feat: add threading to Scheduler, fix desktop background selection freeze issue

kernel/src/Api/Process.hpp

@@ -98,6 +98,8 @@ namespace Montauk {
         for (int i = 0; i < Sched::MaxProcesses && count < maxCount; i++) {
             auto* proc = Sched::GetProcessSlot(i);
             if (!proc || proc->state == Sched::ProcessState::Free) continue;
+            // Skip sibling-thread slots; only show one entry per process.
+            if (proc->primarySlot != i) continue;
 
             buf[count].pid = (int32_t)proc->pid;
             buf[count].parentPid = (int32_t)proc->parentPid;
@@ -154,6 +156,25 @@ namespace Montauk {
         return i;
     }
 
+    // ====================================================================
+    // Threading
+    // ====================================================================
+    static int Sys_ThreadSpawn(uint64_t entry, uint64_t arg, uint64_t userStackTop) {
+        return Sched::SpawnThread(entry, arg, userStackTop);
+    }
+
+    [[noreturn]] static void Sys_ThreadExit(int exitCode) {
+        Sched::ExitCurrentThread(exitCode);
+    }
+
+    static int Sys_ThreadJoin(int tid, int* outExitCode) {
+        return Sched::JoinThread(tid, outExitCode);
+    }
+
+    static int Sys_ThreadSelf() {
+        return Sched::GetCurrentTid();
+    }
+
     static int Sys_Chdir(const char* path) {
         auto* proc = Sched::GetCurrentProcessPtr();
         if (proc == nullptr || path == nullptr) return -1;

kernel/src/Api/Syscall.cpp

@@ -340,6 +340,16 @@ namespace Montauk {
                 return Sys_AudioList((AudioStreamInfo*)frame->arg1, (int)frame->arg2);
             case SYS_AUDIOWAIT:
                 return Sys_AudioWait(frame->arg1, frame->arg2);
+            case SYS_THREAD_SPAWN:
+                return Sys_ThreadSpawn(frame->arg1, frame->arg2, frame->arg3);
+            case SYS_THREAD_EXIT:
+                Sys_ThreadExit((int)frame->arg1);
+                return 0;
+            case SYS_THREAD_JOIN:
+                if (frame->arg2 != 0 && !UserMemory::Writable<int>(frame->arg2)) return -1;
+                return Sys_ThreadJoin((int)frame->arg1, (int*)frame->arg2);
+            case SYS_THREAD_SELF:
+                return Sys_ThreadSelf();
             case SYS_BTSCAN:
                 if ((int64_t)frame->arg2 < 0) return -1;
                 if (!UserMemory::Range(frame->arg1, (uint64_t)frame->arg2 * sizeof(BtScanResult), true)) return -1;

kernel/src/Api/Syscall.hpp

@@ -243,6 +243,12 @@ namespace Montauk {
     static constexpr uint64_t SYS_AUDIOLIST           = 128;
     static constexpr uint64_t SYS_AUDIOWAIT           = 129;
 
+    /* Process.hpp -- threading */
+    static constexpr uint64_t SYS_THREAD_SPAWN        = 130;
+    static constexpr uint64_t SYS_THREAD_EXIT         = 131;
+    static constexpr uint64_t SYS_THREAD_JOIN         = 132;
+    static constexpr uint64_t SYS_THREAD_SELF         = 133;
+
     static constexpr uint32_t CLIPBOARD_MAX_TEXT_BYTES = 256 * 1024;
 
     static constexpr uint32_t IPC_SIGNAL_READABLE   = 1u << 0;