: String, keep: ConflictKeep) {
+    ui.busy_begin();
+    let rx = spawn_request(
+        ui.dirs.control_socket(),
+        Request::ResolveConflict { path, keep },
+    );
+    let ui = ui.clone();
+    glib::spawn_future_local(async move {
+        let result = rx.recv().await;
+        ui.busy_end();
+        match result {
+            Ok(Ok(Response::Ok { message })) => {
+                toast(&ui, &capitalize(&message));
+                refresh_conflicts(&ui, true);
+            }
+            Ok(Ok(Response::Error { message, kind })) => {
+                toast_failure(&ui, "Couldn't resolve the conflict", &message, kind)
+            }
+            _ => toast_error(
+                &ui,
+                "Couldn't resolve the conflict",
+                "The mount service didn't respond.",
+            ),
+        }
+    });
+}
+
+/// First letter upper-cased, for a daemon message used as a sentence.
+fn capitalize(message: &str) -> String {
+    let mut chars = message.chars();
+    match chars.next() {
+        Some(first) => first.to_uppercase().chain(chars).collect(),
+        None => String::new(),
+    }
+}
+
 /// Show a status page in place of the locations list.
 pub(crate) fn locations_status(
     ui: &Rc<Ui>,

crates/pdfs-gui/src/app/pages/status.rs

@@ -618,6 +618,7 @@ pub(crate) fn refresh(ui: &Rc<Ui>) {
         Some("locations") => {
             refresh_locations(ui);
             refresh_queue(ui);
+            refresh_conflicts(ui, false);
         }
         Some("activity") => refresh_activity(ui),
         _ => {}