gate stale todo wakes on an emptiness check (#2678)

hive-agent/src/todos.rs

@@ -223,6 +223,27 @@ impl Todos {
             .collect::<rusqlite::Result<Vec<_>>>()?;
         Ok(rows)
     }
+
+    /// Cheap existence check — `true` when at least one todo row exists
+    /// (across every subsystem). Used to gate a `todo_wake` notification
+    /// against being turned into a turn when its payload has already been
+    /// drained by an earlier turn (see the serve loop's `LocalTodo` arm):
+    /// an `EXISTS` probe, not a full `list` + row materialization, since
+    /// this runs on every wake.
+    ///
+    /// # Errors
+    ///
+    /// Propagates the sqlite query failure.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the connection mutex is poisoned.
+    pub fn has_any(&self) -> Result<bool> {
+        let conn = self.conn.lock().unwrap();
+        let any: bool =
+            conn.query_row("SELECT EXISTS(SELECT 1 FROM todos)", [], |row| row.get(0))?;
+        Ok(any)
+    }
 }
 
 #[cfg(test)]
@@ -279,6 +300,19 @@ mod tests {
         assert!(s.list(None).unwrap().is_empty());
     }
 
+    #[test]
+    fn has_any_reflects_emptiness() {
+        let (_dir, s) = store();
+        assert!(!s.has_any().unwrap(), "fresh store has no todos");
+        let (id, _) = s.upsert("bash", None, "task done", None).unwrap();
+        assert!(s.has_any().unwrap());
+        s.mark_done(id).unwrap();
+        assert!(
+            !s.has_any().unwrap(),
+            "empty again after draining the only row"
+        );
+    }
+
     #[test]
     fn clear_subsystem_wipes_only_its_own() {
         let (_dir, s) = store();