fix(downloads): stop repeating an extension the name already carries

A voice comment's display name is the generated file name, extension
included, so appending the extension again downloaded it as
<uuid>.webm.webm. Both download paths, the single asset route and the
project zip, now append only when the name does not already end in it.

app/api/videos/[videoId]/assets/[assetId]/download/route.ts

@@ -10,6 +10,7 @@ import {
   extractAudioFileNameFromProxyUrl,
   extractVideoFileNameFromProxyUrl,
   getVideoAssetAccessContext,
+  withFileExtension,
 } from '@/lib/video-assets';
 import { buildVideoObjectKey } from '@/lib/video-upload-validation';
 import { logError } from '@/lib/logger';
@@ -55,6 +56,10 @@ function sanitizeFileName(value: string): string {
   return sanitized.length > 0 ? sanitized : 'asset';
 }
 
+function withExtension(displayName: string, extension: string): string {
+  return withFileExtension(sanitizeFileName(displayName), extension);
+}
+
 function toAsciiFileName(value: string): string {
   const normalized = value
     .normalize('NFKD')
@@ -117,7 +122,7 @@ export async function GET(request: NextRequest, { params }: RouteParams) {
       if (!fileName) return apiErrors.badRequest('Invalid image asset URL');
       const key = `images/${fileName}`;
       const extension = fileName.includes('.') ? fileName.slice(fileName.lastIndexOf('.')) : '.png';
-      const downloadName = `${sanitizeFileName(asset.displayName)}${extension}`;
+      const downloadName = withExtension(asset.displayName, extension);
       const contentDisposition = buildContentDisposition(downloadName);
 
       return proxyR2MediaObject({
@@ -139,7 +144,7 @@ export async function GET(request: NextRequest, { params }: RouteParams) {
       if (!fileName) return apiErrors.badRequest('Invalid audio asset URL');
       const key = `voice/${fileName}`;
       const ext = fileName.includes('.') ? fileName.slice(fileName.lastIndexOf('.')) : '.webm';
-      const downloadName = `${sanitizeFileName(asset.displayName)}${ext}`;
+      const downloadName = withExtension(asset.displayName, ext);
       const contentDisposition = buildContentDisposition(downloadName);
       const extKey = ext.replace('.', '');
       const contentType = AUDIO_CONTENT_TYPE_BY_EXTENSION[extKey] || 'audio/webm';
@@ -162,7 +167,7 @@ export async function GET(request: NextRequest, { params }: RouteParams) {
       if (!fileName) return apiErrors.badRequest('Invalid video asset URL');
       const key = buildVideoObjectKey(fileName);
       const ext = fileName.includes('.') ? fileName.slice(fileName.lastIndexOf('.')) : '.mp4';
-      const downloadName = `${sanitizeFileName(asset.displayName)}${ext}`;
+      const downloadName = withExtension(asset.displayName, ext);
       const contentDisposition = buildContentDisposition(downloadName);
       const extKey = ext.replace('.', '');
       const contentType = VIDEO_CONTENT_TYPE_BY_EXTENSION[extKey] || 'video/mp4';

lib/project-download.ts

@@ -4,6 +4,7 @@ import {
   extractImageFileNameFromProxyUrl,
   extractVideoFileNameFromProxyUrl,
   sanitizeAssetDisplayName,
+  withFileExtension,
 } from '@/lib/video-assets';
 
 const DEFAULT_MAX_FILES = 250;
@@ -171,21 +172,21 @@ function buildAssetFileName(videoIndex: number, videoTitle: string, asset: Asset
 
   if (asset.provider === VideoAssetProvider.R2_IMAGE) {
     const fileName = extractImageFileNameFromProxyUrl(asset.sourceUrl);
-    return `${stem}${extensionFromUrl(fileName ?? '', '.png')}`;
+    return withFileExtension(stem, extensionFromUrl(fileName ?? '', '.png'));
   }
   if (asset.provider === VideoAssetProvider.R2_AUDIO) {
     const fileName = extractAudioFileNameFromProxyUrl(asset.sourceUrl);
-    return `${stem}${extensionFromUrl(fileName ?? '', '.webm')}`;
+    return withFileExtension(stem, extensionFromUrl(fileName ?? '', '.webm'));
   }
   if (asset.provider === VideoAssetProvider.R2_VIDEO) {
     const fileName = extractVideoFileNameFromProxyUrl(asset.sourceUrl);
-    return `${stem}${extensionFromUrl(fileName ?? '', '.mp4')}`;
+    return withFileExtension(stem, extensionFromUrl(fileName ?? '', '.mp4'));
   }
   if (asset.provider === VideoAssetProvider.BUNNY) {
-    return `${stem}.mp4`;
+    return withFileExtension(stem, '.mp4');
   }
 
-  return `${stem}.bin`;
+  return withFileExtension(stem, '.bin');
 }
 
 function versionDownloadUrl(version: VersionRow): string | null {

lib/video-assets.ts

@@ -66,6 +66,14 @@ export function sanitizeAssetDisplayName(
   return normalized.slice(0, 200);
 }
 
+/**
+ * A voice comment's display name is the generated file name, extension and all,
+ * so blindly appending the extension named the download `<uuid>.webm.webm`.
+ */
+export function withFileExtension(name: string, extension: string): string {
+  return name.toLowerCase().endsWith(extension.toLowerCase()) ? name : `${name}${extension}`;
+}
+
 export function extractImageKeyFromProxyUrl(url: string): string | null {
   if (!SAFE_IMAGE_PROXY_PATH.test(url)) return null;
   const filename = url.slice(IMAGE_PROXY_PREFIX.length);

tests/api/lib-video-assets.test.ts

@@ -19,6 +19,7 @@ import {
   extractVideoKeyFromProxyUrl,
   getVideoAssetAccessContext,
   sanitizeAssetDisplayName,
+  withFileExtension,
   SAFE_BUNNY_VIDEO_ID,
 } from '@/lib/video-assets';
 import { apiRequest } from '../helpers/request';
@@ -83,6 +84,28 @@ describe('sanitizeAssetDisplayName', () => {
   });
 });
 
+// A voice comment is stored under its generated file name, so its display name
+// already ends in .webm and every download was named `<uuid>.webm.webm`.
+describe('withFileExtension', () => {
+  it('leaves a name that already ends in the extension alone', () => {
+    expect(withFileExtension('33661b60-b658-47f9-bd40-71c32a0a2fdb.webm', '.webm')).toBe(
+      '33661b60-b658-47f9-bd40-71c32a0a2fdb.webm'
+    );
+  });
+
+  it('ignores the case the extension was written in', () => {
+    expect(withFileExtension('Take 2.WEBM', '.webm')).toBe('Take 2.WEBM');
+  });
+
+  it('appends when the name carries no extension', () => {
+    expect(withFileExtension('Voice Comment', '.webm')).toBe('Voice Comment.webm');
+  });
+
+  it('appends when the name ends in a different extension', () => {
+    expect(withFileExtension('clip.mp4', '.webm')).toBe('clip.mp4.webm');
+  });
+});
+
 describe('proxy URL extraction', () => {
   it('derives the image key and file name from a canonical image URL', () => {
     expect(extractImageKeyFromProxyUrl(IMAGE_URL)).toBe(

tests/unit/lib/project-download.test.ts

@@ -1221,6 +1221,30 @@ describe('buildProjectDownloadManifest assets', () => {
     expect(manifest.files[0]?.fileName).toBe('01-Intro-asset-B roll.png');
   });
 
+  // A voice comment's display name is the stored file name, extension included.
+  it('does not repeat an extension the display name already carries', () => {
+    const manifest = buildProjectDownloadManifest(
+      'Project',
+      [
+        video({
+          versions: [],
+          assets: [
+            asset({
+              provider: VideoAssetProvider.R2_AUDIO,
+              displayName: '33661b60-b658-47f9-bd40-71c32a0a2fdb.webm',
+              sourceUrl: '/api/upload/audio/33661b60-b658-47f9-bd40-71c32a0a2fdb.webm',
+            }),
+          ],
+        }),
+      ],
+      { includeAssets: true }
+    );
+
+    expect(manifest.files[0]?.fileName).toBe(
+      '01-Intro-asset-33661b60-b658-47f9-bd40-71c32a0a2fdb.webm'
+    );
+  });
+
   it('always names a bunny asset .mp4 regardless of the source url', () => {
     const manifest = buildProjectDownloadManifest(
       'Project',