feat: material-aware sound occlusion + early reflections for localization

New Acoustics system (globals/acoustics.gd):
- Occlusion: rays from listener to source collect up to 3 occluding bodies;
  each surface's material adds transmission loss and lowers the lowpass
  cutoff. A gunshot through wood stays warm (-8dB, 1.4kHz), brick muffles
  hard (-15dB, 600Hz), concrete harder (-18dB, 450Hz), metal keeps more
  highs (-11dB, 1kHz), glass barely muffles (-5dB, 2.6kHz). Applied via
  each AudioStreamPlayer3D's attenuation filter.
- Early reflections: loud sounds (gunfire, explosions) probe 8 directions
  for nearby walls; each close surface plays a quiet, delayed (path/343ms),
  material-filtered copy from the mirror point — shots audibly slap back
  off structures so players can triangulate. Sub-30ms echoes are skipped
  (they perceptually merge with the direct sound).
- Surface classification: builder-set acoustic_material meta -> node-name
  keywords -> metallic-material inference -> concrete default; cached.

Integration:
- AudioManager.play_3d applies occlusion at fire time and re-filters all
  playing positional sounds every 0.12s (walking behind a wall mid-sound
  audibly muffles it); flight loops opt in via "acoustic_occluded" group
- Remote players' gunshots were entirely SILENT — rpc_play_fire_effects now
  plays the right weapon's shot at the shooter's position, occluded and
  reflected like everything else
- Remote players' footsteps were also silent — now positional + occluded,
  cadence scaled to their speed
- Test level tagged: brick arena walls, wooden platforms/obstacles, metal
  wall-run corridor/rails/dash platforms; dust2 sandstone reads as brick

Tests: debug/acoustics_test.gd (12 checks: per-material loss ordering,
multi-wall stacking, reflection delay/filter, name classification) — all
pass; movement 11/11; smoke 0 failures.

Co-Authored-By: Claude Fable 5 <[email protected]>

debug/acoustics_test.gd

@@ -0,0 +1,111 @@
+extends SceneTree
+
+## Headless test for the Acoustics system:
+##   godot --headless --path . -s res://debug/acoustics_test.gd
+## Builds walls of different materials between a listener and a source and
+## checks occlusion/classification/reflection math behaves as designed.
+
+var _fails := 0
+var _frames := 0
+var _level: Node3D
+
+
+func _check(cond: bool, msg: String) -> void:
+	if cond:
+		print("  OK: ", msg)
+	else:
+		_fails += 1
+		print("  FAIL: ", msg)
+
+
+func _wall(pos: Vector3, size: Vector3, acoustic: String) -> StaticBody3D:
+	var body := StaticBody3D.new()
+	body.name = "Wall_" + acoustic
+	body.set_meta("acoustic_material", acoustic)
+	body.collision_layer = 1
+	var shape := CollisionShape3D.new()
+	shape.shape = BoxShape3D.new()
+	shape.shape.size = size
+	body.add_child(shape)
+	_level.add_child(body)
+	body.position = pos
+	return body
+
+
+func _initialize() -> void:
+	_level = Node3D.new()
+	root.add_child(_level)
+
+
+func _process(_delta: float) -> bool:
+	_frames += 1
+	if _frames < 5:
+		return false  # let physics register the bodies
+
+	if _frames == 5:
+		print("=== Acoustics tests ===")
+		var world := _level.get_world_3d()
+		var listener := Vector3(0, 1, 0)
+		var source := Vector3(0, 1, -10)
+
+		# No wall: clear line
+		var occ := Acoustics.occlusion(world, listener, source)
+		_check(occ.surfaces == 0 and occ.db == 0.0, "clear line of sight -> no occlusion")
+
+		# Wooden wall between
+		var w := _wall(Vector3(0, 1, -5), Vector3(6, 4, 0.4), "wood")
+		return false
+	elif _frames == 10:
+		var world := _level.get_world_3d()
+		var occ := Acoustics.occlusion(world, Vector3(0, 1, 0), Vector3(0, 1, -10))
+		_check(occ.surfaces == 1, "wooden wall -> 1 occluding surface")
+		_check(absf(occ.db - Acoustics.MATERIALS.wood.trans_db) < 0.01,
+			"wood transmission loss applied (%.1f dB)" % occ.db)
+		_check(occ.cutoff == Acoustics.MATERIALS.wood.trans_cutoff,
+			"wood lowpass cutoff (%.0f Hz)" % occ.cutoff)
+
+		# Swap to concrete: heavier loss, deeper muffle
+		for c in _level.get_children():
+			c.set_meta("acoustic_material", "concrete")
+		var occ2 := Acoustics.occlusion(world, Vector3(0, 1, 0), Vector3(0, 1, -10))
+		_check(occ2.db < occ.db, "concrete muffles more than wood (%.1f < %.1f dB)" % [occ2.db, occ.db])
+		_check(occ2.cutoff < occ.cutoff, "concrete cuts more highs (%.0f < %.0f Hz)" % [occ2.cutoff, occ.cutoff])
+
+		# Metal: between wood and concrete in loss, more highs than concrete
+		for c in _level.get_children():
+			c.set_meta("acoustic_material", "metal")
+		var occ3 := Acoustics.occlusion(world, Vector3(0, 1, 0), Vector3(0, 1, -10))
+		_check(occ3.cutoff > occ2.cutoff, "metal passes more highs than concrete")
+
+		# Second wall stacks
+		_wall(Vector3(0, 1, -7), Vector3(6, 4, 0.4), "wood")
+		return false
+	elif _frames == 15:
+		var world := _level.get_world_3d()
+		var occ := Acoustics.occlusion(world, Vector3(0, 1, 0), Vector3(0, 1, -10))
+		_check(occ.surfaces == 2, "two walls -> 2 occluding surfaces (got %d)" % occ.surfaces)
+
+		# Reflections: a big wall beside the source, far enough that the
+		# bounce path is >10m longer than the direct path (>30ms later —
+		# closer echoes perceptually merge and are correctly skipped).
+		_wall(Vector3(15, 1, -10), Vector3(0.4, 8, 10), "metal")
+		return false
+	elif _frames == 20:
+		var world := _level.get_world_3d()
+		var refls := Acoustics.reflections(world, Vector3(0, 1, -10), Vector3(0, 1, -2))
+		_check(refls.size() >= 1, "side wall produces a reflection (got %d)" % refls.size())
+		if refls.size() >= 1:
+			_check(refls[0].delay > 0.0 and refls[0].delay <= 0.35,
+				"reflection delay in range (%.0f ms)" % (refls[0].delay * 1000.0))
+			_check(refls[0].cutoff == Acoustics.MATERIALS.metal.refl_cutoff,
+				"reflection carries metal filter")
+
+		# Classification fallbacks
+		var crate := StaticBody3D.new()
+		crate.name = "wooden_crate_3"
+		_check(Acoustics.classify(crate) == "wood", "name-based classify: crate -> wood")
+		crate.free()
+
+		print("=== Acoustics results: %s ===" % ("ALL PASSED" if _fails == 0 else "%d FAILED" % _fails))
+		return true
+	return false