refactor: styles own their ringing tone directly (Pattern C)

Drop the injected AlarmSound Protocol and the wecker.Sound class. Each style
now owns its tone by using pygame directly; the runner owns only the audio
engine lifecycle (mixer init/quit), button sampling, and cleanup. This is the
seam for future styles that handle their own tone — a 'talk' style would just
import pygame and play speech, with no shared interface to extend.

- styles/base.py: AlarmStyle.__init__(set_led, music_file) + start() + update()
- styles/blink.py: start() loads+plays music via pygame.mixer.music
- styles/simple.py: owns its beep — synthesises a square-wave buffer in
  module (stdlib array+math) and plays it via pygame.mixer.Sound
- wecker.py: setup() brings up the mixer only; run_alarm constructs the style
  and guards start() with a clean log+exit on failure

Tests: a shared tests/conftest.py stubs RPi.GPIO/pygame in sys.modules before
any SUT import (order-independent, removes duplicated inline mocking); the
wecker mock_pygame fixture patches one fresh pygame mock into wecker + both
style modules so assertions see the same calls.

README: tone-ownership and plugin-contract updated.

styles/base.py

@@ -1,44 +1,26 @@
 from abc import ABC, abstractmethod
-from typing import Callable, Protocol
-
-
-class AlarmSound(Protocol):
-    """Audio capability injected into a style so it can own its ringing tone.
-
-    Styles stay free of pygame/GPIO imports (the API process imports them only
-    for name validation); the runner supplies a concrete implementation.
-    """
-
-    def play_music(self, path: str) -> None:
-        """Load and play a music file on an endless loop."""
-        ...
-
-    def play_beep(self) -> None:
-        """Play one short beep tone."""
-        ...
+from typing import Callable
 
 
 class AlarmStyle(ABC):
     """A pluggable alarm behaviour.
 
-    A style owns *its own ringing tone* (via the injected ``sound``) and
-    decides when the alarm stops and what the LED does. It never touches
-    hardware directly: ``set_led`` and ``sound`` are injected by the runner, so
-    styles stay import-safe in the API process (no GPIO/pygame).
+    A style owns *its own ringing tone*: it uses the audio engine (pygame)
+    directly and decides when the alarm stops and what the LED does. It never
+    touches hardware directly: ``set_led`` is injected by the runner, and the
+    runner owns the audio engine lifecycle (mixer init/quit). Styles stay
+    import-safe in the API process — ``import pygame`` does not initialise
+    audio, so the API can import styles just to validate names.
 
-    Lifecycle: construct once with ``set_led``/``sound``/``music_file``; call
-    ``start()`` to begin ringing (kick off the tone and initial LED); then call
-    ``update`` every tick. Return ``False`` from ``update`` to stop the alarm.
+    Lifecycle: construct once with ``set_led``/``music_file``; call ``start()``
+    to begin ringing (kick off the tone and initial LED); then call ``update``
+    every tick. Return ``False`` from ``update`` to stop the alarm.
     """
 
     def __init__(
-        self,
-        set_led: Callable[[bool], None],
-        sound: AlarmSound,
-        music_file: str | None = None,
+        self, set_led: Callable[[bool], None], music_file: str | None = None
     ):
         self.set_led = set_led
-        self.sound = sound
         self.music_file = music_file
 
     def start(self) -> None:

styles/blink.py

@@ -1,6 +1,8 @@
 import logging
 import random
 
+import pygame
+
 from styles.base import AlarmStyle
 
 # State Machine states for the puzzle flow.
@@ -21,8 +23,8 @@ class BlinkStyle(AlarmStyle):
     exactly that many times. A wrong count starts a fresh sequence.
     """
 
-    def __init__(self, set_led, sound, music_file=None):
-        super().__init__(set_led, sound, music_file)
+    def __init__(self, set_led, music_file=None):
+        super().__init__(set_led, music_file)
         self.state = STATE_RINGING
         self.target_blinks = 0
         self.user_presses = 0
@@ -35,7 +37,9 @@ class BlinkStyle(AlarmStyle):
     def start(self):
         # The puzzle rings with music on an endless loop; the LED stays off
         # until the button is pressed to start the blink sequence.
-        self.sound.play_music(self.music_file)
+        pygame.mixer.music.load(self.music_file)
+        pygame.mixer.music.set_volume(1.0)
+        pygame.mixer.music.play(-1)
         self.set_led(False)
 
     def update(self, now, is_pressed):
@@ -130,14 +134,8 @@ class BlinkStyle(AlarmStyle):
 
 if __name__ == "__main__":
     # Self-check: a correct blink sequence stops the alarm.
-    class _StubSound:
-        def play_music(self, path):
-            pass
-
-        def play_beep(self):
-            pass
-
-    style = BlinkStyle(lambda on: None, _StubSound(), "x.mp3")
+    # (Does not call start(), which needs the audio engine.)
+    style = BlinkStyle(lambda on: None, "x.mp3")
 
     assert style.update(100.0, True) is True
     assert style.state == STATE_WAIT_BEFORE_BLINK

styles/simple.py

@@ -1,3 +1,8 @@
+import array
+import math
+
+import pygame
+
 from styles.base import AlarmStyle
 
 # Time between beep retriggers; a short beep followed by this gap gives the
@@ -5,48 +10,73 @@ from styles.base import AlarmStyle
 BEEP_INTERVAL = 0.5
 
 
+def _make_beep_buffer(
+    freq: int = 1000, duration: float = 0.15, rate: int = 44100
+) -> bytes:
+    """Synthesize a short square-wave beep as signed-16-bit stereo PCM.
+
+    Matches the mixer format used by wecker.setup() (rate, -16, 2 channels) so
+    it feeds straight into ``pygame.mixer.Sound``. No audio file, no extra dep.
+    """
+    n = int(rate * duration)
+    buf = array.array("h")
+    for i in range(n):
+        v = 32767 if math.sin(2 * math.pi * freq * (i / rate)) >= 0 else -32767
+        buf.append(v)
+        buf.append(v)  # duplicate to stereo
+    return buf.tobytes()
+
+
+_BEEP_BUFFER = _make_beep_buffer()
+
+
 class SimpleStyle(AlarmStyle):
     """Press the button once to stop. Rings with a repeating beep.
 
-    This style plays no music file; it owns its tone via ``sound.play_beep``.
+    This style plays no music file; it owns its tone via a synthesised square
+    wave played through ``pygame.mixer.Sound``.
     """
 
-    def __init__(self, set_led, sound, music_file=None):
-        super().__init__(set_led, sound, music_file)
+    def __init__(self, set_led, music_file=None):
+        super().__init__(set_led, music_file)
         self._next_beep = 0.0
+        self._beep = None
 
     def start(self):
         # LED solid on so the button is findable in the dark.
         self.set_led(True)
+        self._beep = pygame.mixer.Sound(_BEEP_BUFFER)
 
     def update(self, now, is_pressed):
         self.set_led(True)
         if now >= self._next_beep:
-            self.sound.play_beep()
+            self._beep.play()
             self._next_beep = now + BEEP_INTERVAL
         return not is_pressed  # first press -> False -> stop
 
 
 if __name__ == "__main__":
-    # Self-check: not pressed keeps ringing and beeps; a press stops it.
-    class _StubSound:
+    # Self-check: the timer beeps on the interval and a press stops it.
+    # Bypasses start() (which needs the audio engine) by stubbing the beep.
+
+    class _Beep:
         def __init__(self):
-            self.beeps = 0
+            self.plays = 0
 
-        def play_music(self, path):
-            raise AssertionError("simple style must never play music")
+        def play(self):
+            self.plays += 1
 
-        def play_beep(self):
-            self.beeps += 1
+    style = SimpleStyle(lambda on: None)
+    style._beep = _Beep()
 
-    sound = _StubSound()
-    style = SimpleStyle(lambda on: None, sound)
-    style.start()
     assert style.update(0.0, False) is True
-    assert sound.beeps == 1  # first tick beeps
+    assert style._beep.plays == 1  # first tick beeps
+
     assert style.update(0.4, False) is True  # before interval -> no beep
-    assert sound.beeps == 1
+    assert style._beep.plays == 1
+
     assert style.update(0.5, False) is True  # at interval -> beep
-    assert sound.beeps == 2
+    assert style._beep.plays == 2
+
     assert style.update(0.6, True) is False  # press -> stop
     print("simple self-check ok")