feat: implement context switching, SavedContext with pc/status fields, wire all syscall outcomes and timer preemption

crates/kernel/src/lib.rs

@@ -113,6 +113,29 @@ impl<P: Platform> Kernel<P> {
         self.processes.get(pid).is_ok()
     }
 
+    pub fn thread_context(&self, tid: ThreadId) -> Option<&domain::thread::SavedContext> {
+        self.threads.get(tid).ok().map(|t| t.saved_context())
+    }
+
+    pub fn thread_context_mut(&mut self, tid: ThreadId) -> Option<&mut domain::thread::SavedContext> {
+        self.threads.get_mut(tid).ok().map(|t| t.saved_context_mut())
+    }
+
+    pub fn thread_process(&self, tid: ThreadId) -> Option<ProcessId> {
+        self.threads.get(tid).ok().map(|t| t.process())
+    }
+
+    pub fn current_thread(&self) -> Option<ThreadId> {
+        let core = self.platform.core_id();
+        self.scheduler.current(core)
+    }
+
+    pub fn pick_next_thread(&mut self) -> Option<ThreadId> {
+        use domain::scheduler::Scheduler;
+        let core = self.platform.core_id();
+        self.scheduler.next(core)
+    }
+
     pub fn create_endpoint(&mut self) -> Result<types::id::EndpointId, KernelError> {
         self.endpoints.create().ok_or(KernelError::NoFreeSlot)
     }