The sliding-window pattern serialized discuss to one phase at a time
even when phases had no dependency relationship. Replaced it with a
simple predicate: every undiscussed phase whose dependencies are
satisfied is marked is_next_to_discuss, letting the user pick any of
them from the manager's recommended_actions list.
Closes#2268
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
