feat(#792): agent restart tool — topology-checked restart of direct children

hive-ag3nt/src/mcp.rs

@@ -895,6 +895,29 @@ impl AgentServer {
         .await
     }
 
+    // IMPORTANT: this tool is only available when the `lifecycle` tool group
+    // is granted to this agent. hive-c0re enforces the topology check
+    // server-side: the call is rejected unless `name` is a direct child.
+    #[tool(
+        description = "Restart a direct child sub-agent container (stop + start). \
+            Only succeeds if `name` is a direct child of this agent in the topology \
+            tree — the server enforces this. No approval required."
+    )]
+    async fn restart(&self, Parameters(args): Parameters<RestartArgs>) -> String {
+        let log = format!("{args:?}");
+        let name = args.name.clone();
+        run_tool_envelope("restart", log, async move {
+            let (resp, retries) = self
+                .dispatch(hive_sh4re::AgentRequest::Restart { name: args.name })
+                .await;
+            annotate_retries(
+                format_ack(resp, "restart", format!("restarted {name}")),
+                retries,
+            )
+        })
+        .await
+    }
+
     // IMPORTANT: this tool is capability-gated (`read_host_journal`).
     // It is added to `--allowedTools` by `allowed_capability_tools` only
     // when `HIVE_CAPABILITIES` contains `read_host_journal`. hive-c0re