Clarify robot idle-state definition

Signed-off-by: kjchee <keai_jiang_chee@cgh.com.sg>

Author: kjchee

rmf_task/include/rmf_task/State.hpp

@@ -105,8 +105,11 @@ class State : public CompositeData
   /// CurrentOrientation, or CurrentTime) then this will return a std::nullopt.
   std::optional<rmf_traffic::agv::Plan::Start> extract_plan_start() const;
 
-  /// Check if the robot is idle, i.e. it is not assigned to any task and is
-  /// not currently executing any task.
+  /// Check if the robot is idle.
+  ///
+  /// True if the robot is not executing any task.
+  /// False only when the robot is actively executing a task
+  /// (finishing requests are not counted as execution).
   RMF_TASK_DEFINE_COMPONENT(bool, IsIdle);
   bool is_idle() const;
   State& idle(bool is_idle);