The last thing written to the stdout file descriptor during a run is passed to the next run if it is a JSON encoded string. This JSON encoded string can be used to keep state between runs or to power the data behind a dynamic config.
A good way to use the saved state between runs via stdout is to continue running large syncs sequentially in a 'dynamic sync' process.
Below are some examples of writing to stdout in various languages
echo "Hello World" . "\n"
puts "Hello Word!"