Thanks for the info
One option could be once you start the clients workflow to periodically query it , if the workflow state query returns is true, enable the button in ui for user. User clicking on the button then would send a signal to this workflow confirming completion.
Depending on your load and time requirements you could possibly use advanced visibility as well, meaning your workflow would upsert a custom search attribute value based on your business logic and then instead of querying it directly could periodically check via visibility query, for example:
“WorkflowId=‘’ AND ExecutionStatus=‘Running’ AND MyCustomAttr=‘true’”.
Another option could be a “push” meaning once your workflow performs all the steps and comes to a point where user confirmation is needed, to run an activity/local activity (see this post for detailed info) to trigger an endpoint on your app side as notification that the user button for confirmation should be enabled.