#233: open with fewer enemies, of one kind, arriving in sequence

Measured before changing anything. The ticket's two halves needed opposite
fixes, and the first one made the second worse.

TOO COMPLEX. Variety was gated on fleet size alone, so a player who had
grown early met two kinds of trouble in the first wave they ever saw - a
fleet of four opened on two lancers and three chasers. Each roster entry now
carries a min_wave as well, so the openings teach one enemy at a time
whatever the fleet already looks like.

That alone pushed wave 1 against a fleet of six from a mixed six to SEVEN
chasers: budget that used to buy a lancer now bought two more chasers. So an
early wave also has a size ceiling, 2 + wave_number * 2. Wave 1 is four
chasers at any fleet size; the cap stops binding by wave 6 and nothing about
later balance moves.

  before  wave 1 fleet 4 -> 2 lancers, 3 chasers
          wave 1 fleet 6 -> 1 sniper, 2 lancers, 3 chasers
  after   wave 1 fleet 4 -> 4 chasers
          wave 1 fleet 6 -> 4 chasers

ARRIVE AT THE SAME TIME was literal: the whole wave spawned inside one frame
as a closed ring around the fleet, which reads as a wall rather than as an
attack. The first hull still lands immediately so a wave is never felt as
late, and the rest follow every 0.45s. Same enemies, same bearing, same
total - they simply do not all exist at once.

Four existing cases objected, and each was right to: they encode intents
that still hold LATER - a large wave must be varied, fleet growth must open
more kinds, a wave can field a lancer at all, and killing a wave must bring
the quiet back. The first three now ask at a wave number where variety is
permitted rather than being weakened. The fourth runs the arrivals out
before killing anything, and gained an assertion that doing so ADDS enemies
- which fails if the staggering ever collapses back into one frame.

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

tests/test_lancer_enemy.gd

@@ -262,6 +262,12 @@ func _process(delta: float) -> bool:
 			# the player now is a wave, so that is what has to be able to
 			# produce one - and it must not have displaced the chaser while
 			# doing it.
+			# Read past the openings: #233 gates each kind behind a minimum
+			# WAVE as well as a minimum fleet, so the first waves are chasers
+			# only however large the fleet is. This case is about whether a
+			# wave can field a lancer at all, not about when it starts to.
+			var settled_wave: int = game_state.wave_number
+			game_state.wave_number = 8
 			var kinds: Dictionary = {}
 			var lancer_at: int = 0
 			for size in range(1, 12):
@@ -269,6 +275,7 @@ func _process(delta: float) -> bool:
 					kinds[id] = true
 					if id == "lancer" and lancer_at == 0:
 						lancer_at = size
+			game_state.wave_number = settled_wave
 			if lancer_at == 0:
 				return _fail("no wave against a fleet of 1..11 contains a lancer")
 			if not kinds.has("chaser"):