diff --git a/apps/x/.gitignore b/apps/x/.gitignore
index c2658d7d..db195fb4 100644
--- a/apps/x/.gitignore
+++ b/apps/x/.gitignore
@@ -1 +1,2 @@
 node_modules/
+test-fixtures/
diff --git a/apps/x/apps/main/src/main.ts b/apps/x/apps/main/src/main.ts
index a6d7b4e0..3cfd3f4f 100644
--- a/apps/x/apps/main/src/main.ts
+++ b/apps/x/apps/main/src/main.ts
@@ -31,6 +31,7 @@ import { shutdown as shutdownAnalytics } from "@x/core/dist/analytics/posthog.js
 import { identifyIfSignedIn } from "@x/core/dist/analytics/identify.js";
 
 import { initConfigs } from "@x/core/dist/config/initConfigs.js";
+import { resolveWorkspacePath } from "@x/core/dist/workspace/workspace.js";
 import started from "electron-squirrel-startup";
 import { execSync, exec, execFileSync } from "node:child_process";
 import { promisify } from "node:util";
@@ -133,16 +134,29 @@ const rendererPath = app.isPackaged
   : path.join(__dirname, "../../../renderer/dist"); // Development
 console.log("rendererPath", rendererPath);
 
-// Register custom protocol for serving built renderer files in production.
-// This keeps SPA routes working when users deep link into the packaged app.
+// Register custom protocol for serving built renderer files in production
+// AND for serving local workspace files to the renderer (images, PDFs, video).
+//
+//   app://workspace/<rel-path>  → workspace file (path-traversal guarded)
+//   app://<anything-else>/...   → renderer SPA (existing behavior)
 function registerAppProtocol() {
   protocol.handle("app", (request) => {
     const url = new URL(request.url);
 
-    // url.pathname starts with "/"
-    let urlPath = url.pathname;
+    // Workspace files: app://workspace/<rel-path>
+    if (url.host === "workspace") {
+      try {
+        const relPath = decodeURIComponent(url.pathname).replace(/^\/+/, "");
+        if (!relPath) return new Response("Not Found", { status: 404 });
+        const absPath = resolveWorkspacePath(relPath);
+        return net.fetch(pathToFileURL(absPath).toString());
+      } catch {
+        return new Response("Forbidden", { status: 403 });
+      }
+    }
 
-    // If it's "/" or a SPA route (no extension), serve index.html
+    // Renderer SPA — existing logic
+    let urlPath = url.pathname;
     if (urlPath === "/" || !path.extname(urlPath)) {
       urlPath = "/index.html";
     }
@@ -161,8 +175,8 @@ protocol.registerSchemesAsPrivileged([
       supportFetchAPI: true,
       corsEnabled: true,
       allowServiceWorkers: true,
-      // optional but often helpful:
-      // stream: true,
+      // Required for byte-range requests so <video> seeking works.
+      stream: true,
     },
   },
 ]);
@@ -207,6 +221,9 @@ function createWindow() {
       contextIsolation: true,
       sandbox: true,
       preload: preloadPath,
+      // Enable Chromium's built-in PDFium plugin so <iframe src="*.pdf">
+      // renders PDFs natively (zoom/scroll/print toolbar included).
+      plugins: true,
     },
   });
 
@@ -251,10 +268,10 @@ function createWindow() {
 }
 
 app.whenReady().then(async () => {
-  // Register custom protocol before creating window (for production builds)
-  if (app.isPackaged) {
-    registerAppProtocol();
-  }
+  // Register custom protocol before creating window.
+  // In production this serves the renderer SPA; in dev (and prod) it also
+  // serves workspace files via app://workspace/<rel-path> for media previews.
+  registerAppProtocol();
 
   // Initialize auto-updater (only in production)
   if (app.isPackaged) {
diff --git a/apps/x/apps/renderer/src/App.tsx b/apps/x/apps/renderer/src/App.tsx
index 32386b30..b525462b 100644
--- a/apps/x/apps/renderer/src/App.tsx
+++ b/apps/x/apps/renderer/src/App.tsx
@@ -13,6 +13,12 @@ import { ChatInputWithMentions, type StagedAttachment } from './components/chat-
 import { ChatMessageAttachments } from '@/components/chat-message-attachments'
 import { GraphView, type GraphEdge, type GraphNode } from '@/components/graph-view';
 import { BasesView, type BaseConfig, DEFAULT_BASE_CONFIG } from '@/components/bases-view';
+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 { UnsupportedFileViewer } from '@/components/unsupported-file-viewer';
+import { getViewerType, isCacheableViewerPath } from '@/lib/file-types';
 import { useDebounce } from './hooks/use-debounce';
 import { SidebarContentPanel } from '@/components/sidebar-content';
 import { SuggestedTopicsView } from '@/components/suggested-topics-view';
@@ -1425,6 +1431,13 @@ function App() {
     }
     const requestId = (fileLoadRequestIdRef.current += 1)
     const pathToLoad = selectedPath
+    // Only the markdown editor still consumes fileContent. Every other viewer
+    // (media + UnsupportedFileViewer) self-loads, so skip the generic UTF-8
+    // loader to avoid double-fetching and to avoid slurping binary bytes.
+    if (!pathToLoad.endsWith('.md')) {
+      setFileContent('')
+      return
+    }
     let cancelled = false
     ;(async () => {
       try {
@@ -4715,6 +4728,15 @@ function App() {
                   />
                 </div>
               ) : selectedPath ? (
+                <>
+                {/* 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: isCacheableViewerPath(selectedPath) ? 'block' : 'none' }}
+                >
+                  <PersistentViewerCache activePath={selectedPath} />
+                </div>
+                {!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">
@@ -4824,13 +4846,25 @@ function App() {
                       />
                     )}
                   </div>
+                ) : selectedPath && getViewerType(selectedPath) === 'image' ? (
+                  <div className="flex-1 min-h-0 overflow-hidden">
+                    <ImageFileViewer path={selectedPath} />
+                  </div>
+                ) : selectedPath && getViewerType(selectedPath) === 'video' ? (
+                  <div className="flex-1 min-h-0 overflow-hidden">
+                    <VideoFileViewer path={selectedPath} />
+                  </div>
+                ) : selectedPath && getViewerType(selectedPath) === 'audio' ? (
+                  <div className="flex-1 min-h-0 overflow-hidden">
+                    <AudioFileViewer path={selectedPath} />
+                  </div>
                 ) : (
-                  <div className="flex-1 overflow-auto p-4">
-                    <pre className="text-sm font-mono text-foreground whitespace-pre-wrap">
-                      {fileContent || 'Loading...'}
-                    </pre>
+                  <div className="flex-1 min-h-0 overflow-hidden">
+                    <UnsupportedFileViewer path={selectedPath} />
                   </div>
                 )
+                )}
+                </>
               ) : selectedTask ? (
                 <div className="flex-1 min-h-0 overflow-hidden">
                   <BackgroundTaskDetail
diff --git a/apps/x/apps/renderer/src/components/audio-file-viewer.tsx b/apps/x/apps/renderer/src/components/audio-file-viewer.tsx
new file mode 100644
index 00000000..54d1035d
--- /dev/null
+++ b/apps/x/apps/renderer/src/components/audio-file-viewer.tsx
@@ -0,0 +1,60 @@
+import { useEffect, useState } from 'react'
+import { ExternalLinkIcon, FileAudioIcon } from 'lucide-react'
+
+interface AudioFileViewerProps {
+  path: string
+}
+
+type State = 'loading' | 'ready' | 'error'
+
+function basename(path: string): string {
+  const idx = path.lastIndexOf('/')
+  return idx >= 0 ? path.slice(idx + 1) : path
+}
+
+export function AudioFileViewer({ path }: AudioFileViewerProps) {
+  const [state, setState] = useState<State>('loading')
+
+  useEffect(() => {
+    setState('loading')
+  }, [path])
+
+  const src = `app://workspace/${path.split('/').map(encodeURIComponent).join('/')}`
+
+  if (state === 'error') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-3 px-6 text-center text-muted-foreground">
+        <FileAudioIcon className="size-6" />
+        <p className="text-sm font-medium text-foreground">Cannot play this audio file</p>
+        <p className="max-w-md text-xs">The codec or container format isn&apos;t supported.</p>
+        <button
+          type="button"
+          onClick={() => {
+            void window.ipc.invoke('shell:openPath', { path })
+          }}
+          className="inline-flex items-center gap-1.5 rounded-md border border-border bg-background px-3 py-1.5 text-xs font-medium text-foreground hover:bg-accent"
+        >
+          <ExternalLinkIcon className="size-3.5" />
+          Open in system
+        </button>
+      </div>
+    )
+  }
+
+  return (
+    <div className="flex h-full w-full flex-col items-center justify-center gap-4 bg-muted/30 px-6">
+      <FileAudioIcon className="size-10 text-muted-foreground" />
+      <p className="max-w-md truncate text-sm font-medium text-foreground" title={path}>
+        {basename(path)}
+      </p>
+      <audio
+        key={path}
+        src={src}
+        controls
+        className="w-full max-w-lg"
+        onLoadedMetadata={() => setState('ready')}
+        onError={() => setState('error')}
+      />
+    </div>
+  )
+}
diff --git a/apps/x/apps/renderer/src/components/html-file-viewer.tsx b/apps/x/apps/renderer/src/components/html-file-viewer.tsx
new file mode 100644
index 00000000..994ab73e
--- /dev/null
+++ b/apps/x/apps/renderer/src/components/html-file-viewer.tsx
@@ -0,0 +1,155 @@
+import { useEffect, useState } from 'react'
+import { AlertCircleIcon, ExternalLinkIcon, FileTextIcon, Loader2Icon } from 'lucide-react'
+
+const MAX_SIZE_BYTES = 5 * 1024 * 1024
+const CACHE_MAX_ENTRIES = 20
+
+type CacheEntry = { html: string; mtimeMs: number; size: number }
+const htmlCache = new Map<string, CacheEntry>()
+
+function getCached(path: string, mtimeMs: number, size: number): string | null {
+  const entry = htmlCache.get(path)
+  if (!entry || entry.mtimeMs !== mtimeMs || entry.size !== size) return null
+  // Refresh LRU position
+  htmlCache.delete(path)
+  htmlCache.set(path, entry)
+  return entry.html
+}
+
+function setCached(path: string, html: string, mtimeMs: number, size: number) {
+  htmlCache.set(path, { html, mtimeMs, size })
+  while (htmlCache.size > CACHE_MAX_ENTRIES) {
+    const oldest = htmlCache.keys().next().value
+    if (oldest === undefined) break
+    htmlCache.delete(oldest)
+  }
+}
+
+type ViewerState =
+  | { kind: 'loading' }
+  | { kind: 'loaded'; html: string }
+  | { kind: 'empty' }
+  | { kind: 'tooLarge'; sizeMB: number }
+  | { kind: 'error'; message: string }
+
+interface HtmlFileViewerProps {
+  path: string
+}
+
+export function HtmlFileViewer({ path }: HtmlFileViewerProps) {
+  const [state, setState] = useState<ViewerState>({ kind: 'loading' })
+  const [iframeLoaded, setIframeLoaded] = useState(false)
+
+  useEffect(() => {
+    let cancelled = false
+    setState({ kind: 'loading' })
+    setIframeLoaded(false)
+
+    ;(async () => {
+      try {
+        const stat = await window.ipc.invoke('workspace:stat', { path })
+        if (cancelled) return
+        if (stat.kind !== 'file') {
+          setState({ kind: 'error', message: 'Selected path is not a file.' })
+          return
+        }
+        if (stat.size > MAX_SIZE_BYTES) {
+          setState({ kind: 'tooLarge', sizeMB: stat.size / (1024 * 1024) })
+          return
+        }
+        const cachedHtml = getCached(path, stat.mtimeMs, stat.size)
+        if (cachedHtml !== null) {
+          setState(cachedHtml.trim() === '' ? { kind: 'empty' } : { kind: 'loaded', html: cachedHtml })
+          return
+        }
+        const result = await window.ipc.invoke('workspace:readFile', { path })
+        if (cancelled) return
+        setCached(path, result.data, stat.mtimeMs, stat.size)
+        if (!result.data || result.data.trim() === '') {
+          setState({ kind: 'empty' })
+          return
+        }
+        setState({ kind: 'loaded', html: result.data })
+      } catch (err) {
+        if (cancelled) return
+        const message = err instanceof Error ? err.message : String(err)
+        setState({ kind: 'error', message })
+      }
+    })()
+
+    return () => {
+      cancelled = true
+    }
+  }, [path])
+
+  if (state.kind === 'error') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-2 px-6 text-center text-muted-foreground">
+        <AlertCircleIcon className="size-6 text-destructive" />
+        <p className="text-sm font-medium text-foreground">Could not load preview</p>
+        <p className="max-w-md text-xs">{state.message}</p>
+        <p className="text-xs opacity-60">{path}</p>
+      </div>
+    )
+  }
+
+  if (state.kind === 'empty') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-2 text-muted-foreground">
+        <FileTextIcon className="size-6" />
+        <p className="text-sm">This file is empty</p>
+      </div>
+    )
+  }
+
+  if (state.kind === 'tooLarge') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-3 px-6 text-center text-muted-foreground">
+        <FileTextIcon className="size-6" />
+        <p className="text-sm font-medium text-foreground">File too large to preview</p>
+        <p className="text-xs">
+          {state.sizeMB.toFixed(1)} MB — preview limit is {(MAX_SIZE_BYTES / (1024 * 1024)).toFixed(0)} MB.
+        </p>
+        <button
+          type="button"
+          onClick={() => {
+            void window.ipc.invoke('shell:openPath', { path })
+          }}
+          className="inline-flex items-center gap-1.5 rounded-md border border-border bg-background px-3 py-1.5 text-xs font-medium text-foreground hover:bg-accent"
+        >
+          <ExternalLinkIcon className="size-3.5" />
+          Open in system
+        </button>
+      </div>
+    )
+  }
+
+  // We use `srcDoc` here (not `src=app://workspace/<path>`) so the iframe
+  // gets a null origin with no base URL. Trade-off: relative assets inside
+  // the file — `<link href="./style.css">`, `<img src="./pic.png">`,
+  // `<script src="./foo.js">` — will silently 404. Self-contained HTML
+  // works fine; HTML that ships next to sibling assets will look broken.
+  // TODO: switch to `src=app://workspace/<path>` if we want relative-asset
+  // support; that path also resolves through the existing path-traversal
+  // guard in resolveWorkspacePath.
+  return (
+    <div className="relative h-full w-full">
+      {state.kind === 'loaded' && (
+        <iframe
+          key={path}
+          srcDoc={state.html}
+          sandbox="allow-scripts"
+          className="h-full w-full border-0 bg-white"
+          title="HTML preview"
+          onLoad={() => setIframeLoaded(true)}
+        />
+      )}
+      {(state.kind === 'loading' || !iframeLoaded) && (
+        <div className="absolute inset-0 flex flex-col items-center justify-center gap-3 bg-background text-muted-foreground">
+          <Loader2Icon className="size-6 animate-spin" />
+          <p className="text-sm">Rendering preview…</p>
+        </div>
+      )}
+    </div>
+  )
+}
diff --git a/apps/x/apps/renderer/src/components/image-file-viewer.tsx b/apps/x/apps/renderer/src/components/image-file-viewer.tsx
new file mode 100644
index 00000000..e27924c3
--- /dev/null
+++ b/apps/x/apps/renderer/src/components/image-file-viewer.tsx
@@ -0,0 +1,58 @@
+import { useEffect, useState } from 'react'
+import { ExternalLinkIcon, FileImageIcon, Loader2Icon } from 'lucide-react'
+
+interface ImageFileViewerProps {
+  path: string
+}
+
+type State = 'loading' | 'loaded' | 'error'
+
+export function ImageFileViewer({ path }: ImageFileViewerProps) {
+  const [state, setState] = useState<State>('loading')
+
+  useEffect(() => {
+    setState('loading')
+  }, [path])
+
+  const src = `app://workspace/${path.split('/').map(encodeURIComponent).join('/')}`
+
+  if (state === 'error') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-3 px-6 text-center text-muted-foreground">
+        <FileImageIcon className="size-6" />
+        <p className="text-sm font-medium text-foreground">Cannot preview this image</p>
+        <p className="max-w-md text-xs">The format may be unsupported (e.g. HEIC on Windows).</p>
+        <button
+          type="button"
+          onClick={() => {
+            void window.ipc.invoke('shell:openPath', { path })
+          }}
+          className="inline-flex items-center gap-1.5 rounded-md border border-border bg-background px-3 py-1.5 text-xs font-medium text-foreground hover:bg-accent"
+        >
+          <ExternalLinkIcon className="size-3.5" />
+          Open in system
+        </button>
+      </div>
+    )
+  }
+
+  return (
+    <div className="relative flex h-full w-full items-center justify-center bg-muted/30">
+      <img
+        key={path}
+        src={src}
+        alt={path}
+        className="max-h-full max-w-full object-contain"
+        onLoad={() => setState('loaded')}
+        onError={() => setState('error')}
+        style={state === 'loading' ? { opacity: 0 } : undefined}
+      />
+      {state === 'loading' && (
+        <div className="absolute inset-0 flex flex-col items-center justify-center gap-3 text-muted-foreground">
+          <Loader2Icon className="size-6 animate-spin" />
+          <p className="text-sm">Loading image…</p>
+        </div>
+      )}
+    </div>
+  )
+}
diff --git a/apps/x/apps/renderer/src/components/pdf-file-viewer.tsx b/apps/x/apps/renderer/src/components/pdf-file-viewer.tsx
new file mode 100644
index 00000000..6c8cc48a
--- /dev/null
+++ b/apps/x/apps/renderer/src/components/pdf-file-viewer.tsx
@@ -0,0 +1,56 @@
+import { useEffect, useState } from 'react'
+import { ExternalLinkIcon, FileTextIcon, Loader2Icon } from 'lucide-react'
+
+interface PdfFileViewerProps {
+  path: string
+}
+
+type State = 'loading' | 'ready' | 'error'
+
+export function PdfFileViewer({ path }: PdfFileViewerProps) {
+  const [state, setState] = useState<State>('loading')
+
+  useEffect(() => {
+    setState('loading')
+  }, [path])
+
+  const src = `app://workspace/${path.split('/').map(encodeURIComponent).join('/')}`
+
+  if (state === 'error') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-3 px-6 text-center text-muted-foreground">
+        <FileTextIcon className="size-6" />
+        <p className="text-sm font-medium text-foreground">Cannot preview this PDF</p>
+        <button
+          type="button"
+          onClick={() => {
+            void window.ipc.invoke('shell:openPath', { path })
+          }}
+          className="inline-flex items-center gap-1.5 rounded-md border border-border bg-background px-3 py-1.5 text-xs font-medium text-foreground hover:bg-accent"
+        >
+          <ExternalLinkIcon className="size-3.5" />
+          Open in system
+        </button>
+      </div>
+    )
+  }
+
+  return (
+    <div className="relative h-full w-full">
+      <iframe
+        key={path}
+        src={src}
+        className="h-full w-full border-0 bg-white"
+        title="PDF preview"
+        onLoad={() => setState('ready')}
+        onError={() => setState('error')}
+      />
+      {state === 'loading' && (
+        <div className="absolute inset-0 flex flex-col items-center justify-center gap-3 bg-background text-muted-foreground">
+          <Loader2Icon className="size-6 animate-spin" />
+          <p className="text-sm">Loading PDF…</p>
+        </div>
+      )}
+    </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
new file mode 100644
index 00000000..ca71eca2
--- /dev/null
+++ b/apps/x/apps/renderer/src/components/persistent-viewer-cache.tsx
@@ -0,0 +1,53 @@
+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 renderViewer(path: string): JSX.Element | null {
+  const type = getViewerType(path)
+  if (type === 'html') return <HtmlFileViewer path={path} />
+  if (type === 'pdf') return <PdfFileViewer path={path} />
+  return null
+}
+
+interface PersistentViewerCacheProps {
+  activePath: string
+}
+
+/**
+ * Keeps recently-opened HTML and PDF viewers mounted in the DOM,
+ * toggling visibility instead of unmounting. This preserves iframe
+ * state (PDF page/zoom, HTML scroll/JS state) across file switches.
+ */
+export function PersistentViewerCache({ activePath }: PersistentViewerCacheProps) {
+  const [mountedPaths, setMountedPaths] = useState<string[]>(() =>
+    isCacheableViewerPath(activePath) ? [activePath] : []
+  )
+
+  useEffect(() => {
+    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).
+      if (prev.includes(activePath)) return prev
+      const next = [...prev, activePath]
+      return next.length > CACHE_LIMIT ? next.slice(-CACHE_LIMIT) : next
+    })
+  }, [activePath])
+
+  return (
+    <div className="relative h-full w-full">
+      {mountedPaths.map((p) => (
+        <div
+          key={p}
+          className="absolute inset-0"
+          style={{ display: p === activePath ? 'block' : 'none' }}
+        >
+          {renderViewer(p)}
+        </div>
+      ))}
+    </div>
+  )
+}
diff --git a/apps/x/apps/renderer/src/components/unsupported-file-viewer.tsx b/apps/x/apps/renderer/src/components/unsupported-file-viewer.tsx
new file mode 100644
index 00000000..474d7dba
--- /dev/null
+++ b/apps/x/apps/renderer/src/components/unsupported-file-viewer.tsx
@@ -0,0 +1,149 @@
+import { useEffect, useState } from 'react'
+import { ExternalLinkIcon, FileIcon, FileTextIcon, Loader2Icon } from 'lucide-react'
+
+const TEXT_FALLBACK_MAX_BYTES = 1 * 1024 * 1024 // 1 MB
+
+interface UnsupportedFileViewerProps {
+  path: string
+}
+
+type State =
+  | { kind: 'loading' }
+  | { kind: 'ready'; sizeBytes: number; canShowAsText: boolean }
+  | { kind: 'error'; message: string }
+
+function basename(path: string): string {
+  const idx = path.lastIndexOf('/')
+  return idx >= 0 ? path.slice(idx + 1) : path
+}
+
+function extensionLabel(path: string): string {
+  const name = basename(path)
+  const dot = name.lastIndexOf('.')
+  if (dot < 0) return 'No extension'
+  return name.slice(dot + 1).toUpperCase()
+}
+
+function formatSize(bytes: number): string {
+  if (bytes < 1024) return `${bytes} B`
+  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`
+  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`
+}
+
+export function UnsupportedFileViewer({ path }: UnsupportedFileViewerProps) {
+  const [state, setState] = useState<State>({ kind: 'loading' })
+  const [textContent, setTextContent] = useState<string | null>(null)
+
+  useEffect(() => {
+    let cancelled = false
+    setState({ kind: 'loading' })
+    setTextContent(null)
+
+    ;(async () => {
+      try {
+        const stat = await window.ipc.invoke('workspace:stat', { path })
+        if (cancelled) return
+        if (stat.kind !== 'file') {
+          setState({ kind: 'error', message: 'Selected path is not a file.' })
+          return
+        }
+        setState({
+          kind: 'ready',
+          sizeBytes: stat.size,
+          canShowAsText: stat.size <= TEXT_FALLBACK_MAX_BYTES,
+        })
+      } catch (err) {
+        if (cancelled) return
+        const message = err instanceof Error ? err.message : String(err)
+        setState({ kind: 'error', message })
+      }
+    })()
+
+    return () => {
+      cancelled = true
+    }
+  }, [path])
+
+  async function loadAsText() {
+    try {
+      const result = await window.ipc.invoke('workspace:readFile', { path })
+      setTextContent(result.data)
+    } catch (err) {
+      const message = err instanceof Error ? err.message : String(err)
+      setTextContent(`Failed to read as text: ${message}`)
+    }
+  }
+
+  if (state.kind === 'loading') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-3 text-muted-foreground">
+        <Loader2Icon className="size-6 animate-spin" />
+      </div>
+    )
+  }
+
+  if (state.kind === 'error') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-2 px-6 text-center text-muted-foreground">
+        <FileIcon className="size-6" />
+        <p className="text-sm font-medium text-foreground">Could not open</p>
+        <p className="max-w-md text-xs">{state.message}</p>
+      </div>
+    )
+  }
+
+  if (textContent !== null) {
+    return (
+      <div className="flex h-full w-full flex-col">
+        <div className="flex items-center justify-between border-b border-border bg-muted/30 px-4 py-2 text-xs text-muted-foreground">
+          <span className="truncate">{basename(path)} · plain text view</span>
+          <button
+            type="button"
+            onClick={() => setTextContent(null)}
+            className="text-foreground hover:underline"
+          >
+            Hide
+          </button>
+        </div>
+        <div className="flex-1 overflow-auto p-4">
+          <pre className="text-sm font-mono text-foreground whitespace-pre-wrap">{textContent}</pre>
+        </div>
+      </div>
+    )
+  }
+
+  return (
+    <div className="flex h-full w-full flex-col items-center justify-center gap-3 px-6 text-center text-muted-foreground">
+      <FileIcon className="size-10 text-muted-foreground" />
+      <p className="max-w-md truncate text-sm font-medium text-foreground" title={path}>
+        {basename(path)}
+      </p>
+      <p className="text-xs">
+        {extensionLabel(path)} · {formatSize(state.sizeBytes)}
+      </p>
+      <p className="max-w-md text-xs">No in-app preview for this file type.</p>
+      <div className="flex items-center gap-2">
+        <button
+          type="button"
+          onClick={() => {
+            void window.ipc.invoke('shell:openPath', { path })
+          }}
+          className="inline-flex items-center gap-1.5 rounded-md border border-border bg-background px-3 py-1.5 text-xs font-medium text-foreground hover:bg-accent"
+        >
+          <ExternalLinkIcon className="size-3.5" />
+          Open in system
+        </button>
+        {state.canShowAsText && (
+          <button
+            type="button"
+            onClick={() => void loadAsText()}
+            className="inline-flex items-center gap-1.5 rounded-md border border-border bg-background px-3 py-1.5 text-xs font-medium text-foreground hover:bg-accent"
+          >
+            <FileTextIcon className="size-3.5" />
+            Show as plain text
+          </button>
+        )}
+      </div>
+    </div>
+  )
+}
diff --git a/apps/x/apps/renderer/src/components/video-file-viewer.tsx b/apps/x/apps/renderer/src/components/video-file-viewer.tsx
new file mode 100644
index 00000000..4b5a0d6d
--- /dev/null
+++ b/apps/x/apps/renderer/src/components/video-file-viewer.tsx
@@ -0,0 +1,53 @@
+import { useEffect, useState } from 'react'
+import { ExternalLinkIcon, FileVideoIcon } from 'lucide-react'
+
+interface VideoFileViewerProps {
+  path: string
+}
+
+type State = 'loading' | 'ready' | 'error'
+
+export function VideoFileViewer({ path }: VideoFileViewerProps) {
+  const [state, setState] = useState<State>('loading')
+
+  useEffect(() => {
+    setState('loading')
+  }, [path])
+
+  const src = `app://workspace/${path.split('/').map(encodeURIComponent).join('/')}`
+
+  if (state === 'error') {
+    return (
+      <div className="flex h-full w-full flex-col items-center justify-center gap-3 px-6 text-center text-muted-foreground">
+        <FileVideoIcon className="size-6" />
+        <p className="text-sm font-medium text-foreground">Cannot play this video</p>
+        <p className="max-w-md text-xs">
+          The codec or container format isn&apos;t supported by Chromium (e.g. WMV, AVI, or some MKV files).
+        </p>
+        <button
+          type="button"
+          onClick={() => {
+            void window.ipc.invoke('shell:openPath', { path })
+          }}
+          className="inline-flex items-center gap-1.5 rounded-md border border-border bg-background px-3 py-1.5 text-xs font-medium text-foreground hover:bg-accent"
+        >
+          <ExternalLinkIcon className="size-3.5" />
+          Open in system
+        </button>
+      </div>
+    )
+  }
+
+  return (
+    <div className="flex h-full w-full items-center justify-center bg-black">
+      <video
+        key={path}
+        src={src}
+        controls
+        className="max-h-full max-w-full"
+        onLoadedMetadata={() => setState('ready')}
+        onError={() => setState('error')}
+      />
+    </div>
+  )
+}
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'
+}