simulate: fail fast and clearly for Node agents that can't run simulations

cmd/lk/simulate.go

@@ -744,7 +744,7 @@ func startSimulationAgent(c *simulateConfig, forwardOutput io.Writer) (*AgentPro
 		args = append(args, "--log-format", "colored")
 	}
 
-	return startAgent(AgentStartConfig{
+	cfg := AgentStartConfig{
 		Dir:         c.projectDir,
 		Entrypoint:  c.entrypoint,
 		ProjectType: c.projectType,
@@ -766,7 +766,13 @@ func startSimulationAgent(c *simulateConfig, forwardOutput io.Writer) (*AgentPro
 		},
 		ReadySignal:   "registered worker",
 		ForwardOutput: forwardOutput,
-	})
+	}
+	if c.projectType.IsNode() {
+		if err := checkNodeSDKVersion(cfg, nodeSimulateMinVersion); err != nil {
+			return nil, err
+		}
+	}
+	return startAgent(cfg)
 }
 
 // ciFromEnv reports the pipeline that started this run, so the dashboard can

cmd/lk/simulate_health.go

@@ -25,12 +25,13 @@ import (
 // can cancel the run and surface the worker's error, while tolerating
 // transient "no agent joined" timeouts from connection pacing.
 
-// pythonFatalMarkers are livekit-agents (Python) log lines that only appear on
-// a fatal, non-transient worker error. The JS framework will need its own set.
-var pythonFatalMarkers = []string{
+// fatalMarkers are livekit-agents (Python) and @livekit/agents (Node) log lines
+// that only appear on a fatal, non-transient worker error.
+var fatalMarkers = []string{
 	"unhandled exception while running the job task",
 	"error initializing process",
 	"closing due to unrecoverable error",
+	"error in entry function",
 }
 
 // a single fatal log line can be an isolated job crash
@@ -101,7 +102,7 @@ func countFatalMarkers(logs []string) int {
 
 func isFatalMarker(line string) bool {
 	plain := ansiEscapeRe.ReplaceAllString(line, "")
-	for _, marker := range pythonFatalMarkers {
+	for _, marker := range fatalMarkers {
 		if strings.Contains(plain, marker) {
 			return true
 		}

cmd/lk/simulate_subprocess.go

@@ -100,10 +100,14 @@ func checkTypeStrippingSupport(dir, nodeBin string) error {
 // equivalent floor from server client settings.
 const nodeAgentMinVersion = "1.0.0"
 
-// checkNodeSDKVersion gates a Node agent on nodeAgentMinVersion, resolving the
+// nodeSimulateMinVersion is the first @livekit/agents release with the
+// --simulation flag and LIVEKIT_AGENT_NAME_OVERRIDE, which simulate relies on.
+const nodeSimulateMinVersion = "1.4.11"
+
+// checkNodeSDKVersion gates a Node agent on minVersion, resolving the
 // installed @livekit/agents via the project's own runtime (see
 // agentfs.ResolveInstalledSDKVersion).
-func checkNodeSDKVersion(cfg AgentStartConfig) error {
+func checkNodeSDKVersion(cfg AgentStartConfig, minVersion string) error {
 	// Surface a missing Node binary as its own error rather than folding it
 	// into "package not found".
 	if _, err := agentfs.FindNodeBinary(); err != nil {
@@ -114,8 +118,8 @@ func checkNodeSDKVersion(cfg AgentStartConfig) error {
 		return fmt.Errorf("@livekit/agents not found; install dependencies and make sure this is a LiveKit agent project")
 	}
 	// An unparseable version (e.g. a local "0.0.0-dev" tag) shouldn't block a run.
-	if ok, err := agentfs.IsVersionSatisfied(version, nodeAgentMinVersion); err == nil && !ok {
-		return fmt.Errorf("@livekit/agents version %s is too old, please upgrade to %s or newer", version, nodeAgentMinVersion)
+	if ok, err := agentfs.IsVersionSatisfied(version, minVersion); err == nil && !ok {
+		return fmt.Errorf("@livekit/agents version %s is too old, please upgrade to %s or newer", version, minVersion)
 	}
 	return nil
 }
@@ -295,7 +299,7 @@ func startAgent(cfg AgentStartConfig) (*AgentProcess, error) {
 	// Node resolves the installed package via the runtime so workspace/monorepo
 	// layouts work; Python parses project files against the thin-CLI baseline.
 	if cfg.ProjectType.IsNode() {
-		if err := checkNodeSDKVersion(cfg); err != nil {
+		if err := checkNodeSDKVersion(cfg, nodeAgentMinVersion); err != nil {
 			return nil, err
 		}
 	} else if err := checkPythonSDKVersion(cfg); err != nil {