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/servers/permission-manager/src/lib.rs

@@ -49,6 +49,7 @@ pub fn run() -> ! {
     let consent = consent::TerminalConsent { terminal: TERMINAL };
     let ports = server::Ports { init: INIT, display: Some(DISPLAY), session: Some(SESSION), endpoint: EP };
     let mut srv = server::PermissionServer::new(store, consent, ports, deaths);
+    srv.start_home();
     libkos::println!("permission: serving");
     server_framework::serve(&mut srv, EP)
 }

crates/servers/permission-manager/src/server.rs

@@ -15,6 +15,7 @@ use types::bounded::CapSlot;
 use types::budget::Limits;
 use types::mapping::PagePerms;
 use types::permission::{Permission, PermissionSet};
+use types::display::window::role as display_role;
 use types::start_arg::StartArg;
 
 use crate::consent::{CapabilityNames, TerminalConsent, version};
@@ -27,6 +28,12 @@ const PROGRAM: Limits = Limits { pages: 0, endpoints: 1, notifications: 1, regio
 /// Apps running at once; a death is a bit each on the notification.
 const MAX_RUNNING: usize = 8;
 const MAX_ARGS: usize = 16;
+/// The session's desktop, started with it and again if it dies.
+const HOME: &str = "kos.home";
+/// Home's starts in a session at most: one that keeps dying is left down.
+const MAX_HOMES: u8 = 5;
+/// A launch that no launcher asked for (Home's): nothing staged is its.
+const NO_LAUNCHER: usize = usize::MAX;
 /// Where a client's request page is mapped during its call.
 const PAGE_VA: VirtualAddress = VirtualAddress::from_raw(0x01A0_0000);
 
@@ -66,6 +73,8 @@ pub struct PermissionServer {
     deaths: CapSlot,
     staged: Staged,
     running: [Option<Running>; MAX_RUNNING],
+    /// Home's starts this session.
+    homes: u8,
 }
 
 fn refused(r: Refusal) -> [usize; 4] {
@@ -127,12 +136,12 @@ fn parts(page: &[u8]) -> impl Iterator<Item = &str> {
 impl PermissionServer {
     pub fn new(store: DiskStore, consent: TerminalConsent, ports: Ports, deaths: CapSlot) -> Self {
         let Ports { init, display, session, endpoint } = ports;
-        Self { store, consent, init, display, session, endpoint, deaths, staged: Staged::default(), running: [const { None }; MAX_RUNNING] }
+        Self { store, consent, init, display, session, endpoint, deaths, staged: Staged::default(), running: [const { None }; MAX_RUNNING], homes: 0 }
     }
 
     /// What this device has a server for.
     fn available(&self) -> Capabilities {
-        let mut c = Capabilities::NONE.with(Capability::Storage).with(Capability::Permissions);
+        let mut c = Capabilities::NONE.with(Capability::Storage).with(Capability::Permissions).with(Capability::Launch);
         if self.display.is_some() {
             c = c.with(Capability::Display);
         }
@@ -177,7 +186,27 @@ impl PermissionServer {
             *slot = p;
             n += 1;
         }
-        let args = &args[..n];
+        self.run(badge, &args[..n])
+    }
+
+    /// Starts Home, the session's desktop, unless it runs already or has
+    /// died too often.
+    pub fn start_home(&mut self) {
+        let running = self.running.iter().flatten().any(|r| r.id.as_str() == HOME);
+        if running || self.homes >= MAX_HOMES {
+            return;
+        }
+        self.homes += 1;
+        match self.run(NO_LAUNCHER, &[HOME]) {
+            Ok((process, _)) => {
+                syscall::drop_cap(process);
+            }
+            Err(words) => libkos::println!("permission: home did not start (refused: {})", words[0]),
+        }
+    }
+
+    /// Runs `args[0]` with `args` for the launcher behind `badge`.
+    fn run(&mut self, badge: usize, args: &[&str]) -> Result<(CapSlot, Capabilities), [usize; 4]> {
         let command = *args.first().ok_or(code(reply::NOT_INSTALLED))?;
         let available = self.available();
         let plan = policy::plan_launch(&mut self.store, command, available).map_err(refused)?;
@@ -201,18 +230,27 @@ impl PermissionServer {
             true => self.display.and_then(|d| libkos::display::open(d, plan.app.name.as_str().as_bytes())).map(|o| o.window),
             false => None,
         };
-        // Its brand colour too, which the display adapts to the theme.
-        if let (Some(w), Some(accent)) = (window, plan.app.accent) {
-            libkos::display::set_accent(w, accent.0);
-        }
-        // Managing others through a copy of this endpoint that can do no
-        // more (see `MANAGE_BADGE`).
-        let manage = match plan.granted.contains(Capability::Permissions) {
-            true => {
-                let perms = PermissionSet::empty().with(Permission::Execute).with(Permission::Delegate);
-                syscall::mint(self.endpoint, types::badge::Badge::new(wire::MANAGE_BADGE | index), perms).ok()
+        // Its brand colour too, which the display adapts to the theme, and
+        // what it is: Home, or an app the user may close.
+        if let Some(w) = window {
+            if let Some(accent) = plan.app.accent {
+                libkos::display::set_accent(w, accent.0);
+            }
+            let role = if plan.app.id.as_str() == HOME { display_role::HOME } else { display_role::APP };
+            libkos::display::set_role(w, role);
+        }
+        // Managing others, or launching them, through a copy of this
+        // endpoint that can do no more (see `MANAGE_BADGE`, `LAUNCH_BADGE`).
+        let bits = [(Capability::Permissions, wire::MANAGE_BADGE), (Capability::Launch, wire::LAUNCH_BADGE)]
+            .iter()
+            .filter(|(c, _)| plan.granted.contains(*c))
+            .fold(0, |b, (_, bit)| b | bit);
+        let manage = match bits {
+            0 => None,
+            bits => {
+                let perms = PermissionSet::empty().with(Permission::Execute).with(Permission::Delegate);
+                syscall::mint(self.endpoint, types::badge::Badge::new(bits | index), perms).ok()
             }
-            false => None,
         };
         let session = self.session.filter(|_| plan.granted.contains(Capability::Session));
         let staged = (badge == self.staged.badge).then_some(&self.staged);
@@ -319,8 +357,9 @@ impl PermissionServer {
         code(reply::OK)
     }
 
-    /// Apps behind `bits` died: their data grants go back.
+    /// Apps behind `bits` died: their data grants go back. Home comes back.
     fn reap(&mut self, bits: usize) {
+        let home_died = self.running.iter().enumerate().any(|(i, r)| bits & (1 << i) != 0 && r.as_ref().is_some_and(|r| r.id.as_str() == HOME));
         for (i, slot) in self.running.iter_mut().enumerate() {
             if bits & (1 << i) == 0 {
                 continue;
@@ -334,6 +373,9 @@ impl PermissionServer {
                 syscall::drop_cap(r.process);
             }
         }
+        if home_died {
+            self.start_home();
+        }
     }
 }
 
@@ -407,9 +449,14 @@ fn close_window(window: Option<CapSlot>) {
 }
 
 /// Whether `op` may come through the copy of this endpoint badged `badge`:
-/// a management copy (`permissions`) decides, never installs or launches.
+/// a management copy (`permissions`) decides, never installs or launches;
+/// a launcher's (`launch`) lists and launches, passing nothing along.
 pub fn allowed(badge: usize, op: usize) -> bool {
-    badge & wire::MANAGE_BADGE == 0 || matches!(op, wire::LIST | wire::APPS | wire::REVOKE | wire::ALLOW)
+    let (manage, launch) = (badge & wire::MANAGE_BADGE != 0, badge & wire::LAUNCH_BADGE != 0);
+    if !manage && !launch {
+        return true;
+    }
+    (manage && matches!(op, wire::LIST | wire::APPS | wire::REVOKE | wire::ALLOW)) || (launch && matches!(op, wire::APPS | wire::LAUNCH))
 }
 
 fn revoke(cap: Option<CapSlot>) {

crates/servers/permission-manager/src/store.rs

@@ -202,7 +202,8 @@ impl Store for DiskStore {
                 n += 1;
             }
         });
-        ids.into_iter().flatten().find(|id| self.manifest(id).is_some_and(|m| m.command.as_str() == command))
+        // By its id, or the command the shell runs it as.
+        ids.into_iter().flatten().find(|id| id.as_str() == command || self.manifest(id).is_some_and(|m| m.command.as_str() == command))
     }
 
     fn decision(&mut self, id: &AppId) -> Option<Decision> {

crates/servers/permission-manager/src/tests/mod.rs

@@ -11,5 +11,18 @@ fn a_management_copy_only_decides() {
     for op in [LAUNCH, INSTALL, PASS_OUTPUT, PASS_FOLDER, 99] {
         assert!(!allowed(manager, op), "op {op}");
     }
-    assert!(allowed(5, LAUNCH) && allowed(5, INSTALL), "a launcher's copy does everything");
+    assert!(allowed(5, LAUNCH) && allowed(5, INSTALL), "the shell's copy does everything");
+}
+
+#[test]
+fn a_home_copy_only_lists_and_launches() {
+    use crate::server::allowed;
+    use types::apps::*;
+    let home = LAUNCH_BADGE | 2;
+    assert!(allowed(home, APPS) && allowed(home, LAUNCH));
+    for op in [PASS_OUTPUT, PASS_FOLDER, INSTALL, LIST, REVOKE, ALLOW] {
+        assert!(!allowed(home, op), "op {op}");
+    }
+    let both = LAUNCH_BADGE | MANAGE_BADGE | 2;
+    assert!(allowed(both, LAUNCH) && allowed(both, REVOKE) && !allowed(both, INSTALL));
 }