fix: harden multi-pod delivery and load verification

loadtest/im-pressure/model_test.go

@@ -1,6 +1,25 @@
 package main
 
-import "testing"
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadConfigAppliesBoundedHistoryDefaults(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	raw := []byte(`{"http_base":"https://example.test","endpoints":{"a":["wss://a"],"b":["wss://b"]}}`)
+	if err := os.WriteFile(path, raw, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := loadConfig(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cfg.HistoryWorkers != 48 || cfg.HistoryTimeout != "3m" || cfg.PreflightWorkers != 32 {
+		t.Fatalf("unexpected defaults: %+v", cfg)
+	}
+}
 
 func TestNewManifestDistributesUsersAndEndpoints(t *testing.T) {
 	cfg := &Config{Tenant: "006", UsersPerMachine: 3, Endpoints: map[string][]string{