diff --git a/e2e/auth/session-expiry.spec.ts b/e2e/auth/session-expiry.spec.ts
index 745d3da2..c0d5635d 100644
--- a/e2e/auth/session-expiry.spec.ts
+++ b/e2e/auth/session-expiry.spec.ts
@@ -93,11 +93,22 @@ test.describe('Session expiry', () => {
     await page.goto('/');
     await waitForHydration(page);
 
-    // The storage API answers 401 when no storage connection header is sent
-    // (requires the storage browser to be enabled, as in .env.test).
-    const status = await fetchAndAwaitSessionCheck(page, '/api/storage/buckets');
+    await page.route('**/api/trino/catalog?*', (route) =>
+      route.fulfill({ status: 401, json: { message: 'Authentication required' } })
+    );
+    const status = await fetchAndAwaitSessionCheck(page, '/api/trino/catalog?level=catalogs');
     expect(status).toBe(401);
 
     await expect(page.getByRole('dialog', { name: 'Session expired' })).toBeHidden();
   });
+
+  test('a storage call without a connection is not mistaken for an expired session', async ({
+    page
+  }) => {
+    // Requires the storage browser to be enabled, as in .env.test.
+    const res = await page.request.get('/api/storage/buckets');
+
+    expect(res.status()).toBe(409);
+    expect(await res.json()).toMatchObject({ reason: 'not-connected' });
+  });
 });
diff --git a/messages/de.json b/messages/de.json
index 232ef271..9e35dd45 100644
--- a/messages/de.json
+++ b/messages/de.json
@@ -648,11 +648,12 @@
   "storage_details_unavailable": "Konnte nicht geladen werden",
   "storage_details_custom_metadata": "Benutzerdefinierte Metadaten",
   "storage_details_error_not_connected": "Keine Speicherverbindung konfiguriert",
-  "storage_details_error_fetch_file": "Dateidetails konnten nicht abgerufen werden ({status})",
-  "storage_details_error_fetch_bucket": "Bucket-Details konnten nicht abgerufen werden ({status})",
-  "storage_details_error_fetch_dir_meta": "Verzeichnismetadaten konnten nicht abgerufen werden ({status})",
+  "storage_details_error_fetch_file": "Die Dateidetails konnten nicht geladen werden.",
+  "storage_details_error_fetch_bucket": "Die Bucket-Details konnten nicht geladen werden.",
+  "storage_details_error_fetch_dir_meta": "Die Verzeichnismetadaten konnten nicht geladen werden.",
+  "storage_details_error_access_denied": "Sie haben keine Berechtigung, diese Details anzuzeigen.",
+  "storage_details_error_not_found": "Nicht gefunden. Möglicherweise wurde es verschoben oder gelöscht.",
   "storage_details_error_calc_size": "Die Verzeichnisgröße konnte nicht berechnet werden. Bitte versuchen Sie es erneut.",
-  "storage_details_error_unknown": "Unbekannter Fehler",
   "storage_details_error_no_body": "Kein Antworttext",
   "storage_details_unnamed_rule": "(unbenannt)",
   "storage_details_treemap_aria": "Treemap-Visualisierung der Verzeichnisgrößenverteilung",
diff --git a/messages/en.json b/messages/en.json
index 00d6bc5d..72d650f6 100644
--- a/messages/en.json
+++ b/messages/en.json
@@ -648,11 +648,12 @@
   "storage_details_unavailable": "Could not load",
   "storage_details_custom_metadata": "Custom Metadata",
   "storage_details_error_not_connected": "No storage connection configured",
-  "storage_details_error_fetch_file": "Failed to fetch file details ({status})",
-  "storage_details_error_fetch_bucket": "Failed to fetch bucket details ({status})",
-  "storage_details_error_fetch_dir_meta": "Failed to fetch directory metadata ({status})",
+  "storage_details_error_fetch_file": "Failed to load the file details.",
+  "storage_details_error_fetch_bucket": "Failed to load the bucket details.",
+  "storage_details_error_fetch_dir_meta": "Failed to load the directory metadata.",
+  "storage_details_error_access_denied": "You do not have permission to view these details.",
+  "storage_details_error_not_found": "Not found. It may have been moved or deleted.",
   "storage_details_error_calc_size": "Failed to calculate the directory size. Please try again.",
-  "storage_details_error_unknown": "Unknown error",
   "storage_details_error_no_body": "No response body",
   "storage_details_unnamed_rule": "(unnamed)",
   "storage_details_treemap_aria": "Treemap visualization of directory size composition",
diff --git a/src/architecture-tests/i18n-compliance.spec.ts b/src/architecture-tests/i18n-compliance.spec.ts
index d982ae8e..4f15aee4 100644
--- a/src/architecture-tests/i18n-compliance.spec.ts
+++ b/src/architecture-tests/i18n-compliance.spec.ts
@@ -79,10 +79,6 @@ const KNOWN_UNUSED_KEYS = [
   'storage_details_tree_visualization',
   'storage_details_lifecycle_rule_id',
   'storage_details_lifecycle_status',
-  'storage_details_error_not_connected',
-  'storage_details_error_fetch_file',
-  'storage_details_error_fetch_bucket',
-  'storage_details_error_fetch_dir_meta',
   'storage_details_tab_overview',
   'storage_details_tab_lifecycle',
   'storage_details_bucket_name',
diff --git a/src/hooks.server.ts b/src/hooks.server.ts
index aa317dc0..05575211 100644
--- a/src/hooks.server.ts
+++ b/src/hooks.server.ts
@@ -11,6 +11,7 @@ import { getConnectionFromHeader } from '$lib/server/storage/connection.js';
 import { STORAGE_CONNECTION_ID_HEADER } from '$lib/storage/connection-id-header.js';
 import { storageBrowserEnabled } from '$lib/server/feature-flags.js';
 import { storageEncryptionKey } from '$lib/server/storage/encryption-key.js';
+import { notConnected } from '$lib/server/storage/not-connected.js';
 import { runMigrations } from '$lib/server/migrate.js';
 
 // Allow self-signed TLS certificates in development (e.g. local Trino with self-signed certs).
@@ -102,7 +103,7 @@ const handleStorageConnection: Handle = async ({ event, resolve }) => {
     !event.route.id?.startsWith('/(app)/api/storage/download/manifests/[manifestId]/') &&
     event.route.id !== '/(app)/api/storage/download/manifests';
   if (event.locals.storageConfig === null && requiresConnectionHeader) {
-    throw error(401, 'No storage connection configured');
+    notConnected();
   }
   return resolve(event);
 };
diff --git a/src/lib/components/storage/modals/DetailsModal.svelte b/src/lib/components/storage/modals/DetailsModal.svelte
index 9207ec6d..a09f13b8 100644
--- a/src/lib/components/storage/modals/DetailsModal.svelte
+++ b/src/lib/components/storage/modals/DetailsModal.svelte
@@ -8,7 +8,7 @@
   import IconBucket from '$lib/components/storage/shared/BucketIcon.svelte';
   import * as m from '$lib/paraglide/messages.js';
   import { getStorageState } from '$lib/storage/context.js';
-  import { StorageError } from '$lib/storage/errors.js';
+  import { getDetailsErrorMessage } from '$lib/storage/errors.js';
   import type { FileDetails as FileDetailsType } from '$lib/storage/details-types.js';
   import FileDetails from './details/FileDetails.svelte';
   import DirectoryDetails from './details/DirectoryDetails.svelte';
@@ -54,11 +54,7 @@
     try {
       fileDetails = await storage.api.details({ bucket, key });
     } catch (err) {
-      if (err instanceof StorageError) {
-        loadError = err.message;
-      } else {
-        loadError = err instanceof Error ? err.message : m.storage_details_error_unknown();
-      }
+      loadError = getDetailsErrorMessage(err, m.storage_details_error_fetch_file());
     } finally {
       loading = false;
     }
diff --git a/src/lib/components/storage/modals/PreviewModal.svelte b/src/lib/components/storage/modals/PreviewModal.svelte
index decb11bd..aa703979 100644
--- a/src/lib/components/storage/modals/PreviewModal.svelte
+++ b/src/lib/components/storage/modals/PreviewModal.svelte
@@ -616,7 +616,7 @@
             m.storage_editor_too_large({ limit: formatFileSize(maxEditableFileSize) })
           );
         } else {
-          addToast('error', err.message || m.storage_editor_error());
+          addToast('error', m.storage_editor_error());
         }
       } else {
         addToast('error', m.storage_editor_error());
diff --git a/src/lib/components/storage/modals/details/BucketDetails.svelte b/src/lib/components/storage/modals/details/BucketDetails.svelte
index 14751b62..fed13b19 100644
--- a/src/lib/components/storage/modals/details/BucketDetails.svelte
+++ b/src/lib/components/storage/modals/details/BucketDetails.svelte
@@ -5,7 +5,7 @@
   import IconPerson from 'virtual:icons/material-symbols/person';
   import IconKey from 'virtual:icons/material-symbols/key';
   import { getStorageState } from '$lib/storage/context.js';
-  import { StorageError } from '$lib/storage/errors.js';
+  import { getDetailsErrorMessage } from '$lib/storage/errors.js';
   import type { BucketDetails as BucketDetailsType } from '$lib/storage/details-types.js';
 
   interface Props {
@@ -32,11 +32,7 @@
         if (!cancelled) details = result;
       } catch (err) {
         if (cancelled) return;
-        if (err instanceof StorageError) {
-          error = err.message;
-        } else {
-          error = err instanceof Error ? err.message : m.storage_details_error_unknown();
-        }
+        error = getDetailsErrorMessage(err, m.storage_details_error_fetch_bucket());
       } finally {
         if (!cancelled) loading = false;
       }
diff --git a/src/lib/components/storage/modals/details/DirectoryDetails.svelte b/src/lib/components/storage/modals/details/DirectoryDetails.svelte
index cad14e71..d5d4240f 100644
--- a/src/lib/components/storage/modals/details/DirectoryDetails.svelte
+++ b/src/lib/components/storage/modals/details/DirectoryDetails.svelte
@@ -4,7 +4,7 @@
   import IconWarning from 'virtual:icons/material-symbols/warning';
   import { formatFileSize, keyToName } from '$lib/storage/utils.js';
   import { getStorageState } from '$lib/storage/context.js';
-  import { StorageError } from '$lib/storage/errors.js';
+  import { getDetailsErrorMessage } from '$lib/storage/errors.js';
   import type {
     DirectorySizeEvent,
     DirectoryMetadata,
@@ -54,11 +54,7 @@
       if (bucket === requestedBucket && prefix === requestedPrefix) meta = result;
     } catch (err) {
       if (bucket !== requestedBucket || prefix !== requestedPrefix) return;
-      if (err instanceof StorageError) {
-        metaError = err.message;
-      } else {
-        metaError = err instanceof Error ? err.message : m.storage_details_error_unknown();
-      }
+      metaError = getDetailsErrorMessage(err, m.storage_details_error_fetch_dir_meta());
     }
   }
 
@@ -105,7 +101,7 @@
             } else if (event.type === 'complete') {
               result = event;
             } else if (event.type === 'error') {
-              error = event.message;
+              error = m.storage_details_error_calc_size();
             }
           } catch {
             // skip malformed events
diff --git a/src/lib/server/storage/connection.test.ts b/src/lib/server/storage/connection.test.ts
index fc77eade..51862406 100644
--- a/src/lib/server/storage/connection.test.ts
+++ b/src/lib/server/storage/connection.test.ts
@@ -67,7 +67,8 @@ describe('getConnectionFromHeader', () => {
   it('rejects an unknown connection', async () => {
     selectRows([]);
     await expect(getConnectionFromHeader(request(), 'user-id')).rejects.toMatchObject({
-      status: 401
+      status: 409,
+      body: { reason: 'not-connected' }
     });
   });
 
diff --git a/src/lib/server/storage/connection.ts b/src/lib/server/storage/connection.ts
index bebcc45c..571a0526 100644
--- a/src/lib/server/storage/connection.ts
+++ b/src/lib/server/storage/connection.ts
@@ -5,6 +5,7 @@ import { db } from '$lib/server/db.js';
 import { userStorageConnections } from '$lib/server/schema.js';
 import { decrypt } from './encryption.js';
 import { storageEncryptionKey } from './encryption-key.js';
+import { notConnected } from './not-connected.js';
 import type { S3ConnectionConfig } from './types.js';
 import { logger } from '$lib/server/logging';
 import { STORAGE_CONNECTION_ID_HEADER } from '$lib/storage/connection-id-header.js';
@@ -27,7 +28,7 @@ const AdditionalBucketsSchema = z.array(z.string());
  * {@link LAST_USED_TOUCH_INTERVAL_MS}, so not every storage request hits the database.
  *
  * Returns `null` if the header is absent.
- * Throws 401 if the connection is not found or does not belong to the user.
+ * Throws 409 (`notConnected`) if the connection is not found or does not belong to the user.
  * Throws 500 if decryption fails or the payload does not match the stored schema.
  */
 export async function getConnectionFromHeader(
@@ -48,7 +49,7 @@ export async function getConnectionFromHeader(
 
   if (rows.length === 0) {
     log.warn({ connection_id: connectionId }, 'storage connection not found or unauthorised');
-    throw error(401, 'Storage connection not found');
+    notConnected('Storage connection not found');
   }
 
   const row = rows[0];
diff --git a/src/lib/server/storage/not-connected.ts b/src/lib/server/storage/not-connected.ts
new file mode 100644
index 00000000..44e28364
--- /dev/null
+++ b/src/lib/server/storage/not-connected.ts
@@ -0,0 +1,10 @@
+import { error } from '@sveltejs/kit';
+
+/**
+ * Reject a storage request that has no usable storage connection. A 409 with
+ * `reason: 'not-connected'` keeps it apart from a 401, which means the session
+ * expired and makes the client check the session.
+ */
+export function notConnected(message = 'No storage connection configured'): never {
+  error(409, { message, reason: 'not-connected' });
+}
diff --git a/src/lib/server/storage/request-context.ts b/src/lib/server/storage/request-context.ts
index bb9d0c5c..7f41f149 100644
--- a/src/lib/server/storage/request-context.ts
+++ b/src/lib/server/storage/request-context.ts
@@ -2,6 +2,7 @@ import { error } from '@sveltejs/kit';
 import type { RequestEvent } from '@sveltejs/kit';
 import { getProvider } from './utils.js';
 import { withStorageHttpErrors } from './wrap-provider.js';
+import { notConnected } from './not-connected.js';
 import type { StorageProvider } from './provider.js';
 import { STORAGE_CONNECTION_ID_HEADER } from '$lib/storage/connection-id-header.js';
 import { StorageObjectKeySchema } from '$lib/storage/schemas.js';
@@ -23,14 +24,14 @@ export function requireObjectKey(event: RequestEvent): string {
 
 export function requireConfig(event: RequestEvent) {
   const config = event.locals.storageConfig;
-  if (!config) throw error(401, 'No storage connection configured');
+  if (!config) notConnected();
   return config;
 }
 
 /** The connection id is captured for a manifest, never its decrypted config. */
 export function requireStorageConnectionId(event: RequestEvent): string {
   const connectionId = event.request.headers.get(STORAGE_CONNECTION_ID_HEADER);
-  if (!connectionId) throw error(401, 'No storage connection configured');
+  if (!connectionId) notConnected();
   return connectionId;
 }
 
diff --git a/src/lib/storage/archive.svelte.ts b/src/lib/storage/archive.svelte.ts
index fb746e9a..6b5b528d 100644
--- a/src/lib/storage/archive.svelte.ts
+++ b/src/lib/storage/archive.svelte.ts
@@ -80,7 +80,7 @@ export class ArchiveState {
 
     try {
       await this._fetchArchiveListing();
-    } catch (err) {
+    } catch {
       if (this._archiveNestedPath) {
         this._archiveNestedPath = null;
       } else {
@@ -89,7 +89,7 @@ export class ArchiveState {
       }
       this.archivePrefix = '';
       this.archiveLoading = false;
-      addToast('error', err instanceof Error ? err.message : m.storage_archive_open_error());
+      addToast('error', m.storage_archive_open_error());
     }
   }
 
@@ -102,9 +102,9 @@ export class ArchiveState {
 
     try {
       await this._fetchArchiveListing();
-    } catch (err) {
+    } catch {
       this.archiveLoading = false;
-      addToast('error', err instanceof Error ? err.message : m.storage_archive_open_error());
+      addToast('error', m.storage_archive_open_error());
     }
   }
 
diff --git a/src/lib/storage/errors.spec.ts b/src/lib/storage/errors.spec.ts
index f7b83c3e..cb284c4e 100644
--- a/src/lib/storage/errors.spec.ts
+++ b/src/lib/storage/errors.spec.ts
@@ -1,5 +1,10 @@
 import { describe, it, expect, vi } from 'vitest';
-import { StorageError, getActionErrorMessage, getActionErrorMessageForCode } from './errors.js';
+import {
+  StorageError,
+  getActionErrorMessage,
+  getActionErrorMessageForCode,
+  getDetailsErrorMessage
+} from './errors.js';
 
 const mockMessages = vi.hoisted(() => ({
   storage_download_error_not_connected: () => 'No storage connection configured',
@@ -8,7 +13,10 @@ const mockMessages = vi.hoisted(() => ({
   storage_download_error_server_error: () => 'Server error',
   storage_upload_error_no_such_bucket: () => 'Bucket not found',
   storage_upload_error_invalid_part: () => 'Invalid part',
-  storage_download_error_unknown: () => 'Unknown error'
+  storage_download_error_unknown: () => 'Unknown error',
+  storage_details_error_not_connected: () => 'Details: not connected',
+  storage_details_error_access_denied: () => 'Details: access denied',
+  storage_details_error_not_found: () => 'Details: not found'
 }));
 
 vi.mock('$lib/paraglide/messages.js', () => mockMessages);
@@ -65,3 +73,20 @@ describe('getActionErrorMessageForCode', () => {
     expect(getActionErrorMessageForCode('unknown')).toBe('Unknown error');
   });
 });
+
+describe('getDetailsErrorMessage', () => {
+  it.each([
+    ['not_connected', 'Details: not connected'],
+    ['access_denied', 'Details: access denied'],
+    ['not_found', 'Details: not found'],
+    ['server_error', 'fallback']
+  ])('maps %s', (code, expected) => {
+    expect(getDetailsErrorMessage(new StorageError(code, 'raw server text'), 'fallback')).toBe(
+      expected
+    );
+  });
+
+  it('uses the fallback for errors that are not StorageErrors', () => {
+    expect(getDetailsErrorMessage(new TypeError('Failed to fetch'), 'fallback')).toBe('fallback');
+  });
+});
diff --git a/src/lib/storage/errors.ts b/src/lib/storage/errors.ts
index a8676bed..927e8cdc 100644
--- a/src/lib/storage/errors.ts
+++ b/src/lib/storage/errors.ts
@@ -48,3 +48,18 @@ export function getActionErrorMessage(err: StorageError): string {
 export function getActionErrorMessageForCode(code: string): string {
   return getActionErrorMessage(new StorageError(code, ''));
 }
+
+/** Translated message for a failed details request; `fallback` covers all other failures. */
+export function getDetailsErrorMessage(err: unknown, fallback: string): string {
+  if (!(err instanceof StorageError)) return fallback;
+  switch (err.code) {
+    case 'not_connected':
+      return m.storage_details_error_not_connected();
+    case 'access_denied':
+      return m.storage_details_error_access_denied();
+    case 'not_found':
+      return m.storage_details_error_not_found();
+    default:
+      return fallback;
+  }
+}
diff --git a/src/lib/storage/storage-fetch.spec.ts b/src/lib/storage/storage-fetch.spec.ts
index 55f51612..6c21c7f1 100644
--- a/src/lib/storage/storage-fetch.spec.ts
+++ b/src/lib/storage/storage-fetch.spec.ts
@@ -18,10 +18,6 @@ beforeEach(() => {
 });
 
 describe('mapStatusToCode', () => {
-  it('maps 401 → not_connected', () => {
-    expect(mapStatusToCode(401)).toBe('not_connected');
-  });
-
   it('maps 403 → access_denied', () => {
     expect(mapStatusToCode(403)).toBe('access_denied');
   });
@@ -150,14 +146,22 @@ describe('createStorageFetch', () => {
     });
   });
 
-  it('throws StorageError on 401 with not_connected code', async () => {
+  it.each([
+    [
+      'a 409 with reason not-connected',
+      409,
+      { message: 'x', reason: 'not-connected' },
+      'not_connected'
+    ],
+    ['an edit conflict', 409, { message: 'Changed on the server' }, 'conflict'],
+    ['an expired session', 401, { message: 'Authentication required' }, 'unknown']
+  ])('maps %s', async (_label, status, body, code) => {
     const storageFetch = createStorageFetch(() => 'conn-1');
-    vi.spyOn(globalThis, 'fetch').mockResolvedValue(makeResponse({ status: 401 }));
+    vi.spyOn(globalThis, 'fetch').mockResolvedValue(
+      makeResponse({ status, body: JSON.stringify(body) })
+    );
 
-    await expect(storageFetch('/api/test')).rejects.toThrow(StorageError);
-    await expect(storageFetch('/api/test')).rejects.toMatchObject({
-      code: 'not_connected'
-    });
+    await expect(storageFetch('/api/test')).rejects.toMatchObject({ code });
   });
 
   it('throws StorageError on 400 with unknown code', async () => {
diff --git a/src/lib/storage/storage-fetch.ts b/src/lib/storage/storage-fetch.ts
index 195d7cd8..34ee924b 100644
--- a/src/lib/storage/storage-fetch.ts
+++ b/src/lib/storage/storage-fetch.ts
@@ -23,7 +23,6 @@ import { StorageError } from '$lib/storage/errors.js';
  * `state.svelte.ts`, `download.ts`, and `upload.ts`.
  */
 export function mapStatusToCode(status: number): string {
-  if (status === 401) return 'not_connected';
   if (status === 403) return 'access_denied';
   if (status === 404) return 'not_found';
   if (status === 409) return 'conflict';
@@ -32,6 +31,22 @@ export function mapStatusToCode(status: number): string {
   return 'unknown';
 }
 
+/**
+ * Whether an error body says the request has no usable storage connection.
+ * The server answers that with 409 and `reason: 'not-connected'`, keeping 401
+ * for an expired session.
+ */
+export function isNotConnectedBody(body: unknown): boolean {
+  return (
+    typeof body === 'object' && body !== null && 'reason' in body && body.reason === 'not-connected'
+  );
+}
+
+/** StorageError code for a failed response, given its parsed body. */
+export function errorCodeFor(status: number, body: unknown): string {
+  return isNotConnectedBody(body) ? 'not_connected' : mapStatusToCode(status);
+}
+
 /**
  * Create a `storageFetch` function bound to a connection-ID getter.
  *
@@ -55,7 +70,11 @@ export function createStorageFetch(
     const response = await fetch(path, { ...init, headers });
 
     if (!response.ok) {
-      const code = mapStatusToCode(response.status);
+      const body: unknown = await response
+        .clone()
+        .json()
+        .catch(() => null);
+      const code = errorCodeFor(response.status, body);
       const message =
         (await readErrorMessage(response)) ?? `Request failed with status ${response.status}`;
       throw new StorageError(code, message);
diff --git a/src/lib/storage/upload.ts b/src/lib/storage/upload.ts
index c7fe2a2e..10c01e75 100644
--- a/src/lib/storage/upload.ts
+++ b/src/lib/storage/upload.ts
@@ -14,7 +14,7 @@
 
 import { STORAGE_CONNECTION_ID_HEADER } from '$lib/storage/connection-id-header.js';
 import { StorageError } from '$lib/storage/errors.js';
-import { createStorageFetch, mapStatusToCode } from '$lib/storage/storage-fetch.js';
+import { createStorageFetch, errorCodeFor } from '$lib/storage/storage-fetch.js';
 
 /**
  * Check whether an object with the given key already exists in the bucket.
@@ -84,7 +84,13 @@ export function uploadFile(
         resolve();
         return;
       }
-      const code = mapStatusToCode(xhr.status);
+      let body: unknown = null;
+      try {
+        body = JSON.parse(xhr.responseText);
+      } catch {
+        // Not a JSON error body, e.g. a proxy's error page.
+      }
+      const code = errorCodeFor(xhr.status, body);
       reject(new StorageError(code, `Upload failed with status ${xhr.status}`));
     });
 
diff --git a/src/routes/(app)/api/storage/archive/extract/+server.ts b/src/routes/(app)/api/storage/archive/extract/+server.ts
index 268a190b..3ddf4442 100644
--- a/src/routes/(app)/api/storage/archive/extract/+server.ts
+++ b/src/routes/(app)/api/storage/archive/extract/+server.ts
@@ -1,4 +1,5 @@
 import { error } from '@sveltejs/kit';
+import { notConnected } from '$lib/server/storage/not-connected.js';
 import {
   ArchiveCacheFullError,
   extractArchiveEntry,
@@ -48,7 +49,7 @@ export const GET: RequestHandler = async (event) => {
   const config = locals.storageConfig;
   const connectionId = locals.storageConnectionId;
   if (!config || !connectionId) {
-    throw error(401, 'No storage connection configured');
+    notConnected();
   }
 
   locals.logger.debug(
diff --git a/src/routes/(app)/api/storage/archive/listing/+server.ts b/src/routes/(app)/api/storage/archive/listing/+server.ts
index 2e3088dd..e125c09c 100644
--- a/src/routes/(app)/api/storage/archive/listing/+server.ts
+++ b/src/routes/(app)/api/storage/archive/listing/+server.ts
@@ -1,4 +1,5 @@
 import { error } from '@sveltejs/kit';
+import { notConnected } from '$lib/server/storage/not-connected.js';
 import { ArchiveCacheFullError, listArchiveContents } from '$lib/server/storage/archive.js';
 import { getProvider } from '$lib/server/storage/utils.js';
 import { requireObjectKey } from '$lib/server/storage/request-context.js';
@@ -33,7 +34,7 @@ export const GET: RequestHandler = async (event) => {
   const config = locals.storageConfig;
   const connectionId = locals.storageConnectionId;
   if (!config || !connectionId) {
-    throw error(401, 'No storage connection configured');
+    notConnected();
   }
 
   locals.logger.debug(
diff --git a/src/routes/(app)/api/storage/buckets/+server.ts b/src/routes/(app)/api/storage/buckets/+server.ts
index 255dfc90..a3b3c9ae 100644
--- a/src/routes/(app)/api/storage/buckets/+server.ts
+++ b/src/routes/(app)/api/storage/buckets/+server.ts
@@ -1,4 +1,5 @@
-import { json, error } from '@sveltejs/kit';
+import { json } from '@sveltejs/kit';
+import { notConnected } from '$lib/server/storage/not-connected.js';
 import type { RequestHandler } from './$types';
 import type { BucketDetails } from '$lib/storage/details-types.js';
 import { getConnectionProvider } from '$lib/server/storage/utils.js';
@@ -33,7 +34,7 @@ export const GET: RequestHandler = async (event) => {
 
   const config = event.locals.storageConfig;
   if (!config) {
-    throw error(401, 'No storage connection configured');
+    notConnected();
   }
 
   const listedBuckets = await withStorageHttpErrors(getConnectionProvider(config)).listContainers();
diff --git a/src/routes/(app)/storage/+layout.ts b/src/routes/(app)/storage/+layout.ts
index 22e81c7a..a52cf79a 100644
--- a/src/routes/(app)/storage/+layout.ts
+++ b/src/routes/(app)/storage/+layout.ts
@@ -1,15 +1,18 @@
 import { browser } from '$app/environment';
 import { STORAGE_CONNECTION_ID_HEADER } from '$lib/storage/connection-id-header.js';
 import { connectionStore } from '$lib/storage/connection-store.svelte.js';
+import { isNotConnectedBody } from '$lib/storage/storage-fetch.js';
 import type { LayoutLoad } from './$types';
 
 /** Why the active connection could not be opened; the connect form shows it. */
 type BucketsError = 'access_denied' | 'unreachable' | null;
 
-// 401: the session holds no usable connection, which is not an error.
-function bucketsErrorFor(status: number): BucketsError {
-  if (status === 401) return null;
-  return status === 403 ? 'access_denied' : 'unreachable';
+// No usable connection is not an error: the connect form is all that is needed.
+// A 401 means the session expired, which the session-expired modal reports.
+async function bucketsErrorFor(res: Response): Promise<BucketsError> {
+  const body: unknown = await res.json().catch(() => null);
+  if (res.status === 401 || isNotConnectedBody(body)) return null;
+  return res.status === 403 ? 'access_denied' : 'unreachable';
 }
 
 const DISCONNECTED = {
@@ -75,7 +78,7 @@ export const load: LayoutLoad = async ({ fetch, data }) => {
     if (!res.ok) {
       return {
         ...DISCONNECTED,
-        bucketsError: bucketsErrorFor(res.status),
+        bucketsError: await bucketsErrorFor(res),
         connections,
         hydrating: false as const,
         hasActiveConnection: false as const
diff --git a/src/routes/(app)/storage/browse/[connection]/[bucket]/[...prefix]/+page.ts b/src/routes/(app)/storage/browse/[connection]/[bucket]/[...prefix]/+page.ts
index e24e6e33..8a1535c0 100644
--- a/src/routes/(app)/storage/browse/[connection]/[bucket]/[...prefix]/+page.ts
+++ b/src/routes/(app)/storage/browse/[connection]/[bucket]/[...prefix]/+page.ts
@@ -5,6 +5,7 @@ import { STORAGE_CONNECTION_ID_HEADER } from '$lib/storage/connection-id-header.
 import * as m from '$lib/paraglide/messages.js';
 import type { PageLoad } from './$types';
 import type { StoragePage } from '$lib/storage/types.js';
+import { isNotConnectedBody } from '$lib/storage/storage-fetch.js';
 
 const EMPTY_PAGE: StoragePage = {
   objects: [],
@@ -13,6 +14,15 @@ const EMPTY_PAGE: StoragePage = {
   pageSize: 25
 };
 
+/** A session or connection problem sends the user back to the connect form. */
+async function throwListError(res: Response, bucket: string): Promise<never> {
+  const body: unknown = await res.json().catch(() => null);
+  if (res.status === 401 || isNotConnectedBody(body)) throw redirect(303, '/storage');
+  if (res.status === 403) throw error(403, m.storage_error_access_denied({ bucket }));
+  const message = (body as { message?: string } | null)?.message;
+  throw error(res.status, message ?? 'Failed to load objects');
+}
+
 /**
  * Universal load: fetches the object list from the API.
  *
@@ -54,12 +64,7 @@ export const load: PageLoad = async ({ fetch, url, data, parent }) => {
       throw err;
     }
 
-    if (!res.ok) {
-      if (res.status === 401) throw redirect(303, '/storage');
-      if (res.status === 403) throw error(403, m.storage_error_access_denied({ bucket }));
-      const body = (await res.json().catch(() => ({}))) as { message?: string };
-      throw error(res.status, body.message ?? 'Failed to load objects');
-    }
+    if (!res.ok) await throwListError(res, bucket);
 
     return { connection, bucket, prefix, objects: EMPTY_PAGE, hydrating: true };
   }
@@ -74,12 +79,7 @@ export const load: PageLoad = async ({ fetch, url, data, parent }) => {
     headers: { [STORAGE_CONNECTION_ID_HEADER]: connectionId }
   });
 
-  if (!res.ok) {
-    if (res.status === 401) throw redirect(303, '/storage');
-    if (res.status === 403) throw error(403, m.storage_error_access_denied({ bucket }));
-    const body = (await res.json().catch(() => ({}))) as { message?: string };
-    throw error(res.status, body.message ?? 'Failed to load objects');
-  }
+  if (!res.ok) await throwListError(res, bucket);
 
   const objects = (await res.json()) as StoragePage;
   return { connection, bucket, prefix, objects, hydrating: false };