Charge more for each berth, and show the bill

#220: every berth past the first paid one costs 1.12x the one before it, on
top of the flat per-vessel charge. A linear bill makes the tenth hull no more
of a decision than the second; compounding weighs each addition against the
whole fleet behind it. Shallow on purpose - the thirteenth berth costs about
three and a half times the second, the twentieth about seven and a half.

Fleet Offices gain a menu naming the whole bill per minute, a line per paying
berth with its multiplier, and the arithmetic in words. It renders
fleet_upkeep_breakdown(), which is the calculation the charging loop itself
runs: a readout that summed independently could quote a bill the game does
not take, which is the thing worth preventing here. The test pins that what
the menu quotes for a berth is what that office is charged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019AJMdB7iuHuLFZM1aBu3GD

tests/_fleet_upkeep_preview.gd

@@ -0,0 +1,34 @@
+extends Node2D
+
+# Preview, not a test - #220's upkeep readout with a fleet worth reading:
+# several berths of different hulls, so the per-berth lines, the compounding
+# multiplier and the per-minute total all have something to show.
+#
+#   bash tests/screenshot.sh res://tests/_fleet_upkeep_preview.tscn shots/fleet_upkeep.png 3 720x1280
+
+
+func _ready() -> void:
+	GameState.buildings.clear()
+	GameState.extractors.clear()
+	GameState.transporters.clear()
+	GameState.reset_progression()
+	GameState.intro_active = false
+	GameState.add_building(GameState.BUILDING_MOTHERSHIP, Vector2.ZERO)
+	var office_ids: Array = []
+	for i in range(5):
+		office_ids.append(GameState.add_building(GameState.BUILDING_FLEET_OFFICE,
+			Vector2(400.0 * float(i + 1), 300.0)))
+	var main: Node = load("res://world/Main.tscn").instantiate()
+	add_child(main)
+	main.get_node("AsteroidField").set_process(false)
+	main.get_node("EnemySpawner").set_process(false)
+	# Spawned for real rather than by writing fleet_vessel_types directly: the
+	# Fleet rewrites that from what is actually flying the moment it composes
+	# itself, so a value set beforehand is discarded.
+	main.get_node("Fleet").spawn_ships(6, Vector2.ZERO, PackedStringArray([
+		GameState.VESSEL_INTERCEPTOR, GameState.VESSEL_LASER,
+		GameState.VESSEL_GAS_BOMBER, GameState.VESSEL_DISTORDER,
+		GameState.VESSEL_LASER, GameState.VESSEL_SHIELD]))
+	# One office left unsupplied, so the unpaid marker is visible too.
+	GameState.find_building(int(office_ids[3])).starved = true
+	main.get_node("UI/FleetUpkeepMenu").open_for(int(office_ids[0]))

tests/_fleet_upkeep_preview.tscn

@@ -0,0 +1,6 @@
+[gd_scene load_steps=2 format=3]
+
+[ext_resource type="Script" path="res://tests/_fleet_upkeep_preview.gd" id="1"]
+
+[node name="FleetUpkeepPreview" type="Node2D"]
+script = ExtResource("1")

tests/test_fleet_upkeep_scaling.gd

@@ -0,0 +1,111 @@
+extends SceneTree
+
+# Forgejo #220: the fleet costs more per hull as it grows, and the Fleet
+# Office says so with the arithmetic shown.
+#
+# The interesting failure is not "the sum is wrong" - it is the readout and
+# the charging loop drifting apart, so the menu quotes a bill the game does
+# not take. So what is checked is that the SAME numbers come out of both.
+#
+# Covers:
+#   A. the first paid berth pays the base rate, undialled
+#   B. each berth past it pays more than the one before, compounding
+#   C. the growth is slow - a mid-sized fleet is dearer, not ruinous
+#   D. the breakdown's per-minute total matches its own per-berth charges
+#   E. and the charges it quotes are the ones actually withdrawn
+#   F. an empty berth is quoted nothing
+
+var state: Node
+
+
+func _initialize() -> void:
+	state = root.get_node("GameState")
+	state.buildings.clear()
+	state.transporters.clear()
+	state.reset_progression()
+	state.reset_new_game()
+	state.intro_active = false
+	state.fleet_vessel_types = PackedStringArray()
+
+
+func _process(_delta: float) -> bool:
+	var vessel: String = GameState.VESSEL_LASER
+	var base: Dictionary = state.fleet_office_upkeep(vessel, GameState.BASE_FLEET_SIZE)
+	if base.is_empty():
+		return _fail("a laser berth is charged nothing at all")
+
+	# --- A. the first paid berth is the base rate -------------------
+	if not is_equal_approx(state.fleet_upkeep_scale(GameState.BASE_FLEET_SIZE), 1.0):
+		return _fail("the first paid berth is already dialled up (x%.2f)" \
+			% state.fleet_upkeep_scale(GameState.BASE_FLEET_SIZE))
+
+	# --- B. and every berth after it costs more ---------------------
+	var previous: float = 0.0
+	for slot in range(GameState.BASE_FLEET_SIZE, GameState.BASE_FLEET_SIZE + 12):
+		var scale: float = state.fleet_upkeep_scale(slot)
+		if scale < previous:
+			return _fail("berth %d is cheaper than the one before it" % (slot + 1))
+		previous = scale
+	var twelfth: float = state.fleet_upkeep_scale(GameState.BASE_FLEET_SIZE + 11)
+	if twelfth <= 1.0:
+		return _fail("twelve berths in, upkeep has not risen at all")
+
+	# --- C. slowly, though ------------------------------------------
+	if twelfth > 6.0:
+		return _fail("the twelfth berth costs x%.1f - that is not a slow exponential" % twelfth)
+	print("berth scaling: 1.00 at the first paid berth, x%.2f twelve in" % twelfth)
+
+	# --- D/E/F. the quoted bill IS the charged one ------------------
+	# Three offices, two of them crewed: the third berth stands empty and
+	# must be quoted nothing.
+	var office_ids: Array = []
+	for i in range(3):
+		office_ids.append(state.add_building(GameState.BUILDING_FLEET_OFFICE,
+			Vector2(500.0 * float(i + 1), 0.0)))
+	state.fleet_vessel_types = PackedStringArray([
+		GameState.VESSEL_INTERCEPTOR, vessel, vessel])
+
+	var breakdown: Dictionary = state.fleet_upkeep_breakdown()
+	var berths: Array = breakdown.berths
+	if berths.size() != 2:
+		return _fail("%d berths quoted for a fleet of 3 with 3 offices, expected 2 paying" \
+			% berths.size())
+	if int(berths[1].costs.get(GameState.RESOURCE_ORE, 0)) \
+			<= int(berths[0].costs.get(GameState.RESOURCE_ORE, 0)) - 1:
+		return _fail("the second paid berth is quoted less than the first")
+
+	# The per-minute figure has to be the per-berth charges, at the rate they
+	# are actually taken - not a separate estimate.
+	var charges: float = 60.0 / float(breakdown.charge_seconds)
+	for resource_type in breakdown.per_minute:
+		var summed: float = 0.0
+		for berth in berths:
+			summed += float(berth.costs.get(resource_type, 0)) * charges
+		if not is_equal_approx(float(breakdown.per_minute[resource_type]), summed):
+			return _fail("%s quoted at %.2f/min, its own berths add to %.2f" % [
+				resource_type, float(breakdown.per_minute[resource_type]), summed])
+	print("bill: %s, from %d paying berths" % [breakdown.per_minute, berths.size()])
+
+	# And a charge actually taken matches what was quoted for that berth.
+	var quoted: int = int(berths[0].costs.get(GameState.RESOURCE_ORE, 0))
+	var office: Dictionary = state.find_building(int(office_ids[0]))
+	var store: RefCounted = state.building_inventory(int(office_ids[0]))
+	store.set_amount(GameState.RESOURCE_ORE, 500)
+	store.set_amount(GameState.RESOURCE_ENERGY, 500)
+	var before: int = store.amount(GameState.RESOURCE_ORE)
+	office.upkeep_progress = GameState.FLEET_OFFICE_UPKEEP_SECONDS
+	state._advance_fleet_office_upkeep(0.1)
+	var taken: int = before - store.amount(GameState.RESOURCE_ORE)
+	if taken != quoted:
+		return _fail("berth 2 was quoted %d ore and charged %d" % [quoted, taken])
+	print("what the menu quotes for a berth is what the office pays: %d ore" % taken)
+
+	print("TEST_FLEET_UPKEEP_SCALING: PASS")
+	quit(0)
+	return true
+
+
+func _fail(message: String) -> bool:
+	print("TEST_FLEET_UPKEEP_SCALING: FAIL (%s)" % message)
+	quit(1)
+	return true