Covers the one composer: the three send behaviors (message a live session, continue a finished one on its own agent, start fresh when there is no session to resume), the new-session preset always opening its own run, the slot's Stop and Resume with their no-refire and no-flicker latches, surfaced refusals instead of silent failures, and the options gear returning only once the session ended.

## Before writing SPEC.md files

Read https://raw.githubusercontent.com/brillout/sdd/refs/heads/main/sdd.md
