When developing for Alexa, every skill has a unique Id. This allows me to develop multiple skills, using the same lambda / codebase, that return unique info based on the skill id.
However, from what I've seen with Google Assistant, Actions don't have ids. Requests include a unique userId and the conversationId. And Responses include an intent id -- but there's no way to identify the action itself.
Any ideas / pointers to things I may have missed?
There are a few ways you can approach this, depending on what platform you're using for your webhook.
For both Dialogflow and the Action SDK, you can always specify a unique query parameter as part of the webhook or even have different path portions of the webhook go to the same lambda and examine either the query value or the path. This has the benefit that you're in full control of what the possible values are.
If you're using Dialogflow, there is a unique IntentID for each Intent that comes through. This might be one way to track which one has been invoked. But this seems somewhat kludgy.
Also for Dialogflow, you can set unique headers in the Dialogflow console, and then examine the value of these headers in your webhook. Again, this has the advantage of giving you control of the value.
The Action SDK doesn't have that feature, but it does transmit a JWT token in the Authorization header. This token is for verifying it has come from the correct project (and from Google), but once you've decoded it (and verified it), the aud field should contain the same project ID as the project in the Action Console.