feat(#391): add base TTS provider and factory classes

Add the BaseTTSProvider abstract class and TTS provider factory that were
part of the tiered TTS architecture but missed from the previous commit.

- BaseTTSProvider: abstract base with synthesize(), listVoices(), isHealthy()
- tts-provider.factory: creates Kokoro/Chatterbox/Piper providers from config
- 30 tests (22 base provider + 8 factory)

Refs #391

apps/api/src/speech/providers/base-tts.provider.spec.ts

@@ -0,0 +1,329 @@
+/**
+ * BaseTTSProvider Unit Tests
+ *
+ * Tests the abstract base class for OpenAI-compatible TTS providers.
+ * Uses a concrete test implementation to exercise the base class logic.
+ *
+ * Issue #391
+ */
+
+import { describe, it, expect, beforeEach, vi, type Mock } from "vitest";
+import { BaseTTSProvider } from "./base-tts.provider";
+import type { SpeechTier, SynthesizeOptions, AudioFormat } from "../interfaces/speech-types";
+
+// ==========================================
+// Mock OpenAI SDK
+// ==========================================
+
+const mockCreate = vi.fn();
+
+vi.mock("openai", () => {
+  class MockOpenAI {
+    audio = {
+      speech: {
+        create: mockCreate,
+      },
+    };
+  }
+  return { default: MockOpenAI };
+});
+
+// ==========================================
+// Concrete test implementation
+// ==========================================
+
+class TestTTSProvider extends BaseTTSProvider {
+  readonly name = "test-provider";
+  readonly tier: SpeechTier = "default";
+
+  constructor(baseURL: string, defaultVoice?: string, defaultFormat?: AudioFormat) {
+    super(baseURL, defaultVoice, defaultFormat);
+  }
+}
+
+// ==========================================
+// Test helpers
+// ==========================================
+
+/**
+ * Create a mock Response-like object that mimics OpenAI SDK's audio.speech.create() return.
+ * The OpenAI SDK returns a Response object with arrayBuffer() method.
+ */
+function createMockAudioResponse(audioData: Uint8Array): { arrayBuffer: Mock } {
+  return {
+    arrayBuffer: vi.fn().mockResolvedValue(audioData.buffer),
+  };
+}
+
+describe("BaseTTSProvider", () => {
+  let provider: TestTTSProvider;
+
+  const testBaseURL = "http://localhost:8880/v1";
+  const testVoice = "af_heart";
+  const testFormat: AudioFormat = "mp3";
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    provider = new TestTTSProvider(testBaseURL, testVoice, testFormat);
+  });
+
+  // ==========================================
+  // Constructor
+  // ==========================================
+
+  describe("constructor", () => {
+    it("should create an instance with provided configuration", () => {
+      expect(provider).toBeDefined();
+      expect(provider.name).toBe("test-provider");
+      expect(provider.tier).toBe("default");
+    });
+
+    it("should use default voice 'alloy' when none provided", () => {
+      const defaultProvider = new TestTTSProvider(testBaseURL);
+      expect(defaultProvider).toBeDefined();
+    });
+
+    it("should use default format 'mp3' when none provided", () => {
+      const defaultProvider = new TestTTSProvider(testBaseURL, "voice-1");
+      expect(defaultProvider).toBeDefined();
+    });
+  });
+
+  // ==========================================
+  // synthesize()
+  // ==========================================
+
+  describe("synthesize", () => {
+    it("should synthesize text and return a SynthesisResult with audio buffer", async () => {
+      const audioBytes = new Uint8Array([0x49, 0x44, 0x33, 0x04, 0x00]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      const result = await provider.synthesize("Hello, world!");
+
+      expect(result).toBeDefined();
+      expect(result.audio).toBeInstanceOf(Buffer);
+      expect(result.audio.length).toBe(audioBytes.length);
+      expect(result.format).toBe("mp3");
+      expect(result.voice).toBe("af_heart");
+      expect(result.tier).toBe("default");
+    });
+
+    it("should pass correct parameters to OpenAI SDK", async () => {
+      const audioBytes = new Uint8Array([0x01, 0x02]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      await provider.synthesize("Test text");
+
+      expect(mockCreate).toHaveBeenCalledWith({
+        model: "tts-1",
+        input: "Test text",
+        voice: "af_heart",
+        response_format: "mp3",
+        speed: 1.0,
+      });
+    });
+
+    it("should use custom voice from options", async () => {
+      const audioBytes = new Uint8Array([0x01]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      const options: SynthesizeOptions = { voice: "custom_voice" };
+      const result = await provider.synthesize("Hello", options);
+
+      expect(mockCreate).toHaveBeenCalledWith(expect.objectContaining({ voice: "custom_voice" }));
+      expect(result.voice).toBe("custom_voice");
+    });
+
+    it("should use custom format from options", async () => {
+      const audioBytes = new Uint8Array([0x01]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      const options: SynthesizeOptions = { format: "wav" };
+      const result = await provider.synthesize("Hello", options);
+
+      expect(mockCreate).toHaveBeenCalledWith(expect.objectContaining({ response_format: "wav" }));
+      expect(result.format).toBe("wav");
+    });
+
+    it("should use custom speed from options", async () => {
+      const audioBytes = new Uint8Array([0x01]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      const options: SynthesizeOptions = { speed: 1.5 };
+      await provider.synthesize("Hello", options);
+
+      expect(mockCreate).toHaveBeenCalledWith(expect.objectContaining({ speed: 1.5 }));
+    });
+
+    it("should throw an error when synthesis fails", async () => {
+      mockCreate.mockRejectedValue(new Error("Connection refused"));
+
+      await expect(provider.synthesize("Hello")).rejects.toThrow(
+        "TTS synthesis failed for test-provider: Connection refused"
+      );
+    });
+
+    it("should throw an error when response arrayBuffer fails", async () => {
+      const mockResponse = {
+        arrayBuffer: vi.fn().mockRejectedValue(new Error("Read error")),
+      };
+      mockCreate.mockResolvedValue(mockResponse);
+
+      await expect(provider.synthesize("Hello")).rejects.toThrow(
+        "TTS synthesis failed for test-provider: Read error"
+      );
+    });
+
+    it("should handle empty text input gracefully", async () => {
+      const audioBytes = new Uint8Array([]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      const result = await provider.synthesize("");
+
+      expect(result.audio).toBeInstanceOf(Buffer);
+      expect(result.audio.length).toBe(0);
+    });
+
+    it("should handle non-Error exceptions", async () => {
+      mockCreate.mockRejectedValue("string error");
+
+      await expect(provider.synthesize("Hello")).rejects.toThrow(
+        "TTS synthesis failed for test-provider: string error"
+      );
+    });
+  });
+
+  // ==========================================
+  // listVoices()
+  // ==========================================
+
+  describe("listVoices", () => {
+    it("should return default voice list with the configured default voice", async () => {
+      const voices = await provider.listVoices();
+
+      expect(voices).toBeInstanceOf(Array);
+      expect(voices.length).toBeGreaterThan(0);
+
+      const defaultVoice = voices.find((v) => v.isDefault === true);
+      expect(defaultVoice).toBeDefined();
+      expect(defaultVoice?.id).toBe("af_heart");
+      expect(defaultVoice?.tier).toBe("default");
+    });
+
+    it("should set tier correctly on all returned voices", async () => {
+      const voices = await provider.listVoices();
+
+      for (const voice of voices) {
+        expect(voice.tier).toBe("default");
+      }
+    });
+  });
+
+  // ==========================================
+  // isHealthy()
+  // ==========================================
+
+  describe("isHealthy", () => {
+    it("should return true when the TTS server is reachable", async () => {
+      // Mock global fetch for health check
+      const mockFetch = vi.fn().mockResolvedValue({
+        ok: true,
+        status: 200,
+      });
+      vi.stubGlobal("fetch", mockFetch);
+
+      const healthy = await provider.isHealthy();
+
+      expect(healthy).toBe(true);
+      expect(mockFetch).toHaveBeenCalled();
+
+      vi.unstubAllGlobals();
+    });
+
+    it("should return false when the TTS server is unreachable", async () => {
+      const mockFetch = vi.fn().mockRejectedValue(new Error("ECONNREFUSED"));
+      vi.stubGlobal("fetch", mockFetch);
+
+      const healthy = await provider.isHealthy();
+
+      expect(healthy).toBe(false);
+
+      vi.unstubAllGlobals();
+    });
+
+    it("should return false when the TTS server returns an error status", async () => {
+      const mockFetch = vi.fn().mockResolvedValue({
+        ok: false,
+        status: 503,
+      });
+      vi.stubGlobal("fetch", mockFetch);
+
+      const healthy = await provider.isHealthy();
+
+      expect(healthy).toBe(false);
+
+      vi.unstubAllGlobals();
+    });
+
+    it("should use the base URL for the health check", async () => {
+      const mockFetch = vi.fn().mockResolvedValue({ ok: true, status: 200 });
+      vi.stubGlobal("fetch", mockFetch);
+
+      await provider.isHealthy();
+
+      // Should call a health-related endpoint at the base URL
+      const calledUrl = mockFetch.mock.calls[0][0] as string;
+      expect(calledUrl).toContain("localhost:8880");
+
+      vi.unstubAllGlobals();
+    });
+
+    it("should set a timeout for the health check", async () => {
+      const mockFetch = vi.fn().mockResolvedValue({ ok: true, status: 200 });
+      vi.stubGlobal("fetch", mockFetch);
+
+      await provider.isHealthy();
+
+      // Should pass an AbortSignal for timeout
+      const fetchOptions = mockFetch.mock.calls[0][1] as RequestInit;
+      expect(fetchOptions.signal).toBeDefined();
+
+      vi.unstubAllGlobals();
+    });
+  });
+
+  // ==========================================
+  // Default values
+  // ==========================================
+
+  describe("default values", () => {
+    it("should use 'alloy' as default voice when none specified", async () => {
+      const defaultProvider = new TestTTSProvider(testBaseURL);
+      const audioBytes = new Uint8Array([0x01]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      await defaultProvider.synthesize("Hello");
+
+      expect(mockCreate).toHaveBeenCalledWith(expect.objectContaining({ voice: "alloy" }));
+    });
+
+    it("should use 'mp3' as default format when none specified", async () => {
+      const defaultProvider = new TestTTSProvider(testBaseURL);
+      const audioBytes = new Uint8Array([0x01]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      await defaultProvider.synthesize("Hello");
+
+      expect(mockCreate).toHaveBeenCalledWith(expect.objectContaining({ response_format: "mp3" }));
+    });
+
+    it("should use speed 1.0 as default speed", async () => {
+      const audioBytes = new Uint8Array([0x01]);
+      mockCreate.mockResolvedValue(createMockAudioResponse(audioBytes));
+
+      await provider.synthesize("Hello");
+
+      expect(mockCreate).toHaveBeenCalledWith(expect.objectContaining({ speed: 1.0 }));
+    });
+  });
+});

apps/api/src/speech/providers/base-tts.provider.ts

@@ -0,0 +1,189 @@
+/**
+ * Base TTS Provider
+ *
+ * Abstract base class implementing common OpenAI-compatible TTS logic.
+ * All concrete TTS providers (Kokoro, Chatterbox, Piper) extend this class.
+ *
+ * Uses the OpenAI SDK with a configurable baseURL to communicate with
+ * OpenAI-compatible speech synthesis endpoints.
+ *
+ * Issue #391
+ */
+
+import { Logger } from "@nestjs/common";
+import OpenAI from "openai";
+import type { ITTSProvider } from "../interfaces/tts-provider.interface";
+import type {
+  SpeechTier,
+  SynthesizeOptions,
+  SynthesisResult,
+  VoiceInfo,
+  AudioFormat,
+} from "../interfaces/speech-types";
+
+/** Default TTS model identifier used for OpenAI-compatible APIs */
+const DEFAULT_MODEL = "tts-1";
+
+/** Default voice when none is configured */
+const DEFAULT_VOICE = "alloy";
+
+/** Default audio format */
+const DEFAULT_FORMAT: AudioFormat = "mp3";
+
+/** Default speech speed multiplier */
+const DEFAULT_SPEED = 1.0;
+
+/** Health check timeout in milliseconds */
+const HEALTH_CHECK_TIMEOUT_MS = 5000;
+
+/**
+ * Abstract base class for OpenAI-compatible TTS providers.
+ *
+ * Provides common logic for:
+ * - Synthesizing text to audio via OpenAI SDK's audio.speech.create()
+ * - Listing available voices (with a default implementation)
+ * - Health checking the TTS endpoint
+ *
+ * Subclasses must set `name` and `tier` properties and may override
+ * `listVoices()` to provide provider-specific voice lists.
+ *
+ * @example
+ * ```typescript
+ * class KokoroProvider extends BaseTTSProvider {
+ *   readonly name = "kokoro";
+ *   readonly tier: SpeechTier = "default";
+ *
+ *   constructor(baseURL: string) {
+ *     super(baseURL, "af_heart", "mp3");
+ *   }
+ * }
+ * ```
+ */
+export abstract class BaseTTSProvider implements ITTSProvider {
+  abstract readonly name: string;
+  abstract readonly tier: SpeechTier;
+
+  protected readonly logger: Logger;
+  protected readonly client: OpenAI;
+  protected readonly baseURL: string;
+  protected readonly defaultVoice: string;
+  protected readonly defaultFormat: AudioFormat;
+
+  /**
+   * Create a new BaseTTSProvider.
+   *
+   * @param baseURL - The base URL for the OpenAI-compatible TTS endpoint
+   * @param defaultVoice - Default voice ID to use when none is specified in options
+   * @param defaultFormat - Default audio format to use when none is specified in options
+   */
+  constructor(
+    baseURL: string,
+    defaultVoice: string = DEFAULT_VOICE,
+    defaultFormat: AudioFormat = DEFAULT_FORMAT
+  ) {
+    this.baseURL = baseURL;
+    this.defaultVoice = defaultVoice;
+    this.defaultFormat = defaultFormat;
+    this.logger = new Logger(this.constructor.name);
+
+    this.client = new OpenAI({
+      baseURL,
+      apiKey: "not-needed", // Self-hosted services don't require an API key
+    });
+  }
+
+  /**
+   * Synthesize text to audio using the OpenAI-compatible TTS endpoint.
+   *
+   * Calls `client.audio.speech.create()` with the provided text and options,
+   * then converts the response to a Buffer.
+   *
+   * @param text - Text to convert to speech
+   * @param options - Optional synthesis parameters (voice, format, speed)
+   * @returns Synthesis result with audio buffer and metadata
+   * @throws {Error} If synthesis fails
+   */
+  async synthesize(text: string, options?: SynthesizeOptions): Promise<SynthesisResult> {
+    const voice = options?.voice ?? this.defaultVoice;
+    const format = options?.format ?? this.defaultFormat;
+    const speed = options?.speed ?? DEFAULT_SPEED;
+
+    try {
+      const response = await this.client.audio.speech.create({
+        model: DEFAULT_MODEL,
+        input: text,
+        voice,
+        response_format: format,
+        speed,
+      });
+
+      const arrayBuffer = await response.arrayBuffer();
+      const audio = Buffer.from(arrayBuffer);
+
+      return {
+        audio,
+        format,
+        voice,
+        tier: this.tier,
+      };
+    } catch (error: unknown) {
+      const message = error instanceof Error ? error.message : String(error);
+      this.logger.error(`TTS synthesis failed: ${message}`);
+      throw new Error(`TTS synthesis failed for ${this.name}: ${message}`);
+    }
+  }
+
+  /**
+   * List available voices for this provider.
+   *
+   * Default implementation returns the configured default voice.
+   * Subclasses should override this to provide a full voice list
+   * from their specific TTS engine.
+   *
+   * @returns Array of voice information objects
+   */
+  listVoices(): Promise<VoiceInfo[]> {
+    return Promise.resolve([
+      {
+        id: this.defaultVoice,
+        name: this.defaultVoice,
+        tier: this.tier,
+        isDefault: true,
+      },
+    ]);
+  }
+
+  /**
+   * Check if the TTS server is reachable and healthy.
+   *
+   * Performs a simple HTTP request to the base URL's models endpoint
+   * to verify the server is running and responding.
+   *
+   * @returns true if the server is reachable, false otherwise
+   */
+  async isHealthy(): Promise<boolean> {
+    try {
+      // Extract the base URL without the /v1 path for health checking
+      const healthUrl = this.baseURL.replace(/\/v1\/?$/, "/v1/models");
+      const controller = new AbortController();
+      const timeoutId = setTimeout(() => {
+        controller.abort();
+      }, HEALTH_CHECK_TIMEOUT_MS);
+
+      try {
+        const response = await fetch(healthUrl, {
+          method: "GET",
+          signal: controller.signal,
+        });
+
+        return response.ok;
+      } finally {
+        clearTimeout(timeoutId);
+      }
+    } catch (error: unknown) {
+      const message = error instanceof Error ? error.message : String(error);
+      this.logger.warn(`Health check failed for ${this.name}: ${message}`);
+      return false;
+    }
+  }
+}

apps/api/src/speech/providers/tts-provider.factory.spec.ts

@@ -0,0 +1,279 @@
+/**
+ * TTS Provider Factory Unit Tests
+ *
+ * Tests the factory that creates and registers TTS providers based on config.
+ *
+ * Issue #391
+ */
+
+import { describe, it, expect, vi } from "vitest";
+import { createTTSProviders } from "./tts-provider.factory";
+import type { SpeechConfig } from "../speech.config";
+import type { SpeechTier } from "../interfaces/speech-types";
+
+// ==========================================
+// Mock OpenAI SDK
+// ==========================================
+
+vi.mock("openai", () => {
+  class MockOpenAI {
+    audio = {
+      speech: {
+        create: vi.fn(),
+      },
+    };
+  }
+  return { default: MockOpenAI };
+});
+
+// ==========================================
+// Test helpers
+// ==========================================
+
+function createTestConfig(overrides?: Partial<SpeechConfig>): SpeechConfig {
+  return {
+    stt: {
+      enabled: false,
+      baseUrl: "http://speaches:8000/v1",
+      model: "whisper",
+      language: "en",
+    },
+    tts: {
+      default: {
+        enabled: false,
+        url: "http://kokoro-tts:8880/v1",
+        voice: "af_heart",
+        format: "mp3",
+      },
+      premium: {
+        enabled: false,
+        url: "http://chatterbox-tts:8881/v1",
+      },
+      fallback: {
+        enabled: false,
+        url: "http://openedai-speech:8000/v1",
+      },
+    },
+    limits: {
+      maxUploadSize: 25_000_000,
+      maxDurationSeconds: 600,
+      maxTextLength: 4096,
+    },
+    ...overrides,
+  };
+}
+
+describe("createTTSProviders", () => {
+  // ==========================================
+  // Empty map when nothing enabled
+  // ==========================================
+
+  describe("when no TTS tiers are enabled", () => {
+    it("should return an empty map", () => {
+      const config = createTestConfig();
+      const providers = createTTSProviders(config);
+
+      expect(providers).toBeInstanceOf(Map);
+      expect(providers.size).toBe(0);
+    });
+  });
+
+  // ==========================================
+  // Default tier
+  // ==========================================
+
+  describe("when default tier is enabled", () => {
+    it("should create a provider for the default tier", () => {
+      const config = createTestConfig({
+        tts: {
+          default: {
+            enabled: true,
+            url: "http://kokoro-tts:8880/v1",
+            voice: "af_heart",
+            format: "mp3",
+          },
+          premium: { enabled: false, url: "" },
+          fallback: { enabled: false, url: "" },
+        },
+      });
+
+      const providers = createTTSProviders(config);
+
+      expect(providers.size).toBe(1);
+      expect(providers.has("default")).toBe(true);
+
+      const provider = providers.get("default");
+      expect(provider).toBeDefined();
+      expect(provider?.tier).toBe("default");
+      expect(provider?.name).toBe("kokoro");
+    });
+  });
+
+  // ==========================================
+  // Premium tier
+  // ==========================================
+
+  describe("when premium tier is enabled", () => {
+    it("should create a provider for the premium tier", () => {
+      const config = createTestConfig({
+        tts: {
+          default: { enabled: false, url: "", voice: "", format: "" },
+          premium: {
+            enabled: true,
+            url: "http://chatterbox-tts:8881/v1",
+          },
+          fallback: { enabled: false, url: "" },
+        },
+      });
+
+      const providers = createTTSProviders(config);
+
+      expect(providers.size).toBe(1);
+      expect(providers.has("premium")).toBe(true);
+
+      const provider = providers.get("premium");
+      expect(provider).toBeDefined();
+      expect(provider?.tier).toBe("premium");
+      expect(provider?.name).toBe("chatterbox");
+    });
+  });
+
+  // ==========================================
+  // Fallback tier
+  // ==========================================
+
+  describe("when fallback tier is enabled", () => {
+    it("should create a provider for the fallback tier", () => {
+      const config = createTestConfig({
+        tts: {
+          default: { enabled: false, url: "", voice: "", format: "" },
+          premium: { enabled: false, url: "" },
+          fallback: {
+            enabled: true,
+            url: "http://openedai-speech:8000/v1",
+          },
+        },
+      });
+
+      const providers = createTTSProviders(config);
+
+      expect(providers.size).toBe(1);
+      expect(providers.has("fallback")).toBe(true);
+
+      const provider = providers.get("fallback");
+      expect(provider).toBeDefined();
+      expect(provider?.tier).toBe("fallback");
+      expect(provider?.name).toBe("piper");
+    });
+  });
+
+  // ==========================================
+  // Multiple tiers
+  // ==========================================
+
+  describe("when multiple tiers are enabled", () => {
+    it("should create providers for all enabled tiers", () => {
+      const config = createTestConfig({
+        tts: {
+          default: {
+            enabled: true,
+            url: "http://kokoro-tts:8880/v1",
+            voice: "af_heart",
+            format: "mp3",
+          },
+          premium: {
+            enabled: true,
+            url: "http://chatterbox-tts:8881/v1",
+          },
+          fallback: {
+            enabled: true,
+            url: "http://openedai-speech:8000/v1",
+          },
+        },
+      });
+
+      const providers = createTTSProviders(config);
+
+      expect(providers.size).toBe(3);
+      expect(providers.has("default")).toBe(true);
+      expect(providers.has("premium")).toBe(true);
+      expect(providers.has("fallback")).toBe(true);
+    });
+
+    it("should create providers only for enabled tiers", () => {
+      const config = createTestConfig({
+        tts: {
+          default: {
+            enabled: true,
+            url: "http://kokoro-tts:8880/v1",
+            voice: "af_heart",
+            format: "mp3",
+          },
+          premium: { enabled: false, url: "" },
+          fallback: {
+            enabled: true,
+            url: "http://openedai-speech:8000/v1",
+          },
+        },
+      });
+
+      const providers = createTTSProviders(config);
+
+      expect(providers.size).toBe(2);
+      expect(providers.has("default")).toBe(true);
+      expect(providers.has("premium")).toBe(false);
+      expect(providers.has("fallback")).toBe(true);
+    });
+  });
+
+  // ==========================================
+  // Provider properties
+  // ==========================================
+
+  describe("provider properties", () => {
+    it("should implement ITTSProvider interface methods", () => {
+      const config = createTestConfig({
+        tts: {
+          default: {
+            enabled: true,
+            url: "http://kokoro-tts:8880/v1",
+            voice: "af_heart",
+            format: "mp3",
+          },
+          premium: { enabled: false, url: "" },
+          fallback: { enabled: false, url: "" },
+        },
+      });
+
+      const providers = createTTSProviders(config);
+      const provider = providers.get("default");
+
+      expect(provider).toBeDefined();
+      expect(typeof provider?.synthesize).toBe("function");
+      expect(typeof provider?.listVoices).toBe("function");
+      expect(typeof provider?.isHealthy).toBe("function");
+    });
+
+    it("should return providers as a Map<SpeechTier, ITTSProvider>", () => {
+      const config = createTestConfig({
+        tts: {
+          default: {
+            enabled: true,
+            url: "http://kokoro-tts:8880/v1",
+            voice: "af_heart",
+            format: "mp3",
+          },
+          premium: { enabled: false, url: "" },
+          fallback: { enabled: false, url: "" },
+        },
+      });
+
+      const providers = createTTSProviders(config);
+
+      // Verify the map keys are valid SpeechTier values
+      for (const [tier] of providers) {
+        expect(["default", "premium", "fallback"]).toContain(tier as SpeechTier);
+      }
+    });
+  });
+});

apps/api/src/speech/providers/tts-provider.factory.ts

@@ -0,0 +1,112 @@
+/**
+ * TTS Provider Factory
+ *
+ * Creates and registers TTS providers based on speech configuration.
+ * Reads enabled flags and URLs from config and instantiates the appropriate
+ * provider for each tier.
+ *
+ * Each tier maps to a specific TTS engine:
+ * - default: Kokoro-FastAPI (CPU, always available)
+ * - premium: Chatterbox (GPU, voice cloning)
+ * - fallback: Piper via OpenedAI Speech (ultra-lightweight CPU)
+ *
+ * Issue #391
+ */
+
+import { Logger } from "@nestjs/common";
+import { BaseTTSProvider } from "./base-tts.provider";
+import type { ITTSProvider } from "../interfaces/tts-provider.interface";
+import type { SpeechTier, AudioFormat } from "../interfaces/speech-types";
+import type { SpeechConfig } from "../speech.config";
+
+// ==========================================
+// Concrete provider classes
+// ==========================================
+
+/**
+ * Kokoro TTS provider (default tier).
+ * CPU-based, always available, Apache 2.0 license.
+ */
+class KokoroProvider extends BaseTTSProvider {
+  readonly name = "kokoro";
+  readonly tier: SpeechTier = "default";
+}
+
+/**
+ * Chatterbox TTS provider (premium tier).
+ * GPU required, voice cloning capable, MIT license.
+ */
+class ChatterboxProvider extends BaseTTSProvider {
+  readonly name = "chatterbox";
+  readonly tier: SpeechTier = "premium";
+
+  constructor(baseURL: string) {
+    super(baseURL, "default", "mp3");
+  }
+}
+
+/**
+ * Piper TTS provider via OpenedAI Speech (fallback tier).
+ * Ultra-lightweight CPU, GPL license.
+ */
+class PiperProvider extends BaseTTSProvider {
+  readonly name = "piper";
+  readonly tier: SpeechTier = "fallback";
+
+  constructor(baseURL: string) {
+    super(baseURL, "alloy", "mp3");
+  }
+}
+
+// ==========================================
+// Factory function
+// ==========================================
+
+const logger = new Logger("TTSProviderFactory");
+
+/**
+ * Create and register TTS providers based on the speech configuration.
+ *
+ * Only creates providers for tiers that are enabled in the config.
+ * Returns a Map keyed by SpeechTier for use with the TTS_PROVIDERS injection token.
+ *
+ * @param config - Speech configuration with TTS tier settings
+ * @returns Map of enabled TTS providers keyed by tier
+ */
+export function createTTSProviders(config: SpeechConfig): Map<SpeechTier, ITTSProvider> {
+  const providers = new Map<SpeechTier, ITTSProvider>();
+
+  // Default tier: Kokoro
+  if (config.tts.default.enabled) {
+    const provider = new KokoroProvider(
+      config.tts.default.url,
+      config.tts.default.voice,
+      config.tts.default.format as AudioFormat
+    );
+    providers.set("default", provider);
+    logger.log(`Registered default TTS provider: kokoro at ${config.tts.default.url}`);
+  }
+
+  // Premium tier: Chatterbox
+  if (config.tts.premium.enabled) {
+    const provider = new ChatterboxProvider(config.tts.premium.url);
+    providers.set("premium", provider);
+    logger.log(`Registered premium TTS provider: chatterbox at ${config.tts.premium.url}`);
+  }
+
+  // Fallback tier: Piper
+  if (config.tts.fallback.enabled) {
+    const provider = new PiperProvider(config.tts.fallback.url);
+    providers.set("fallback", provider);
+    logger.log(`Registered fallback TTS provider: piper at ${config.tts.fallback.url}`);
+  }
+
+  if (providers.size === 0) {
+    logger.warn("No TTS providers are enabled. TTS synthesis will not be available.");
+  } else {
+    const tierNames = Array.from(providers.keys()).join(", ");
+    logger.log(`TTS providers ready: ${tierNames} (${String(providers.size)} total)`);
+  }
+
+  return providers;
+}