feat: add SYS_GETCAPS syscall to retrieve process capabilities

kernel/src/Api/BuildNo.hpp

@@ -12,4 +12,4 @@
 
 #pragma once
 
-#define MONTAUK_BUILD_NUMBER 220
+#define MONTAUK_BUILD_NUMBER 221

kernel/src/Api/Process.hpp

@@ -140,6 +140,16 @@ namespace montauk::abi {
         return childPid;
     }
 
+    // The calling process's own capability masks.
+    static int Sys_GetCaps(SpawnCapabilities* out) {
+        auto* proc = Sched::GetCurrentProcessPtr();
+        if (proc == nullptr || out == nullptr) return -1;
+        out->permitted = proc->permittedCaps;
+        out->effective = proc->effectiveCaps;
+        out->delegable = proc->delegableCaps;
+        return 0;
+    }
+
     // Copy the absolute path this process was spawned from (argv[0]).
     static int Sys_GetExecPath(char* buf, uint64_t maxLen) {
         auto* proc = Sched::GetCurrentProcessPtr();

kernel/src/Api/Syscall.cpp

@@ -510,6 +510,9 @@ namespace montauk::abi {
                 // holds no device capability to spend on it.
                 if (!UserMemory::Writable<BatteryInfo>(frame->arg1)) return -1;
                 return Sys_BatteryInfo((BatteryInfo*)frame->arg1);
+            case SYS_GETCAPS:
+                if (!UserMemory::Writable<SpawnCapabilities>(frame->arg1)) return -1;
+                return Sys_GetCaps((SpawnCapabilities*)frame->arg1);
             case SYS_THREAD_SPAWN:
                 return Sys_ThreadSpawn(frame->arg1, frame->arg2, frame->arg3);
             case SYS_THREAD_EXIT:

kernel/src/Api/Syscall.hpp

@@ -346,6 +346,9 @@ namespace montauk::abi {
     /* Battery.hpp -- ACPI battery status */
     static constexpr uint64_t SYS_BATTERYINFO          = 188;  // (BatteryInfo*) -> 0, -1 no battery device
 
+    /* Process.hpp -- the caller's own capability masks. */
+    static constexpr uint64_t SYS_GETCAPS              = 189;  // (SpawnCapabilities*) -> 0, -1 bad pointer
+
     /* Kernel-owned process capabilities. User identities may namespace
        per-user resources, but never participate in authorization decisions. */
     static constexpr uint64_t CAP_PROCESS_ADMIN = 1ULL << 0;