Host: workspaces (always) and encrypted folder sync (AppConfig::with_sync) commands; SiteHooks::backup_sections and backup_section_names say what a backup and sync carry; commands::WORKSPACES, commands::SYNC, testkit::assert_sync_guards

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

crates/waybetter-host/src/app.rs

@@ -89,6 +89,9 @@ pub struct AppConfig {
     /// Google Fonts (install, remove, preview; the cache in app data): serves [`commands::GFONTS`]
     /// and calls [`SiteHooks::fonts_changed`]. Needs the `net` feature.
     pub fonts: bool,
+    /// Encrypted folder sync of the settings backup: serves [`commands::SYNC`] and needs
+    /// [`SiteHooks::backup_sections`]. ([`commands::WORKSPACES`] is served for every app.)
+    pub sync: bool,
     /// Native updates and the hotfix channel: serves [`commands::UPDATE`] and runs the update loop.
     /// Needs `updater` (the plugin) and the `net` feature.
     #[cfg(feature = "net")]
@@ -117,6 +120,7 @@ impl AppConfig {
             store: None,
             media: false,
             fonts: false,
+            sync: false,
             #[cfg(feature = "net")]
             updates: None,
         }
@@ -129,6 +133,12 @@ impl AppConfig {
         self
     }
 
+    /// Serves the sync commands ([`commands::SYNC`]).
+    pub const fn with_sync(mut self) -> Self {
+        self.sync = true;
+        self
+    }
+
     /// Serves the Google Fonts commands ([`commands::GFONTS`]).
     pub const fn with_fonts(mut self) -> Self {
         self.fonts = true;
@@ -229,6 +239,18 @@ pub trait SiteHooks: Send + Sync + 'static {
     /// theme, and the font bytes, again.
     fn fonts_changed(&self, _app: &AppHandle) {}
 
+    /// The app's native settings as backup sections (themes, plugins, tweaks, ... keyed by section
+    /// name, from app data): what a backup and [`commands::SYNC`] carry besides the shell's own
+    /// storage. By default none.
+    fn backup_sections(&self, _app: &AppHandle) -> Result<serde_json::Map<String, serde_json::Value>, String> {
+        Ok(serde_json::Map::new())
+    }
+
+    /// The names of the sections an import may carry (others are dropped). By default none.
+    fn backup_section_names(&self) -> &'static [&'static str] {
+        &[]
+    }
+
     /// `tab` was laid out for `item` (existing or new), before it is placed.
     fn tab_placed(&self, _app: &AppHandle, _tab: &Webview, _item: &TabLayout) {}
 
@@ -1147,6 +1169,11 @@ fn store_handler() -> impl Fn(tauri::ipc::Invoke<Wry>) -> bool + Send + Sync + '
     |_| false
 }
 
+/// The workspaces and sync commands ([`commands::WORKSPACES`], [`commands::SYNC`]).
+fn sync_handler() -> impl Fn(tauri::ipc::Invoke<Wry>) -> bool + Send + Sync + 'static {
+    crate::sync_commands::handler()
+}
+
 /// The update commands ([`commands::UPDATE`]): with the `net` feature only.
 #[cfg(feature = "net")]
 fn update_handler() -> impl Fn(tauri::ipc::Invoke<Wry>) -> bool + Send + Sync + 'static {
@@ -1208,6 +1235,7 @@ impl App {
         let media_handler = media_handler();
         let fonts_handler = fonts_handler();
         let update_handler = update_handler();
+        let sync_handler = sync_handler();
         let builder = tauri::Builder::<Wry>::default()
             // Must be first: a second launch focuses the running window instead of fighting over
             // the app's data and WebView profile (and hands over its link).
@@ -1288,6 +1316,7 @@ impl App {
                 #[cfg(feature = "net")]
                 crate::store_commands::init(&handle, &config);
                 crate::media_commands::init(&handle);
+                crate::sync_commands::init(&handle);
                 #[cfg(feature = "net")]
                 crate::fonts_commands::init(&handle);
                 #[cfg(feature = "net")]
@@ -1314,6 +1343,8 @@ impl App {
                     fonts_handler(invoke)
                 } else if commands::UPDATE.contains(&invoke.message.command()) {
                     update_handler(invoke)
+                } else if commands::WORKSPACES.contains(&invoke.message.command()) || commands::SYNC.contains(&invoke.message.command()) {
+                    sync_handler(invoke)
                 } else if commands::is_host(invoke.message.command()) {
                     host_handler(invoke)
                 } else {