feat: add inherited sessions and desktop session teardown

programs/include/Api/Syscall.hpp

@@ -125,6 +125,8 @@ namespace montauk::abi {
     // User management
     static constexpr uint64_t SYS_SETUSER       = 92;
     static constexpr uint64_t SYS_GETUSER       = 93;
+    static constexpr uint64_t SYS_SETSESSION    = 174;
+    static constexpr uint64_t SYS_KILLSESSION   = 175;
     static constexpr uint64_t SYS_FRENAME       = 94;
     static constexpr uint64_t SYS_GETCWD        = 95;
     static constexpr uint64_t SYS_CHDIR         = 96;

programs/include/libc/montauk.h

@@ -76,6 +76,8 @@ extern "C" {
 #define MTK_SYS_GETENVIRON         171
 #define MTK_SYS_SETENVIRON         172
 #define MTK_SYS_SPAWN_ENV          173
+#define MTK_SYS_SETSESSION         174
+#define MTK_SYS_KILLSESSION        175
 #define MTK_SYS_CHILDIO_READ       50
 #define MTK_SYS_CHILDIO_WRITE      51
 #define MTK_SYS_CHILDIO_WRITEKEY   52
@@ -428,6 +430,14 @@ static inline int mtk_kill(int pid) {
     return (int)_mtk_syscall1(MTK_SYS_KILL, (long)pid);
 }
 
+static inline int mtk_setsession(void) {
+    return (int)_mtk_syscall0(MTK_SYS_SETSESSION);
+}
+
+static inline int mtk_killsession(int session_id) {
+    return (int)_mtk_syscall1(MTK_SYS_KILLSESSION, (long)session_id);
+}
+
 static inline int mtk_proclist(mtk_procinfo *buf, int max) {
     return (int)_mtk_syscall2(MTK_SYS_PROCLIST, (long)buf, (long)max);
 }

programs/include/montauk/syscall.h

@@ -458,6 +458,12 @@ namespace montauk {
     inline int kill(int pid) {
         return (int)syscall1(montauk::abi::SYS_KILL, (uint64_t)pid);
     }
+    inline int setsession() {
+        return (int)syscall0(montauk::abi::SYS_SETSESSION);
+    }
+    inline int killsession(int sessionId) {
+        return (int)syscall1(montauk::abi::SYS_KILLSESSION, (uint64_t)sessionId);
+    }
     inline int devlist(montauk::abi::DevInfo* buf, int max) {
         return (int)syscall2(montauk::abi::SYS_DEVLIST, (uint64_t)buf, (uint64_t)max);
     }

programs/man/syscalls.2

@@ -65,6 +65,16 @@
     Terminate another process by PID.
         int montauk::kill(int pid);
 
+.B SYS_SETSESSION (174)
+    Make the calling process the leader of a new process session. Processes
+    spawned afterward inherit the session identifier.
+        int montauk::setsession();
+
+.B SYS_KILLSESSION (175)
+    Terminate all live processes in a process session. Returns the number of
+    members signalled; repeat until zero to wait for complete teardown.
+        int montauk::killsession(int sessionId);
+
 .B SYS_CHDIR (96)
     Change the calling process's current working directory.
         int montauk::chdir(const char* path);

programs/src/desktop/main.cpp

@@ -895,6 +895,11 @@ static bool existing_desktop_running() {
 }
 
 extern "C" void _start() {
+    // External applications and all of their descendants inherit this stable
+    // desktop-session ID. login.elf uses it to tear down the complete session
+    // after Log Out, Shutdown, or Reboot returns control to the supervisor.
+    montauk::setsession();
+
     if (existing_desktop_running()) {
         gui::dialogs::message_box(
             "Desktop Already Running",

programs/src/login/login.hpp

@@ -40,6 +40,8 @@ enum SessionMode {
     SESSION_CONSOLE,
 };
 
+void terminate_desktop_session(int session_id);
+
 struct LoginState {
     gui::Framebuffer fb;
     int screen_w, screen_h;

programs/src/login/login_input.cpp

@@ -63,6 +63,9 @@ void launch_session(LoginState* ls) {
     if (pid >= 0) {
         montauk::setuser(pid, ls->username);
         montauk::waitpid(pid);
+        if (ls->session_mode == SESSION_DESKTOP) {
+            terminate_desktop_session(pid);
+        }
     }
 
     // The desktop hands off a graceful power-off by posting a request and
@@ -99,6 +102,21 @@ gui::Rect login_field_rect(const LoginLayout& lo, LoginState* ls, int idx) {
 
 } // namespace
 
+void terminate_desktop_session(int session_id) {
+    if (session_id < 0) return;
+
+    // Killing is asynchronous because a member may currently be executing on
+    // another CPU or inside a syscall. Repeat until the kernel observes the
+    // session empty; no member can spawn another process after that point.
+    //
+
+    const int timeout_ms = 2000;
+    for (int waited = 0; waited < timeout_ms; waited++) {
+        if (montauk::killsession(session_id) <= 0) return;
+        montauk::sleep_ms(1);
+    }
+}
+
 LoginField get_field(LoginState* ls, int field) {
     if (ls->mode == MODE_FIRST_BOOT) {
         switch (field) {

programs/src/login/main.cpp

@@ -29,6 +29,7 @@ static void maybe_run_setup_session() {
     if (pid >= 0) {
         montauk::setuser(pid, user);
         montauk::waitpid(pid);
+        terminate_desktop_session(pid);
     }
 
     montauk::user::clear_session();