Add artillery enemy with telegraphed AOE (#46)

EnemyArtilleryComponent is a stationary siege piece (slow drift toward
the fleet, deliberately no pursuit component) that fires at the fleet
centroid on a long cooldown via a standalone ArtilleryShell -
telegraph ring (~1.8s, growing radius plus a filling countdown arc) ->
slow visible travel -> AOE explosion via Ship.take_damage() on every
player_ships node inside, same all-or-nothing shield absorption as
every other damage source. The shell is independent of the enemy that
fired it (added to the tree root, like EnemyProjectile/Projectile) so
the shooter dying mid-flight doesn't cancel an already-telegraphed
shot, and the impact point is fixed at fire time - never re-aimed at
where the fleet moves to afterward.

Part of the #40 conquest-mechanic breakdown.

tests/_artillery_telegraph_gas_preview.gd

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+extends Node2D
+
+
+func _ready() -> void:
+	GameState.planet_name = "Violet Tempest"
+	GameState.planet_id = "artillery_preview_gas"
+	GameState.planet_definition_id = "gas_giant"
+	GameState.surviving_ship_count = 3
+	var surface: Node = load("res://PlanetSurface.tscn").instantiate()
+	surface.get_node("SurfaceController").fade_duration = 0.0
+	add_child(surface)
+
+	var shell: Node = load("res://ArtilleryShell.tscn").instantiate()
+	shell.telegraph_time = 10.0   # frozen mid-countdown for the screenshot
+	shell.aoe_radius = 220.0
+	surface.add_child(shell)
+	shell.launch(Vector2(-600, -600), Vector2.ZERO)
+	shell.telegraph_left = shell.telegraph_time * 0.45
+	shell.set_process(false)
+	shell.queue_redraw()

tests/_artillery_telegraph_gas_preview.gd.uid

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+uid://be13xddivhtr

tests/_artillery_telegraph_gas_preview.tscn

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+[gd_scene load_steps=2 format=3]
+
+[ext_resource type="Script" path="res://tests/_artillery_telegraph_gas_preview.gd" id="1"]
+
+[node name="ArtilleryTelegraphGasPreview" type="Node2D"]
+script = ExtResource("1")

tests/_artillery_telegraph_rocky_preview.gd

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+extends Node2D
+
+
+func _ready() -> void:
+	GameState.planet_name = "Kepler's Rest"
+	GameState.planet_id = "artillery_preview_rocky"
+	GameState.planet_definition_id = "rocky"
+	GameState.surviving_ship_count = 3
+	var surface: Node = load("res://PlanetSurface.tscn").instantiate()
+	surface.get_node("SurfaceController").fade_duration = 0.0
+	add_child(surface)
+
+	var shell: Node = load("res://ArtilleryShell.tscn").instantiate()
+	shell.telegraph_time = 10.0   # frozen mid-countdown for the screenshot
+	shell.aoe_radius = 220.0
+	surface.add_child(shell)
+	shell.launch(Vector2(-600, -600), Vector2.ZERO)
+	shell.telegraph_left = shell.telegraph_time * 0.45
+	shell.set_process(false)
+	shell.queue_redraw()

tests/_artillery_telegraph_rocky_preview.gd.uid

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+uid://dlaxr7it3582h

tests/_artillery_telegraph_rocky_preview.tscn

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+[gd_scene load_steps=2 format=3]
+
+[ext_resource type="Script" path="res://tests/_artillery_telegraph_rocky_preview.gd" id="1"]
+
+[node name="ArtilleryTelegraphRockyPreview" type="Node2D"]
+script = ExtResource("1")

tests/test_artillery_enemy.gd

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+extends SceneTree
+
+# Headless gameplay test: run with
+#   godot --headless -s res://tests/test_artillery_enemy.gd
+# Verifies:
+#   1. the telegraph is visible (phase == TELEGRAPHING) for the whole
+#      window before any damage lands
+#   2. a ship that leaves the blast radius before impact takes no damage;
+#      one that stays takes the full hit
+#   3. a shielded ship inside the blast survives, losing exactly one charge
+#   4. the impact point is fixed at fire time - moving the fleet after the
+#      shot is launched does not redirect it (tested through the real
+#      EnemyArtilleryComponent, since that's what could tempt "aim at the
+#      fleet's live position" instead of its position at fire time)
+
+# Resolved via load() inside _initialize(), NOT a top-level `const ...
+# preload(...)` - a top-level preload in a script-mode ENTRY point (-s
+# this_file.gd) evaluates during this file's own early compilation, which
+# can happen before autoloads are registered. See test_capture_points.gd
+# for the full explanation.
+var ARTILLERY_SHELL_SCRIPT: Script
+
+var game_state: Node
+var main: Node
+var fleet: Node
+var shell: Node
+var ship_inside: Node
+var ship_leaves: Node
+var shield_ship: Node
+var far_ship: Node
+var artillery: Node
+var art_component: Node
+var live_shell: Node
+var recorded_target: Vector2 = Vector2.ZERO
+var impact_point: Vector2 = Vector2.ZERO
+var travel_time: float = 0.0
+var stage2_wait: float = 0.0
+var stage5_wait: float = 0.0
+var stage: int = 0
+var elapsed: float = 0.0
+
+
+func _initialize() -> void:
+	ARTILLERY_SHELL_SCRIPT = load("res://ArtilleryShell.gd")
+	game_state = root.get_node("GameState")
+	game_state.buildings.clear()
+	game_state.extractors.clear()
+	game_state.transporters.clear()
+	game_state.stored_vessels.clear()
+	game_state.build_time_scale = 0.02
+	game_state.reset_progression()
+	game_state.rocks = 2000
+	main = load("res://Main.tscn").instantiate()
+	root.add_child(main)
+	fleet = main.get_node("Fleet")
+
+
+func _process(delta: float) -> bool:
+	elapsed += delta
+	match stage:
+		0:
+			if elapsed < 0.1:
+				return false
+			main.get_node("EnemySpawner").set_process(false)
+			main.get_node("AsteroidField").set_process(false)
+			for a in get_nodes_in_group("asteroids"):
+				a.queue_free()
+
+			impact_point = Vector2(5000, 0)
+			fleet.spawn_ships(1, impact_point)
+			ship_inside = fleet.ships[0]
+			ship_inside.position = impact_point
+
+			fleet.add_ship(GameState.VESSEL_INTERCEPTOR)
+			ship_leaves = fleet.ships[fleet.ships.size() - 1]
+			ship_leaves.position = impact_point + Vector2(100, 0)
+
+			fleet.add_ship(GameState.VESSEL_SHIELD)
+			shield_ship = fleet.ships[fleet.ships.size() - 1]
+			shield_ship.position = impact_point + Vector2(-100, 0)
+
+			var origin: Vector2 = impact_point + Vector2(400, 400)
+			travel_time = origin.distance_to(impact_point) / 300.0
+			shell = load("res://ArtilleryShell.tscn").instantiate()
+			shell.telegraph_time = 1.0
+			shell.shell_speed = 300.0
+			shell.aoe_radius = 220.0
+			shell.damage = 3
+			main.add_child(shell)
+			shell.launch(origin, impact_point)
+
+			elapsed = 0.0
+			stage = 1
+			return false
+		1:
+			# Mid-telegraph: nobody hurt yet, still visibly telegraphing.
+			if elapsed < shell.telegraph_time * 0.8:
+				return false
+			if shell.phase != ARTILLERY_SHELL_SCRIPT.Phase.TELEGRAPHING:
+				return _fail("shell left the telegraph phase too early")
+			if not is_instance_valid(ship_inside) or not is_instance_valid(ship_leaves) \
+					or not is_instance_valid(shield_ship):
+				return _fail("damage landed before the telegraph window finished")
+
+			# Ship B clears the blast radius now, well before impact.
+			ship_leaves.position = impact_point + Vector2(2000, 0)
+			# Captured once, as a plain float: the shell frees itself once
+			# it resolves, so re-reading shell.telegraph_time from inside
+			# the wait condition below (evaluated every frame) would touch
+			# a freed object on any frame after that.
+			stage2_wait = shell.telegraph_time * 0.2 + travel_time + 1.5
+			elapsed = 0.0
+			stage = 2
+			return false
+		2:
+			# Enough time for the remaining telegraph, travel, and the full
+			# explosion visual to resolve.
+			if elapsed < stage2_wait:
+				return false
+			if is_instance_valid(ship_inside):
+				return _fail("a ship that stayed inside the blast radius survived")
+			if not is_instance_valid(ship_leaves):
+				return _fail("a ship that left the blast radius before impact was still hit")
+			if not is_instance_valid(shield_ship):
+				return _fail("a shielded ship inside the blast was destroyed instead of absorbing the hit")
+			if shield_ship.shield_charges != 0:
+				return _fail("shield charges did not drop to 0 after absorbing the artillery hit (charges=%d)" %
+					shield_ship.shield_charges)
+			print("stayed=destroyed left=survived shielded=absorbed-one-charge")
+
+			# --- Part B: the impact point does not home onto a fleet that
+			# moves after the shot is fired ---------------------------------
+			fleet.spawn_ships(1, Vector2(9000, 0))
+			far_ship = fleet.ships[0]
+			artillery = load("res://Enemy.tscn").instantiate()
+			artillery.enemy_id = "artillery"
+			artillery.position = far_ship.position + Vector2(300, 0)
+			main.add_child(artillery)
+			art_component = artillery.get_component("artillery")
+			art_component.cooldown_left = 0.0
+			art_component.telegraph_time = 0.3
+			art_component.fire_cooldown = 999.0   # only the one shot for this check
+			elapsed = 0.0
+			stage = 3
+			return false
+		3:
+			if elapsed < 0.15:
+				return false
+			# The shell is added to the tree root (a sibling of main, not
+			# its child - see EnemyArtilleryComponent.tick()), so it has to
+			# be found via its group, not main.get_children().
+			var shells: Array = get_nodes_in_group("artillery_shells")
+			if shells.is_empty():
+				return _fail("artillery enemy did not fire when in range and off cooldown")
+			live_shell = shells[0]
+			recorded_target = live_shell.target
+
+			far_ship.position += Vector2(4000, 0)   # flee well clear of the recorded target
+			elapsed = 0.0
+			stage = 4
+			return false
+		4:
+			# Check the target field WHILE the shell is still alive - it
+			# frees itself right after exploding, so this has to happen
+			# before that, not after.
+			if elapsed < 0.3:
+				return false
+			if not is_instance_valid(live_shell):
+				return _fail("shell resolved implausibly fast - timing assumption broke")
+			if live_shell.target != recorded_target:
+				return _fail("shell target changed after the fleet moved - it homed instead of staying fixed")
+			# Captured once, as a plain float: far_ship's own weapon can
+			# destroy the artillery enemy (and with it art_component) well
+			# before this wait ends, so the condition below must not keep
+			# re-reading a property off a node that might already be freed.
+			stage5_wait = art_component.telegraph_time + (300.0 / 180.0) + 1.5
+			elapsed = 0.0
+			stage = 5
+			return false
+		5:
+			if elapsed < stage5_wait:
+				return false
+			if not is_instance_valid(far_ship):
+				return _fail("fleeing ship was hit by a shot aimed at its old position - homing occurred")
+			print("shell held its fire-time target and did not home onto the fleeing ship")
+			print("TEST_ARTILLERY_ENEMY: PASS")
+			quit(0)
+			return true
+	return false
+
+
+func _fail(message: String) -> bool:
+	print("TEST_ARTILLERY_ENEMY: FAIL (%s)" % message)
+	quit(1)
+	return true

tests/test_artillery_enemy.gd.uid

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+uid://cv3lvd01j4kp