harness: add request_next_turn MCP tool — immediate self-continuation (closes #216)

hive-ag3nt/src/bin/hive-ag3nt.rs

@@ -273,6 +273,11 @@ async fn serve(
                 if pending > 0 {
                     tracing::info!(%pending, "pending messages after turn; fetching next");
                 }
+                // `request_next_turn` MCP tool: agent wrote a sentinel
+                // requesting an immediate self-continuation turn. Clear
+                // the file and inject a synthetic wake so the outer loop
+                // fires a bare turn even if the inbox is empty.
+                check_and_inject_continue(socket, label).await;
             }
             Ok(AgentResponse::Messages { .. }) => {
                 // Idle: empty list = nothing pending. Brief sleep
@@ -408,3 +413,41 @@ async fn fetch_agent_post_turn_counts(socket: &Path) -> (Option<u64>, Option<u64
     (threads, reminders)
 }
 
+/// Check for the `request_next_turn` sentinel file. If present, remove it
+/// and inject a synthetic `from: "self", body: "continue"` message so the
+/// serve loop fires an immediate follow-up turn even when the inbox is empty.
+/// Best-effort: any I/O error is logged and ignored (the agent just waits
+/// for a real message as normal).
+async fn check_and_inject_continue(socket: &Path, label: &str) {
+    let sentinel = hive_ag3nt::paths::state_dir().join("hyperhive-continue");
+    if !sentinel.exists() {
+        return;
+    }
+    if let Err(e) = std::fs::remove_file(&sentinel) {
+        tracing::warn!(error = %e, "check_and_inject_continue: remove sentinel failed");
+        return;
+    }
+    // Sentinel was present: inject a wake so the outer loop fires immediately.
+    // Route through the `Wake` request which is already wired in agent_server.
+    let res = client::request::<_, AgentResponse>(
+        socket,
+        &AgentRequest::Wake {
+            from: "self".into(),
+            body: "continue".into(),
+        },
+    )
+    .await;
+    match res {
+        Ok(AgentResponse::Ok) => {
+            tracing::info!(%label, "request_next_turn: injected self-continue wake");
+        }
+        Ok(AgentResponse::Err { message }) => {
+            tracing::warn!(%message, "check_and_inject_continue: wake rejected");
+        }
+        Err(e) => {
+            tracing::warn!(error = ?e, "check_and_inject_continue: wake transport error");
+        }
+        _ => {}
+    }
+}
+