fixed (bug) Audio not looping after ending.

src/audio/audio_manager.h

@@ -66,6 +66,12 @@ public:
     // for tests; the real lookup is through getPlaybackDevices().
     static std::string resolvePlaybackDeviceName(SDL_AudioDeviceID id);
 
+    // Builds the SDL_PropertiesID passed to MIX_PlayTrack() for tracks that
+    // loop forever (MIX_PROP_PLAY_LOOPS_NUMBER = -1). Exposed for tests; no
+    // mixer, track, or audio device is required. The caller owns the property
+    // set and must release it with SDL_DestroyProperties().
+    static SDL_PropertiesID createInfiniteLoopOptions();
+
     // Playback control
     bool playTrack(const std::string& wav_filename);
     void stopTrack();
@@ -97,6 +103,11 @@ private:
     void startFadeIn(int slotIndex, float seconds);
     std::string displayNameFor(const std::string& wav_filename) const;
 
+    // Starts the track on the given slot with infinite looping. The track must
+    // already be loaded on the slot. Calling this on a playing/stopped/fading
+    // track restarts it (cancelling any in-flight stop-fade).
+    bool playTrackLooping(int slotIndex);
+
     // Recreates the mixer on the given playback device id (0 = system default).
     // Called with mutex_ held. Preserves playback state: whichever track was
     // playing on the active slot is reloaded and resumed at full gain, an