diff --git a/client/src/App.tsx b/client/src/App.tsx
index 4179c1a9..31ac7787 100644
--- a/client/src/App.tsx
+++ b/client/src/App.tsx
@@ -93,7 +93,15 @@ export default function App() {
 
   useEffect(() => {
     if (!location.pathname.startsWith('/shared/') && !location.pathname.startsWith('/public/') && !location.pathname.startsWith('/login')) {
-      loadUser()
+      // If the persist snapshot already has an authenticated user, validate
+      // silently so the PWA shell renders immediately without a spinner.
+      const alreadyAuthenticated = useAuthStore.getState().isAuthenticated
+      if (alreadyAuthenticated) {
+        useAuthStore.setState({ isLoading: false })
+        loadUser({ silent: true })
+      } else {
+        loadUser()
+      }
     }
     authApi.getAppConfig().then(async (config: { demo_mode?: boolean; dev_mode?: boolean; is_prerelease?: boolean; has_maps_key?: boolean; version?: string; timezone?: string; require_mfa?: boolean; trip_reminders_enabled?: boolean; permissions?: Record<string, PermissionLevel> }) => {
       if (config?.demo_mode) setDemoMode(true)
diff --git a/client/src/components/Collab/CollabNotes.tsx b/client/src/components/Collab/CollabNotes.tsx
index 2585cabf..2d6f253c 100644
--- a/client/src/components/Collab/CollabNotes.tsx
+++ b/client/src/components/Collab/CollabNotes.tsx
@@ -7,6 +7,7 @@ import remarkBreaks from 'remark-breaks'
 import { Plus, Trash2, Pin, PinOff, Pencil, X, Check, StickyNote, Settings, ExternalLink, Maximize2, Loader2 } from 'lucide-react'
 import { collabApi } from '../../api/client'
 import { getAuthUrl } from '../../api/authUrl'
+import { openFile } from '../../utils/fileDownload'
 import { useCanDo } from '../../store/permissionsStore'
 import { useTripStore } from '../../store/tripStore'
 import { addListener, removeListener } from '../../api/websocket'
@@ -111,10 +112,7 @@ function FilePreviewPortal({ file, onClose }: FilePreviewPortalProps) {
   const isPdf = file.mime_type === 'application/pdf'
   const isTxt = file.mime_type?.startsWith('text/')
 
-  const openInNewTab = async () => {
-    const u = await getAuthUrl(rawUrl, 'download')
-    window.open(u, '_blank', 'noreferrer')
-  }
+  const openInNewTab = () => openFile(rawUrl).catch(() => {})
 
   return ReactDOM.createPortal(
     <div style={{ position: 'fixed', inset: 0, background: 'rgba(0,0,0,0.88)', zIndex: 10000, display: 'flex', alignItems: 'center', justifyContent: 'center', padding: 16 }} onClick={onClose}>
diff --git a/client/src/components/Files/FileManager.tsx b/client/src/components/Files/FileManager.tsx
index b4b4e200..6092806a 100644
--- a/client/src/components/Files/FileManager.tsx
+++ b/client/src/components/Files/FileManager.tsx
@@ -10,6 +10,7 @@ import { useCanDo } from '../../store/permissionsStore'
 import { useTripStore } from '../../store/tripStore'
 
 import { getAuthUrl } from '../../api/authUrl'
+import { downloadFile, openFile } from '../../utils/fileDownload'
 
 function isImage(mimeType) {
   if (!mimeType) return false
@@ -30,16 +31,8 @@ function formatSize(bytes) {
   return `${(bytes / 1024 / 1024).toFixed(1)} MB`
 }
 
-async function triggerDownload(url: string, filename: string) {
-  const authUrl = await getAuthUrl(url, 'download')
-  const res = await fetch(authUrl)
-  const blob = await res.blob()
-  const a = document.createElement('a')
-  a.href = URL.createObjectURL(blob)
-  a.download = filename
-  document.body.appendChild(a)
-  a.click()
-  setTimeout(() => { URL.revokeObjectURL(a.href); a.remove() }, 100)
+function triggerDownload(url: string, filename: string) {
+  downloadFile(url, filename).catch(() => {})
 }
 
 function formatDateWithLocale(dateStr, locale) {
@@ -120,7 +113,7 @@ function ImageLightbox({ files, initialIndex, onClose }: ImageLightboxProps) {
         </span>
         <div style={{ display: 'flex', gap: 8, flexShrink: 0 }}>
           <button
-            onClick={async () => { const u = await getAuthUrl(file.url, 'download'); window.open(u, '_blank', 'noreferrer') }}
+            onClick={() => openFile(file.url).catch(() => {})}
             style={{ background: 'none', border: 'none', cursor: 'pointer', color: 'rgba(255,255,255,0.7)', display: 'flex', padding: 4 }}
             title={t('files.openTab')}>
             <ExternalLink size={16} />
@@ -750,7 +743,7 @@ export default function FileManager({ files = [], onUpload, onDelete, onUpdate,
               <span style={{ fontSize: 13, fontWeight: 600, color: 'var(--text-primary)', overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap', flex: 1 }}>{previewFile.original_name}</span>
               <div style={{ display: 'flex', alignItems: 'center', gap: 8, flexShrink: 0 }}>
                 <button
-                  onClick={async () => { const u = await getAuthUrl(previewFile.url, 'download'); window.open(u, '_blank', 'noreferrer') }}
+                  onClick={() => openFile(previewFile.url).catch(() => {})}
                   style={{ display: 'flex', alignItems: 'center', gap: 4, fontSize: 12, color: 'var(--text-muted)', background: 'none', border: 'none', cursor: 'pointer', textDecoration: 'none', padding: '4px 8px', borderRadius: 6, transition: 'color 0.15s' }}
                   onMouseEnter={e => (e.currentTarget as HTMLElement).style.color = 'var(--text-primary)'}
                   onMouseLeave={e => (e.currentTarget as HTMLElement).style.color = 'var(--text-muted)'}>
@@ -778,7 +771,7 @@ export default function FileManager({ files = [], onUpload, onDelete, onUpdate,
               title={previewFile.original_name}
             >
               <p style={{ padding: 24, textAlign: 'center', color: 'var(--text-muted)' }}>
-                <button onClick={async () => { const u = await getAuthUrl(previewFile.url, 'download'); window.open(u, '_blank', 'noopener noreferrer') }} style={{ color: 'var(--text-primary)', textDecoration: 'underline', background: 'none', border: 'none', cursor: 'pointer', font: 'inherit' }}>{t('files.downloadPdf')}</button>
+                <button onClick={() => openFile(previewFile.url).catch(() => {})} style={{ color: 'var(--text-primary)', textDecoration: 'underline', background: 'none', border: 'none', cursor: 'pointer', font: 'inherit' }}>{t('files.downloadPdf')}</button>
               </p>
             </object>
           </div>
diff --git a/client/src/components/Planner/PlaceInspector.tsx b/client/src/components/Planner/PlaceInspector.tsx
index 58ffbf99..be1da19b 100644
--- a/client/src/components/Planner/PlaceInspector.tsx
+++ b/client/src/components/Planner/PlaceInspector.tsx
@@ -1,5 +1,5 @@
 import React, { useState, useEffect, useRef, useCallback, useMemo } from 'react'
-import { getAuthUrl } from '../../api/authUrl'
+import { openFile } from '../../utils/fileDownload'
 import Markdown from 'react-markdown'
 import remarkGfm from 'remark-gfm'
 import { X, Clock, MapPin, ExternalLink, Phone, Euro, Edit2, Trash2, Plus, Minus, ChevronDown, ChevronUp, FileText, Upload, File, FileImage, Star, Navigation, Users, Mountain, TrendingUp } from 'lucide-react'
@@ -589,7 +589,7 @@ export default function PlaceInspector({
               {filesExpanded && placeFiles.length > 0 && (
                 <div style={{ padding: '0 12px 10px', display: 'flex', flexDirection: 'column', gap: 4 }}>
                   {placeFiles.map(f => (
-                    <button key={f.id} onClick={async () => { const u = await getAuthUrl(f.url, 'download'); window.open(u, '_blank', 'noopener noreferrer') }} style={{ display: 'flex', alignItems: 'center', gap: 8, textDecoration: 'none', cursor: 'pointer', background: 'none', border: 'none', width: '100%', textAlign: 'left' }}>
+                    <button key={f.id} onClick={() => openFile(f.url).catch(() => {})} style={{ display: 'flex', alignItems: 'center', gap: 8, textDecoration: 'none', cursor: 'pointer', background: 'none', border: 'none', width: '100%', textAlign: 'left' }}>
                       {(f.mime_type || '').startsWith('image/') ? <FileImage size={12} color="#6b7280" /> : <File size={12} color="#6b7280" />}
                       <span style={{ fontSize: 12, color: 'var(--text-secondary)', flex: 1, overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap' }}>{f.original_name}</span>
                       {f.file_size && <span style={{ fontSize: 11, color: 'var(--text-faint)', flexShrink: 0 }}>{formatFileSize(f.file_size)}</span>}
diff --git a/client/src/components/Planner/ReservationModal.tsx b/client/src/components/Planner/ReservationModal.tsx
index ad17acd6..a70924ed 100644
--- a/client/src/components/Planner/ReservationModal.tsx
+++ b/client/src/components/Planner/ReservationModal.tsx
@@ -10,7 +10,7 @@ import { useToast } from '../shared/Toast'
 import { useTranslation } from '../../i18n'
 import { CustomDatePicker } from '../shared/CustomDateTimePicker'
 import CustomTimePicker from '../shared/CustomTimePicker'
-import { getAuthUrl } from '../../api/authUrl'
+import { openFile } from '../../utils/fileDownload'
 import type { Day, Place, Reservation, TripFile, AssignmentsMap, Accommodation } from '../../types'
 
 const TYPE_OPTIONS = [
@@ -587,7 +587,7 @@ export function ReservationModal({ isOpen, onClose, onSave, reservation, days, p
               <div key={f.id} style={{ display: 'flex', alignItems: 'center', gap: 8, padding: '5px 10px', background: 'var(--bg-secondary)', borderRadius: 8 }}>
                 <FileText size={12} style={{ color: 'var(--text-muted)', flexShrink: 0 }} />
                 <span style={{ flex: 1, fontSize: 12, color: 'var(--text-secondary)', overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap' }}>{f.original_name}</span>
-                <a href="#" onClick={async (e) => { e.preventDefault(); const u = await getAuthUrl(f.url, 'download'); window.open(u, '_blank', 'noreferrer') }} style={{ color: 'var(--text-faint)', display: 'flex', flexShrink: 0, cursor: 'pointer' }}><ExternalLink size={11} /></a>
+                <a href="#" onClick={(e) => { e.preventDefault(); openFile(f.url).catch(() => {}) }} style={{ color: 'var(--text-faint)', display: 'flex', flexShrink: 0, cursor: 'pointer' }}><ExternalLink size={11} /></a>
                 <button type="button" onClick={async () => {
                   // Always unlink, never delete the file
                   // Clear primary reservation_id if it points to this reservation
diff --git a/client/src/components/Planner/ReservationsPanel.tsx b/client/src/components/Planner/ReservationsPanel.tsx
index 030385e0..95942a9a 100644
--- a/client/src/components/Planner/ReservationsPanel.tsx
+++ b/client/src/components/Planner/ReservationsPanel.tsx
@@ -10,7 +10,7 @@ import {
   Calendar, Hash, CheckCircle2, Circle, Pencil, Trash2, Plus, ChevronDown, ChevronRight, Users,
   ExternalLink, BookMarked, Lightbulb, Link2, Clock,
 } from 'lucide-react'
-import { getAuthUrl } from '../../api/authUrl'
+import { openFile } from '../../utils/fileDownload'
 import type { Reservation, Day, TripFile, AssignmentsMap } from '../../types'
 
 interface AssignmentLookupEntry {
@@ -253,7 +253,7 @@ function ReservationCard({ r, tripId, onEdit, onDelete, files = [], onNavigateTo
           <div style={{ fontSize: 9, fontWeight: 600, color: 'var(--text-faint)', textTransform: 'uppercase', letterSpacing: '0.03em', marginBottom: 3 }}>{t('files.title')}</div>
           <div style={{ padding: '4px 8px', borderRadius: 7, background: 'var(--bg-secondary)', display: 'flex', flexDirection: 'column', gap: 3 }}>
             {attachedFiles.map(f => (
-              <a key={f.id} href="#" onClick={async (e) => { e.preventDefault(); const u = await getAuthUrl(f.url, 'download'); window.open(u, '_blank', 'noreferrer') }} style={{ display: 'flex', alignItems: 'center', gap: 4, textDecoration: 'none', cursor: 'pointer' }}>
+              <a key={f.id} href="#" onClick={(e) => { e.preventDefault(); openFile(f.url).catch(() => {}) }} style={{ display: 'flex', alignItems: 'center', gap: 4, textDecoration: 'none', cursor: 'pointer' }}>
                 <FileText size={9} style={{ color: 'var(--text-faint)', flexShrink: 0 }} />
                 <span style={{ fontSize: 10, color: 'var(--text-muted)', flex: 1, overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap' }}>{f.original_name}</span>
               </a>
diff --git a/client/src/store/authStore.ts b/client/src/store/authStore.ts
index f677889b..3897aa26 100644
--- a/client/src/store/authStore.ts
+++ b/client/src/store/authStore.ts
@@ -1,4 +1,5 @@
 import { create } from 'zustand'
+import { persist } from 'zustand/middleware'
 import { authApi } from '../api/client'
 import { connect, disconnect } from '../api/websocket'
 import type { User } from '../types'
@@ -55,7 +56,9 @@ interface AuthState {
 // Sequence counter to prevent stale loadUser responses from overwriting fresh auth state
 let authSequence = 0
 
-export const useAuthStore = create<AuthState>((set, get) => ({
+export const useAuthStore = create<AuthState>()(
+  persist(
+  (set, get) => ({
   user: null,
   isAuthenticated: false,
   isLoading: true,
@@ -255,4 +258,25 @@ export const useAuthStore = create<AuthState>((set, get) => ({
       throw new Error(error)
     }
   },
-}))
+  }),
+  {
+    name: 'trek_auth_snapshot',
+    // Only persist the minimal user snapshot needed to avoid redirecting to
+    // login when the PWA reopens offline. The JWT remains in the httpOnly
+    // cookie and is still validated by the server on every request.
+    // maps_api_key is intentionally excluded — it's an API key that should
+    // not sit in localStorage any longer than the active session requires.
+    partialize: (state) => ({
+      isAuthenticated: state.isAuthenticated,
+      user: state.user ? {
+        id: state.user.id,
+        username: state.user.username,
+        email: state.user.email,
+        role: state.user.role,
+        avatar_url: state.user.avatar_url,
+        mfa_enabled: state.user.mfa_enabled,
+        must_change_password: state.user.must_change_password,
+      } : null,
+    }),
+  }
+))
diff --git a/client/src/utils/fileDownload.ts b/client/src/utils/fileDownload.ts
new file mode 100644
index 00000000..b9904472
--- /dev/null
+++ b/client/src/utils/fileDownload.ts
@@ -0,0 +1,81 @@
+// MIME types safe to open inline (will not execute script in any browser).
+// Everything else (text/html, image/svg+xml, text/javascript, …) is forced to
+// download so a maliciously-named upload cannot run code in the TREK origin.
+const SAFE_INLINE_TYPES = new Set([
+  'application/pdf',
+  'image/png',
+  'image/jpeg',
+  'image/gif',
+  'image/webp',
+  'image/avif',
+  'image/bmp',
+  'image/tiff',
+])
+
+/**
+ * Asserts that `url` is a relative same-origin path so that
+ * `credentials: 'include'` cannot be used to send the session cookie to an
+ * external host (e.g. if an attacker somehow controls the `url` value).
+ */
+function assertRelativeUrl(url: string): void {
+  if (!url.startsWith('/') || url.startsWith('//') || url.startsWith('/\\')) {
+    throw new Error(`Refusing to fetch non-relative URL: ${url}`)
+  }
+}
+
+function triggerAnchorDownload(blobUrl: string, filename?: string): void {
+  const a = document.createElement('a')
+  a.href = blobUrl
+  if (filename) a.download = filename
+  document.body.appendChild(a)
+  a.click()
+  setTimeout(() => { URL.revokeObjectURL(blobUrl); a.remove() }, 100)
+}
+
+/**
+ * Fetches a protected file using cookie auth (credentials: include) and
+ * triggers a browser download. Works inside PWA standalone mode because the
+ * fetch stays in the PWA's WebView rather than handing off to the system
+ * browser (which would lose the session cookie).
+ */
+export async function downloadFile(url: string, filename?: string): Promise<void> {
+  assertRelativeUrl(url)
+  const resp = await fetch(url, { credentials: 'include' })
+  if (!resp.ok) throw new Error(resp.status === 401 ? 'Unauthorized' : `HTTP ${resp.status}`)
+  const blob = await resp.blob()
+  const blobUrl = URL.createObjectURL(blob)
+  triggerAnchorDownload(blobUrl, filename)
+}
+
+/**
+ * Fetches a protected file using cookie auth and opens it in a new tab as a
+ * blob URL. The blob URL is same-origin to the PWA context so no system
+ * browser handoff occurs, fixing the auth error in PWA standalone mode.
+ *
+ * Only PDFs and raster images are opened inline. All other MIME types
+ * (including text/html and image/svg+xml which can execute script) are forced
+ * to download so that an uploaded file cannot run code in the TREK origin.
+ *
+ * Falls back to a download trigger if the popup is blocked.
+ */
+export async function openFile(url: string, filename?: string): Promise<void> {
+  assertRelativeUrl(url)
+  const resp = await fetch(url, { credentials: 'include' })
+  if (!resp.ok) throw new Error(resp.status === 401 ? 'Unauthorized' : `HTTP ${resp.status}`)
+  const blob = await resp.blob()
+  const blobUrl = URL.createObjectURL(blob)
+
+  // Force download for MIME types that can execute script when rendered inline
+  if (!SAFE_INLINE_TYPES.has(blob.type)) {
+    triggerAnchorDownload(blobUrl, filename)
+    return
+  }
+
+  const win = window.open(blobUrl, '_blank', 'noreferrer')
+  if (win) {
+    setTimeout(() => URL.revokeObjectURL(blobUrl), 30_000)
+  } else {
+    // Popup blocked — fall back to download
+    triggerAnchorDownload(blobUrl, filename)
+  }
+}
diff --git a/client/tests/unit/stores/authStore.test.ts b/client/tests/unit/stores/authStore.test.ts
index 5b26919a..5b25145f 100644
--- a/client/tests/unit/stores/authStore.test.ts
+++ b/client/tests/unit/stores/authStore.test.ts
@@ -439,4 +439,53 @@ describe('authStore', () => {
       uploadSpy.mockRestore();
     });
   });
+
+  describe('FE-STORE-AUTH-PERSIST-001: logout resets persisted snapshot', () => {
+    it('snapshot has isAuthenticated:false after logout (PWA offline will redirect to login)', () => {
+      useAuthStore.setState({ user: buildUser(), isAuthenticated: true });
+
+      useAuthStore.getState().logout();
+
+      const snapshot = JSON.parse(localStorage.getItem('trek_auth_snapshot') ?? '{}');
+      expect(snapshot?.state?.isAuthenticated).toBe(false);
+      expect(snapshot?.state?.user).toBeNull();
+    });
+  });
+
+  describe('FE-STORE-AUTH-PERSIST-002: 401 resets persisted snapshot', () => {
+    it('snapshot has isAuthenticated:false after 401 (expired session clears offline access)', async () => {
+      useAuthStore.setState({ user: buildUser(), isAuthenticated: true });
+
+      server.use(
+        http.get('/api/auth/me', () =>
+          HttpResponse.json({ error: 'Unauthorized' }, { status: 401 })
+        )
+      );
+
+      await useAuthStore.getState().loadUser();
+
+      const snapshot = JSON.parse(localStorage.getItem('trek_auth_snapshot') ?? '{}');
+      expect(snapshot?.state?.isAuthenticated).toBe(false);
+      expect(useAuthStore.getState().isAuthenticated).toBe(false);
+    });
+  });
+
+  describe('FE-STORE-AUTH-PERSIST-003: network error preserves snapshot', () => {
+    it('snapshot retains isAuthenticated:true on network error (offline PWA skips login screen)', async () => {
+      useAuthStore.setState({ user: buildUser(), isAuthenticated: true });
+
+      server.use(
+        http.get('/api/auth/me', () =>
+          HttpResponse.json({ error: 'Server error' }, { status: 500 })
+        )
+      );
+
+      await useAuthStore.getState().loadUser();
+
+      // Persist middleware writes the state; isAuthenticated must stay true
+      const snapshot = JSON.parse(localStorage.getItem('trek_auth_snapshot') ?? '{}');
+      expect(snapshot?.state?.isAuthenticated).toBe(true);
+      expect(useAuthStore.getState().isAuthenticated).toBe(true);
+    });
+  });
 });
diff --git a/client/tests/unit/utils/fileDownload.test.ts b/client/tests/unit/utils/fileDownload.test.ts
new file mode 100644
index 00000000..89632017
--- /dev/null
+++ b/client/tests/unit/utils/fileDownload.test.ts
@@ -0,0 +1,135 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { downloadFile, openFile } from '../../../src/utils/fileDownload'
+
+function makeFetchMock(status: number, blob: Blob = new Blob(['data'], { type: 'application/pdf' })) {
+  return vi.fn().mockResolvedValue({
+    status,
+    ok: status >= 200 && status < 300,
+    blob: () => Promise.resolve(blob),
+  })
+}
+
+beforeEach(() => {
+  vi.spyOn(URL, 'createObjectURL').mockReturnValue('blob:mock-url')
+  vi.spyOn(URL, 'revokeObjectURL').mockImplementation(() => {})
+  vi.spyOn(document.body, 'appendChild').mockImplementation((el) => el)
+  vi.spyOn(document.body, 'removeChild').mockImplementation((el) => el)
+  vi.useFakeTimers()
+})
+
+afterEach(() => {
+  vi.restoreAllMocks()
+  vi.useRealTimers()
+})
+
+describe('assertRelativeUrl (URL guard)', () => {
+  it('rejects absolute http URLs', async () => {
+    await expect(downloadFile('https://evil.com/x')).rejects.toThrow('Refusing to fetch non-relative URL')
+  })
+  it('rejects protocol-relative URLs', async () => {
+    await expect(downloadFile('//evil.com/x')).rejects.toThrow('Refusing to fetch non-relative URL')
+  })
+  it('allows relative paths', async () => {
+    vi.stubGlobal('fetch', makeFetchMock(200))
+    vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {})
+    await expect(downloadFile('/trips/1/files/2/download')).resolves.toBeUndefined()
+  })
+})
+
+describe('downloadFile', () => {
+  it('fetches with credentials:include and triggers anchor download', async () => {
+    const fetchMock = makeFetchMock(200)
+    vi.stubGlobal('fetch', fetchMock)
+
+    const clickSpy = vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {})
+
+    await downloadFile('/uploads/files/test.pdf', 'test.pdf')
+
+    expect(fetchMock).toHaveBeenCalledWith('/uploads/files/test.pdf', { credentials: 'include' })
+    expect(URL.createObjectURL).toHaveBeenCalled()
+    expect(clickSpy).toHaveBeenCalled()
+
+    // Revoke happens after setTimeout(100)
+    vi.runAllTimers()
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith('blob:mock-url')
+  })
+
+  it('sets download attribute to filename when provided', async () => {
+    vi.stubGlobal('fetch', makeFetchMock(200))
+    vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {})
+
+    await downloadFile('/uploads/files/report.pdf', 'report.pdf')
+
+    // Check anchor was created with download attribute
+    const appendCalls = (document.body.appendChild as ReturnType<typeof vi.fn>).mock.calls
+    const anchor = appendCalls[0]?.[0] as HTMLAnchorElement
+    expect(anchor.download).toBe('report.pdf')
+  })
+
+  it('throws on 401 response', async () => {
+    vi.stubGlobal('fetch', makeFetchMock(401))
+    await expect(downloadFile('/uploads/files/secret.pdf')).rejects.toThrow('Unauthorized')
+    expect(URL.createObjectURL).not.toHaveBeenCalled()
+  })
+})
+
+describe('openFile', () => {
+  it('fetches with credentials:include and opens blob URL in new tab', async () => {
+    vi.stubGlobal('fetch', makeFetchMock(200))
+    const mockWin = { closed: false }
+    const openSpy = vi.spyOn(window, 'open').mockReturnValue(mockWin as Window)
+
+    await openFile('/uploads/files/doc.pdf')
+
+    expect(window.fetch).toHaveBeenCalledWith('/uploads/files/doc.pdf', { credentials: 'include' })
+    expect(URL.createObjectURL).toHaveBeenCalled()
+    expect(openSpy).toHaveBeenCalledWith('blob:mock-url', '_blank', 'noreferrer')
+
+    // Revoke happens after 30s timeout
+    vi.runAllTimers()
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith('blob:mock-url')
+  })
+
+  it('falls back to anchor download when popup is blocked', async () => {
+    vi.stubGlobal('fetch', makeFetchMock(200))
+    vi.spyOn(window, 'open').mockReturnValue(null)
+    const clickSpy = vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {})
+
+    await openFile('/uploads/files/doc.pdf')
+
+    expect(clickSpy).toHaveBeenCalled()
+    vi.runAllTimers()
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith('blob:mock-url')
+  })
+
+  it('throws on 401 response', async () => {
+    vi.stubGlobal('fetch', makeFetchMock(401, new Blob([], { type: 'application/pdf' })))
+    await expect(openFile('/uploads/files/secret.pdf')).rejects.toThrow('Unauthorized')
+    expect(URL.createObjectURL).not.toHaveBeenCalled()
+  })
+
+  it('forces download for unsafe MIME types (HTML, SVG) instead of opening inline', async () => {
+    const htmlBlob = new Blob(['<script>alert(1)</script>'], { type: 'text/html' })
+    vi.stubGlobal('fetch', makeFetchMock(200, htmlBlob))
+    const openSpy = vi.spyOn(window, 'open').mockReturnValue({} as Window)
+    const clickSpy = vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {})
+
+    await openFile('/uploads/files/malicious.html')
+
+    // Must NOT open inline — download anchor clicked instead
+    expect(openSpy).not.toHaveBeenCalled()
+    expect(clickSpy).toHaveBeenCalled()
+  })
+
+  it('forces download for SVG MIME type', async () => {
+    const svgBlob = new Blob(['<svg><script>alert(1)</script></svg>'], { type: 'image/svg+xml' })
+    vi.stubGlobal('fetch', makeFetchMock(200, svgBlob))
+    vi.spyOn(window, 'open').mockReturnValue({} as Window)
+    const clickSpy = vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {})
+
+    await openFile('/uploads/files/malicious.svg')
+
+    expect(window.open).not.toHaveBeenCalled()
+    expect(clickSpy).toHaveBeenCalled()
+  })
+})