power: proper shutdown via UEFI ResetSystem (ACPI S5)

- uefi.rs: full EFI_RUNTIME_SERVICES layout with reset_system at index 10
  (spec order); EfiResetSystem type + RESET_* constants
- power.rs: stash the runtime-services table pre-EBS; poweroff() calls
  ResetSystem(EfiResetShutdown) — still callable after ExitBootServices
  because we never call SetVirtualAddressMap, so the pointers keep
  working with physical addresses; falls back to the hlt loop
- shell: 'poweroff' and 'exit' shut the machine down (QEMU exits),
  'halt' keeps the plain hlt loop

1 files changed, 13 insertions, 9 deletions

diff --git a/shell/src/lib.rs b/shell/src/lib.rs
index 4d5ba9c..5cab122 100644
--- a/shell/src/lib.rs
+++ b/shell/src/lib.rs
@@ -40,7 +40,8 @@ pub fn run() -> ! {
             "help" => cmd_help(),
             "echo" => cmd_echo(args),
             "clear" => cmd_clear(),
-            "halt" | "poweroff" | "exit" => cmd_halt(),
+            "halt" => cmd_halt(),
+            "poweroff" | "exit" => cmd_poweroff(),
             "hello" => {
                 gop_println!("World!");
                 serial_println!("World!");
@@ -123,10 +124,11 @@ fn cmd_help() {
     gop_println!("  mem      — show memory info");
     gop_println!("  mmap     — dump the UEFI memory map");
     gop_println!("  stress   — stress-test heap/page allocators");
-    gop_println!("  halt     — halt the system");
-    gop_println!("  exit     — alias for halt");
+    gop_println!("  halt     — halt the system (hlt loop)");
+    gop_println!("  poweroff — shut down via ACPI (ResetSystem)");
+    gop_println!("  exit     — alias for poweroff");
     serial_println!("available commands:");
-    serial_println!("  help, echo, clear, hello, info, mem, mmap, stress, halt, exit");
+    serial_println!("  help, echo, clear, hello, info, mem, mmap, stress, halt, poweroff, exit");
 }
 
 fn cmd_echo(args: &str) {
@@ -359,11 +361,13 @@ fn cmd_stress(args: &str) {
 fn cmd_halt() -> ! {
     gop_println!("halting...");
     serial_println!("halting...");
-    loop {
-        unsafe {
-            core::arch::asm!("cli; hlt");
-        }
-    }
+    rsnix::power::halt()
+}
+
+fn cmd_poweroff() -> ! {
+    gop_println!("shutting down...");
+    serial_println!("shutting down...");
+    rsnix::power::poweroff()
 }
 
 // ---------------------------------------------------------------------------