Navmesh: Check if agent destination can be reached

hi iam working on a puzzle game with several maze parts which looks like this one:

so in the beginning you have a randomly rotated maze and have to "un-rotate" each part/the whole maze by clicking on the parts:

the goal is to let the player run threw the maze (using navmeshes) as soon as the start and finish point is connected

but now comes the part where i am stuck. how can i check if the start and finish point is connected? so that the player starts to run as soon as it is possible?

currently the player just go wherever i click, even if its not possible, using this code:

 using UnityEngine;
 
 public class NavMesh : MonoBehaviour {
     NavMeshAgent agent;
     
     void Start() {
         agent = GetComponent<NavMeshAgent>();
     }
     
     void Update() {
         if (Input.GetMouseButtonDown(0)) {
             RaycastHit hit;
             
             if (Physics.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), out hit, 100)) {
                 agent.destination = hit.point;
             }
         }
     }
 }

i guess i could do something like:

 case NavMeshPathStatus.PathComplete:

but i dont know how i can combine and use this