diff --git a/AGENTS.md b/AGENTS.md
index fc2eeaed..e6fbf176 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -57,6 +57,10 @@ Notification message preparation utilities for system notifications, including t
 WebSocket protocol utilities for terminal input handling including message normalization, control frame parsing, and rate limiting.
 - Module docs: `packages/web/server/lib/terminal/DOCUMENTATION.md`
 
+##### tts
+Server-side text-to-speech services and summarization helpers for `/api/tts/*` endpoints.
+- Module docs: `packages/web/server/lib/tts/DOCUMENTATION.md`
+
 ##### skills-catalog
 Skills catalog management including discovery, installation, and configuration of agent skill packages.
 - Module docs: `packages/web/server/lib/skills-catalog/DOCUMENTATION.md`
diff --git a/packages/web/server/index.js b/packages/web/server/index.js
index becf3d5a..72e0af74 100644
--- a/packages/web/server/index.js
+++ b/packages/web/server/index.js
@@ -6879,7 +6879,7 @@ async function main(options = {}) {
       }
 
       // Dynamically import the TTS service (ESM)
-      const { ttsService } = await import('./lib/tts-service.js');
+      const { ttsService } = await import('./lib/tts/index.js');
 
       // Check availability - either server-configured or client-provided API key
       const hasServerKey = ttsService.isAvailable();
@@ -6896,7 +6896,7 @@ async function main(options = {}) {
       // Optionally summarize long text before speaking using zen API
       if (summarize && textToSpeak.length > threshold) {
         try {
-          const { summarizeText } = await import('./lib/summarization-service.js');
+          const { summarizeText } = await import('./lib/tts/index.js');
           const speakZenModel = await resolveZenModel(typeof req.body?.zenModel === 'string' ? req.body.zenModel : undefined);
           const result = await summarizeText({ text: textToSpeak, threshold, maxLength, zenModel: speakZenModel });
           
@@ -6956,7 +6956,7 @@ async function main(options = {}) {
   });
 
   // Import summarization service
-  const { summarizeText, sanitizeForTTS } = await import('./lib/summarization-service.js');
+  const { summarizeText, sanitizeForTTS } = await import('./lib/tts/index.js');
 
   app.post('/api/tts/summarize', async (req, res) => {
     try {
@@ -6981,7 +6981,7 @@ async function main(options = {}) {
   // TTS status endpoint
   app.get('/api/tts/status', async (_req, res) => {
     try {
-      const { ttsService } = await import('./lib/tts-service.js');
+      const { ttsService } = await import('./lib/tts/index.js');
       res.json({
         available: ttsService.isAvailable(),
         voices: [
diff --git a/packages/web/server/lib/tts/DOCUMENTATION.md b/packages/web/server/lib/tts/DOCUMENTATION.md
new file mode 100644
index 00000000..73d5ab84
--- /dev/null
+++ b/packages/web/server/lib/tts/DOCUMENTATION.md
@@ -0,0 +1,134 @@
+# TTS Module Documentation
+
+## Purpose
+This module provides server-side Text-to-Speech services using OpenAI's TTS API, along with text summarization and sanitization utilities for preparing content for speech synthesis.
+
+## Entrypoints and structure
+- `packages/web/server/lib/tts/index.js`: Public entrypoint imported by `packages/web/server/index.js`.
+- `packages/web/server/lib/tts/service.js`: TTS service implementation with OpenAI integration.
+- `packages/web/server/lib/tts/summarization.js`: Text summarization and sanitization utilities using opencode.ai zen API.
+
+## Public exports
+
+### TTS Service (from service.js)
+- `ttsService`: Singleton instance of TTSService class.
+- `TTSService`: TTS service class for OpenAI audio generation.
+- `TTS_VOICES`: Array of supported OpenAI voice identifiers.
+
+### Summarization (from summarization.js)
+- `summarizeText({ text, threshold, maxLength, zenModel })`: Summarizes text for TTS output using opencode.ai zen API.
+- `sanitizeForTTS(text)`: Sanitizes text by removing markdown, URLs, file paths, and other non-speakable content.
+
+## Constants
+
+### Voice identifiers
+- `TTS_VOICES`: Array of supported OpenAI voices: `['alloy', 'ash', 'ballad', 'coral', 'echo', 'fable', 'nova', 'onyx', 'sage', 'shimmer', 'verse', 'marin', 'cedar']`.
+
+### Summarization defaults
+- `SUMMARIZE_TIMEOUT_MS`: 30000 (30 seconds timeout for zen API requests).
+
+### Default values
+- `summarizeText` defaults: `threshold` = 200, `maxLength` = 500, `zenModel` = 'gpt-5-nano'.
+- `generateSpeechStream` defaults: `voice` = 'coral', `model` = 'gpt-4o-mini-tts', `speed` = 1.0.
+- `generateSpeechBuffer` defaults: `voice` = 'coral', `model` = 'gpt-4o-mini-tts', `speed` = 1.0.
+
+## TTSService methods
+
+### `isAvailable()`
+Returns boolean indicating whether OpenAI API key is configured (checks environment variable `OPENAI_API_KEY` or OpenCode auth file).
+
+### `generateSpeechStream(options)`
+Generates speech and returns as a web stream for direct streaming to clients.
+- Options: `text` (required), `voice`, `model`, `speed`, `instructions`, `apiKey`.
+- Returns: `{ stream: ReadableStream, contentType: 'audio/mpeg' }`.
+- Throws: Error if API key not configured or text is empty.
+
+### `generateSpeechBuffer(options)`
+Generates speech and returns as Buffer for caching purposes.
+- Options: `text` (required), `voice`, `model`, `speed`, `instructions`.
+- Returns: Buffer containing MP3 audio data.
+- Throws: Error if API key not configured or text is empty.
+
+## Response contracts
+
+### `summarizeText`
+Returns object with:
+- `summary`: Sanitized summary text or original text (if not summarized).
+- `summarized`: Boolean indicating if summarization was performed.
+- `reason`: Optional string explaining why summarization was skipped (e.g., 'Text under threshold', 'Request timed out').
+- `originalLength`: Optional number for original text length.
+- `summaryLength`: Optional number for summarized text length.
+
+### `sanitizeForTTS`
+Returns sanitized string with markdown, URLs, file paths, and special characters removed.
+
+### `generateSpeechStream`
+Returns object with:
+- `stream`: ReadableStream of MP3 audio data.
+- `contentType`: Always 'audio/mpeg'.
+
+### `generateSpeechBuffer`
+Returns Buffer containing MP3 audio data.
+
+## API key resolution
+OpenAI API keys are resolved in order:
+1. Environment variable `OPENAI_API_KEY`.
+2. OpenCode auth file (`auth.openai`, `auth.codex`, or `auth.chatgpt`).
+3. Supports both string format (just token) and object format (with `access` or `token` fields).
+
+## Usage in web server
+The TTS module is used by `packages/web/server/index.js` for:
+- Generating speech streams for client playback.
+- Generating speech buffers for caching.
+- Summarizing long messages before TTS synthesis.
+- Sanitizing text to remove non-speakable content.
+
+The server-side TTS approach bypasses mobile Safari's audio context restrictions by generating audio on the server and streaming to clients.
+
+## Notes for contributors
+
+### Adding new TTS features
+1. Add new methods to `packages/web/server/lib/tts/service.js` TTSService class.
+2. Export public functions from `packages/web/server/lib/tts/index.js`.
+3. Follow existing patterns for API key resolution and error handling.
+4. Ensure all text is sanitized before TTS synthesis.
+5. Consider adding new voice options to `TTS_VOICES` constant.
+
+### Text sanitization
+- Always call `sanitizeForTTS` on text before passing to TTS generation.
+- The sanitization removes markdown, code blocks, URLs, file paths, shell commands, and special characters.
+- This prevents the TTS from reading out technical formatting that sounds unnatural.
+
+### Error handling
+- `generateSpeechStream` and `generateSpeechBuffer` throw descriptive errors for missing API keys or empty text.
+- `summarizeText` catches zen API errors and falls back to original text with `summarized: false`.
+- All errors are logged to console with `[TTSService]` or `[Summarize]` prefix.
+
+### API key management
+- TTSService caches OpenAI client instance and recreates when API key changes.
+- API key changes are detected by comparing with `_lastApiKey` property.
+- This allows dynamic API key updates without server restart.
+
+### Testing
+- Run `bun run type-check`, `bun run lint`, and `bun run build` before finalizing changes.
+- Test API key resolution with environment variable and auth file.
+- Test speech generation with various text lengths and voice options.
+- Test summarization behavior above and below threshold.
+- Test sanitization with markdown, URLs, and code blocks.
+- Verify streaming and buffer generation produce valid MP3 audio.
+
+## Verification notes
+
+### Manual verification
+1. Configure OpenAI API key via environment variable or OpenCode settings.
+2. Test `ttsService.isAvailable()` returns true.
+3. Call `ttsService.generateSpeechStream({ text: 'Hello world' })` and verify stream is returned.
+4. Call `ttsService.generateSpeechBuffer({ text: 'Hello world' })` and verify Buffer is returned.
+5. Test `summarizeText` with text above and below threshold.
+6. Test `sanitizeForTTS` with markdown, URLs, and code blocks.
+
+### API endpoint verification
+1. Start web server and access TTS endpoint via client.
+2. Verify audio plays correctly in browser.
+3. Test on mobile Safari to verify bypass of audio context restrictions.
+4. Test with long messages to verify summarization is triggered.
diff --git a/packages/web/server/lib/tts/index.js b/packages/web/server/lib/tts/index.js
new file mode 100644
index 00000000..7630a270
--- /dev/null
+++ b/packages/web/server/lib/tts/index.js
@@ -0,0 +1,16 @@
+/**
+ * TTS Module Entry Point
+ *
+ * Public export surface for the Text-to-Speech domain module.
+ */
+
+export {
+  ttsService,
+  TTSService,
+  TTS_VOICES,
+} from './service.js';
+
+export {
+  summarizeText,
+  sanitizeForTTS,
+} from './summarization.js';
diff --git a/packages/web/server/lib/tts-service.js b/packages/web/server/lib/tts/service.js
similarity index 98%
rename from packages/web/server/lib/tts-service.js
rename to packages/web/server/lib/tts/service.js
index 13e63aeb..2c761d47 100644
--- a/packages/web/server/lib/tts-service.js
+++ b/packages/web/server/lib/tts/service.js
@@ -6,7 +6,7 @@
  */
 
 import OpenAI from 'openai';
-import { readAuthFile } from './opencode/auth.js';
+import { readAuthFile } from '../opencode/auth.js';
 
 // Voice options from OpenAI
 export const TTS_VOICES = [
diff --git a/packages/web/server/lib/summarization-service.js b/packages/web/server/lib/tts/summarization.js
similarity index 100%
rename from packages/web/server/lib/summarization-service.js
rename to packages/web/server/lib/tts/summarization.js