Host: developer mode (dev_* commands and the watcher) is served for every app that sets AppConfig::with_dev; SiteHooks::dev_theme_apply and dev_theme_end carry the app's theme file; commands::DEV, testkit::assert_dev_guards

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

crates/waybetter-host/src/app.rs

@@ -92,6 +92,10 @@ pub struct AppConfig {
     /// 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,
+    /// Developer mode (live reload of plugins, custom CSS and a theme file): serves
+    /// [`commands::DEV`] and runs the watcher while it is on; the theme file is the app's
+    /// ([`SiteHooks::dev_theme_apply`]).
+    pub dev: 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")]
@@ -121,6 +125,7 @@ impl AppConfig {
             media: false,
             fonts: false,
             sync: false,
+            dev: false,
             #[cfg(feature = "net")]
             updates: None,
         }
@@ -133,6 +138,12 @@ impl AppConfig {
         self
     }
 
+    /// Serves the developer-mode commands ([`commands::DEV`]).
+    pub const fn with_dev(mut self) -> Self {
+        self.dev = true;
+        self
+    }
+
     /// Serves the sync commands ([`commands::SYNC`]).
     pub const fn with_sync(mut self) -> Self {
         self.sync = true;
@@ -251,6 +262,16 @@ pub trait SiteHooks: Send + Sync + 'static {
         &[]
     }
 
+    /// Developer mode: show the theme file the owner picked (read `path`, make it the theme preview
+    /// in every site tab). An error is shown with its file and line. By default themes are not
+    /// supported and this does nothing.
+    fn dev_theme_apply(&self, _app: &AppHandle, _path: &std::path::Path) -> Result<(), crate::devmode::DevError> {
+        Ok(())
+    }
+
+    /// Developer mode ended (or the theme file was cleared): end the preview [`Self::dev_theme_apply`] made.
+    fn dev_theme_end(&self, _app: &AppHandle) {}
+
     /// `tab` was laid out for `item` (existing or new), before it is placed.
     fn tab_placed(&self, _app: &AppHandle, _tab: &Webview, _item: &TabLayout) {}
 
@@ -1169,6 +1190,11 @@ fn store_handler() -> impl Fn(tauri::ipc::Invoke<Wry>) -> bool + Send + Sync + '
     |_| false
 }
 
+/// The developer-mode commands ([`commands::DEV`]).
+fn dev_handler() -> impl Fn(tauri::ipc::Invoke<Wry>) -> bool + Send + Sync + 'static {
+    crate::dev_commands::handler()
+}
+
 /// 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()
@@ -1236,6 +1262,7 @@ impl App {
         let fonts_handler = fonts_handler();
         let update_handler = update_handler();
         let sync_handler = sync_handler();
+        let dev_handler = dev_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).
@@ -1317,6 +1344,7 @@ impl App {
                 crate::store_commands::init(&handle, &config);
                 crate::media_commands::init(&handle);
                 crate::sync_commands::init(&handle);
+                crate::dev_commands::init(&handle);
                 #[cfg(feature = "net")]
                 crate::fonts_commands::init(&handle);
                 #[cfg(feature = "net")]
@@ -1345,6 +1373,8 @@ impl App {
                     update_handler(invoke)
                 } else if commands::WORKSPACES.contains(&invoke.message.command()) || commands::SYNC.contains(&invoke.message.command()) {
                     sync_handler(invoke)
+                } else if commands::DEV.contains(&invoke.message.command()) {
+                    dev_handler(invoke)
                 } else if commands::is_host(invoke.message.command()) {
                     host_handler(invoke)
                 } else {