CHALLENGE 3: A Custom Signal, Emitted and Connected
====================================================================

TASK
----
Declare a custom signal called coin_collected(amount: int) on one
node. Emit it with a sample amount, and connect a function on a
different node that prints a message using the amount it received.

SCENE STRUCTURE
----------------
Root (Node2D)
|-- Coin (Node2D)   <- declares and emits the signal
|-- Player (Node2D) <- listens for it

SOLUTION CODE - coin.gd (attached to Coin)
---------------------------------------------
extends Node2D

signal coin_collected(amount: int)

func _ready() -> void:
    # In a real game this would fire from a collision, not _ready() -
    # here it's simulated for the sake of the exercise.
    coin_collected.emit(10)

SOLUTION CODE - root.gd (attached to Root)
---------------------------------------------
extends Node2D

func _ready() -> void:
    $Coin.coin_collected.connect(_on_coin_collected)

func _on_coin_collected(amount: int) -> void:
    print("Collected a coin worth ", amount, " points!")

OUTPUT
------
Collected a coin worth 10 points!

WHY THIS WORKS AS AN ANSWER
----------------------------
signal coin_collected(amount: int) declares a new, typed signal on
Coin - the (amount: int) part means anything that connects to this
signal will receive one int argument when it fires, the same way a
typed function parameter works.

The connection has to be made in Root's own _ready(), not Coin's,
because Root is the one node that can see both $Coin and its own
listener function - Coin itself doesn't need to know Player or Root
exist at all, which is exactly the decoupling the chapter's tip box
described.

coin_collected.emit(10) fires the signal with 10 as the amount.
Because root.gd already connected _on_coin_collected to that signal
before it fired, Godot automatically calls that function with 10 as
its argument the moment .emit() runs - producing the printed message
without Coin ever calling _on_coin_collected directly by name.