feat(loadtest): sync add real 500-session capacity harness

internal/loadharness/process_limit_unix.go

@@ -0,0 +1,21 @@
+//go:build darwin || linux
+
+package loadharness
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/unix"
+)
+
+func validateProcessCapacity(sessions int) error {
+	var limit unix.Rlimit
+	if err := unix.Getrlimit(unix.RLIMIT_NOFILE, &limit); err != nil {
+		return fmt.Errorf("read open-file limit: %w", err)
+	}
+	required := minimumOpenFiles(sessions)
+	if limit.Cur < uint64(required) {
+		return fmt.Errorf("open-file soft limit %d is below required %d for %d sessions; raise it before running the load", limit.Cur, required, sessions)
+	}
+	return nil
+}