static auto mark = time(nullptr);
auto mark_str = std::string(",") + std::to_string(mark);
auto marked_system_boot_reason = system_boot_reason + mark_str;
the number after “," looks like simply from time(nullptr)
$ adb shell getprop persist.sys.boot.reason.history cold,28 cold,29 cold,27 reboot,factory_reset,1653457758