using Wit.ai HTML api.
Posting /converse message I get the response of type:action with action name, then I execute some my own code. How then make POST with context-key to wit API to get an answer from the robot?
Also how to trigger robot message when user do not need to say anything?
Your own code (the action you need to run) is responsible for updating the context (e.g. adding a key "forecast" with value "sunny"). In your Wit.ai /converse calls, you provide the context in the body.
See the example in the documentation: https://wit.ai/docs/http/20160526#post--converse-link
You can call your
sendaction when you want to trigger a robot message.