# speech — Agent Context

> Part of the `apps/api/src` layer. Speech-to-text (STT) and text-to-speech (TTS) services.

## Module Structure

```
speech/
├── speech.module.ts           # NestJS module (conditional provider registration)
├── speech.config.ts           # Environment validation + typed config (registerAs)
├── speech.config.spec.ts      # 51 config validation tests
├── speech.constants.ts        # NestJS injection tokens (STT_PROVIDER, TTS_PROVIDERS)
├── speech.controller.ts       # REST endpoints (transcribe, synthesize, voices, health)
├── speech.controller.spec.ts  # Controller tests
├── speech.service.ts          # High-level service with fallback orchestration
├── speech.service.spec.ts     # Service tests
├── speech.gateway.ts          # WebSocket gateway (/speech namespace)
├── speech.gateway.spec.ts     # Gateway tests
├── dto/
│   ├── transcribe.dto.ts      # Transcription request DTO (class-validator)
│   ├── synthesize.dto.ts      # Synthesis request DTO (class-validator)
│   └── index.ts               # Barrel export
├── interfaces/
│   ├── speech-types.ts        # Shared types (SpeechTier, AudioFormat, options, results)
│   ├── stt-provider.interface.ts  # ISTTProvider contract
│   ├── tts-provider.interface.ts  # ITTSProvider contract
│   └── index.ts               # Barrel export
├── pipes/
│   ├── audio-validation.pipe.ts   # Validates uploaded audio (MIME type, size)
│   ├── audio-validation.pipe.spec.ts
│   ├── text-validation.pipe.ts    # Validates TTS text input (non-empty, max length)
│   ├── text-validation.pipe.spec.ts
│   └── index.ts               # Barrel export
└── providers/
    ├── base-tts.provider.ts       # Abstract base class (OpenAI SDK + common logic)
    ├── base-tts.provider.spec.ts
    ├── kokoro-tts.provider.ts     # Default tier (CPU, 53 voices, 8 languages)
    ├── kokoro-tts.provider.spec.ts
    ├── chatterbox-tts.provider.ts # Premium tier (GPU, voice cloning, emotion control)
    ├── chatterbox-tts.provider.spec.ts
    ├── piper-tts.provider.ts      # Fallback tier (CPU, lightweight, Raspberry Pi)
    ├── piper-tts.provider.spec.ts
    ├── speaches-stt.provider.ts   # STT provider (Whisper via Speaches)
    ├── speaches-stt.provider.spec.ts
    ├── tts-provider.factory.ts    # Factory: creates providers from config
    └── tts-provider.factory.spec.ts
```

## Codebase Patterns

### Provider Pattern (BaseTTSProvider + Factory)

All TTS providers extend `BaseTTSProvider`:

```typescript
export class MyNewProvider extends BaseTTSProvider {
  readonly name = "my-provider";
  readonly tier: SpeechTier = "default"; // or "premium" or "fallback"

  constructor(baseURL: string) {
    super(baseURL, "default-voice-id", "mp3");
  }

  // Override listVoices() for custom voice catalog
  override listVoices(): Promise<VoiceInfo[]> { ... }

  // Override synthesize() only if non-standard API behavior is needed
  // (see ChatterboxTTSProvider for example with extra body params)
}
```

The base class handles:

- OpenAI SDK client creation with custom `baseURL` and `apiKey: "not-needed"`
- Standard `synthesize()` via `client.audio.speech.create()`
- Default `listVoices()` returning just the default voice
- `isHealthy()` via GET to the `/v1/models` endpoint

### Config Pattern

Config follows the existing pattern (`auth.config.ts`, `federation.config.ts`):

- Export `isSttEnabled()`, `isTtsEnabled()`, etc. (boolean checks from env)
- Export `validateSpeechConfig()` (called at module init, throws on missing required vars)
- Export `getSpeechConfig()` (typed config object with defaults)
- Export `speechConfig = registerAs("speech", ...)` for NestJS ConfigModule

Boolean env parsing: `value === "true" || value === "1"`. No default-true.

### Conditional Provider Registration

In `speech.module.ts`:

- STT provider uses `isSttEnabled()` at module definition time to decide whether to register
- TTS providers use a factory function injected with `ConfigService`
- `@Optional()` decorator on `SpeechService`'s `sttProvider` handles the case where STT is disabled

### Injection Tokens

```typescript
// speech.constants.ts
export const STT_PROVIDER = Symbol("STT_PROVIDER"); // ISTTProvider
export const TTS_PROVIDERS = Symbol("TTS_PROVIDERS"); // Map<SpeechTier, ITTSProvider>
```

### Fallback Chain

TTS fallback order: `premium` -> `default` -> `fallback`

- Chain starts at the requested tier and goes downward
- Only tiers that are both enabled AND have a registered provider are attempted
- `ServiceUnavailableException` if all providers fail

### WebSocket Gateway

- Separate `/speech` namespace (not on the main gateway)
- Authentication mirrors the main WS gateway pattern (token extraction from handshake)
- One session per client, accumulates audio chunks in memory
- Chunks concatenated and transcribed on `stop-transcription`
- Session cleanup on disconnect

## How to Add a New TTS Provider

1. **Create the provider class** in `providers/`:

```typescript
// providers/my-tts.provider.ts
import { BaseTTSProvider } from "./base-tts.provider";
import type { SpeechTier } from "../interfaces/speech-types";

export class MyTtsProvider extends BaseTTSProvider {
  readonly name = "my-provider";
  readonly tier: SpeechTier = "default"; // Choose tier

  constructor(baseURL: string) {
    super(baseURL, "default-voice", "mp3");
  }

  override listVoices(): Promise<VoiceInfo[]> {
    // Return your voice catalog
  }
}
```

2. **Add env vars** to `speech.config.ts`:
   - Add enabled check function
   - Add URL to validation in `validateSpeechConfig()`
   - Add config section in `getSpeechConfig()`

3. **Register in factory** (`tts-provider.factory.ts`):

```typescript
if (config.tts.myTier.enabled) {
  const provider = new MyTtsProvider(config.tts.myTier.url);
  providers.set("myTier", provider);
}
```

4. **Add env vars** to `.env.example`

5. **Write tests** following existing patterns (mock OpenAI SDK, test synthesis + listVoices + isHealthy)

## How to Add a New STT Provider

1. **Implement `ISTTProvider`** (does not use a base class -- STT has only one implementation currently)
2. **Add config section** similar to `stt` in `speech.config.ts`
3. **Register** in `speech.module.ts` providers array with `STT_PROVIDER` token
4. **Write tests** following `speaches-stt.provider.spec.ts` pattern

## Common Gotchas

- **OpenAI SDK `apiKey`**: Self-hosted services do not require an API key. Use `apiKey: "not-needed"` when creating the OpenAI client.
- **`toFile()` import**: The `toFile` helper is imported from `"openai"` (not from a subpath). Used in the STT provider to convert Buffer to a File-like object for multipart upload.
- **Health check URL**: `BaseTTSProvider.isHealthy()` calls `GET /v1/models`. The base URL is expected to end with `/v1`.
- **Voice ID prefix parsing**: Kokoro voice IDs encode language + gender in first two characters. See `parseVoicePrefix()` in `kokoro-tts.provider.ts`.
- **Chatterbox extra body params**: The `reference_audio` (base64) and `exaggeration` fields are passed via the OpenAI SDK by casting the request body. This works because the SDK passes through unknown fields.
- **WebSocket auth**: The gateway checks `auth.token`, then `query.token`, then `Authorization` header (in that order). Match this in test setup.
- **Config validation timing**: `validateSpeechConfig()` runs at module init (`onModuleInit`), not at provider construction. This means a misconfigured provider will fail at startup, not at first request.

## Test Patterns

### Mocking OpenAI SDK

All provider tests mock the OpenAI SDK. Pattern:

```typescript
vi.mock("openai", () => ({
  default: vi.fn().mockImplementation(() => ({
    audio: {
      speech: {
        create: vi.fn().mockResolvedValue({
          arrayBuffer: () => Promise.resolve(new ArrayBuffer(10)),
        }),
      },
      transcriptions: {
        create: vi.fn().mockResolvedValue({
          text: "transcribed text",
          language: "en",
          duration: 3.5,
        }),
      },
    },
    models: { list: vi.fn().mockResolvedValue({ data: [] }) },
  })),
}));
```

### Mocking Config Injection

```typescript
const mockConfig: SpeechConfig = {
  stt: { enabled: true, baseUrl: "http://test:8000/v1", model: "test-model", language: "en" },
  tts: {
    default: { enabled: true, url: "http://test:8880/v1", voice: "af_heart", format: "mp3" },
    premium: { enabled: false, url: "" },
    fallback: { enabled: false, url: "" },
  },
  limits: { maxUploadSize: 25000000, maxDurationSeconds: 600, maxTextLength: 4096 },
};
```

### Config Test Pattern

`speech.config.spec.ts` saves and restores `process.env` around each test:

```typescript
let savedEnv: NodeJS.ProcessEnv;
beforeEach(() => {
  savedEnv = { ...process.env };
});
afterEach(() => {
  process.env = savedEnv;
});
```

## Key Files

| File                                | Purpose                                                                  |
| ----------------------------------- | ------------------------------------------------------------------------ |
| `speech.module.ts`                  | Module registration with conditional providers                           |
| `speech.config.ts`                  | All speech env vars + validation (51 tests)                              |
| `speech.service.ts`                 | Core service: transcribe, synthesize (with fallback), listVoices         |
| `speech.controller.ts`              | REST endpoints: POST transcribe, POST synthesize, GET voices, GET health |
| `speech.gateway.ts`                 | WebSocket streaming transcription (/speech namespace)                    |
| `providers/base-tts.provider.ts`    | Abstract base for all TTS providers (OpenAI SDK wrapper)                 |
| `providers/tts-provider.factory.ts` | Creates provider instances from config                                   |
| `interfaces/speech-types.ts`        | All shared types: SpeechTier, AudioFormat, options, results              |
