get_current_navigation_path not returning a path

[mortal breach]

I want to find the total distance of the path that an agent is following. This is so I can determine if the the calculated path is out of reach for the agent (i.e. prevent targeting through walls)
I don't see a method to do this in the documentation (distance_to_target appears to return the distance from the agent to the target, not the length of the path). So my plan was to calculate it using get_current_navigation_path, but it appears to not return a value even when a path is clearly being followed (see picture). Am I doing something wrong with navigation / are there different approaches to solve my issue?

Relevant code:

extends CharacterBody2D

const SPEED = 100.0
var state = MOVEMENT_STATES.IDLE
var tracking

@onready var nav_agent = $NavigationAgent2D

enum MOVEMENT_STATES {
    IDLE,
    WANDER,
    FOLLOW,
    RUN
} 

func _physics_process(delta):
    if tracking != null and state != MOVEMENT_STATES.FOLLOW:
        if _get_target_distance() <= $TargetDetection/CollisionShape2D.get_shape().get_radius():
            state = MOVEMENT_STATES.FOLLOW
    
    match state:
        MOVEMENT_STATES.FOLLOW:
            var direction = to_local(nav_agent.get_next_path_position())
            $MovementController.move(direction, SPEED)
    
    move_and_slide()

func _on_target_detection_body_entered(body):
    tracking = body
    nav_agent.set_target_position(tracking.global_position)
    $Timer.start()
    # if player is higher level than self, run
    # have target range increased based on player level ? 

func _on_target_detection_body_exited(body):
    if body == tracking and state != MOVEMENT_STATES.FOLLOW:
        tracking = null
        $Timer.stop()

func _on_timer_timeout():
    nav_agent.set_target_position(tracking.global_position)
    print(nav_agent.get_current_navigation_path()) #<----

func _get_target_distance() -> float:
    var points = nav_agent.get_current_navigation_path()
    var length = 1
    var distance = 0.0
    while length < points.size():
        distance += points[0].distance_to(points[1])
    return distance

Want to prevent tracking in scenario like this, where distance from start to end is clearly larger than the detection radius

[cursive sigil]

@mortal breach You could check through the tilemap if surrounding area of the entity is near a wall or the direct straight line of the entity being tracked is not a wall. You can also use raycast, I guess that could be more drain than needed and less efficient when it comes to performance.