feat(audio): Add managed TTS engine service with OpenAI /v1/audio/speech compatibility #11

🎯 Objective & Overview

Integrate a dedicated, lightweight Text-to-Speech (TTS) engine service—primarily Kokoro-FastAPI (CPU/GPU, Apache 2.0, 82M params) or AllTalk TTS—into LocalLLMServerManager. Provide full process lifecycle management and an OpenAI-compatible /v1/audio/speech proxy.

📂 Files & Components to Touch

1. Configuration (LocalLLMServerManager.Shared/Models/AppSettings.cs):
   • Add:
     • string AudioEngineExecutablePath = "" (Path to python script, binary, or docker command)
     • string AudioEngineUrl = "http://127.0.0.1:8880"
     • string PreferredAudioVoice = "af_heart"
2. Process Management (Services/AiEngineManager.cs & Interfaces/IAiEngineManager.cs):
   • Add Task<bool> StartAudioEngineAsync(string executablePath, ILogger logger)
   • Add Task<bool> StopAudioEngineAsync(ILogger logger)
   • Add Process? AudioProcess { get; }
3. Endpoints (Endpoints/EngineEndpoints.cs & Endpoints/ModelProxyEndpoints.cs):
   • POST /api/audio/start — Spawns the audio engine process or starts the docker container.
   • POST /api/audio/stop — Gracefully stops the process.
   • POST /v1/audio/speech — Proxies OpenAI-format speech requests to AudioEngineUrl/v1/audio/speech.
   • GET /api/audio/voices — Returns list of available voice profiles.
4. Tool Discovery (Services/ToolDiscoveryService.cs):
   • Auto-detect local Kokoro/AllTalk installations and Docker container availability.

🔌 API Contract

POST /v1/audio/speech (OpenAI Compatibility Standard)

{
  "model": "kokoro",
  "input": "The quick brown fox jumps over the lazy dog.",
  "voice": "af_heart",
  "response_format": "mp3",
  "speed": 1.0
}

Response: 200 OK with binary audio/mpeg or audio/wav stream.

🛠️ Step-by-Step Implementation Guide

1. Update AppSettings.cs with the new audio configuration properties.
2. Implement start/stop process handlers in AiEngineManager.cs.
3. Add the proxy route in ModelProxyEndpoints.cs streaming chunked audio responses directly back to the HTTP client.
4. Update UI settings in SettingsTabControl.axaml to display the Audio Engine status, path, and test voice synthesizer.

🧪 Verification

• dotnet build
• dotnet test --filter Category!=LiveExternal
• npm run lint & npx tsc --noEmit