feat: add inline simulation using debug_traceCall

tools/preconf-rpc/main.go

@@ -223,13 +223,20 @@ var (
 		Value:   "",
 	}
 
-	optionSimulationURL = &cli.StringFlag{
+	optionSimulationURLs = &cli.StringSliceFlag{
 		Name:     "simulation-url",
-		Usage:    "URL for the transaction simulation service",
+		Usage:    "URL(s) for the transaction simulation service. Multiple URLs can be specified for fallback support (first URL is primary, others are fallbacks)",
 		EnvVars:  []string{"PRECONF_RPC_SIMULATION_URL"},
 		Required: true,
 	}
 
+	optionUseInlineSimulation = &cli.BoolFlag{
+		Name:    "use-inline-simulation",
+		Usage:   "Use inline simulation via debug_traceCall instead of external rethsim service. When false (default), uses external rethsim. When true, uses debug_traceCall (requires RPC with debug API support like Alchemy, Infura, or Erigon)",
+		EnvVars: []string{"PRECONF_RPC_USE_INLINE_SIMULATION"},
+		Value:   false,
+	}
+
 	optionBackrunnerAPIURL = &cli.StringFlag{
 		Name:     "backrunner-api-url",
 		Usage:    "URL for the transaction backrun service",
@@ -357,7 +364,8 @@ func main() {
 			optionBidderThreshold,
 			optionBidderTopup,
 			optionAuthToken,
-			optionSimulationURL,
+			optionSimulationURLs,
+			optionUseInlineSimulation,
 			optionBackrunnerAPIURL,
 			optionBackrunnerRPCURL,
 			optionBackrunnerAPIKey,
@@ -458,7 +466,8 @@ func main() {
 				PricerAPIKey:           c.String(optionBlocknativeAPIKey.Name),
 				Webhooks:               c.StringSlice(optionWebhookURLs.Name),
 				Token:                  c.String(optionAuthToken.Name),
-				SimulatorURL:           c.String(optionSimulationURL.Name),
+				SimulatorURLs:          c.StringSlice(optionSimulationURLs.Name),
+				UseInlineSimulation:    c.Bool(optionUseInlineSimulation.Name),
 				BackrunnerAPIURL:       c.String(optionBackrunnerAPIURL.Name),
 				BackrunnerRPC:          c.String(optionBackrunnerRPCURL.Name),
 				BackrunnerAPIKey:       c.String(optionBackrunnerAPIKey.Name),

tools/preconf-rpc/service/service.go

@@ -78,7 +78,8 @@ type Config struct {
 	PricerAPIKey           string
 	Webhooks               []string
 	Token                  string
-	SimulatorURL           string
+	SimulatorURLs          []string
+	UseInlineSimulation    bool
 	BackrunnerRPC          string
 	BackrunnerAPIURL       string
 	BackrunnerAPIKey       string
@@ -270,8 +271,31 @@ func New(config *Config) (*Service, error) {
 	healthChecker.Register(health.CloseChannelHealthCheck("BlockTracker", blockTrackerDone))
 	s.closers = append(s.closers, channelCloser(blockTrackerDone))
 
-	simulator := sim.NewSimulator(config.SimulatorURL)
-	metricsRegistry.MustRegister(simulator.Metrics()...)
+	// Create simulator based on feature flag
+	// When UseInlineSimulation is true, uses debug_traceCall via standard RPC (Alchemy, Infura, Erigon)
+	// When false (default), uses external rethsim API for backward compatibility
+	// Multiple URLs can be provided for fallback support
+	if len(config.SimulatorURLs) == 0 {
+		return nil, fmt.Errorf("at least one simulation URL is required")
+	}
+	var simulator sender.Simulator
+	var simulatorMetrics []prometheus.Collector
+	if config.UseInlineSimulation {
+		inlineSim, err := sim.NewInlineSimulator(config.SimulatorURLs, config.Logger)
+		if err != nil {
+			return nil, fmt.Errorf("failed to create inline simulator: %w", err)
+		}
+		simulator = inlineSim
+		simulatorMetrics = inlineSim.Metrics()
+		s.closers = append(s.closers, inlineSim) // close RPC clients on shutdown
+		config.Logger.Info("using inline simulator (debug_traceCall)", "endpointCount", len(config.SimulatorURLs))
+	} else {
+		externalSim := sim.NewSimulator(config.SimulatorURLs, config.Logger)
+		simulator = externalSim
+		simulatorMetrics = externalSim.Metrics()
+		config.Logger.Info("using external simulator (rethsim)", "endpointCount", len(config.SimulatorURLs))
+	}
+	metricsRegistry.MustRegister(simulatorMetrics...)
 
 	var pointsTracker PointsTracker
 	if config.PointsAPIURL == "" {