A way to indicate in the interactive mode that the current module is complete

This would be useful to trigger a check that the completed module fully implements its interface.

cf #993

Start by reading issue #993 and the interactive-mode implementation to understand the existing module workflow. Determine how a completion signal should be expressed and how the interface check should be triggered. Done means the interactive mode can recognize a completed module and verify that it fully implements its interface.

Written by the indexing model from the issue text.