For example, if someone wanted to make a journal skill it might ask "What would you like to add for your journal today?"
Some users may have a response that would be several sentences long or maybe even a few minutes. Is there any hard limit to how long a user's response/query to an action can be?
For anyone still looking for this answer, after some digging I found it nested deep in the Google Cloud Docs as I was looking to build something similar.
Maximum detect intent text input length is 256 characters.
There are also some handy limits so check it out. https://cloud.google.com/dialogflow/quotas