feat(desktop): home app (system-only launch cap, LAUNCH_BADGE: apps+launch only), pm starts it with session (relaunch <=5); display keys F1/Alt+Tab next, F2 home, F4 close app (ROLE from launcher, terminal exempt), close returns to previous window; closed window -> app exits; shell 'name &'; launch by id; pm stack 8, storage 16 clients

crates/drivers/input/virtio/src/keymap.rs

@@ -6,6 +6,16 @@ pub const LEFT_SHIFT: u16 = 42;
 pub const RIGHT_SHIFT: u16 = 54;
 pub const LEFT_CTRL: u16 = 29;
 pub const RIGHT_CTRL: u16 = 97;
+pub const LEFT_ALT: u16 = 56;
+pub const RIGHT_ALT: u16 = 100;
+/// Alt+Tab is the display's window switch, the same key as F1
+/// (`types::display::window::SWITCH_KEY`).
+const SWITCH: Key = Key::Function(1);
+
+/// What a key is with Alt held: only Alt+Tab means anything.
+pub fn with_alt(key: Key) -> Option<Key> {
+    (key == Key::Tab).then_some(SWITCH)
+}
 
 /// A letter typed with Ctrl held is its control character, as on a
 /// terminal: Ctrl+C is 3. Anything else is itself.
@@ -54,6 +64,12 @@ pub fn key(code: u16, shift: bool) -> Option<Key> {
 mod tests {
     use super::*;
 
+    #[test]
+    fn alt_tab_switches_windows_and_other_alt_keys_are_nothing() {
+        assert_eq!(with_alt(Key::Tab), Some(Key::Function(1)));
+        assert_eq!(with_alt(Key::Char(b'a')), None);
+    }
+
     #[test]
     fn function_keys_are_numbered() {
         assert_eq!(key(59, false), Some(Key::Function(1)));

crates/drivers/input/virtio/src/lib.rs

@@ -36,6 +36,7 @@ pub struct VirtioInputDevice {
     next_avail: u16,
     shift: bool,
     ctrl: bool,
+    alt: bool,
 }
 
 impl VirtioInputDevice {
@@ -61,6 +62,7 @@ impl VirtioInputDevice {
             next_avail: 0,
             shift: false,
             ctrl: false,
+            alt: false,
         };
         dev.fill_queue();
         Some(dev)
@@ -129,8 +131,13 @@ impl InputDevice for VirtioInputDevice {
                 self.ctrl = ev_value != 0;
                 continue;
             }
+            if ev_type == EV_KEY && matches!(ev_code, keymap::LEFT_ALT | keymap::RIGHT_ALT) {
+                self.alt = ev_value != 0;
+                continue;
+            }
             if ev_type == EV_KEY {
                 let key = keymap::key(ev_code, self.shift).map(|k| if self.ctrl { keymap::with_ctrl(k) } else { k });
+                let key = if self.alt { key.and_then(keymap::with_alt) } else { key };
                 if let Some(key) = key {
                     if ev_value == KEY_PRESS {
                         return Some(InputEvent::KeyDown(key));