hive-c0re: graceful agent stop — quiesce harness, flush state, then stop

hive-ag3nt/src/mcp.rs

@@ -79,6 +79,10 @@ impl From<hive_sh4re::Response> for SocketReply {
             hive_sh4re::Response::HostJournal { content } => Self::HostJournal(content),
             hive_sh4re::Response::Schedules { schedules } => Self::Schedules(schedules),
             hive_sh4re::Response::Containers { containers } => Self::Containers(containers),
+            // A graceful stop is pending — the inbox is fenced. If claude polls
+            // `recv` during its stop-checkpoint turn, present it as an empty
+            // inbox (the serve loop is the real handler of this signal).
+            hive_sh4re::Response::GracefulStop => Self::Messages(Vec::new()),
             hive_sh4re::Response::AgentMeta {
                 name,
                 running,