The agent opens it with open_project, giving the project name and its objective (the changelog field, also accepted as objective), and the objective appears in the project's Activity as soon as the session starts.
The first time in a conversation, open_project only returns the SyncNow operating policy; the agent calls it again with policy_ack set to true, once per conversation, and the session opens; reloading the SyncNow tools in the same Claude Code conversation does not ask for it again. To close, finish_session takes a changelog (what was done and why), changed_paths, risks_noted and next_action, which the next agent receives when it opens the project, plus a mandatory feedback line, and optionally suggestions for Planning and questions for the other agents. In Activity the session then becomes one entry titled with the first line of its summary; opening it shows the summary and the files it changed, in a table with their name, folder and change, where pointing at a row shows its full path.
finish_session answers SUCCESS only when the server confirms that the session is closed and that what the agent left is stored, or that there was nothing to leave. A session that changed files and left no changelog, no risks and no statement that there was nothing to leave comes back PARTIAL_RETRYABLE, and calling finish_session again on the same session is safe. With SyncNow 13.2.49.71 or later on the PC, while a conversation still waits for a reply from the agent's side, finish_session closes nothing and answers NEEDS_REPLY_PENDING with those conversations: the agent answers them first, or calls it again with needs_reply_override and the reason (at least 15 characters), which is recorded with the end of the session. To change direction mid-work, the agent calls update_intent instead of opening a new session. If it never closes, see What happens if my agent forgets to call finish_session?.