LaunchAgents not work by SMAppService.agent().register() API

After app running, here is some scenarios:

register a LaunchAgent

let service = SMAppService.agent(plistName: "com.zhangeek.agent.plist")
do {
    try service.register()
    print("Successfully registered \(service)")
}catch {
    print("Unable to register \(error)")
}

Property List file Contents/Library/LaunchAgents/com.zhangeek.agent.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.zhangeek.agent</string>
    <key>BundleProgram</key>
    <string>Contents/Resources/server</string>
    <key>StandardOutPath</key>
    <string>/tmp/agent.log</string>
    <key>StandardErrorPath</key>
    <string>/tmp/agent.log</string>
</dict>
</plist>

server executable binary built by golang

func main() {
   for {
      fmt.Println(time.Now().Format(time.RFC3339))
      time.Sleep(1 * time.Second)
   }
}

My Question: why /tmp/agent.log is empty and launchAgent not found in result launchctl list.