X11 backend: right-click titlebar window menu, matching Wayland's own

Closes the one real gap an X11/Wayland feature-parity audit found this
session (desktop icons, window-position memory, and static exclusive-zone
reservation were already shared or Wayland-only by nature - see
docs/TODO.md's own audit entry for the full breakdown).

MenuAction/ContextMenu (row set, labels, row_at hit-testing) move from
crates/wayland/src/context_menu.rs into crates/core/src/context_menu.rs --
pure state and geometry with nothing Wayland-specific in it, so X11
needing the same rows is shared data, not duplicated logic. The Wayland
crate's own context_menu.rs is now a one-line re-export so every existing
crate::context_menu::... call site keeps working unchanged.

X11 has no compositor-level input dispatch to intercept every click the
way Wayland's input/pointer.rs does, so the X11 side
(crates/x11/src/platform/context_menu.rs, new) draws the menu into its own
small override-redirect popup window and grabs the pointer for the
duration so a click anywhere dismisses it, matching the Wayland backend's
own convention. events.rs's ButtonPress handler now reads the real button
number instead of hardcoding every press as a left click - a real latent
bug (right-clicking a titlebar button would have silently performed its
left-click action).

Live-verified end to end in an isolated Xvfb + srdwm --x11 instance: full
row set including the workspace picker, Minimize runs and closes the
menu, a second window's menu dismisses cleanly on outside click, normal
focus/click behaviour continues working afterward.

See docs/TODO.md for the full investigation and verification narrative.

5 files changed, 222 insertions, 7 deletions

diff --git a/crates/x11/src/platform/connect.rs b/crates/x11/src/platform/connect.rs
index 060b3d2..ee8906d 100644
--- a/crates/x11/src/platform/connect.rs
+++ b/crates/x11/src/platform/connect.rs
@@ -98,6 +98,7 @@ impl X11Platform {
             ipc,
             appmenu_registrar: Some(srdwm_platform::AppmenuRegistrarState::new()),
             struts: HashMap::new(),
+            context_menu: None,
         })
     }
 
diff --git a/crates/x11/src/platform/context_menu.rs b/crates/x11/src/platform/context_menu.rs
new file mode 100644
index 0000000..9238f6a
--- /dev/null
+++ b/crates/x11/src/platform/context_menu.rs
@@ -0,0 +1,153 @@
+//! Right-click titlebar window menu - the X11 half of `srdwm_core::
+//! context_menu`. The Wayland backend renders this into a shared
+//! compositor buffer; X11 has no equivalent (there is no single "every
+//! surface" compositor here, just ordinary X windows), so this draws it
+//! into its own small override-redirect popup window with the same GC/
+//! font `redraw_decoration` already uses for the titlebar itself.
+//!
+//! Row set and hit-testing come from `srdwm_core::context_menu`, unchanged
+//! from the Wayland backend - see that module's own doc comment for why
+//! it moved there. Foreign-toplevel state broadcasting
+//! (`foreign_toplevel::send_state` on the Wayland side) has no X11
+//! equivalent - that protocol is Wayland-only - so `run_context_menu_
+//! action` below is otherwise the same action set with that one line
+//! dropped.
+
+use super::*;
+use srdwm_core::context_menu::{ContextMenu, MenuAction};
+use x11rb::protocol::xproto::{ChangeGCAux, CoordMode, Point};
+
+impl X11Platform {
+    /// Opens the menu for `window` with its top-left corner at `pos`
+    /// (root-window pixels, wherever the right-click landed), clamped so
+    /// it never opens off the right/bottom edge of the screen. Grabs the
+    /// pointer for the duration: X11 has no single compositor-level input
+    /// dispatch to intercept every click the way the Wayland backend's
+    /// `input/pointer.rs` does, so an active grab on the root window is
+    /// what makes "click anywhere else dismisses the menu" work at all --
+    /// without it, a click over some other client's window would go
+    /// straight to that client and never reach us.
+    pub(super) fn open_context_menu(&mut self, window: WindowId, pos: (i32, i32)) -> PlatformResult<()> {
+        let Some(mut menu) = ({
+            let wm = self.wm.borrow();
+            ContextMenu::open(&wm, window, pos)
+        }) else {
+            return Ok(());
+        };
+
+        let screen = &self.conn.setup().roots[0];
+        let (sw, sh) = (screen.width_in_pixels as i32, screen.height_in_pixels as i32);
+        let x = menu.pos.0.max(0).min((sw - menu.width as i32).max(0));
+        let y = menu.pos.1.max(0).min((sh - menu.height()).max(0));
+        menu.pos = (x, y);
+
+        let popup = self.conn.generate_id().map_err(err)?;
+        let aux = CreateWindowAux::new()
+            .override_redirect(1)
+            .event_mask(EventMask::EXPOSURE)
+            .background_pixel(screen.white_pixel);
+        self.conn
+            .create_window(COPY_DEPTH_FROM_PARENT, popup, self.root, x as i16, y as i16, menu.width as u16, menu.height() as u16, 0, WindowClass::INPUT_OUTPUT, 0, &aux)
+            .map_err(err)?;
+        self.conn.map_window(popup).map_err(err)?;
+        self.conn.configure_window(popup, &ConfigureWindowAux::new().stack_mode(StackMode::ABOVE)).map_err(err)?;
+
+        // `owner_events: false` - every button event while this grab is
+        // active is reported against `grab_window` (root) regardless of
+        // which window the pointer is physically over, carrying the same
+        // absolute `root_x`/`root_y` the normal per-window path already
+        // uses for hit-testing. Best-effort: a failed grab (another
+        // client already holds one, vanishingly rare in practice) still
+        // leaves the menu visible and closeable by re-clicking its own
+        // rows, just without the "click elsewhere" dismissal.
+        let _ = self
+            .conn
+            .grab_pointer(false, self.root, EventMask::BUTTON_PRESS, GrabMode::ASYNC, GrabMode::ASYNC, x11rb::NONE, x11rb::NONE, x11rb::CURRENT_TIME)
+            .map_err(err)?
+            .reply();
+        self.conn.flush().map_err(err)?;
+
+        self.context_menu = Some((menu, popup));
+        self.redraw_context_menu()
+    }
+
+    /// Repaints every row into the popup window - called once on open
+    /// (there's no live hover highlight here either, same as the Wayland
+    /// backend's own `render_context_menu`) and again on `Expose` (the
+    /// popup has no backing store, so anything that uncovers it needs a
+    /// real repaint, unlike the Wayland side where the buffer is already
+    /// composited).
+    pub(super) fn redraw_context_menu(&mut self) -> PlatformResult<()> {
+        let Some((menu, popup)) = &self.context_menu else { return Ok(()) };
+        let popup = *popup;
+        let (width, row_height, total_height) = (menu.width, menu.row_height, menu.height());
+        let theme = self.wm.borrow().theme;
+        let bg = rgb_to_pixel(theme.titlebar_bg);
+        let fg = rgb_to_pixel(theme.titlebar_fg_focused);
+
+        self.conn.change_gc(self.gc, &ChangeGCAux::new().foreground(bg)).map_err(err)?;
+        self.conn.poly_fill_rectangle(popup, self.gc, &[Rectangle { x: 0, y: 0, width: width as u16, height: total_height as u16 }]).map_err(err)?;
+        self.conn.change_gc(self.gc, &ChangeGCAux::new().foreground(fg).font(self.font)).map_err(err)?;
+
+        for (i, (label, action)) in menu.items.iter().enumerate() {
+            let row_y = i as i32 * row_height as i32;
+            if matches!(action, MenuAction::Separator) {
+                let mid = row_y + row_height as i32 / 2;
+                self.conn.poly_line(CoordMode::ORIGIN, popup, self.gc, &[Point { x: 8, y: mid as i16 }, Point { x: width as i16 - 8, y: mid as i16 }]).map_err(err)?;
+                continue;
+            }
+            self.conn.image_text8(popup, self.gc, 10, (row_y + 20) as i16, label.as_bytes()).map_err(err)?;
+        }
+        self.conn.flush().map_err(err)?;
+        Ok(())
+    }
+
+    /// Closes the currently-open menu, if any - a no-op otherwise, so
+    /// every dismissal path (a row picked, a click outside, the window it
+    /// belongs to closing underneath it) can call this unconditionally.
+    pub(super) fn close_context_menu(&mut self) -> PlatformResult<()> {
+        if let Some((_, popup)) = self.context_menu.take() {
+            self.conn.ungrab_pointer(x11rb::CURRENT_TIME).map_err(err)?;
+            self.conn.destroy_window(popup).map_err(err)?;
+            self.conn.flush().map_err(err)?;
+        }
+        Ok(())
+    }
+
+    /// Runs whichever action a click on `row` selected - the X11
+    /// equivalent of the Wayland backend's `state/menu.rs::run_context_
+    /// menu_action`, same action set minus the Wayland-only foreign-
+    /// toplevel broadcast.
+    pub(super) fn run_context_menu_action(&mut self, window: WindowId, action: MenuAction) -> PlatformResult<()> {
+        match action {
+            MenuAction::Minimize => {
+                self.wm.borrow_mut().minimize_window(window);
+                if let Some(frame) = self.frame_for(window) {
+                    self.conn.unmap_window(frame).map_err(err)?;
+                }
+            }
+            MenuAction::ToggleMaximize => {
+                self.wm.borrow_mut().toggle_maximize(window);
+                self.sync_geometry(window)?;
+            }
+            MenuAction::ToggleFullscreen => {
+                self.wm.borrow_mut().toggle_fullscreen(window);
+                self.sync_geometry(window)?;
+            }
+            MenuAction::ToggleFloating => {
+                self.wm.borrow_mut().toggle_floating(window);
+                self.sync_geometry(window)?;
+            }
+            MenuAction::ToggleAlwaysOnTop => {
+                self.wm.borrow_mut().toggle_always_on_top(window);
+            }
+            MenuAction::MoveToWorkspace(workspace) => {
+                self.wm.borrow_mut().move_window_to_workspace(window, workspace);
+            }
+            MenuAction::Close => self.request_close(window)?,
+            MenuAction::Separator => {}
+        }
+        self.conn.flush().map_err(err)?;
+        Ok(())
+    }
+}
diff --git a/crates/x11/src/platform/events.rs b/crates/x11/src/platform/events.rs
index 30e3f8d..10f96a9 100644
--- a/crates/x11/src/platform/events.rs
+++ b/crates/x11/src/platform/events.rs
@@ -70,30 +70,70 @@ impl X11Platform {
             }
             XEvent::ButtonPress(ev) => {
                 let (x, y) = (ev.root_x as i32, ev.root_y as i32);
+                let button = match ev.detail {
+                    1 => MouseButton::Left,
+                    2 => MouseButton::Middle,
+                    3 => MouseButton::Right,
+                    other => MouseButton::Other(other),
+                };
+
+                // The context menu, if open, captures every press: a click
+                // inside resolves whichever row it landed on, a click
+                // anywhere else just dismisses it - same "one click, one
+                // action" rule the Wayland backend's own input/pointer.rs
+                // follows, and why `open_context_menu` grabs the pointer
+                // (see that method's own doc comment for why X11 needs to).
+                if self.context_menu.is_some() {
+                    let (row_action, menu_window) = {
+                        let (menu, _) = self.context_menu.as_ref().unwrap();
+                        (menu.row_at(x, y).map(|r| menu.items[r].1), menu.window)
+                    };
+                    match row_action {
+                        Some(srdwm_core::context_menu::MenuAction::Separator) => {}
+                        Some(action) => {
+                            self.close_context_menu()?;
+                            self.run_context_menu_action(menu_window, action)?;
+                        }
+                        None => self.close_context_menu()?,
+                    }
+                    return Ok(Some(Event::MouseButtonPress { button, x, y }));
+                }
+
                 let hit = self.wm.borrow().hit_test(x, y);
                 if let Some((id, hit)) = hit {
                     self.raise_and_focus(id)?;
-                    match hit {
-                        TitlebarHit::Drag => self.wm.borrow_mut().start_drag(id, x, y),
-                        TitlebarHit::Close => self.request_close(id)?,
-                        TitlebarHit::Maximize => {
+                    match (button, hit) {
+                        (MouseButton::Left, TitlebarHit::Drag) => self.wm.borrow_mut().start_drag(id, x, y),
+                        (MouseButton::Left, TitlebarHit::Close) => self.request_close(id)?,
+                        (MouseButton::Left, TitlebarHit::Maximize) => {
                             self.wm.borrow_mut().toggle_maximize(id);
                             self.sync_geometry(id)?;
                         }
-                        TitlebarHit::Minimize => {
+                        (MouseButton::Left, TitlebarHit::Minimize) => {
                             self.wm.borrow_mut().minimize_window(id);
                             if let Some(frame) = self.frame_for(id) {
                                 self.conn.unmap_window(frame).map_err(err)?;
                             }
                         }
-                        TitlebarHit::Resize(edge) => self.wm.borrow_mut().start_resize(id, edge, x, y),
+                        (MouseButton::Left, TitlebarHit::Resize(edge)) => self.wm.borrow_mut().start_resize(id, edge, x, y),
+                        // Right-click on the titlebar's own drag area: the
+                        // window menu (minimize/maximize/fullscreen/
+                        // floating/always-on-top/move-to-workspace/close).
+                        // Any other button/hit combination - right-click
+                        // on a button, middle-click anywhere - just
+                        // raises/focuses (already done above) and does
+                        // nothing further, matching real desktops (a
+                        // right-click on a titlebar button is not itself
+                        // a button action).
+                        (MouseButton::Right, TitlebarHit::Drag) => self.open_context_menu(id, (x, y))?,
+                        _ => {}
                     }
                     self.conn.flush().map_err(err)?;
                 }
                 // Let the click through to the client (we grabbed it SYNC).
                 self.conn.allow_events(x11rb::protocol::xproto::Allow::REPLAY_POINTER, ev.time).map_err(err)?;
                 self.conn.flush().map_err(err)?;
-                Ok(Some(Event::MouseButtonPress { button: MouseButton::Left, x, y }))
+                Ok(Some(Event::MouseButtonPress { button, x, y }))
             }
             XEvent::ButtonRelease(ev) => {
                 let mut wm = self.wm.borrow_mut();
@@ -141,6 +181,13 @@ impl X11Platform {
                 Ok(Some(Event::KeyRelease { key_name, modifiers: Self::modifiers_from_state(ev.state.into()) }))
             }
             XEvent::Expose(ev) => {
+                // The popup has no backing store, unlike the compositor-
+                // side Wayland menu - anything that uncovers it needs a
+                // real repaint.
+                if self.context_menu.as_ref().is_some_and(|(_, popup)| *popup == ev.window) {
+                    let _ = self.redraw_context_menu();
+                    return Ok(None);
+                }
                 let target = self.frames.iter().find(|(_, f)| f.frame == ev.window).map(|(&id, _)| id);
                 if let Some(id) = target {
                     let w = self.wm.borrow().window(id).cloned_for_render();
diff --git a/crates/x11/src/platform/mod.rs b/crates/x11/src/platform/mod.rs
index 8ca2299..e22b3f7 100644
--- a/crates/x11/src/platform/mod.rs
+++ b/crates/x11/src/platform/mod.rs
@@ -198,6 +198,12 @@ pub struct X11Platform {
     /// window) - so this can't be folded into the existing managed-
     /// window bookkeeping.
     struts: HashMap<XWindow, Strut>,
+    /// The currently-open right-click titlebar window menu, if any --
+    /// the built row set/geometry alongside the override-redirect popup
+    /// window it's drawn into. See `context_menu.rs`'s module doc comment
+    /// for why X11 needs its own popup window and pointer grab where the
+    /// Wayland backend just reads a compositor-space struct.
+    context_menu: Option<(srdwm_core::context_menu::ContextMenu, XWindow)>,
 }
 
 
@@ -215,6 +221,7 @@ impl ClonedForRender for Option<&CoreWindow> {
 
 mod actions;
 mod connect;
+mod context_menu;
 mod events;
 mod global_menu;
 mod struts;
diff --git a/crates/x11/src/platform/window.rs b/crates/x11/src/platform/window.rs
index 997981f..bce71ca 100644
--- a/crates/x11/src/platform/window.rs
+++ b/crates/x11/src/platform/window.rs
@@ -156,6 +156,13 @@ impl X11Platform {
         if let Some(frame) = self.frames.remove(&id) {
             let _ = self.conn.destroy_window(frame.frame);
         }
+        // A closed window's own context menu (opened right before, say, a
+        // client that immediately quits) would otherwise dangle - its
+        // `MenuAction::Close`/etc. would target a `WindowId` `remove_
+        // window` below has already forgotten.
+        if self.context_menu.as_ref().is_some_and(|(menu, _)| menu.window == id) {
+            let _ = self.close_context_menu();
+        }
         self.wm.borrow_mut().remove_window(id);
         let _ = self.conn.flush();
         Some(Event::WindowDestroyed(id))