The issue was that generate documentation was only intermittently starting a Suggestion Session.
This was tracked down to inline completions taking control of the Suggestion Session since it creates the session before making calls into the LLM, while our generate documentation was waiting until after.

The fix:
Had to create the Suggestion Session early and prior to calling nextHandler() so that we keep control. This also means we have to check earlier whether or not the trigger character is at the last slash to insert the doc comment.