I did some minimal testing by defining a custom fact with just a large number:

cat > lib/facter/large.rb <<EOF
Facter.add(:large) do
  setcode do
    9223371665325424640
  end
end
EOF

Then applying the following manifest does work (with Puppet 6.28.0):

if $facts['large'] > 1000 {
  file { '/tmp/bla':
    ensure => file,
    content => String($facts['large']),
  }
}

My next guess was some conversion in custom types, but also there with a small custom type I couldn't easily reproduce it:

Puppet::Type.newtype(:largenumber) do
  ensurable
  newparam(:name)
  newproperty(:content)
end

Puppet::Type.type(:largenumber).provide(:default) do
  mk_resource_methods

  def self.instances
    []
  end

  def self.prefetch(resources)
    resources.each do |name, resource|
      if File.exist?(name)
        resource.provider = new(ensure: :present, content: JSON.load(File.read(name)))
      else
        resource.provider = new(ensure: :absent)
      end
    end
  end

  def create
    require 'json'
    File.write(name, JSON.dump(resource.should(:content)))
    @property_hash[:ensure] = :present
    @property_hash[:content] = resource.should(:content)
  end

  def flush
    require 'json'
    File.write(name, JSON.dump(@property_hash[:content]))
  end

  def exists?
    return File.file?(name)
  end
end

That also happily wrote out the content.

So it needs some further investigation where it's happening.

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