feat(kernel): add Exit and ExitThread syscalls with process cleanup

crates/kernel/src/tests/exit.rs

@@ -0,0 +1,25 @@
+use super::*;
+use crate::{SyscallOutcome, SyscallResult};
+use domain::syscall::Syscall;
+
+#[test]
+fn exit_thread_terminates_caller() {
+    let (mut k, _) = kernel_with_process();
+    let outcome = k.handle_syscall(Syscall::ExitThread);
+    assert!(matches!(outcome, SyscallOutcome::TerminateCaller));
+}
+
+#[test]
+fn exit_terminates_process_and_all_threads() {
+    let (mut k, _) = kernel_with_process();
+    let outcome = k.handle_syscall(Syscall::Exit);
+    assert!(matches!(outcome, SyscallOutcome::TerminateCaller));
+}
+
+#[test]
+fn exit_thread_last_thread_destroys_process() {
+    let (mut k, pid) = kernel_with_process();
+    k.handle_syscall(Syscall::ExitThread);
+    // Process should be gone since it had only one thread
+    assert!(k.process_exists(pid) == false);
+}

crates/kernel/src/tests/mod.rs

@@ -1,3 +1,4 @@
+mod exit;
 mod simple;
 
 use domain::memory::page_pool::PagePool;