add agent-facing compact tool gated on context usage

hive-agent-mcp/src/mcp/mod.rs

@@ -587,6 +587,29 @@ impl AgentServer {
         .await
     }
 
+    #[tool(
+        description = "Compact the current session's context, mirroring the operator's \
+            dashboard `/compact` button. Gated: only honoured when this agent's last \
+            completed turn used more than 66% of the effective context window — below \
+            that the call is refused with an explanation and has no effect. On a pass, \
+            queues compaction for the end of the current turn (same deferred mechanism \
+            the dashboard button uses, so it never races a live claude process); the \
+            usual pre-compaction notes-checkpoint turn still fires first. No args."
+    )]
+    async fn compact(&self) -> String {
+        run_tool_envelope("compact", String::new(), async move {
+            match dial_agent_socket(&hive_agent_sock::Request::Compact).await {
+                Some(hive_agent_sock::Response::Ok) => {
+                    "compact queued — will run at the end of the current turn".to_owned()
+                }
+                Some(hive_agent_sock::Response::Err { message }) => message,
+                Some(other) => format!("compact: unexpected response: {other:?}"),
+                None => "compact failed: in-agent socket unavailable".to_owned(),
+            }
+        })
+        .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.