feat: implement kernel capability model

programs/src/desktop/main.cpp

@@ -834,6 +834,19 @@ void gui::desktop_run(DesktopState* ds) {
 
         if (now >= nextClockPollMs) {
             nextClockPollMs = now + 1000;
+
+            // A power request can be posted by anything in this session that
+            // holds CAP_POWER_REQUEST -- the shell's shutdown builtin, run in
+            // a terminal window, is the common case. login only reads it once
+            // the session leader exits, so ending the session is our job; it
+            // is the same handoff desktop_request_power() performs, just
+            // reached from a request we did not originate.
+            int pendingPower = montauk::power_request_pending();
+            if (pendingPower == montauk::abi::POWER_REQ_SHUTDOWN ||
+                pendingPower == montauk::abi::POWER_REQ_REBOOT) {
+                montauk::exit(0);
+            }
+
             uint64_t clockToken = desktop_clock_token();
             if (clockToken != lastClockToken) {
                 lastClockToken = clockToken;