Kelvin crashes on cgroup directories it can't access

[ddelnano]

An end user I'm working with has seen the Kelvin Pod crash when trying to access a cgroup directory it doesn't have access to. This specific cgroup is a CrowdStrike falcon-sensor, which might have stricter protections/permissions in place since it is designed with anti tamper mechanisms.

We should ensure that our cgroup directory iteration does not try to recurse into directories that the given PEM/Kelvin doesn't have access to. Below is the stack trace from this specific report:

I20260311 21:15:10.392350     1 cgroup_path_resolver.cc:150] Auto-discovered CGroup base path: /sys/fs/cgroup/cpu,cpuacct

libc++abi: terminating due to uncaught exception of type std::__1::__fs::filesystem::filesystem_error: filesystem error: in recursive_directory_iterator::operator++(): attempting recursion into "/sys/fs/cgroup/cpu,cpuacct/system.slice/falcon-sensor.service/sandbox.falcon": Permission denied

E20260311 21:15:10.411677     1 signal_action.cc:63] Caught Aborted, suspect faulting address 0x277400000001. Trace:

**************************

PC: @     0x7f60d7632472  (unknown)  abort

    @     0x55a086d04326  (unknown)  abort_message

    @     0x55a086cee1eb  (unknown)  demangling_terminate_handler()

    @     0x55a086d03fc3  (unknown)  std::__terminate()

    @     0x55a086d05cf6  (unknown)  __cxa_rethrow

    @     0x55a086cec446  (unknown)  std::__1::__fs::filesystem::detail::(anonymous namespace)::ErrorHandler<>::report()

    @     0x55a086cecfbc  (unknown)  std::__1::__fs::filesystem::recursive_directory_iterator::__try_recursion()

    @     0x55a086cecbe0  (unknown)  std::__1::__fs::filesystem::recursive_directory_iterator::__increment()

    @     0x55a086683b19  (unknown)  px::md::FindSelfCGroupProcs()

    @     0x55a086684fa2  (unknown)  px::md::AutoDiscoverCGroupTemplate()

    @     0x55a086685799  (unknown)  px::md::CGroupPathResolver::Create()

    @     0x55a086681df4  (unknown)  px::md::CGroupMetadataReader::CGroupMetadataReader()

    @     0x55a086681d59  (unknown)  px::md::CGroupMetadataReader::CGroupMetadataReader()

    @     0x55a085cda1da  (unknown)  px::md::AgentMetadataStateManagerImpl::AgentMetadataStateManagerImpl()

    @     0x55a085cd048d  (unknown)  _ZNSt3__111make_uniqueB6v15006IN2px2md29AgentMetadataStateManagerImplEJRNS_12basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEEERjSB_SA_RN4sole4uuidEbRKNS1_6system6ConfigEPNS2_19AgentMetadataFilterESD_SA_SA_PNS1_5eve    @     0x55a085cce25a  (unknown)  px::vizier::agent::Manager::PostRegisterHook()