feat(audio): add turbo engagement cue

Game/scripts/audio_manager.gd

@@ -8,6 +8,7 @@ const MAX_INTENSITY := 1.0
 
 var enabled := true
 var _engine_player: AudioStreamPlayer
+var _engine_turbo := false
 
 
 func bind_tree_buttons(root: Node) -> void:
@@ -50,9 +51,13 @@ func play_goal() -> void:
 
 func set_engine_state(thrust: float, turbo: bool) -> void:
 	var amount := clamp_intensity(thrust)
+	var rising_turbo := should_play_turbo_cue(_engine_turbo, turbo, amount)
 	if not enabled or amount <= 0.01:
 		stop_engine()
 		return
+	if rising_turbo:
+		_play_tone(260.0, 0.16, 0.16)
+	_engine_turbo = turbo
 	if _engine_player == null or not is_instance_valid(_engine_player):
 		_engine_player = AudioStreamPlayer.new()
 		_engine_player.stream = _engine_stream()
@@ -65,6 +70,7 @@ func set_engine_state(thrust: float, turbo: bool) -> void:
 func stop_engine() -> void:
 	if _engine_player != null and is_instance_valid(_engine_player):
 		_engine_player.stop()
+	_engine_turbo = false
 
 
 static func engine_pitch(thrust: float, turbo: bool) -> float:
@@ -77,6 +83,10 @@ static func engine_volume(thrust: float, turbo: bool) -> float:
 	return clampf(0.015 + amount * 0.045 + (0.025 if turbo and amount > 0.01 else 0.0), 0.0, 0.1)
 
 
+static func should_play_turbo_cue(previous_turbo: bool, turbo: bool, thrust: float) -> bool:
+	return turbo and not previous_turbo and clamp_intensity(thrust) > 0.01
+
+
 static func clamp_intensity(value: float) -> float:
 	if not is_finite(value):
 		return 0.0

Game/tests/cases/test_audio_manager.gd

@@ -32,3 +32,10 @@ func test_engine_mix_is_bounded_and_turbo_is_audible() -> void:
 	assert_true(AudioManager.engine_pitch(1.0, true) > AudioManager.engine_pitch(1.0, false), "turbo raises engine pitch")
 	assert_true(AudioManager.engine_volume(1.0, true) > AudioManager.engine_volume(1.0, false), "turbo raises engine volume")
 	assert_true(AudioManager.engine_volume(100.0, true) <= 0.1, "engine volume remains bounded")
+
+
+func test_turbo_state_is_only_a_rising_edge_for_the_engine_cue() -> void:
+	assert_true(AudioManager.should_play_turbo_cue(false, true, 0.8), "turbo engagement emits a cue")
+	assert_true(not AudioManager.should_play_turbo_cue(true, true, 0.8), "held turbo does not retrigger")
+	assert_true(not AudioManager.should_play_turbo_cue(false, true, 0.0), "turbo at idle thrust is silent")
+	assert_true(not AudioManager.should_play_turbo_cue(false, false, 0.8), "ordinary thrust emits no turbo cue")

TODO.md

@@ -14,7 +14,7 @@ The training pipeline is built — see `TRAINING.md` (self-play PPO via the vend
 
 The largest gap between this and a AAA-feeling product is presentation, not code. Sequenced after the above for pragmatic reasons, but this is the highest impact per hour.
 
-- [ ] **Audio — authored sound design remains open.** A dependency-free procedural `AudioManager` now provides safe UI/countdown/impact/goal hooks, an engine tone pitched/levelled from local thrust and turbo state, and is wired into kickoff, goal, ball-contact, and menu events; replace the placeholder tones with authored engine/turbo/impact/wall/goal/crowd/music assets after selecting distributable files and mixing them on real hardware.
+- [ ] **Audio — authored sound design remains open.** A dependency-free procedural `AudioManager` now provides safe UI/countdown/impact/goal hooks, an engine tone pitched/levelled from local thrust and turbo state plus a rising-edge turbo cue, and is wired into kickoff, goal, ball-contact, and menu events; replace the placeholder tones with authored engine/turbo/impact/wall/goal/crowd/music assets after selecting distributable files and mixing them on real hardware.
 - [ ] Custom font + a real `Theme` resource for the HUD. `ThemeDB.fallback_font` at 10-13 px reads as a debug overlay.
 - [ ] **Video settings are implemented; profiling/visual QA remains.** `video_settings.gd` and the settings menu expose graphics presets, AA, vsync, FPS caps, resolution scaling, glow, and brightness, with preset-gated SDFGI/SSIL/SSAO/shadows. The remaining gate is measuring the preset ladder and image quality on low/mid-tier reference hardware in the live editor; no further control wiring is implied by this TODO.
 

multiplayer-next.md

@@ -1627,6 +1627,6 @@ Signed MatchNet claims now also require exact JSON string/integer types for ever
 
 Presentation progress: a shared `Game/themes/cosmic_clash_theme.tres` now gives the menu, lobby, matchmaking, and settings surfaces consistent button, input, option, and label styling. The custom-font portion of `TODO.md` remains open until a distributable font asset is selected.
 
-The audio TODO now has a runtime foundation: `AudioManager` generates bounded placeholder tones for kickoff countdowns, camera-reported ball impacts, goals, UI clicks, and a local thrust/turbo-pitched engine loop without adding binary assets; authored sound design and production audio QA remain open.
+The audio TODO now has a runtime foundation: `AudioManager` generates bounded placeholder tones for kickoff countdowns, camera-reported ball impacts, goals, UI clicks, a local thrust/turbo-pitched engine loop, and a rising-edge turbo cue without adding binary assets; authored sound design and production audio QA remain open.
 
 The video-settings TODO is likewise locally implemented: presets, vsync, refresh-derived FPS caps, and resolution scaling are wired through `VideoSettings` and the settings menu. The remaining acceptance work is low/mid-tier hardware frame-time and image-quality profiling, which cannot be certified from this workspace.