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.

2 files changed, 197 insertions, 0 deletions

diff --git a/crates/core/src/context_menu.rs b/crates/core/src/context_menu.rs
new file mode 100644
index 0000000..30b1e8f
--- /dev/null
+++ b/crates/core/src/context_menu.rs
@@ -0,0 +1,195 @@
+//! Right-click titlebar window menu - the one titlebar interaction
+//! virtually every desktop WM has always offered. Backend-agnostic: this
+//! is pure state and geometry (which rows exist, which one a point falls
+//! on), not pixels. The Wayland backend renders it via
+//! `decoration::render_context_menu`; the X11 backend draws it with raw
+//! XCB calls the same way it already draws its own titlebar.
+//!
+//! Originally lived only in the Wayland crate; moved here once the X11
+//! backend needed the same row set and hit-testing rather than a second,
+//! drifting copy of the same logic - this data has no Wayland-specific
+//! content at all, so duplicating it would just be two copies of the same
+//! bug waiting to happen.
+
+use crate::{WindowManager, WindowId, WorkspaceId, TITLEBAR_HEIGHT};
+
+#[derive(Clone, Copy)]
+pub enum MenuAction {
+    Minimize,
+    ToggleMaximize,
+    ToggleFullscreen,
+    ToggleFloating,
+    ToggleAlwaysOnTop,
+    MoveToWorkspace(WorkspaceId),
+    Close,
+    /// Not a real action - a purely visual divider row. `row_at` still
+    /// resolves a click on one to `Some(index)` (it occupies a real row,
+    /// same as any other), so the dispatch site is what actually no-ops
+    /// on it, same "the row exists but does nothing" contract a real
+    /// desktop's own menu separators have.
+    Separator,
+}
+
+pub struct ContextMenu {
+    pub window: WindowId,
+    /// Top-left corner, in global (output-independent) space - same frame
+    /// `Window.geometry` and every other rendered element's position uses.
+    pub pos: (i32, i32),
+    pub width: u32,
+    pub row_height: u32,
+    pub items: Vec<(&'static str, MenuAction)>,
+}
+
+const MENU_WIDTH: u32 = 170;
+
+impl ContextMenu {
+    /// Builds the menu for `window`, opening with its top-left corner at
+    /// `pos` (wherever the right-click landed). Labels reflect the
+    /// window's *current* state - "Maximize" flips to "Restore", "Always
+    /// on Top" gets a checkmark prefix once pinned - same convention
+    /// every native window menu uses, rather than a static label that
+    /// silently means the opposite of what it says half the time.
+    pub fn open(wm: &WindowManager, window: WindowId, pos: (i32, i32)) -> Option<Self> {
+        let w = wm.window(window)?;
+        let maximize_label = if w.maximized { "Restore" } else { "Maximize" };
+        let fullscreen_label = if w.fullscreen { "Exit Fullscreen" } else { "Fullscreen" };
+        let floating_label = if w.floating { "\u{2713} Floating" } else { "Floating" };
+        let pin_label = if w.always_on_top { "\u{2713} Always on Top" } else { "Always on Top" };
+        let mut items = vec![
+            ("Minimize", MenuAction::Minimize),
+            (maximize_label, MenuAction::ToggleMaximize),
+            (fullscreen_label, MenuAction::ToggleFullscreen),
+            (floating_label, MenuAction::ToggleFloating),
+            (pin_label, MenuAction::ToggleAlwaysOnTop),
+        ];
+        // One row per *other* workspace - skips the window's own current
+        // one, since "move to the workspace it's already on" isn't a real
+        // action. Flattened rather than a real submenu - `workspace.count`
+        // is small in practice (this project's own default config uses 6),
+        // so the menu stays a reasonable height without one.
+        let others: Vec<&crate::Workspace> = wm.workspaces().iter().filter(|ws| ws.id != w.workspace).collect();
+        if !others.is_empty() {
+            items.push(("\u{2500}\u{2500}\u{2500} Move to Workspace \u{2500}\u{2500}\u{2500}", MenuAction::Separator));
+            for ws in others {
+                // `Workspace.name` is `&'static`-incompatible (a real
+                // `String`, user-configurable via `workspace.names`) --
+                // `Box::leak` turns it into the `&'static str` this
+                // struct's own `items` field is typed for.
+                let label: &'static str = Box::leak(ws.name.clone().into_boxed_str());
+                items.push((label, MenuAction::MoveToWorkspace(ws.id)));
+            }
+        }
+        items.push(("\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}\u{2500}", MenuAction::Separator));
+        items.push(("Close", MenuAction::Close));
+        Some(Self { window, pos, width: MENU_WIDTH, row_height: TITLEBAR_HEIGHT, items })
+    }
+
+    pub fn height(&self) -> i32 {
+        self.row_height as i32 * self.items.len() as i32
+    }
+
+    /// Which row (if any) global-space point `(x, y)` falls on.
+    pub fn row_at(&self, x: i32, y: i32) -> Option<usize> {
+        if x < self.pos.0 || x >= self.pos.0 + self.width as i32 {
+            return None;
+        }
+        let rel_y = y - self.pos.1;
+        if rel_y < 0 || rel_y >= self.height() {
+            return None;
+        }
+        Some((rel_y / self.row_height as i32) as usize)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::Window;
+
+    fn wm_with_window() -> (WindowManager, WindowId) {
+        let mut wm = WindowManager::new();
+        wm.set_monitors(vec![crate::Monitor::new(0, "primary", crate::Rect::new(0, 0, 1920, 1080))]);
+        let id = wm.alloc_window_id();
+        wm.add_window(Window::new(id, "a"));
+        (wm, id)
+    }
+
+    #[test]
+    fn open_labels_maximize_action_by_current_state() {
+        let (mut wm, id) = wm_with_window();
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        assert_eq!(menu.items[1].0, "Maximize");
+
+        wm.toggle_maximize(id);
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        assert_eq!(menu.items[1].0, "Restore");
+    }
+
+    #[test]
+    fn open_marks_pinned_state_on_the_always_on_top_row() {
+        let (mut wm, id) = wm_with_window();
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        // Minimize, Maximize, Fullscreen, Floating, then Always on Top.
+        assert_eq!(menu.items[4].0, "Always on Top");
+
+        wm.toggle_always_on_top(id);
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        assert!(menu.items[4].0.starts_with('\u{2713}'), "pinned state must be visible on the label itself");
+    }
+
+    #[test]
+    fn open_returns_none_for_a_window_that_no_longer_exists() {
+        let (wm, id) = wm_with_window();
+        assert!(ContextMenu::open(&wm, id + 999, (0, 0)).is_none());
+    }
+
+    #[test]
+    fn single_workspace_gets_no_move_to_workspace_section() {
+        let (wm, id) = wm_with_window();
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        assert!(!menu.items.iter().any(|(label, _)| label.contains("Workspace")));
+        assert_eq!(menu.items.len(), 7, "Minimize, Maximize, Fullscreen, Floating, Always on Top, one separator, Close");
+    }
+
+    #[test]
+    fn a_second_workspace_adds_a_move_row_but_not_for_its_own_workspace() {
+        let (mut wm, id) = wm_with_window();
+        wm.add_workspace("2", "dynamic");
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        let workspace_rows: Vec<&str> = menu
+            .items
+            .iter()
+            .filter_map(|(label, action)| matches!(action, MenuAction::MoveToWorkspace(_)).then_some(*label))
+            .collect();
+        assert_eq!(workspace_rows, vec!["2"], "only the OTHER workspace gets a row, not the window's own");
+    }
+
+    #[test]
+    fn clicking_a_separator_row_is_distinguishable_from_a_real_action() {
+        let (mut wm, id) = wm_with_window();
+        wm.add_workspace("2", "dynamic");
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        let separator_count = menu.items.iter().filter(|(_, a)| matches!(a, MenuAction::Separator)).count();
+        assert_eq!(separator_count, 2, "one before the workspace section, one before Close");
+    }
+
+    #[test]
+    fn row_at_maps_a_point_to_the_right_row() {
+        let (wm, id) = wm_with_window();
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        assert_eq!(menu.row_at(150, 100), Some(0), "top of the first row");
+        assert_eq!(menu.row_at(150, 100 + TITLEBAR_HEIGHT as i32 - 1), Some(0), "bottom of the first row");
+        assert_eq!(menu.row_at(150, 100 + TITLEBAR_HEIGHT as i32), Some(1), "top of the second row");
+        assert_eq!(menu.row_at(150, 100 + menu.height() - 1), Some(menu.items.len() - 1), "last row, last pixel");
+    }
+
+    #[test]
+    fn row_at_is_none_outside_the_menus_bounds() {
+        let (wm, id) = wm_with_window();
+        let menu = ContextMenu::open(&wm, id, (100, 100)).unwrap();
+        assert_eq!(menu.row_at(99, 110), None, "just left of the menu");
+        assert_eq!(menu.row_at(100 + MENU_WIDTH as i32, 110), None, "just right of the menu");
+        assert_eq!(menu.row_at(150, 99), None, "just above the menu");
+        assert_eq!(menu.row_at(150, 100 + menu.height()), None, "just below the menu");
+    }
+}
diff --git a/crates/core/src/lib.rs b/crates/core/src/lib.rs
index 7905504..066d6d2 100644
--- a/crates/core/src/lib.rs
+++ b/crates/core/src/lib.rs
@@ -1,3 +1,4 @@
+pub mod context_menu;
 pub mod event;
 pub mod geometry;
 pub mod keysyms;
@@ -11,6 +12,7 @@ pub mod theme;
 pub mod window;
 pub mod workspace;
 
+pub use context_menu::{ContextMenu, MenuAction};
 pub use event::{canonicalize_key_combo, key_combo_string, parse_key_combo, Event, MouseButton, Modifiers};
 pub use geometry::Rect;
 pub use layout::{Layout, MasterStackLayout, NoOpLayout, TilingConfig};