Enable private caching headers for segment audio routes

src/app/api/tts/segments/audio/fallback/route.ts

@@ -1,6 +1,7 @@
 import { NextRequest, NextResponse } from 'next/server';
 import { isS3Configured } from '@/lib/server/storage/s3';
 import {
+  buildSegmentAudioCacheHeaders,
   resolveCompletedSegmentAudio,
   streamAudioBuffer,
   ttsSegmentsS3NotConfiguredResponse,
@@ -20,7 +21,7 @@ export async function GET(request: NextRequest) {
     return new NextResponse(streamAudioBuffer(audio), {
       headers: {
         'Content-Type': 'audio/mpeg',
-        'Cache-Control': 'no-store',
+        ...buildSegmentAudioCacheHeaders('fallback'),
       },
     });
   } catch (error) {

src/app/api/tts/segments/audio/presign/route.ts

@@ -1,6 +1,7 @@
 import { NextRequest, NextResponse } from 'next/server';
 import { isS3Configured } from '@/lib/server/storage/s3';
 import {
+  buildSegmentAudioCacheHeaders,
   resolveCompletedSegmentAudio,
   ttsSegmentsS3NotConfiguredResponse,
 } from '@/lib/server/tts/segments-audio';
@@ -24,13 +25,13 @@ export async function GET(request: NextRequest) {
       });
       return NextResponse.redirect(fallbackUrl, {
         status: 307,
-        headers: { 'Cache-Control': 'no-store' },
+        headers: buildSegmentAudioCacheHeaders('redirect'),
       });
     }
 
     return NextResponse.redirect(directUrl, {
       status: 307,
-      headers: { 'Cache-Control': 'no-store' },
+      headers: buildSegmentAudioCacheHeaders('redirect'),
     });
   } catch (error) {
     console.error('Error creating segment audio signature:', error);

src/lib/server/tts/segments-audio.ts

@@ -11,6 +11,10 @@ export type ResolvedSegmentAudio = {
   audioKey: string;
 };
 
+export const TTS_SEGMENT_REDIRECT_CACHE_CONTROL = 'private, max-age=60, stale-while-revalidate=30';
+export const TTS_SEGMENT_FALLBACK_CACHE_CONTROL = 'private, max-age=300, stale-while-revalidate=60';
+export const TTS_SEGMENT_AUDIO_VARY = 'Cookie, Authorization';
+
 export function ttsSegmentsS3NotConfiguredResponse(): NextResponse {
   return NextResponse.json(
     { error: 'TTS segments storage is not configured. Set S3_* environment variables.' },
@@ -27,6 +31,15 @@ export function streamAudioBuffer(buffer: Buffer): ReadableStream<Uint8Array> {
   });
 }
 
+export function buildSegmentAudioCacheHeaders(kind: 'redirect' | 'fallback'): Record<string, string> {
+  return {
+    'Cache-Control': kind === 'redirect'
+      ? TTS_SEGMENT_REDIRECT_CACHE_CONTROL
+      : TTS_SEGMENT_FALLBACK_CACHE_CONTROL,
+    Vary: TTS_SEGMENT_AUDIO_VARY,
+  };
+}
+
 export async function resolveCompletedSegmentAudio(
   request: NextRequest,
 ): Promise<ResolvedSegmentAudio | Response> {

tests/unit/tts-segments-audio-cache.spec.ts

@@ -0,0 +1,23 @@
+import { expect, test } from '@playwright/test';
+import {
+  buildSegmentAudioCacheHeaders,
+  TTS_SEGMENT_AUDIO_VARY,
+  TTS_SEGMENT_FALLBACK_CACHE_CONTROL,
+  TTS_SEGMENT_REDIRECT_CACHE_CONTROL,
+} from '../../src/lib/server/tts/segments-audio';
+
+test.describe('tts segment audio cache headers', () => {
+  test('builds redirect cache headers', () => {
+    expect(buildSegmentAudioCacheHeaders('redirect')).toEqual({
+      'Cache-Control': TTS_SEGMENT_REDIRECT_CACHE_CONTROL,
+      Vary: TTS_SEGMENT_AUDIO_VARY,
+    });
+  });
+
+  test('builds fallback cache headers', () => {
+    expect(buildSegmentAudioCacheHeaders('fallback')).toEqual({
+      'Cache-Control': TTS_SEGMENT_FALLBACK_CACHE_CONTROL,
+      Vary: TTS_SEGMENT_AUDIO_VARY,
+    });
+  });
+});