feat(#401): add speech services config and env vars

Add SpeechConfig with typed configuration and startup validation for
STT (Whisper/Speaches), TTS default (Kokoro), TTS premium (Chatterbox),
and TTS fallback (Piper/OpenedAI). Includes registerAs factory for
NestJS ConfigModule integration, .env.example documentation, and 51
unit tests covering all validation paths.

Refs #401

apps/api/AGENTS.md

@@ -4,15 +4,22 @@
 
 ## Patterns
 
-<!-- Add module-specific patterns as you discover them -->
+- **Config validation pattern**: Config files use exported validation functions + typed getter functions (not class-validator). See `auth.config.ts`, `federation.config.ts`, `speech/speech.config.ts`. Pattern: export `isXEnabled()`, `validateXConfig()`, and `getXConfig()` functions.
+- **Config registerAs**: `speech.config.ts` also exports a `registerAs("speech", ...)` factory for NestJS ConfigModule namespaced injection. Use `ConfigModule.forFeature(speechConfig)` in module imports and access via `this.config.get<string>('speech.stt.baseUrl')`.
+- **Conditional config validation**: When a service has an enabled flag (e.g., `STT_ENABLED`), URL/connection vars are only required when enabled. Validation throws with a helpful message suggesting how to disable.
+- **Boolean env parsing**: Use `value === "true" || value === "1"` pattern. No default-true -- all services default to disabled when env var is unset.
 
 ## Gotchas
 
-<!-- Add things that trip up agents in this module -->
+- **Prisma client must be generated** before `tsc --noEmit` will pass. Run `pnpm prisma:generate` first. Pre-existing type errors from Prisma are expected in worktrees without generated client.
+- **Pre-commit hooks**: lint-staged runs on staged files. If other packages' files are staged, their lint must pass too. Only stage files you intend to commit.
+- **vitest runs all test files**: Even when targeting a specific test file, vitest loads all spec files. Many will fail if Prisma client isn't generated -- this is expected. Check only your target file's pass/fail status.
 
 ## Key Files
 
-| File | Purpose |
-| ---- | ------- |
-
-<!-- Add important files in this directory -->
+| File                                  | Purpose                                                                |
+| ------------------------------------- | ---------------------------------------------------------------------- |
+| `src/speech/speech.config.ts`         | Speech services env var validation and typed config (STT, TTS, limits) |
+| `src/speech/speech.config.spec.ts`    | Unit tests for speech config validation (51 tests)                     |
+| `src/auth/auth.config.ts`             | Auth/OIDC config validation (reference pattern)                        |
+| `src/federation/federation.config.ts` | Federation config validation (reference pattern)                       |

apps/api/src/speech/speech.config.spec.ts

@@ -0,0 +1,458 @@
+/**
+ * Speech Configuration Tests
+ *
+ * Issue #401: Tests for speech services environment variable validation
+ * Tests cover STT, TTS (default, premium, fallback), and speech limits configuration.
+ */
+
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import {
+  isSttEnabled,
+  isTtsEnabled,
+  isTtsPremiumEnabled,
+  isTtsFallbackEnabled,
+  validateSpeechConfig,
+  getSpeechConfig,
+  type SpeechConfig,
+} from "./speech.config";
+
+describe("speech.config", () => {
+  const originalEnv = { ...process.env };
+
+  beforeEach(() => {
+    // Clear all speech-related env vars before each test
+    delete process.env.STT_ENABLED;
+    delete process.env.STT_BASE_URL;
+    delete process.env.STT_MODEL;
+    delete process.env.STT_LANGUAGE;
+    delete process.env.TTS_ENABLED;
+    delete process.env.TTS_DEFAULT_URL;
+    delete process.env.TTS_DEFAULT_VOICE;
+    delete process.env.TTS_DEFAULT_FORMAT;
+    delete process.env.TTS_PREMIUM_ENABLED;
+    delete process.env.TTS_PREMIUM_URL;
+    delete process.env.TTS_FALLBACK_ENABLED;
+    delete process.env.TTS_FALLBACK_URL;
+    delete process.env.SPEECH_MAX_UPLOAD_SIZE;
+    delete process.env.SPEECH_MAX_DURATION_SECONDS;
+    delete process.env.SPEECH_MAX_TEXT_LENGTH;
+  });
+
+  afterEach(() => {
+    process.env = { ...originalEnv };
+  });
+
+  // ==========================================
+  // STT enabled check
+  // ==========================================
+  describe("isSttEnabled", () => {
+    it("should return false when STT_ENABLED is not set", () => {
+      expect(isSttEnabled()).toBe(false);
+    });
+
+    it("should return false when STT_ENABLED is 'false'", () => {
+      process.env.STT_ENABLED = "false";
+      expect(isSttEnabled()).toBe(false);
+    });
+
+    it("should return false when STT_ENABLED is '0'", () => {
+      process.env.STT_ENABLED = "0";
+      expect(isSttEnabled()).toBe(false);
+    });
+
+    it("should return false when STT_ENABLED is empty string", () => {
+      process.env.STT_ENABLED = "";
+      expect(isSttEnabled()).toBe(false);
+    });
+
+    it("should return true when STT_ENABLED is 'true'", () => {
+      process.env.STT_ENABLED = "true";
+      expect(isSttEnabled()).toBe(true);
+    });
+
+    it("should return true when STT_ENABLED is '1'", () => {
+      process.env.STT_ENABLED = "1";
+      expect(isSttEnabled()).toBe(true);
+    });
+  });
+
+  // ==========================================
+  // TTS enabled check
+  // ==========================================
+  describe("isTtsEnabled", () => {
+    it("should return false when TTS_ENABLED is not set", () => {
+      expect(isTtsEnabled()).toBe(false);
+    });
+
+    it("should return false when TTS_ENABLED is 'false'", () => {
+      process.env.TTS_ENABLED = "false";
+      expect(isTtsEnabled()).toBe(false);
+    });
+
+    it("should return true when TTS_ENABLED is 'true'", () => {
+      process.env.TTS_ENABLED = "true";
+      expect(isTtsEnabled()).toBe(true);
+    });
+
+    it("should return true when TTS_ENABLED is '1'", () => {
+      process.env.TTS_ENABLED = "1";
+      expect(isTtsEnabled()).toBe(true);
+    });
+  });
+
+  // ==========================================
+  // TTS premium enabled check
+  // ==========================================
+  describe("isTtsPremiumEnabled", () => {
+    it("should return false when TTS_PREMIUM_ENABLED is not set", () => {
+      expect(isTtsPremiumEnabled()).toBe(false);
+    });
+
+    it("should return false when TTS_PREMIUM_ENABLED is 'false'", () => {
+      process.env.TTS_PREMIUM_ENABLED = "false";
+      expect(isTtsPremiumEnabled()).toBe(false);
+    });
+
+    it("should return true when TTS_PREMIUM_ENABLED is 'true'", () => {
+      process.env.TTS_PREMIUM_ENABLED = "true";
+      expect(isTtsPremiumEnabled()).toBe(true);
+    });
+  });
+
+  // ==========================================
+  // TTS fallback enabled check
+  // ==========================================
+  describe("isTtsFallbackEnabled", () => {
+    it("should return false when TTS_FALLBACK_ENABLED is not set", () => {
+      expect(isTtsFallbackEnabled()).toBe(false);
+    });
+
+    it("should return false when TTS_FALLBACK_ENABLED is 'false'", () => {
+      process.env.TTS_FALLBACK_ENABLED = "false";
+      expect(isTtsFallbackEnabled()).toBe(false);
+    });
+
+    it("should return true when TTS_FALLBACK_ENABLED is 'true'", () => {
+      process.env.TTS_FALLBACK_ENABLED = "true";
+      expect(isTtsFallbackEnabled()).toBe(true);
+    });
+  });
+
+  // ==========================================
+  // validateSpeechConfig
+  // ==========================================
+  describe("validateSpeechConfig", () => {
+    describe("when all services are disabled", () => {
+      it("should not throw when no speech services are enabled", () => {
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+
+      it("should not throw when services are explicitly disabled", () => {
+        process.env.STT_ENABLED = "false";
+        process.env.TTS_ENABLED = "false";
+        process.env.TTS_PREMIUM_ENABLED = "false";
+        process.env.TTS_FALLBACK_ENABLED = "false";
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+    });
+
+    describe("STT validation", () => {
+      beforeEach(() => {
+        process.env.STT_ENABLED = "true";
+      });
+
+      it("should throw when STT is enabled but STT_BASE_URL is missing", () => {
+        expect(() => validateSpeechConfig()).toThrow("STT_BASE_URL");
+        expect(() => validateSpeechConfig()).toThrow(
+          "STT is enabled (STT_ENABLED=true) but required environment variables are missing"
+        );
+      });
+
+      it("should throw when STT_BASE_URL is empty string", () => {
+        process.env.STT_BASE_URL = "";
+        expect(() => validateSpeechConfig()).toThrow("STT_BASE_URL");
+      });
+
+      it("should throw when STT_BASE_URL is whitespace only", () => {
+        process.env.STT_BASE_URL = "   ";
+        expect(() => validateSpeechConfig()).toThrow("STT_BASE_URL");
+      });
+
+      it("should not throw when STT is enabled and STT_BASE_URL is set", () => {
+        process.env.STT_BASE_URL = "http://speaches:8000/v1";
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+
+      it("should suggest disabling STT in error message", () => {
+        expect(() => validateSpeechConfig()).toThrow("STT_ENABLED=false");
+      });
+    });
+
+    describe("TTS default validation", () => {
+      beforeEach(() => {
+        process.env.TTS_ENABLED = "true";
+      });
+
+      it("should throw when TTS is enabled but TTS_DEFAULT_URL is missing", () => {
+        expect(() => validateSpeechConfig()).toThrow("TTS_DEFAULT_URL");
+        expect(() => validateSpeechConfig()).toThrow(
+          "TTS is enabled (TTS_ENABLED=true) but required environment variables are missing"
+        );
+      });
+
+      it("should throw when TTS_DEFAULT_URL is empty string", () => {
+        process.env.TTS_DEFAULT_URL = "";
+        expect(() => validateSpeechConfig()).toThrow("TTS_DEFAULT_URL");
+      });
+
+      it("should not throw when TTS is enabled and TTS_DEFAULT_URL is set", () => {
+        process.env.TTS_DEFAULT_URL = "http://kokoro-tts:8880/v1";
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+
+      it("should suggest disabling TTS in error message", () => {
+        expect(() => validateSpeechConfig()).toThrow("TTS_ENABLED=false");
+      });
+    });
+
+    describe("TTS premium validation", () => {
+      beforeEach(() => {
+        process.env.TTS_PREMIUM_ENABLED = "true";
+      });
+
+      it("should throw when TTS premium is enabled but TTS_PREMIUM_URL is missing", () => {
+        expect(() => validateSpeechConfig()).toThrow("TTS_PREMIUM_URL");
+        expect(() => validateSpeechConfig()).toThrow(
+          "TTS premium is enabled (TTS_PREMIUM_ENABLED=true) but required environment variables are missing"
+        );
+      });
+
+      it("should throw when TTS_PREMIUM_URL is empty string", () => {
+        process.env.TTS_PREMIUM_URL = "";
+        expect(() => validateSpeechConfig()).toThrow("TTS_PREMIUM_URL");
+      });
+
+      it("should not throw when TTS premium is enabled and TTS_PREMIUM_URL is set", () => {
+        process.env.TTS_PREMIUM_URL = "http://chatterbox-tts:8881/v1";
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+
+      it("should suggest disabling TTS premium in error message", () => {
+        expect(() => validateSpeechConfig()).toThrow("TTS_PREMIUM_ENABLED=false");
+      });
+    });
+
+    describe("TTS fallback validation", () => {
+      beforeEach(() => {
+        process.env.TTS_FALLBACK_ENABLED = "true";
+      });
+
+      it("should throw when TTS fallback is enabled but TTS_FALLBACK_URL is missing", () => {
+        expect(() => validateSpeechConfig()).toThrow("TTS_FALLBACK_URL");
+        expect(() => validateSpeechConfig()).toThrow(
+          "TTS fallback is enabled (TTS_FALLBACK_ENABLED=true) but required environment variables are missing"
+        );
+      });
+
+      it("should throw when TTS_FALLBACK_URL is empty string", () => {
+        process.env.TTS_FALLBACK_URL = "";
+        expect(() => validateSpeechConfig()).toThrow("TTS_FALLBACK_URL");
+      });
+
+      it("should not throw when TTS fallback is enabled and TTS_FALLBACK_URL is set", () => {
+        process.env.TTS_FALLBACK_URL = "http://openedai-speech:8000/v1";
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+
+      it("should suggest disabling TTS fallback in error message", () => {
+        expect(() => validateSpeechConfig()).toThrow("TTS_FALLBACK_ENABLED=false");
+      });
+    });
+
+    describe("multiple services enabled simultaneously", () => {
+      it("should validate all enabled services", () => {
+        process.env.STT_ENABLED = "true";
+        process.env.TTS_ENABLED = "true";
+        // Missing both STT_BASE_URL and TTS_DEFAULT_URL
+
+        expect(() => validateSpeechConfig()).toThrow("STT_BASE_URL");
+      });
+
+      it("should pass when all enabled services are properly configured", () => {
+        process.env.STT_ENABLED = "true";
+        process.env.STT_BASE_URL = "http://speaches:8000/v1";
+        process.env.TTS_ENABLED = "true";
+        process.env.TTS_DEFAULT_URL = "http://kokoro-tts:8880/v1";
+        process.env.TTS_PREMIUM_ENABLED = "true";
+        process.env.TTS_PREMIUM_URL = "http://chatterbox-tts:8881/v1";
+        process.env.TTS_FALLBACK_ENABLED = "true";
+        process.env.TTS_FALLBACK_URL = "http://openedai-speech:8000/v1";
+
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+    });
+
+    describe("limits validation", () => {
+      it("should throw when SPEECH_MAX_UPLOAD_SIZE is not a valid number", () => {
+        process.env.SPEECH_MAX_UPLOAD_SIZE = "not-a-number";
+        expect(() => validateSpeechConfig()).toThrow("SPEECH_MAX_UPLOAD_SIZE");
+        expect(() => validateSpeechConfig()).toThrow("must be a positive integer");
+      });
+
+      it("should throw when SPEECH_MAX_UPLOAD_SIZE is negative", () => {
+        process.env.SPEECH_MAX_UPLOAD_SIZE = "-100";
+        expect(() => validateSpeechConfig()).toThrow("SPEECH_MAX_UPLOAD_SIZE");
+      });
+
+      it("should throw when SPEECH_MAX_UPLOAD_SIZE is zero", () => {
+        process.env.SPEECH_MAX_UPLOAD_SIZE = "0";
+        expect(() => validateSpeechConfig()).toThrow("SPEECH_MAX_UPLOAD_SIZE");
+      });
+
+      it("should throw when SPEECH_MAX_DURATION_SECONDS is not a valid number", () => {
+        process.env.SPEECH_MAX_DURATION_SECONDS = "abc";
+        expect(() => validateSpeechConfig()).toThrow("SPEECH_MAX_DURATION_SECONDS");
+      });
+
+      it("should throw when SPEECH_MAX_TEXT_LENGTH is not a valid number", () => {
+        process.env.SPEECH_MAX_TEXT_LENGTH = "xyz";
+        expect(() => validateSpeechConfig()).toThrow("SPEECH_MAX_TEXT_LENGTH");
+      });
+
+      it("should not throw when limits are valid positive integers", () => {
+        process.env.SPEECH_MAX_UPLOAD_SIZE = "50000000";
+        process.env.SPEECH_MAX_DURATION_SECONDS = "1200";
+        process.env.SPEECH_MAX_TEXT_LENGTH = "8192";
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+
+      it("should not throw when limits are not set (uses defaults)", () => {
+        expect(() => validateSpeechConfig()).not.toThrow();
+      });
+    });
+  });
+
+  // ==========================================
+  // getSpeechConfig
+  // ==========================================
+  describe("getSpeechConfig", () => {
+    it("should return default values when no env vars are set", () => {
+      const config = getSpeechConfig();
+
+      expect(config.stt.enabled).toBe(false);
+      expect(config.stt.baseUrl).toBe("http://speaches:8000/v1");
+      expect(config.stt.model).toBe("Systran/faster-whisper-large-v3-turbo");
+      expect(config.stt.language).toBe("en");
+
+      expect(config.tts.default.enabled).toBe(false);
+      expect(config.tts.default.url).toBe("http://kokoro-tts:8880/v1");
+      expect(config.tts.default.voice).toBe("af_heart");
+      expect(config.tts.default.format).toBe("mp3");
+
+      expect(config.tts.premium.enabled).toBe(false);
+      expect(config.tts.premium.url).toBe("http://chatterbox-tts:8881/v1");
+
+      expect(config.tts.fallback.enabled).toBe(false);
+      expect(config.tts.fallback.url).toBe("http://openedai-speech:8000/v1");
+
+      expect(config.limits.maxUploadSize).toBe(25000000);
+      expect(config.limits.maxDurationSeconds).toBe(600);
+      expect(config.limits.maxTextLength).toBe(4096);
+    });
+
+    it("should use custom env var values when set", () => {
+      process.env.STT_ENABLED = "true";
+      process.env.STT_BASE_URL = "http://custom-stt:9000/v1";
+      process.env.STT_MODEL = "custom-model";
+      process.env.STT_LANGUAGE = "fr";
+
+      process.env.TTS_ENABLED = "true";
+      process.env.TTS_DEFAULT_URL = "http://custom-tts:9001/v1";
+      process.env.TTS_DEFAULT_VOICE = "custom_voice";
+      process.env.TTS_DEFAULT_FORMAT = "wav";
+
+      process.env.TTS_PREMIUM_ENABLED = "true";
+      process.env.TTS_PREMIUM_URL = "http://custom-premium:9002/v1";
+
+      process.env.TTS_FALLBACK_ENABLED = "true";
+      process.env.TTS_FALLBACK_URL = "http://custom-fallback:9003/v1";
+
+      process.env.SPEECH_MAX_UPLOAD_SIZE = "50000000";
+      process.env.SPEECH_MAX_DURATION_SECONDS = "1200";
+      process.env.SPEECH_MAX_TEXT_LENGTH = "8192";
+
+      const config = getSpeechConfig();
+
+      expect(config.stt.enabled).toBe(true);
+      expect(config.stt.baseUrl).toBe("http://custom-stt:9000/v1");
+      expect(config.stt.model).toBe("custom-model");
+      expect(config.stt.language).toBe("fr");
+
+      expect(config.tts.default.enabled).toBe(true);
+      expect(config.tts.default.url).toBe("http://custom-tts:9001/v1");
+      expect(config.tts.default.voice).toBe("custom_voice");
+      expect(config.tts.default.format).toBe("wav");
+
+      expect(config.tts.premium.enabled).toBe(true);
+      expect(config.tts.premium.url).toBe("http://custom-premium:9002/v1");
+
+      expect(config.tts.fallback.enabled).toBe(true);
+      expect(config.tts.fallback.url).toBe("http://custom-fallback:9003/v1");
+
+      expect(config.limits.maxUploadSize).toBe(50000000);
+      expect(config.limits.maxDurationSeconds).toBe(1200);
+      expect(config.limits.maxTextLength).toBe(8192);
+    });
+
+    it("should return typed SpeechConfig object", () => {
+      const config: SpeechConfig = getSpeechConfig();
+
+      // Verify structure matches the SpeechConfig type
+      expect(config).toHaveProperty("stt");
+      expect(config).toHaveProperty("tts");
+      expect(config).toHaveProperty("limits");
+      expect(config.tts).toHaveProperty("default");
+      expect(config.tts).toHaveProperty("premium");
+      expect(config.tts).toHaveProperty("fallback");
+    });
+
+    it("should handle partial env var overrides", () => {
+      process.env.STT_ENABLED = "true";
+      process.env.STT_BASE_URL = "http://custom-stt:9000/v1";
+      // STT_MODEL and STT_LANGUAGE not set, should use defaults
+
+      const config = getSpeechConfig();
+
+      expect(config.stt.enabled).toBe(true);
+      expect(config.stt.baseUrl).toBe("http://custom-stt:9000/v1");
+      expect(config.stt.model).toBe("Systran/faster-whisper-large-v3-turbo");
+      expect(config.stt.language).toBe("en");
+    });
+
+    it("should parse numeric limits correctly", () => {
+      process.env.SPEECH_MAX_UPLOAD_SIZE = "10000000";
+      const config = getSpeechConfig();
+      expect(typeof config.limits.maxUploadSize).toBe("number");
+      expect(config.limits.maxUploadSize).toBe(10000000);
+    });
+  });
+
+  // ==========================================
+  // registerAs integration
+  // ==========================================
+  describe("speechConfig (registerAs factory)", () => {
+    it("should be importable as a config namespace factory", async () => {
+      const { speechConfig } = await import("./speech.config");
+      expect(speechConfig).toBeDefined();
+      expect(speechConfig.KEY).toBe("CONFIGURATION(speech)");
+    });
+
+    it("should return config object when called", async () => {
+      const { speechConfig } = await import("./speech.config");
+      const config = speechConfig() as SpeechConfig;
+      expect(config).toHaveProperty("stt");
+      expect(config).toHaveProperty("tts");
+      expect(config).toHaveProperty("limits");
+    });
+  });
+});

apps/api/src/speech/speech.config.ts

@@ -0,0 +1,304 @@
+/**
+ * Speech Services Configuration
+ *
+ * Issue #401: Environment variables and validation for STT (speech-to-text),
+ * TTS (text-to-speech), and speech service limits.
+ *
+ * Validates conditional requirements at startup:
+ * - STT_BASE_URL is required when STT_ENABLED=true
+ * - TTS_DEFAULT_URL is required when TTS_ENABLED=true
+ * - TTS_PREMIUM_URL is required when TTS_PREMIUM_ENABLED=true
+ * - TTS_FALLBACK_URL is required when TTS_FALLBACK_ENABLED=true
+ */
+
+import { registerAs } from "@nestjs/config";
+
+// ==========================================
+// Default values
+// ==========================================
+
+const STT_DEFAULTS = {
+  baseUrl: "http://speaches:8000/v1",
+  model: "Systran/faster-whisper-large-v3-turbo",
+  language: "en",
+} as const;
+
+const TTS_DEFAULT_DEFAULTS = {
+  url: "http://kokoro-tts:8880/v1",
+  voice: "af_heart",
+  format: "mp3",
+} as const;
+
+const TTS_PREMIUM_DEFAULTS = {
+  url: "http://chatterbox-tts:8881/v1",
+} as const;
+
+const TTS_FALLBACK_DEFAULTS = {
+  url: "http://openedai-speech:8000/v1",
+} as const;
+
+const LIMITS_DEFAULTS = {
+  maxUploadSize: 25_000_000,
+  maxDurationSeconds: 600,
+  maxTextLength: 4096,
+} as const;
+
+// ==========================================
+// Types
+// ==========================================
+
+export interface SttConfig {
+  enabled: boolean;
+  baseUrl: string;
+  model: string;
+  language: string;
+}
+
+export interface TtsDefaultConfig {
+  enabled: boolean;
+  url: string;
+  voice: string;
+  format: string;
+}
+
+export interface TtsPremiumConfig {
+  enabled: boolean;
+  url: string;
+}
+
+export interface TtsFallbackConfig {
+  enabled: boolean;
+  url: string;
+}
+
+export interface TtsConfig {
+  default: TtsDefaultConfig;
+  premium: TtsPremiumConfig;
+  fallback: TtsFallbackConfig;
+}
+
+export interface SpeechLimitsConfig {
+  maxUploadSize: number;
+  maxDurationSeconds: number;
+  maxTextLength: number;
+}
+
+export interface SpeechConfig {
+  stt: SttConfig;
+  tts: TtsConfig;
+  limits: SpeechLimitsConfig;
+}
+
+// ==========================================
+// Helper: parse boolean env var
+// ==========================================
+
+function parseBooleanEnv(value: string | undefined): boolean {
+  return value === "true" || value === "1";
+}
+
+// ==========================================
+// Enabled checks
+// ==========================================
+
+/**
+ * Check if speech-to-text (STT) is enabled via environment variable.
+ */
+export function isSttEnabled(): boolean {
+  return parseBooleanEnv(process.env.STT_ENABLED);
+}
+
+/**
+ * Check if text-to-speech (TTS) default engine is enabled via environment variable.
+ */
+export function isTtsEnabled(): boolean {
+  return parseBooleanEnv(process.env.TTS_ENABLED);
+}
+
+/**
+ * Check if TTS premium engine (Chatterbox) is enabled via environment variable.
+ */
+export function isTtsPremiumEnabled(): boolean {
+  return parseBooleanEnv(process.env.TTS_PREMIUM_ENABLED);
+}
+
+/**
+ * Check if TTS fallback engine (Piper/OpenedAI) is enabled via environment variable.
+ */
+export function isTtsFallbackEnabled(): boolean {
+  return parseBooleanEnv(process.env.TTS_FALLBACK_ENABLED);
+}
+
+// ==========================================
+// Validation helpers
+// ==========================================
+
+/**
+ * Check if an environment variable has a non-empty value.
+ */
+function isEnvVarSet(envVar: string): boolean {
+  const value = process.env[envVar];
+  return value !== undefined && value.trim() !== "";
+}
+
+/**
+ * Validate that required env vars are set when a service is enabled.
+ * Throws with a helpful error message listing missing vars and how to disable.
+ */
+function validateRequiredVars(
+  serviceName: string,
+  enabledFlag: string,
+  requiredVars: string[]
+): void {
+  const missingVars: string[] = [];
+
+  for (const envVar of requiredVars) {
+    if (!isEnvVarSet(envVar)) {
+      missingVars.push(envVar);
+    }
+  }
+
+  if (missingVars.length > 0) {
+    throw new Error(
+      `${serviceName} is enabled (${enabledFlag}=true) but required environment variables are missing or empty: ${missingVars.join(", ")}. ` +
+        `Either set these variables or disable by setting ${enabledFlag}=false.`
+    );
+  }
+}
+
+/**
+ * Validate that a numeric env var, if set, is a positive integer.
+ */
+function validatePositiveInteger(envVar: string): void {
+  const value = process.env[envVar];
+  if (value === undefined || value.trim() === "") {
+    return; // Not set, will use default
+  }
+
+  const parsed = parseInt(value, 10);
+  if (isNaN(parsed) || parsed <= 0 || String(parsed) !== value.trim()) {
+    throw new Error(`${envVar} must be a positive integer. Current value: "${value}".`);
+  }
+}
+
+// ==========================================
+// Main validation
+// ==========================================
+
+/**
+ * Validates speech configuration at startup.
+ * Call this during module initialization to fail fast if misconfigured.
+ *
+ * Validates:
+ * - STT_BASE_URL is set when STT_ENABLED=true
+ * - TTS_DEFAULT_URL is set when TTS_ENABLED=true
+ * - TTS_PREMIUM_URL is set when TTS_PREMIUM_ENABLED=true
+ * - TTS_FALLBACK_URL is set when TTS_FALLBACK_ENABLED=true
+ * - Numeric limits are positive integers (when set)
+ *
+ * @throws Error if any required configuration is missing or invalid
+ */
+export function validateSpeechConfig(): void {
+  // STT validation
+  if (isSttEnabled()) {
+    validateRequiredVars("STT", "STT_ENABLED", ["STT_BASE_URL"]);
+  }
+
+  // TTS default validation
+  if (isTtsEnabled()) {
+    validateRequiredVars("TTS", "TTS_ENABLED", ["TTS_DEFAULT_URL"]);
+  }
+
+  // TTS premium validation
+  if (isTtsPremiumEnabled()) {
+    validateRequiredVars("TTS premium", "TTS_PREMIUM_ENABLED", ["TTS_PREMIUM_URL"]);
+  }
+
+  // TTS fallback validation
+  if (isTtsFallbackEnabled()) {
+    validateRequiredVars("TTS fallback", "TTS_FALLBACK_ENABLED", ["TTS_FALLBACK_URL"]);
+  }
+
+  // Limits validation (only if set, otherwise defaults are used)
+  validatePositiveInteger("SPEECH_MAX_UPLOAD_SIZE");
+  validatePositiveInteger("SPEECH_MAX_DURATION_SECONDS");
+  validatePositiveInteger("SPEECH_MAX_TEXT_LENGTH");
+}
+
+// ==========================================
+// Config getter
+// ==========================================
+
+/**
+ * Get the full speech configuration object with typed values and defaults.
+ *
+ * @returns SpeechConfig with all STT, TTS, and limits configuration
+ */
+export function getSpeechConfig(): SpeechConfig {
+  return {
+    stt: {
+      enabled: isSttEnabled(),
+      baseUrl: process.env.STT_BASE_URL ?? STT_DEFAULTS.baseUrl,
+      model: process.env.STT_MODEL ?? STT_DEFAULTS.model,
+      language: process.env.STT_LANGUAGE ?? STT_DEFAULTS.language,
+    },
+    tts: {
+      default: {
+        enabled: isTtsEnabled(),
+        url: process.env.TTS_DEFAULT_URL ?? TTS_DEFAULT_DEFAULTS.url,
+        voice: process.env.TTS_DEFAULT_VOICE ?? TTS_DEFAULT_DEFAULTS.voice,
+        format: process.env.TTS_DEFAULT_FORMAT ?? TTS_DEFAULT_DEFAULTS.format,
+      },
+      premium: {
+        enabled: isTtsPremiumEnabled(),
+        url: process.env.TTS_PREMIUM_URL ?? TTS_PREMIUM_DEFAULTS.url,
+      },
+      fallback: {
+        enabled: isTtsFallbackEnabled(),
+        url: process.env.TTS_FALLBACK_URL ?? TTS_FALLBACK_DEFAULTS.url,
+      },
+    },
+    limits: {
+      maxUploadSize: parseInt(
+        process.env.SPEECH_MAX_UPLOAD_SIZE ?? String(LIMITS_DEFAULTS.maxUploadSize),
+        10
+      ),
+      maxDurationSeconds: parseInt(
+        process.env.SPEECH_MAX_DURATION_SECONDS ?? String(LIMITS_DEFAULTS.maxDurationSeconds),
+        10
+      ),
+      maxTextLength: parseInt(
+        process.env.SPEECH_MAX_TEXT_LENGTH ?? String(LIMITS_DEFAULTS.maxTextLength),
+        10
+      ),
+    },
+  };
+}
+
+// ==========================================
+// NestJS ConfigModule registerAs factory
+// ==========================================
+
+/**
+ * NestJS ConfigModule namespace factory for speech configuration.
+ *
+ * Usage in a module:
+ * ```typescript
+ * import { speechConfig } from './speech.config';
+ *
+ * @Module({
+ *   imports: [ConfigModule.forFeature(speechConfig)],
+ * })
+ * export class SpeechModule {}
+ * ```
+ *
+ * Then inject via ConfigService:
+ * ```typescript
+ * constructor(private config: ConfigService) {
+ *   const sttUrl = this.config.get<string>('speech.stt.baseUrl');
+ * }
+ * ```
+ */
+export const speechConfig = registerAs("speech", (): SpeechConfig => {
+  return getSpeechConfig();
+});