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]>

globals/audio_manager.gd

@@ -40,6 +40,20 @@ const BUS_HINTS := {
 	"reload": "Weapons",
 }
 
+## weapon_name (as broadcast in fire RPCs) -> fire sound id.
+const WEAPON_SOUND_IDS := {
+	"AK-47": "ak47_fire", "M4": "m4_fire", "MP7": "mp7_fire",
+	"DMR": "dmr_fire", "AWP": "awp_fire",
+	"Double Barrel Shotgun": "shotgun_fire", "Nail Gun": "nailgun_fire",
+	"Plasma Gun": "plasma_fire", "Rocket Launcher": "rocket_fire",
+	"Rocket Swarm": "swarm_fire", "Mortar": "mortar_fire",
+	"Knife": "knife_swing",
+}
+
+## Sounds loud enough to slap back off nearby walls (early reflections).
+const OCCLUSION_TICK := 0.12
+var _occlusion_accum := 0.0
+
 
 func _ready() -> void:
 	_setup_buses()
@@ -48,6 +62,33 @@ func _ready() -> void:
 	print("AudioManager: %d sounds registered" % _library.size())
 
 
+func _physics_process(delta: float) -> void:
+	# Re-filter playing positional sounds as the listener/source move so
+	# walking behind a wall audibly muffles loops and long tails too.
+	_occlusion_accum += delta
+	if _occlusion_accum < OCCLUSION_TICK:
+		return
+	_occlusion_accum = 0.0
+	var cam := get_viewport().get_camera_3d()
+	if cam == null:
+		return
+	var listener := cam.global_position
+	for p in _pool_3d:
+		if p.playing and not p.get_meta("is_reflection", false):
+			Acoustics.apply_occlusion(p, Acoustics.occlusion(
+				cam.get_world_3d(), listener, p.global_position))
+	# External looping players (projectile flight sounds, etc.) opt in by
+	# joining this group.
+	for node in get_tree().get_nodes_in_group("acoustic_occluded"):
+		if node is AudioStreamPlayer3D and node.playing and node.is_inside_tree():
+			Acoustics.apply_occlusion(node, Acoustics.occlusion(
+				cam.get_world_3d(), listener, node.global_position))
+
+
+func weapon_sound_id(weapon_name: String) -> String:
+	return WEAPON_SOUND_IDS.get(weapon_name, "")
+
+
 # ── Bus layout ────────────────────────────────────────────────────────────────
 
 func _setup_buses() -> void:
@@ -156,7 +197,9 @@ func _build_pools() -> void:
 		_pool_2d.append(p)
 
 
-## Play a positional sound. Safe to call every frame — players are pooled.
+## Play a positional sound with material-aware occlusion; loud sounds also
+## spawn early reflections off nearby surfaces so they can be located.
+## Safe to call every frame — players are pooled.
 func play_3d(id: String, global_pos: Vector3, volume_db_offset: float = 0.0,
 		pitch_scale: float = 1.0) -> AudioStreamPlayer3D:
 	var entry = _library.get(id)
@@ -169,10 +212,43 @@ func play_3d(id: String, global_pos: Vector3, volume_db_offset: float = 0.0,
 	player.volume_db = entry["volume_db"] + volume_db_offset
 	player.pitch_scale = pitch_scale * randf_range(1.0 - entry["pitch_var"], 1.0 + entry["pitch_var"])
 	player.global_position = global_pos
+	player.set_meta("is_reflection", false)
+	var cam := get_viewport().get_camera_3d()
+	if cam:
+		var occ := Acoustics.occlusion(cam.get_world_3d(), cam.global_position, global_pos)
+		Acoustics.apply_occlusion(player, occ)
+		if _is_loud(id):
+			_spawn_reflections(player.stream, global_pos, cam, entry, volume_db_offset)
+	else:
+		Acoustics.apply_occlusion(player, { "db": 0.0, "cutoff": Acoustics.OPEN_CUTOFF, "surfaces": 0 })
 	player.play()
 	return player
 
 
+func _is_loud(id: String) -> bool:
+	return id.findn("fire") != -1 or id.findn("explosion") != -1
+
+
+## Delayed, filtered copies of a loud sound from nearby wall mirror points.
+func _spawn_reflections(stream: AudioStream, source: Vector3, cam: Camera3D,
+		entry: Dictionary, volume_db_offset: float) -> void:
+	var refls := Acoustics.reflections(cam.get_world_3d(), source, cam.global_position)
+	for r in refls:
+		get_tree().create_timer(r.delay).timeout.connect(func():
+			var p := _pool_3d[_next_3d]
+			_next_3d = (_next_3d + 1) % POOL_SIZE_3D
+			p.stream = stream
+			p.bus = entry["bus"]
+			p.volume_db = entry["volume_db"] + volume_db_offset + r.db
+			p.pitch_scale = randf_range(0.97, 1.0)
+			p.global_position = r.point
+			p.set_meta("is_reflection", true)
+			p.attenuation_filter_cutoff_hz = r.cutoff
+			p.attenuation_filter_db = Acoustics.DEFAULT_FILTER_DB
+			p.play()
+		)
+
+
 ## Play a non-positional sound (UI clicks, local confirms).
 func play_ui(id: String, volume_db_offset: float = 0.0) -> AudioStreamPlayer:
 	var entry = _library.get(id)