#229, #234: one voice per volley, and gas within reach of the spawn

#229 - a volley got louder for every ship in it.

Every hull owns its gun and asks for its own shot sound, so eight ships
firing on the same cooldown started eight voices playing the SAME sample in
the same frame. Those amplitudes add, so a full fleet was the loudest thing
in the game by a wide margin.

play() now takes a per-sound coalescing window. A volley is one event to the
ear, so it gets one voice. 70ms, which the test checks is inside the fastest
gun's 500ms cooldown - it collapses "six guns at once", never "six shots in
a row". PICKUP and ASTEROID_BREAK get one too: ore arrives in bursts when a
rock breaks and that is one pickup to the ear. Deaths and the boss scream
are left alone deliberately - several things dying together IS several
events.

test_sfx's pool-saturation case was driven by shots, which can no longer
saturate anything by design. It is driven by deaths now, which is what the
pool actually has to absorb, and it gained a case asserting a volley takes
one voice - measured against the real pool rather than the gate.

#234 - gas was not reliably in reach of the opening.

Gas giants are gated behind two independent noise fields, the SPACE biome
AND the planet roll, so whether any sat near the spawn was luck. Measured,
this seed lost: ZERO gas planets within four chunks, the nearest five away
past five rocky ones. Gas is an early need - the burner, ammunition - so the
opening cannot depend on the noise being kind.

SPAWN_GAS_GIANT_CHUNK at (2, -2), authored like OCTOPUS_BIOME_CENTER rather
than found by searching outward: a fixed chunk is reproducible from anywhere
without walking the map, which is what the rest of WorldGen is built on.

The override is applied AFTER every rng draw, for the same reason the dev
planting is - forcing one chunk must not shift what any other chunk rolls.
Confirmed by probe: the five other planets within four chunks are identical
before and after, and the distant gas giants at (-5,-4) and (0,-5) are still
where they were.

Both verified in reverse: without the window, "8 ships firing together
started 8 shot sounds"; without the chunk, "no gas planet within 4 chunks of
the spawn".

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

audio/Sfx.gd

@@ -73,6 +73,35 @@ const LEVELS: Dictionary = {
 	BLACK_HOLE: -11.0,
 }
 
+# Forgejo #229: how long a sound blocks another of its own kind.
+#
+# Every hull fires its own gun and asks for its own shot sound, so a fleet
+# firing a volley started one voice per ship - the same sample, in the same
+# frame, at the same level. Those amplitudes ADD, so the volley got louder
+# for every ship added, and a full fleet was the loudest thing in the game
+# by a wide margin.
+#
+# A volley is one event to the ear, so it gets one voice. The window is
+# shorter than any weapon's cooldown, so consecutive volleys are still heard
+# individually - it collapses "six guns at once", never "six shots in a row".
+#
+# Deaths and the boss scream are absent deliberately: several things dying
+# together IS several events, and each is rare enough not to stack.
+const COALESCE_MSEC: Dictionary = {
+	SHOT: 70,
+	# Ore comes in bursts when a rock breaks, and a burst is one pickup to
+	# the ear. Quieter than a shot but far more frequent (see LEVELS).
+	PICKUP: 60,
+	# Rocks break in twos and threes - that is in the pitch spread comment
+	# below, and it is the same stacking problem.
+	ASTEROID_BREAK: 60,
+}
+
+# When each sound last started, keyed by id. Static because play() is, and
+# the pool outlives every scene that uses it.
+static var _last_started_msec: Dictionary = {}
+
+
 # Shots vary a little in pitch so a stream of them does not turn into one
 # flat machine-gun note. The deaths do not: they are events, and a wobbling
 # explosion sounds broken rather than varied.
@@ -128,6 +157,13 @@ static func play(tree: SceneTree, id: String) -> void:
 	var stream: AudioStream = SOUNDS[id] as AudioStream
 	if stream == null:
 		return
+	var window: int = int(COALESCE_MSEC.get(id, 0))
+	if window > 0:
+		var now: int = Time.get_ticks_msec()
+		var last: int = int(_last_started_msec.get(id, -1000000))
+		if now - last < window:
+			return
+		_last_started_msec[id] = now
 	var pool: Node = _pool(tree)
 	var voice: AudioStreamPlayer = null
 	for child in pool.get_children():