chore: import upstream snapshot with attribution

internal/platform/mem_linux.go

@@ -0,0 +1,22 @@
+//go:build linux
+
+package platform
+
+import "golang.org/x/sys/unix"
+
+// HostPhysicalMemoryBytes returns total physical RAM in bytes via
+// sysinfo(2). Totalram is reported in units of Unit bytes; both fields are
+// widened to uint64 so the multiply is correct on 32-bit arches too.
+// Returns 0 when the syscall fails, so a caller that derives a budget from
+// it can fall back cleanly to "host RAM unknown".
+func HostPhysicalMemoryBytes() uint64 {
+	var si unix.Sysinfo_t
+	if err := unix.Sysinfo(&si); err != nil {
+		return 0
+	}
+	unit := uint64(si.Unit)
+	if unit == 0 {
+		unit = 1
+	}
+	return uint64(si.Totalram) * unit
+}