diff --git a/apps/x/apps/renderer/src/App.tsx b/apps/x/apps/renderer/src/App.tsx
index 39cf44e2..4fd75591 100644
--- a/apps/x/apps/renderer/src/App.tsx
+++ b/apps/x/apps/renderer/src/App.tsx
@@ -17,6 +17,7 @@ import { ImageFileViewer } from '@/components/image-file-viewer';
 import { VideoFileViewer } from '@/components/video-file-viewer';
 import { AudioFileViewer } from '@/components/audio-file-viewer';
 import { PersistentViewerCache } from '@/components/persistent-viewer-cache';
+import { getViewerType, isMediaPath, isCacheableViewerPath } from '@/lib/file-types';
 import { useDebounce } from './hooks/use-debounce';
 import { SidebarContentPanel } from '@/components/sidebar-content';
 import { SuggestedTopicsView } from '@/components/suggested-topics-view';
@@ -1428,10 +1429,10 @@ function App() {
     }
     const requestId = (fileLoadRequestIdRef.current += 1)
     const pathToLoad = selectedPath
-    // Media viewers (HTML, image, video, PDF) self-load via app:// protocol.
+    // Media viewers (HTML, image, video, audio, PDF) self-load via app:// protocol.
     // Skip the generic UTF-8 loader so we don't trash fileContent with binary
     // bytes or double-fetch large files.
-    if (/\.(html?|png|jpe?g|webp|gif|svg|avif|bmp|ico|mp4|mov|webm|m4v|pdf|mp3|wav|m4a|ogg|flac|aac)$/i.test(pathToLoad)) {
+    if (isMediaPath(pathToLoad)) {
       setFileContent('')
       return
     }
@@ -4725,11 +4726,11 @@ function App() {
                 {/* Always-mounted persistent cache for HTML/PDF — hidden when active file is something else, so iframes preserve scroll/page/zoom across switches. */}
                 <div
                   className="flex-1 min-h-0 overflow-hidden"
-                  style={{ display: /\.(html?|pdf)$/i.test(selectedPath) ? 'block' : 'none' }}
+                  style={{ display: isCacheableViewerPath(selectedPath) ? 'block' : 'none' }}
                 >
                   <PersistentViewerCache activePath={selectedPath} />
                 </div>
-                {!/\.(html?|pdf)$/i.test(selectedPath) && (
+                {!isCacheableViewerPath(selectedPath) && (
                 selectedPath.endsWith('.md') ? (
                   <div className="flex-1 min-h-0 flex flex-row overflow-hidden">
                     <div className="flex-1 min-h-0 flex flex-col overflow-hidden">
@@ -4839,15 +4840,15 @@ function App() {
                       />
                     )}
                   </div>
-                ) : selectedPath && /\.(png|jpe?g|webp|gif|svg|avif|bmp|ico)$/i.test(selectedPath) ? (
+                ) : selectedPath && getViewerType(selectedPath) === 'image' ? (
                   <div className="flex-1 min-h-0 overflow-hidden">
                     <ImageFileViewer path={selectedPath} />
                   </div>
-                ) : selectedPath && /\.(mp4|mov|webm|m4v)$/i.test(selectedPath) ? (
+                ) : selectedPath && getViewerType(selectedPath) === 'video' ? (
                   <div className="flex-1 min-h-0 overflow-hidden">
                     <VideoFileViewer path={selectedPath} />
                   </div>
-                ) : selectedPath && /\.(mp3|wav|m4a|ogg|flac|aac)$/i.test(selectedPath) ? (
+                ) : selectedPath && getViewerType(selectedPath) === 'audio' ? (
                   <div className="flex-1 min-h-0 overflow-hidden">
                     <AudioFileViewer path={selectedPath} />
                   </div>
diff --git a/apps/x/apps/renderer/src/components/persistent-viewer-cache.tsx b/apps/x/apps/renderer/src/components/persistent-viewer-cache.tsx
index d655b929..ca71eca2 100644
--- a/apps/x/apps/renderer/src/components/persistent-viewer-cache.tsx
+++ b/apps/x/apps/renderer/src/components/persistent-viewer-cache.tsx
@@ -1,22 +1,14 @@
 import { useEffect, useState } from 'react'
 import { HtmlFileViewer } from './html-file-viewer'
 import { PdfFileViewer } from './pdf-file-viewer'
+import { getViewerType, isCacheableViewerPath } from '@/lib/file-types'
 
 const CACHE_LIMIT = 3
 
-function isCacheable(path: string): boolean {
-  const lower = path.toLowerCase()
-  return lower.endsWith('.html') || lower.endsWith('.htm') || lower.endsWith('.pdf')
-}
-
 function renderViewer(path: string): JSX.Element | null {
-  const lower = path.toLowerCase()
-  if (lower.endsWith('.html') || lower.endsWith('.htm')) {
-    return <HtmlFileViewer path={path} />
-  }
-  if (lower.endsWith('.pdf')) {
-    return <PdfFileViewer path={path} />
-  }
+  const type = getViewerType(path)
+  if (type === 'html') return <HtmlFileViewer path={path} />
+  if (type === 'pdf') return <PdfFileViewer path={path} />
   return null
 }
 
@@ -31,11 +23,11 @@ interface PersistentViewerCacheProps {
  */
 export function PersistentViewerCache({ activePath }: PersistentViewerCacheProps) {
   const [mountedPaths, setMountedPaths] = useState<string[]>(() =>
-    isCacheable(activePath) ? [activePath] : []
+    isCacheableViewerPath(activePath) ? [activePath] : []
   )
 
   useEffect(() => {
-    if (!isCacheable(activePath)) return
+    if (!isCacheableViewerPath(activePath)) return
     setMountedPaths((prev) => {
       // Never reorder existing entries — moving a keyed iframe in the DOM
       // detaches it, which causes the browser to re-navigate (state lost).
diff --git a/apps/x/apps/renderer/src/lib/file-types.ts b/apps/x/apps/renderer/src/lib/file-types.ts
new file mode 100644
index 00000000..d4477f7a
--- /dev/null
+++ b/apps/x/apps/renderer/src/lib/file-types.ts
@@ -0,0 +1,56 @@
+/**
+ * Single source of truth for which file types the knowledge viewer renders.
+ *
+ * Both the App.tsx loader-skip check and the render-switch consume this so
+ * adding a new extension is a one-place edit. The persistent-viewer-cache
+ * also uses it to decide what to keep mounted.
+ */
+
+export type ViewerType = 'html' | 'image' | 'video' | 'audio' | 'pdf'
+
+const VIEWER_BY_EXT: Record<string, ViewerType> = {
+  html: 'html',
+  htm: 'html',
+  png: 'image',
+  jpg: 'image',
+  jpeg: 'image',
+  webp: 'image',
+  gif: 'image',
+  svg: 'image',
+  avif: 'image',
+  bmp: 'image',
+  ico: 'image',
+  mp4: 'video',
+  mov: 'video',
+  webm: 'video',
+  m4v: 'video',
+  mp3: 'audio',
+  wav: 'audio',
+  m4a: 'audio',
+  ogg: 'audio',
+  flac: 'audio',
+  aac: 'audio',
+  pdf: 'pdf',
+}
+
+function extensionOf(path: string): string {
+  const lower = path.toLowerCase()
+  const dot = lower.lastIndexOf('.')
+  return dot >= 0 ? lower.slice(dot + 1) : ''
+}
+
+/** Returns the viewer type for a path, or null if no media viewer handles it. */
+export function getViewerType(path: string): ViewerType | null {
+  return VIEWER_BY_EXT[extensionOf(path)] ?? null
+}
+
+/** True if the path is rendered by one of the dedicated media viewers. */
+export function isMediaPath(path: string): boolean {
+  return getViewerType(path) !== null
+}
+
+/** True if the viewer for this path participates in the persistent mount cache. */
+export function isCacheableViewerPath(path: string): boolean {
+  const t = getViewerType(path)
+  return t === 'html' || t === 'pdf'
+}