diff --git a/README.md b/README.md
index 9fe5a65..d9c885e 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,8 @@
 
 RuDS is a native Rust blogging desktop application and the successor to bDS2. It manages local projects from authoring through preview, static-site generation, integrity checks, and publishing while preserving the existing bDS filesystem and SQLite formats.
 
+The desktop is a single-window application: closing its window persists UI state and exits RuDS.
+
 The project is under active development. Core blogging workflows are broadly available; remaining core work and optional extensions are tracked separately.
 
 ## Available Features
diff --git a/crates/bds-ui/src/app.rs b/crates/bds-ui/src/app.rs
index f90fba3..d761f81 100644
--- a/crates/bds-ui/src/app.rs
+++ b/crates/bds-ui/src/app.rs
@@ -186,6 +186,7 @@ pub enum Message {
         task_id: TaskId,
         result: Result<engine::blogmark::BlogmarkImportResult, String>,
     },
+    WindowCloseRequested,
     MainWindowLoaded(Option<window::Id>),
     EmbeddedPreviewReady(Result<(), String>),
     EmbeddedStylePreviewReady(Result<(), String>),
@@ -1363,6 +1364,11 @@ impl BdsApp {
 
     pub fn update(&mut self, message: Message) -> Task<Message> {
         match message {
+            Message::WindowCloseRequested => {
+                self.persist_project_ui_state();
+                iced::exit()
+            }
+
             // ── Menu event dispatch ──
             Message::MenuEvent(id) => {
                 if let Some(action) = self.menu_registry.lookup(&id) {
@@ -3583,6 +3589,7 @@ impl BdsApp {
             }
             _ => None,
         });
+        let window_close_sub = window::close_requests().map(|_| Message::WindowCloseRequested);
 
         // Global mouse tracking for sidebar resize dragging.
         // The 4px drag handle mouse_area only fires on_press; move/release
@@ -3637,6 +3644,7 @@ impl BdsApp {
             domain_event_tick,
             toast_tick,
             file_drop_sub,
+            window_close_sub,
             drag_sub,
             menu_interaction_sub,
             menu_expand_tick,
diff --git a/crates/bds-ui/src/main.rs b/crates/bds-ui/src/main.rs
index dc656c1..ef33127 100644
--- a/crates/bds-ui/src/main.rs
+++ b/crates/bds-ui/src/main.rs
@@ -30,15 +30,20 @@ fn main() -> anyhow::Result<()> {
     iced::application("bDS", BdsApp::update, BdsApp::view)
         .subscription(BdsApp::subscription)
         .theme(|_| inputs::app_theme())
-        .window(iced::window::Settings {
-            size: iced::Size::new(1200.0, 800.0),
-            icon: Some(icon),
-            ..Default::default()
-        })
+        .window(desktop_window_settings(Some(icon)))
         .run_with(BdsApp::new)?;
     Ok(())
 }
 
+fn desktop_window_settings(icon: Option<iced::window::Icon>) -> iced::window::Settings {
+    iced::window::Settings {
+        size: iced::Size::new(1200.0, 800.0),
+        icon,
+        exit_on_close_request: false,
+        ..Default::default()
+    }
+}
+
 fn current_platform() -> Platform {
     #[cfg(target_os = "macos")]
     return Platform::MacOs;
@@ -49,3 +54,13 @@ fn current_platform() -> Platform {
     #[allow(unreachable_code)]
     Platform::Windows
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn single_window_close_is_owned_by_the_application() {
+        assert!(!desktop_window_settings(None).exit_on_close_request);
+    }
+}
diff --git a/specs/layout.allium b/specs/layout.allium
index affcf6b..6a2a448 100644
--- a/specs/layout.allium
+++ b/specs/layout.allium
@@ -19,6 +19,7 @@ surface LayoutControlSurface {
         TogglePanelRequested()
         ToggleAssistantSidebarRequested()
         ActivityClicked(activity_id)
+        CloseWindowRequested()
 }
 
 surface LayoutRuntimeSurface {
@@ -55,6 +56,13 @@ value AppShell {
     status_bar: StatusBar
 }
 
+rule CloseSingleWindow {
+    when: CloseWindowRequested()
+    ensures: ExitApplication()
+    -- bDS2 and RuDS are single-window applications. Closing that window
+    -- persists application-owned state and terminates the process.
+}
+
 surface AppShellSurface {
     context shell: AppShell