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/apps/home/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "home"
+version = "0.1.0"
+edition = "2024"
+
+[[bin]]
+name = "home"
+test = false
+bench = false
+
+[dependencies]
+types = { workspace = true }
+libkos = { workspace = true }
+k-ui = { workspace = true }
+manifest = { workspace = true }

crates/apps/home/manifest.toml

@@ -0,0 +1,10 @@
+[app]
+id      = "kos.home"
+name    = "Home"
+version = "1.0.0"
+binary  = "home"
+author  = "K-OS"
+memory  = "3 MiB"
+
+[capabilities]
+required = ["display", "launch"]

crates/apps/home/src/main.rs

@@ -0,0 +1,118 @@
+//! Home: the session's desktop, which the permission manager starts with
+//! it. It lists every app with a window and opens one when it is pressed,
+//! as many as there is room for, each in its own window. A system app:
+//! `launch` is only ever granted to apps on the system image.
+
+#![no_std]
+#![forbid(unsafe_code)]
+#![no_main]
+
+extern crate alloc;
+extern crate libkos;
+
+use alloc::format;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use k_ui::{App, Element, Spacing, TextColour, TextStyle, column, list_item, text};
+use libkos::apps::Apps;
+use manifest::{Capabilities, Capability};
+use types::address::VirtualAddress;
+use types::apps::reply;
+
+/// Where the request page for the permission manager is mapped.
+const REQUEST_PAGE_VA: VirtualAddress = VirtualAddress::from_raw(0x0190_0000);
+const LISTING: usize = 4096;
+const ME: &str = "kos.home";
+
+struct Entry {
+    id: String,
+    name: String,
+}
+
+struct Home {
+    apps: Option<Apps>,
+    entries: Vec<Entry>,
+    /// What went wrong last, shown until the next press.
+    trouble: Option<String>,
+}
+
+#[derive(Clone, Copy)]
+enum Event {
+    /// Open the `n`th app listed.
+    Open(usize),
+}
+
+impl Home {
+    /// Every installed app that has a window, but Home.
+    fn reload(&mut self) {
+        let Some(apps) = &self.apps else { return };
+        // On the heap: an app's stack is a few pages.
+        let mut buf = alloc::vec![0u8; LISTING];
+        let Ok(n) = apps.apps(&mut buf) else { return };
+        let text = core::str::from_utf8(&buf[..n]).unwrap_or("");
+        self.entries = libkos::apps::entries(text)
+            .filter(|e| e.id != ME)
+            .filter(|e| Capabilities::from_bits(e.required).union(Capabilities::from_bits(e.optional)).contains(Capability::Display))
+            .map(|e| Entry { id: e.id.to_string(), name: e.name.to_string() })
+            .collect();
+    }
+
+    fn open(&mut self, index: usize) {
+        let (Some(apps), Some(e)) = (&self.apps, self.entries.get(index)) else { return };
+        self.trouble = match apps.launch(&[e.id.as_str()], None, None) {
+            // Its window comes to the front; it runs on its own.
+            Ok((process, _)) => {
+                libkos::syscall::drop_cap(process);
+                None
+            }
+            Err(r) if r.code == reply::BUSY => Some("There is no room for another app: close one first (F4).".to_string()),
+            Err(r) => Some(format!("{} did not open (code {}).", e.name, r.code)),
+        };
+        self.reload();
+    }
+}
+
+impl App for Home {
+    type Event = Event;
+
+    fn init() -> Self {
+        let apps = libkos::start::permissions().and_then(|ep| Apps::connect(ep, REQUEST_PAGE_VA));
+        let mut home = Home { apps, entries: Vec::new(), trouble: None };
+        home.reload();
+        home
+    }
+
+    fn update(&mut self, event: Event) {
+        match event {
+            Event::Open(i) => self.open(i),
+        }
+    }
+
+    fn view(&self) -> Element<Event> {
+        let hint = "Enter opens an app. Alt+Tab or F1: the next window. F2: back here. F4: close the app in front.";
+        let mut view = column()
+            .padding(Spacing::Xl)
+            .gap(Spacing::Md)
+            .child(text("Home").style(TextStyle::Heading))
+            .child(text(hint).style(TextStyle::Caption).colour(TextColour::Secondary))
+            .children(self.entries.iter().enumerate().map(|(i, e)| list_item(e.name.clone(), Event::Open(i)).subtitle(e.id.clone())));
+        if self.entries.is_empty() {
+            view = view.child(text("No apps with a window are installed."));
+        }
+        if let Some(t) = &self.trouble {
+            view = view.child(text(t.clone()).colour(TextColour::Accent));
+        }
+        view.into()
+    }
+
+    /// Home is not left: Escape stays.
+    fn back(&mut self) -> bool {
+        true
+    }
+}
+
+libkos::entry!(main);
+
+fn main() {
+    k_ui::run::<Home>();
+}