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

core/GameState.gd

@@ -776,6 +776,16 @@ signal fleet_upkeep_failed(slot_index: int, vessel_type: String)
 # ticket asks for and needs no second table to fall out of step with.
 const FLEET_OFFICE_UPKEEP_SECONDS: float = 25.0
 const FLEET_OFFICE_UPKEEP_DIVISOR: int = 8
+# #220: and each berth costs more than the one before it. A flat per-vessel
+# charge means a big fleet is only linearly harder to keep, so the tenth hull
+# is no more of a decision than the second; compounding makes every addition
+# weigh against the whole fleet behind it.
+#
+# Deliberately shallow - the ticket asks for a slow one. At 1.12 the thirteenth
+# berth costs about three and a half times the second, and the twentieth about
+# seven and a half. A steeper rate reaches "unaffordable" while the player is
+# still learning what the fleet is for.
+const FLEET_UPKEEP_GROWTH: float = 1.12
 
 
 # Offices in the order they were built, which is the order they are matched to
@@ -800,16 +810,62 @@ func supplied_fleet_office_count() -> int:
 # What one berth costs per charge, for the vessel actually sitting in it. An
 # empty answer means this vessel is free to keep - which is true of nothing
 # the crafter builds, and is what an unknown type falls back to.
-func fleet_office_upkeep(vessel_type: String) -> Dictionary:
+# What one berth costs per charge. `slot_index` is the fleet position it
+# keeps, so the first berth past the free one pays the base rate and every
+# berth after it pays the compounded one (#220).
+func fleet_office_upkeep(vessel_type: String, slot_index: int = BASE_FLEET_SIZE) -> Dictionary:
 	var upkeep: Dictionary = {}
+	var scale: float = fleet_upkeep_scale(slot_index)
 	for resource_type in product_costs(vessel_type):
 		var share: int = int(ceil(float(product_costs(vessel_type)[resource_type])
-			/ float(FLEET_OFFICE_UPKEEP_DIVISOR)))
+			/ float(FLEET_OFFICE_UPKEEP_DIVISOR) * scale))
 		if share > 0:
 			upkeep[resource_type] = share
 	return upkeep
 
 
+# The multiplier on a berth at this fleet position. The free hull and the
+# first paid berth both sit at 1.0, so the curve starts where the charging
+# starts rather than partway up it.
+func fleet_upkeep_scale(slot_index: int) -> float:
+	return pow(FLEET_UPKEEP_GROWTH, maxi(slot_index - BASE_FLEET_SIZE, 0))
+
+
+# The whole bill, berth by berth, for the readout #220 asks for: what each
+# one is keeping, what it is charged, and what that is per minute. Computed
+# here rather than in the menu so the numbers shown are the numbers charged -
+# a readout that recomputes them separately can disagree with the loop that
+# actually takes the resources.
+func fleet_upkeep_breakdown() -> Dictionary:
+	var berths: Array = []
+	var per_minute: Dictionary = {}
+	var charges_per_minute: float = 60.0 / FLEET_OFFICE_UPKEEP_SECONDS
+	var offices: Array = fleet_offices()
+	for i in range(offices.size()):
+		var slot_index: int = i + BASE_FLEET_SIZE
+		var vessel_type: String = fleet_office_vessel(slot_index)
+		if vessel_type == "":
+			continue  # a berth standing empty is charged nothing
+		var costs: Dictionary = fleet_office_upkeep(vessel_type, slot_index)
+		berths.append({
+			"slot": slot_index + 1,
+			"vessel_type": vessel_type,
+			"scale": fleet_upkeep_scale(slot_index),
+			"costs": costs,
+			"starved": bool(offices[i].get("starved", false)),
+		})
+		for resource_type in costs:
+			per_minute[resource_type] = float(per_minute.get(resource_type, 0.0)) \
+				+ float(costs[resource_type]) * charges_per_minute
+	return {
+		"berths": berths,
+		"per_minute": per_minute,
+		"charge_seconds": FLEET_OFFICE_UPKEEP_SECONDS,
+		"divisor": FLEET_OFFICE_UPKEEP_DIVISOR,
+		"growth": FLEET_UPKEEP_GROWTH,
+	}
+
+
 # The vessel an office is answerable for, or "" when the fleet is smaller than
 # the berths built for it - an office with nothing in it costs nothing.
 func fleet_office_vessel(slot_index: int) -> String:
@@ -841,7 +897,8 @@ func _advance_fleet_office_upkeep(delta: float) -> void:
 			office.upkeep_progress = progress
 			continue
 		office.upkeep_progress = progress - FLEET_OFFICE_UPKEEP_SECONDS
-		var upkeep: Dictionary = fleet_office_upkeep(vessel_type)
+		var upkeep: Dictionary = fleet_office_upkeep(vessel_type,
+			i + BASE_FLEET_SIZE)
 		var inventory: RefCounted = _inventory_for_record(office)
 		var affordable: bool = true
 		for resource_type in upkeep: