Add specific View Scope For Selected Files (#6050)

## Fix 1 — Viewer bug (8 tools)

8 tools called `useFileSelection()` directly instead of routing through
`useBaseTool`. In the viewer, this meant they operated on **all selected
files**
instead of only the one being viewed. For example: 10 files loaded,
viewing
file 3, running Add Stamp — all 10 files got stamped.

**Root cause:** These tools had no view-scope awareness.
`useFileSelection()`
returns the raw workbench selection with no knowledge of which file is
active in
the viewer.

**Fix:** A new hook `useViewScopedFiles` was introduced:

```ts
// Viewer → only the active file
// Everywhere else → all loaded files
const selectedFiles = useViewScopedFiles();
```

The 8 tools were updated to call this instead of `useFileSelection()`.

**Tools fixed:** Add Stamp, Add Watermark, Add Password, Add Page
Numbers,
Add Attachments, Reorganize Pages, OCR, Convert

---

## Fix 2 — Page selector / active files context (all tools)

`useBaseTool` returned `selectedFiles` (checked files only) in
non-viewer
contexts. In the page selector this is typically empty or stale — not
the full
set of loaded files that tools should operate on.

**Fix:** `useBaseTool` was updated to use `useViewScopedFiles`, which
returns
all loaded files in non-viewer contexts. This affected every tool via
`useBaseTool`.

---

## Workarounds for Compare & Merge

Two tools intentionally need all loaded files regardless of view, so
they use
`ignoreViewerScope: true` in `useBaseTool`.

**Compare** — needs exactly 2 files for its Original/Edited slots.
Scoping to
one file would break the comparison entirely. `ignoreViewerScope: true`
is set
and `disableScopeHints: true` hides the "(this file)" button label hint.
The
slot auto-mapping logic was also improved alongside this fix.

**Merge** — needs 2+ files; merging a single file is meaningless. Rather
than
leaving the button silently disabled, Merge now:
- Auto-redirects to the active files view on first open from the viewer
- If the user navigates back to the viewer, shows a disabled button with
a hint
  and a "Go to active files view" shortcut button

---

## How to Test

---

## Fix 1 — 8 tools (viewer scoping)

### Test steps (same for each)
1. Load 3 PDFs into workbench
2. Open viewer, navigate to file 2
3. Open the tool, configure settings, run
4. ✅ Only file 2 is in the results
5. ✅ Button label shows **"[Action] (this file)"**
6. ✅ A note below the button reads **"Only applying to: [filename]"**

| Tool | What to configure |
|---|---|
| **Add Stamp** | Enter any text stamp or upload an image stamp |
| **Add Watermark** | Select text watermark, enter any text |
| **Add Page Numbers** | Leave defaults |
| **Add Password** | Enter any owner + user password |
| **Add Attachments** | Attach any small file |
| **Reorganize Pages** | Enter a page range e.g. `1,2` |
| **OCR** | Leave default language |
| **Convert** | Convert PDF → any format |

---

## Fix 2 — All tools (page selector context)

### Test steps
1. Load 3 PDFs into workbench
2. Open the page selector view 
3. Open any tool from the sidebar, run it
4. ✅ All 3 files are processed (not zero or a stale subset)

---

## Compare (intentionally ignores view scope)

**A — Auto-fill with exactly 2 files**
1. Load exactly 2 PDFs
2. Open Compare from either the viewer or active files view
3. ✅ Both slots are filled automatically (Original + Edited)
4. ✅ No scope hint appears on the button

**B — Manual selection with 3+ files**
1. Load 3+ PDFs
2. Open Compare
3. ✅ The first 2 files fill the slots
4. ✅ A 3rd file does not add a 3rd slot (capped at 2)

**C — File removed mid-session**
1. Load 2 PDFs, let Compare auto-fill both slots
2. Remove one file from the workbench
3. ✅ The corresponding slot clears; the other slot is unchanged

**D — Viewer mode**
1. Load 2 PDFs, open viewer
2. Open Compare from the viewer sidebar
3. ✅ Both files are still available for slot selection (not scoped to
current file)

---

## Merge (intentionally ignores view scope, disabled in viewer)

**A — Auto-redirect on first open from viewer**
1. Load 2+ PDFs, open the viewer
2. Open Merge from the viewer sidebar
3. ✅ Immediately redirected to the active files view

**B — Viewer mode disabled state (after navigating back)**
1. From the active files view, open Merge, then navigate back to the
viewer
2. ✅ Execute button is **disabled** with tooltip "Switch to the file
editor to select multiple files"
3. ✅ A note appears: *"Merge needs 2 or more files. Head to the file
editor to select them."*
4. ✅ A **"Go to active files view"** button is shown; clicking it
navigates back

**C — Active files view works normally**
1. Load 3 PDFs, open Merge from the active files view
2. ✅ All 3 files appear in the merge list
3. ✅ Button shows **"Merge (3 files)"**
4. Run the merge
5. ✅ Output is a single PDF containing all 3 files

---

## Button label behaviour (all tools)

| Context | Expected button text |
|---|---|
| Viewer, 1 file loaded | `[Action]` (no suffix) |
| Viewer, 2+ files loaded | `[Action] (this file)` |
| Active files view, 1 file loaded | `[Action]` (no suffix) |
| Active files view, 2+ files loaded | `[Action] (N files)` |
| Merge in viewer | disabled — no suffix |
| Compare | never shows scope suffix (`disableScopeHints: true`) |

---------

Co-authored-by: Reece Browne <[email protected]>

frontend/public/locales/en-GB/translation.toml

@@ -4422,6 +4422,8 @@ title = "Markdown To PDF"
 submit = "Merge"
 tags = "merge,Page operations,Back end,server side"
 title = "Merge"
+viewerModeHint = "Merge needs 2 or more files. Head to the file editor to select them."
+goToFileEditor = "Go to file editor"
 
 [merge.error]
 failed = "An error occurred while merging the PDFs."
@@ -7523,6 +7525,11 @@ endpointUnavailable = "This tool is unavailable on your server."
 endpointUnavailableClickable = "Not available in this mode. Click to sign in."
 invalidParams = "Fill in the required settings."
 noFiles = "Add a file to get started."
+viewerMode = "Switch to the file editor to select multiple files."
+singleFileScope = "Only applying to: {{fileName}}"
+scopeThisFile = "this file"
+scopeFiles = "files"
+selectFilesHint = "Select files in Active Files to run this tool"
 
 [tools]
 noSearchResults = "No tools found"

frontend/src/core/components/fileEditor/FileEditor.tsx

@@ -52,8 +52,8 @@ const FileEditor = ({
   // Get navigation actions
   const { actions: navActions } = useNavigationActions();
 
-  // Get viewer context for setting active file index
+  // Get viewer context for setting active file index and ID
-  const { setActiveFileIndex } = useViewer();
+  const { setActiveFileIndex, setActiveFileId } = useViewer();
 
   // Get file selection context
   const { setSelectedFiles } = useFileSelection();
@@ -351,12 +351,11 @@ const FileEditor = ({
   const handleViewFile = useCallback((fileId: FileId) => {
     const index = activeStirlingFileStubs.findIndex(r => r.id === fileId);
     if (index !== -1) {
-      // Set the file as selected in context, sync the viewer index, and switch to viewer
+      setActiveFileId(fileId as string);
-      setSelectedFiles([fileId]);
       setActiveFileIndex(index);
       navActions.setWorkbench('viewer');
     }
-  }, [activeStirlingFileStubs, setSelectedFiles, setActiveFileIndex, navActions.setWorkbench]);
+  }, [activeStirlingFileStubs, setActiveFileId, setActiveFileIndex, navActions.setWorkbench]);
 
   const handleLoadFromStorage = useCallback(async (selectedFiles: File[]) => {
     if (selectedFiles.length === 0) return;

frontend/src/core/components/fileEditor/FileEditorThumbnail.tsx

@@ -26,11 +26,11 @@ import { formatFileSize } from '@app/utils/fileUtils';
 import ToolChain from '@app/components/shared/ToolChain';
 import HoverActionMenu, { HoverAction } from '@app/components/shared/HoverActionMenu';
 import { downloadFile } from '@app/services/downloadService';
-import FileEditorFileName from '@app/components/fileEditor/FileEditorFileName';
 import { PrivateContent } from '@app/components/shared/PrivateContent';
 import UploadToServerModal from '@app/components/shared/UploadToServerModal';
 import ShareFileModal from '@app/components/shared/ShareFileModal';
 import { useAppConfig } from '@app/contexts/AppConfigContext';
+import { truncateCenter } from '@app/utils/textUtils';
 
 
 
@@ -461,8 +461,8 @@ const FileEditorThumbnail = ({
         marginTop: '0.5rem',
         marginBottom: '0.5rem',
       }}>
-        <Text  size="lg" fw={700} className={styles.title}  lineClamp={2} style={{ display: 'flex', alignItems: 'center', justifyContent: 'center', gap: '0.25rem' }}>
+        <Text size="lg" fw={700} className={styles.title} title={file.name}>
-          <FileEditorFileName file={file} />
+          <PrivateContent>{truncateCenter(file.name, 40)}</PrivateContent>
         </Text>
         <Text
           size="sm"

frontend/src/core/components/shared/FileDropdownMenu.tsx

@@ -6,16 +6,7 @@ import CloseIcon from '@mui/icons-material/Close';
 import FitText from '@app/components/shared/FitText';
 import { PrivateContent } from '@app/components/shared/PrivateContent';
 import { FileId } from '@app/types/file';
-
+import { truncateCenter } from '@app/utils/textUtils';
-// Truncate text from the center: "very-long-filename.pdf" -> "very-lo...ame.pdf"
-function truncateCenter(text: string, maxLength: number = 25): string {
-  if (text.length <= maxLength) return text;
-  const ellipsis = '...';
-  const charsToShow = maxLength - ellipsis.length;
-  const frontChars = Math.ceil(charsToShow / 2);
-  const backChars = Math.floor(charsToShow / 2);
-  return text.substring(0, frontChars) + ellipsis + text.substring(text.length - backChars);
-}
 
 interface FileDropdownMenuProps {
   displayName: string;

frontend/src/core/components/tools/shared/OperationButton.tsx

@@ -53,6 +53,7 @@ const OperationButton = ({
       : t('tool.endpointUnavailable', 'This tool is unavailable on your server.'),
     noFiles: t('tool.noFiles', 'Add a file to get started.'),
     invalidParams: t('tool.invalidParams', 'Fill in the required settings.'),
+    viewerMode: t('tool.viewerMode', 'Switch to the file editor to select multiple files.'),
   };
 
   const tooltipLabel = blockedByBackend

frontend/src/core/components/tools/shared/ScopedOperationButton.tsx

@@ -0,0 +1,66 @@
+import { Text } from '@mantine/core';
+import { useTranslation } from 'react-i18next';
+import OperationButton, { OperationButtonProps } from '@app/components/tools/shared/OperationButton';
+import { StirlingFile } from '@app/types/fileContext';
+import { useAllFiles } from '@app/contexts/FileContext';
+import { useViewer } from '@app/contexts/ViewerContext';
+import { useNavigationState } from '@app/contexts/NavigationContext';
+
+export interface ScopedOperationButtonProps extends OperationButtonProps {
+  selectedFiles: StirlingFile[];
+  disableScopeHints?: boolean;
+}
+
+/**
+ * Wraps OperationButton with scope-aware button text and a filename note.
+ *
+ * - Viewer mode (multiple files loaded): appends "(this file)" to button text and
+ *   shows a note naming the exact file that will be processed.
+ * - File-editor mode with N>1 selected files: appends "(N files)" to button text.
+ * - File-editor mode with 0 selected files: shows a hint to select files.
+ * - All other cases: no change to button text or layout.
+ */
+export function ScopedOperationButton({ selectedFiles, disableScopeHints, ...props }: ScopedOperationButtonProps) {
+  const { t } = useTranslation();
+  const { workbench } = useNavigationState();
+  const { activeFileIndex } = useViewer();
+  const { files: allFiles } = useAllFiles();
+
+  const isViewerMode = workbench === 'viewer';
+  const isFileEditorMode = workbench === 'fileEditor';
+  const hasMultipleFilesLoaded = allFiles.length > 1;
+  const baseText = props.submitText ?? t('submit', 'Submit');
+
+  const disabledForViewerMode = props.disabledReason === 'viewerMode';
+
+  let scopedText = baseText;
+  if (!disableScopeHints && !disabledForViewerMode) {
+    if (isViewerMode && hasMultipleFilesLoaded) {
+      scopedText = `${baseText} (${t('tool.scopeThisFile', 'this file')})`;
+    } else if (!isViewerMode && selectedFiles.length > 1) {
+      scopedText = `${baseText} (${selectedFiles.length} ${t('tool.scopeFiles', 'files')})`;
+    }
+  }
+
+  const viewerFileName = !disableScopeHints && !disabledForViewerMode && isViewerMode && hasMultipleFilesLoaded
+    ? allFiles[activeFileIndex]?.name
+    : null;
+
+  const showSelectFilesHint = !disableScopeHints && isFileEditorMode && allFiles.length > 0 && selectedFiles.length === 0;
+
+  return (
+    <>
+      <OperationButton {...props} submitText={scopedText} />
+      {viewerFileName && (
+        <Text size="xs" c="dimmed" ta="center" mx="md" mt={2}>
+          {t('tool.singleFileScope', 'Only applying to: {{fileName}}', { fileName: viewerFileName })}
+        </Text>
+      )}
+      {showSelectFilesHint && (
+        <Text size="xs" c="dimmed" ta="center" mx="md" mt={2}>
+          {t('tool.selectFilesHint', 'Select files in Active Files to run this tool')}
+        </Text>
+      )}
+    </>
+  );
+}

frontend/src/core/components/tools/shared/createToolFlow.tsx

@@ -1,7 +1,7 @@
 import React from 'react';
 import { Stack } from '@mantine/core';
 import { createToolSteps, ToolStepProvider } from '@app/components/tools/shared/ToolStep';
-import OperationButton from '@app/components/tools/shared/OperationButton';
+import { ScopedOperationButton } from '@app/components/tools/shared/ScopedOperationButton';
 import { ToolOperationHook } from '@app/hooks/tools/shared/useToolOperation';
 import { ToolWorkflowTitle, ToolWorkflowTitleProps } from '@app/components/tools/shared/ToolWorkflowTitle';
 import { StirlingFile } from '@app/types/fileContext';
@@ -57,6 +57,8 @@ export interface ExecuteButtonConfig {
   disabled?: boolean;
   testId?: string;
   showCloudBadge?: boolean;
+  /** Suppress the automatic "(this file)" / "(N files)" scope hints in the button text. */
+  disableScopeHints?: boolean;
 }
 
 export interface ReviewStepConfig<TParams = unknown> {
@@ -77,6 +79,8 @@ export interface ToolFlowConfig<TParams = unknown> {
   // Optional preview content rendered between steps and the execute button
   preview?: React.ReactNode;
   executeButton?: ExecuteButtonConfig;
+  /** Optional content rendered immediately below the execute button (e.g. contextual help). */
+  belowExecuteButton?: React.ReactNode;
   review: ReviewStepConfig<TParams>;
   forceStepNumbers?: boolean;
 }
@@ -128,7 +132,10 @@ export function createToolFlow<TParams = unknown>(config: ToolFlowConfig<TParams
             : eb.paramsValid === false       ? 'invalidParams'
             : null;
           return (
-            <OperationButton
+            <>
+              <ScopedOperationButton
+                selectedFiles={config.files.selectedFiles ?? []}
+                disableScopeHints={eb.disableScopeHints}
                 onClick={eb.onClick}
                 isLoading={config.review.operation.isLoading}
                 disabled={eb.disabled}
@@ -139,6 +146,8 @@ export function createToolFlow<TParams = unknown>(config: ToolFlowConfig<TParams
                 data-testid={eb.testId}
                 data-tour="run-button"
               />
+              {config.belowExecuteButton}
+            </>
           );
         })()}
 

frontend/src/core/components/viewer/EmbedPdfViewer.tsx

@@ -176,8 +176,6 @@ const EmbedPdfViewerContent = ({
   // Similar to scroll preservation - track rotation across file reloads
   const pendingRotationRestoreRef = useRef<number | null>(null);
   const rotationRestoreAttemptsRef = useRef<number>(0);
-  // Track the file ID we should be viewing after a save (to handle list reordering)
-  const pendingFileIdRef = useRef<string | null>(null);
 
   const formApplyInProgressRef = useRef(false);
 
@@ -188,11 +186,12 @@ const EmbedPdfViewerContent = ({
   const redactionTrackerRef = useRef<RedactionPendingTrackerAPI>(null);
 
   // Get current file from FileContext
-  const { selectors, state } = useFileState();
+  const { selectors } = useFileState();
   const { actions } = useFileActions();
   const activeFiles = selectors.getFiles();
+  const activeFilesRef = useRef(activeFiles);
+  activeFilesRef.current = activeFiles;
   const activeFileIds = activeFiles.map(f => f.fileId);
-  const selectedFileIds = state.ui.selectedFileIds;
 
   // Navigation guard for unsaved changes
   const { setHasUnsavedChanges, registerUnsavedChangesChecker, unregisterUnsavedChangesChecker, registerNavigationWarningHandlers, unregisterNavigationWarningHandlers } = useNavigationGuard();
@@ -277,41 +276,46 @@ const EmbedPdfViewerContent = ({
   const [internalActiveFileIndex, setInternalActiveFileIndex] = useState(0);
   const activeFileIndex = externalActiveFileIndex ?? internalActiveFileIndex;
   const setActiveFileIndex = externalSetActiveFileIndex ?? setInternalActiveFileIndex;
-  const hasInitializedFromSelection = useRef(false);
 
-  // When viewer opens with a selected file, switch to that file
+  // activeFileId (from ViewerContext) is the stable source of truth.
+  // We derive activeFileIndex from it so reorders after tool operations don't lose the viewed file.
+  const { activeFileId, setActiveFileId } = useViewer();
+
+  // Stable string key representing the current file list order.
+  // Using a joined ID string avoids depending on the activeFiles array reference,
+  // which is a new object every render and would cause an infinite effect loop.
+  const fileIdsKey = activeFiles.map(f => f.fileId).join(',');
+
+  // When the file list actually changes, re-derive activeFileIndex from the stable activeFileId.
   useEffect(() => {
-    if (!hasInitializedFromSelection.current && selectedFileIds.length > 0 && activeFiles.length > 0) {
+    if (!activeFileId || activeFiles.length === 0) return;
-      const selectedFileId = selectedFileIds[0];
+    const newIndex = activeFiles.findIndex(f => f.fileId === activeFileId);
-      const index = activeFiles.findIndex(f => f.fileId === selectedFileId);
+    if (newIndex !== -1 && newIndex !== activeFileIndex) {
-      if (index !== -1 && index !== activeFileIndex) {
+      setActiveFileIndex(newIndex);
-        setActiveFileIndex(index);
     }
-      hasInitializedFromSelection.current = true;
+  }, [fileIdsKey, activeFileId]); // stable primitives — no infinite loop
-    }
-  }, [selectedFileIds, activeFiles, activeFileIndex]);
 
-  // Reset active tab if it's out of bounds
+  // When the user manually switches file tabs, keep activeFileId in sync.
+  // Skips the initial mount to avoid overwriting an activeFileId set by handleViewFile.
+  const activeFileIndexMountedRef = useRef(false);
+  useEffect(() => {
+    if (!activeFileIndexMountedRef.current) {
+      activeFileIndexMountedRef.current = true;
+      return;
+    }
+    const fileId = activeFilesRef.current[activeFileIndex]?.fileId;
+    if (fileId && fileId !== activeFileId) {
+      setActiveFileId(fileId);
+    }
+  }, [activeFileIndex]);
+
+  // Reset active tab if it's out of bounds (safety net)
   useEffect(() => {
     if (activeFileIndex >= activeFiles.length && activeFiles.length > 0) {
       setActiveFileIndex(0);
     }
   }, [activeFiles.length, activeFileIndex]);
 
-  // After saving a file, the list may reorder (sorted by version).
-  // Track the saved file's ID and update activeFileIndex to follow it.
-  useEffect(() => {
-    if (pendingFileIdRef.current && activeFiles.length > 0) {
-      const targetFileId = pendingFileIdRef.current;
-      const newIndex = activeFiles.findIndex(f => f.fileId === targetFileId);
-      if (newIndex !== -1 && newIndex !== activeFileIndex) {
-        setActiveFileIndex(newIndex);
-      }
-      // Clear the pending file ID once we've found and switched to it
-      pendingFileIdRef.current = null;
-    }
-  }, [activeFiles, activeFileIndex, setActiveFileIndex]);
-
   // Determine which file to display
   const currentFile = React.useMemo(() => {
     if (previewFile) {
@@ -627,11 +631,9 @@ const EmbedPdfViewerContent = ({
       // Store the rotation to restore after file replacement
       pendingRotationRestoreRef.current = currentRotation;
       rotationRestoreAttemptsRef.current = 0;
-      // Store the new file ID so we can track it after the list reorders
+      // Track the new file ID so the viewer follows it after the list reorders
       const newFileId = stubs[0]?.id;
-      if (newFileId) {
+      if (newFileId) setActiveFileId(newFileId);
-        pendingFileIdRef.current = newFileId;
-      }
 
       // Step 4: Consume only the current file (replace in context)
       await actions.consumeFiles([currentFileId], stirlingFiles, stubs);
@@ -682,11 +684,9 @@ const EmbedPdfViewerContent = ({
       pendingRotationRestoreRef.current = currentRotation;
       rotationRestoreAttemptsRef.current = 0;
 
-      // Store the new file ID for tracking
+      // Track the new file ID so the viewer follows it after the list reorders
       const newFileId = stubs[0]?.id;
-      if (newFileId) {
+      if (newFileId) setActiveFileId(newFileId);
-        pendingFileIdRef.current = newFileId;
-      }
 
       // Replace the current file in context
       await actions.consumeFiles([currentFileId], stirlingFiles, stubs);
@@ -738,9 +738,7 @@ const EmbedPdfViewerContent = ({
       rotationRestoreAttemptsRef.current = 0;
 
       const newFileId = stubs[0]?.id;
-      if (newFileId) {
+      if (newFileId) setActiveFileId(newFileId);
-        pendingFileIdRef.current = newFileId;
-      }
 
       await actions.consumeFiles([currentFileId], stirlingFiles, stubs);
     } catch (error) {

frontend/src/core/contexts/NavigationContext.tsx

@@ -260,9 +260,11 @@ export const NavigationProvider: React.FC<{
           return;
         }
 
-        // Look up the tool in the registry to get its proper workbench
+        // Look up the tool in the registry to get its proper workbench.
+        // Regular tools have no workbench preference — keep the current view so
+        // opening a tool doesn't unexpectedly switch the user to the viewer.
         const tool = isValidToolId(toolId) ? toolRegistry[toolId] : null;
-        const workbench = tool ? (tool.workbench || getDefaultWorkbench()) : getDefaultWorkbench();
+        const workbench = (tool && tool.workbench) ? tool.workbench : state.workbench;
 
         // Validate toolId and convert to ToolId type
         const validToolId = isValidToolId(toolId) ? toolId : null;

frontend/src/core/contexts/ToolWorkflowContext.tsx

@@ -317,14 +317,12 @@ export function ToolWorkflowProvider({ children }: ToolWorkflowProviderProps) {
     const validToolId = isValidToolId(toolId) ? toolId : null;
     actions.setSelectedTool(validToolId);
 
-    // Get the tool from registry to determine workbench
+    // Switch workbench only when required: leaving a custom view, or the tool declares one.
     const tool = getSelectedTool(toolId);
     if (wasInCustomWorkbench) {
       actions.setWorkbench(getDefaultWorkbench());
     } else if (tool && tool.workbench) {
       actions.setWorkbench(tool.workbench);
-    } else {
-      actions.setWorkbench(getDefaultWorkbench());
     }
 
     // Clear search query when selecting a tool
@@ -342,8 +340,6 @@ export function ToolWorkflowProvider({ children }: ToolWorkflowProviderProps) {
       actions.setWorkbench(getDefaultWorkbench());
     } else if (tool && tool.workbench) {
       actions.setWorkbench(tool.workbench);
-    } else {
-      actions.setWorkbench(getDefaultWorkbench());
     }
     setSearchQuery('');
     setLeftPanelView('toolContent');

frontend/src/core/contexts/ViewerContext.tsx

@@ -120,7 +120,9 @@ export interface ViewerContextType {
   isAnnotationMode: boolean;
   setAnnotationMode: (enabled: boolean) => void;
 
-  // Active file index for multi-file viewing
+  // Active file tracking — ID is the stable source of truth; index is derived from it
+  activeFileId: string | null;
+  setActiveFileId: (id: string | null) => void;
   activeFileIndex: number;
   setActiveFileIndex: (index: number) => void;
 
@@ -204,6 +206,7 @@ export const ViewerProvider: React.FC<ViewerProviderProps> = ({ children }) => {
   const [isSearchInterfaceVisible, setSearchInterfaceVisible] = useState(false);
   const [isAnnotationsVisible, setIsAnnotationsVisible] = useState(true);
   const [isAnnotationMode, setIsAnnotationModeState] = useState(false);
+  const [activeFileId, setActiveFileId] = useState<string | null>(null);
   const [activeFileIndex, setActiveFileIndex] = useState(0);
   const [pdfRenderMode, setPdfRenderModeState] = useState<PdfRenderMode>(
     () => preferencesService.getPreference('pdfRenderMode')
@@ -485,7 +488,9 @@ export const ViewerProvider: React.FC<ViewerProviderProps> = ({ children }) => {
     isAnnotationMode,
     setAnnotationMode,
 
-    // Active file index
+    // Active file tracking
+    activeFileId,
+    setActiveFileId,
     activeFileIndex,
     setActiveFileIndex,
 

frontend/src/core/hooks/tools/overlayPdfs/useOverlayPdfsParameters.ts

@@ -1,3 +1,4 @@
+import { useCallback } from 'react';
 import { BaseParameters } from '@app/types/parameters';
 import { useBaseParameters, type BaseParametersHook } from '@app/hooks/tools/shared/useBaseParameters';
 
@@ -20,7 +21,7 @@ export const defaultParameters: OverlayPdfsParameters = {
 export type OverlayPdfsParametersHook = BaseParametersHook<OverlayPdfsParameters>;
 
 export const useOverlayPdfsParameters = (): OverlayPdfsParametersHook => {
-  return useBaseParameters<OverlayPdfsParameters>({
+  const base = useBaseParameters<OverlayPdfsParameters>({
     defaultParameters,
     endpointName: 'overlay-pdfs',
     validateFn: (params) => {
@@ -32,6 +33,18 @@ export const useOverlayPdfsParameters = (): OverlayPdfsParametersHook => {
       return true;
     },
   });
+
+  // Overlay files are chosen independently of the base file selection, so they
+  // must survive the parameter reset that fires when the workbench selection
+  // transitions from 0 → 1+ files. Only mode/position/counts are reset.
+  const resetParameters = useCallback(() => {
+    base.setParameters(prev => ({
+      ...defaultParameters,
+      overlayFiles: prev.overlayFiles,
+    }));
+  }, [base.setParameters]);
+
+  return { ...base, resetParameters };
 };
 
 

frontend/src/core/hooks/tools/shared/toolOperationTypes.ts

@@ -19,6 +19,7 @@ export type ExecuteDisabledReason =
   | 'endpointUnavailable'
   | 'noFiles'
   | 'invalidParams'
+  | 'viewerMode'
   | null;
 
 /**

frontend/src/core/hooks/tools/shared/useBaseTool.ts

@@ -1,6 +1,6 @@
 import { useEffect, useCallback, useRef } from 'react';
-import { useFileSelection } from '@app/contexts/FileContext';
 import { useEndpointEnabled } from '@app/hooks/useEndpointConfig';
+import { useViewScopedFiles } from '@app/hooks/tools/shared/useViewScopedFiles';
 import { BaseToolProps } from '@app/types/tool';
 import { ToolOperationHook } from '@app/hooks/tools/shared/useToolOperation';
 import { BaseParametersHook } from '@app/hooks/tools/shared/useBaseParameters';
@@ -38,14 +38,24 @@ export function useBaseTool<TParams, TParamsHook extends BaseParametersHook<TPar
   useParams: () => TParamsHook,
   useOperation: () => ToolOperationHook<TParams>,
   props: BaseToolProps,
-  options?: { minFiles?: number }
+  options?: {
+    minFiles?: number;
+    /** When true, uses the full file selection rather than the viewer-scoped single file. */
+    ignoreViewerScope?: boolean;
+  }
 ): BaseToolReturn<TParams, TParamsHook> {
   const minFiles = options?.minFiles ?? 1;
+  const ignoreViewerScope = options?.ignoreViewerScope ?? false;
   const { onPreviewFile, onComplete, onError } = props;
 
-  // File selection
+  const viewerScopedFiles = useViewScopedFiles(ignoreViewerScope);
-  const { selectedFiles } = useFileSelection();
+
-  const previousFileCount = useRef(selectedFiles.length);
+  // In viewer mode: scope to the single displayed file (unless ignoreViewerScope).
+  // In fileEditor with a selection: scope to the selected files.
+  // All other cases (pageEditor, custom, no selection): use all loaded files.
+  const effectiveFiles = viewerScopedFiles;
+
+  const previousFileCount = useRef(effectiveFiles.length);
 
   // Prevent reset immediately after operation completes (when consumeFiles auto-selects outputs)
   const skipNextSelectionResetRef = useRef(false);
@@ -59,7 +69,7 @@ export function useBaseTool<TParams, TParamsHook extends BaseParametersHook<TPar
   const { enabled: endpointEnabled, loading: endpointLoading } = useEndpointEnabled(params.getEndpointName());
 
   // Standard computed state - defined early so it's available in useEffects
-  const hasFiles = selectedFiles.length >= minFiles;
+  const hasFiles = effectiveFiles.length >= minFiles;
   const hasResults = operation.files.length > 0 || operation.downloadUrl !== null;
   const settingsCollapsed = !hasFiles || hasResults;
 
@@ -77,13 +87,13 @@ export function useBaseTool<TParams, TParamsHook extends BaseParametersHook<TPar
     }
   }, [hasResults]);
 
-  // Reset results when user manually changes file selection
+  // Reset results when effective files change (viewer file switch or selection change)
   useEffect(() => {
-    if (selectedFiles.length === 0) return;
+    if (effectiveFiles.length === 0) return;
 
-    const currentSelection = selectedFiles.map(f => f.fileId).sort().join(',');
+    const currentSelection = effectiveFiles.map(f => f.fileId).sort().join(',');
 
-    if (currentSelection === previousSelectionRef.current) return; // No change
+    if (currentSelection === previousSelectionRef.current) return;
 
     // Skip reset if this is the auto-selection after operation completed
     if (skipNextSelectionResetRef.current) {
@@ -92,15 +102,14 @@ export function useBaseTool<TParams, TParamsHook extends BaseParametersHook<TPar
       return;
     }
 
-    // User manually selected different files - reset results
     previousSelectionRef.current = currentSelection;
     operation.resetResults();
     onPreviewFile?.(null);
-  }, [selectedFiles]);
+  }, [effectiveFiles]);
 
   // Reset parameters when transitioning from 0 files to at least 1 file
   useEffect(() => {
-    const currentFileCount = selectedFiles.length;
+    const currentFileCount = effectiveFiles.length;
     const prevFileCount = previousFileCount.current;
 
     if (prevFileCount === 0 && currentFileCount > 0) {
@@ -108,12 +117,12 @@ export function useBaseTool<TParams, TParamsHook extends BaseParametersHook<TPar
     }
 
     previousFileCount.current = currentFileCount;
-  }, [selectedFiles.length]);
+  }, [effectiveFiles.length]);
 
   // Standard handlers
   const handleExecute = useCallback(async () => {
     try {
-      await operation.executeOperation(params.parameters, selectedFiles);
+      await operation.executeOperation(params.parameters, effectiveFiles);
       if (operation.files && onComplete) {
         onComplete(operation.files);
       }
@@ -123,7 +132,7 @@ export function useBaseTool<TParams, TParamsHook extends BaseParametersHook<TPar
         onError(message);
       }
     }
-  }, [operation, params.parameters, selectedFiles, onComplete, onError, toolName]);
+  }, [operation, params.parameters, effectiveFiles, onComplete, onError, toolName]);
 
   const handleThumbnailClick = useCallback((file: File) => {
     onPreviewFile?.(file);
@@ -143,7 +152,7 @@ export function useBaseTool<TParams, TParamsHook extends BaseParametersHook<TPar
 
   return {
     // File management
-    selectedFiles,
+    selectedFiles: effectiveFiles,
 
     // Tool-specific hooks
     params,

frontend/src/core/hooks/tools/shared/useToolOperation.ts

@@ -1,8 +1,9 @@
-import { useCallback, useRef, useEffect } from 'react';
+import { useCallback, useRef, useEffect, useContext } from 'react';
 import apiClient from '@app/services/apiClient';
 import { useTranslation } from 'react-i18next';
 import { useFileContext } from '@app/contexts/FileContext';
 import { useNavigationActions } from '@app/contexts/NavigationContext';
+import { ViewerContext } from '@app/contexts/ViewerContext';
 import { useToolState } from '@app/hooks/tools/shared/useToolState';
 import { useToolApiCalls, type ApiCallsConfig } from '@app/hooks/tools/shared/useToolApiCalls';
 import { useToolResources } from '@app/hooks/tools/shared/useToolResources';
@@ -63,6 +64,8 @@ export const useToolOperation = <TParams>(
   const { t } = useTranslation();
   const { addFiles, consumeFiles, undoConsumeFiles, selectors } = useFileContext();
   const { actions: navActions } = useNavigationActions();
+  const viewerContext = useContext(ViewerContext);
+  const setActiveFileId = viewerContext?.setActiveFileId ?? (() => {});
 
   // Composed hooks
   const { state, actions } = useToolState();
@@ -348,6 +351,9 @@ export const useToolOperation = <TParams>(
           const toConsumeInputIds = successSourceIds.filter((id) => inputFileIds.includes(id));
           console.debug('[useToolOperation] Consuming files (version)', { inputCount: inputFileIds.length, toConsume: toConsumeInputIds.length });
           const outputFileIds = await consumeFiles(toConsumeInputIds, outputStirlingFiles, outputStirlingFileStubs);
+          // Tell the viewer to follow the replacement file — consumeFiles prepends the new file
+          // to the list, so activeFileIndex would point to the wrong file without this.
+          if (outputFileIds.length === 1) setActiveFileId(outputFileIds[0]);
 
           // Notify on desktop when processing completes
           await notifyPdfProcessingComplete(outputFileIds.length);

frontend/src/core/hooks/tools/shared/useViewScopedFiles.ts

@@ -0,0 +1,32 @@
+import { useMemo } from 'react';
+import { useAllFiles, useSelectedFiles } from '@app/contexts/FileContext';
+import { useViewer } from '@app/contexts/ViewerContext';
+import { useNavigationState } from '@app/contexts/NavigationContext';
+import { StirlingFile } from '@app/types/fileContext';
+
+/**
+ * Returns the effective file set for tool operations.
+ *
+ * - Viewer: scopes to the single file currently shown, unless ignoreViewerScope is true.
+ * - FileEditor: scopes to the selected subset (empty selection → empty → button disabled).
+ * - PageEditor / custom workbenches: returns all loaded files (selection tracks pages, not files).
+ */
+export function useViewScopedFiles(ignoreViewerScope = false): StirlingFile[] {
+  const { activeFileIndex } = useViewer();
+  const { files: allFiles } = useAllFiles();
+  const { workbench } = useNavigationState();
+  const { selectedFiles } = useSelectedFiles();
+
+  return useMemo(() => {
+    if (workbench === 'viewer' && !ignoreViewerScope) {
+      const viewerFile = allFiles[activeFileIndex];
+      return viewerFile ? [viewerFile] : allFiles;
+    }
+
+    if (workbench === 'fileEditor') {
+      return selectedFiles;
+    }
+
+    return allFiles;
+  }, [workbench, allFiles, activeFileIndex, selectedFiles, ignoreViewerScope]);
+}

frontend/src/core/tools/AddAttachments.tsx

@@ -1,6 +1,6 @@
 import { useEffect } from "react";
 import { useTranslation } from "react-i18next";
-import { useFileSelection } from "@app/contexts/FileContext";
+import { useViewScopedFiles } from "@app/hooks/tools/shared/useViewScopedFiles";
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 import { BaseToolProps, ToolComponent } from "@app/types/tool";
 import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
@@ -12,7 +12,7 @@ import { useAddAttachmentsTips } from "@app/components/tooltips/useAddAttachment
 
 const AddAttachments = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
   const { t } = useTranslation();
-  const { selectedFiles } = useFileSelection();
+  const selectedFiles = useViewScopedFiles();
   const addAttachmentsTips = useAddAttachmentsTips();
 
   const params = useAddAttachmentsParameters();

frontend/src/core/tools/AddPageNumbers.tsx

@@ -1,6 +1,6 @@
 import { useEffect } from "react";
 import { useTranslation } from "react-i18next";
-import { useFileSelection } from "@app/contexts/FileContext";
+import { useViewScopedFiles } from "@app/hooks/tools/shared/useViewScopedFiles";
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 import { BaseToolProps, ToolComponent } from "@app/types/tool";
 import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
@@ -12,7 +12,7 @@ import AddPageNumbersAppearanceSettings from "@app/components/tools/addPageNumbe
 
 const AddPageNumbers = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
   const { t } = useTranslation();
-  const { selectedFiles } = useFileSelection();
+  const selectedFiles = useViewScopedFiles();
 
   const params = useAddPageNumbersParameters();
   const operation = useAddPageNumbersOperation();

frontend/src/core/tools/AddPassword.tsx

@@ -1,7 +1,7 @@
 import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
-import { useFileSelection } from "@app/contexts/FileContext";
+import { useViewScopedFiles } from "@app/hooks/tools/shared/useViewScopedFiles";
 
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 
@@ -16,7 +16,7 @@ import { BaseToolProps, ToolComponent } from "@app/types/tool";
 
 const AddPassword = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
   const { t } = useTranslation();
-  const { selectedFiles } = useFileSelection();
+  const selectedFiles = useViewScopedFiles();
 
   const [collapsedPermissions, setCollapsedPermissions] = useState(true);
 

frontend/src/core/tools/AddStamp.tsx

@@ -1,9 +1,9 @@
 import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
-import { useFileSelection } from "@app/contexts/FileContext";
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 import { BaseToolProps, ToolComponent } from "@app/types/tool";
 import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
+import { useViewScopedFiles } from "@app/hooks/tools/shared/useViewScopedFiles";
 import { useAddStampParameters } from "@app/components/tools/addStamp/useAddStampParameters";
 import { useAddStampOperation } from "@app/components/tools/addStamp/useAddStampOperation";
 import { Stack, Text } from "@mantine/core";
@@ -17,7 +17,7 @@ import StampPositionFormattingSettings from "@app/components/tools/addStamp/Stam
 
 const AddStamp = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
   const { t } = useTranslation();
-  const { selectedFiles } = useFileSelection();
+  const selectedFiles = useViewScopedFiles();
 
   const [quickPositionModeSelected, setQuickPositionModeSelected] = useState(false);
   const [customPositionModeSelected, setCustomPositionModeSelected] = useState(true);

frontend/src/core/tools/AddWatermark.tsx

@@ -1,7 +1,7 @@
 import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
-import { useFileSelection } from "@app/contexts/FileContext";
+import { useViewScopedFiles } from "@app/hooks/tools/shared/useViewScopedFiles";
 
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 
@@ -24,7 +24,7 @@ import { BaseToolProps, ToolComponent } from "@app/types/tool";
 
 const AddWatermark = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
   const { t } = useTranslation();
-  const { selectedFiles } = useFileSelection();
+  const selectedFiles = useViewScopedFiles();
 
   const [collapsedType, setCollapsedType] = useState(false);
   const [collapsedStyle, setCollapsedStyle] = useState(true);

frontend/src/core/tools/Compare.tsx

@@ -23,9 +23,9 @@ import type { FileId } from '@app/types/file';
 import type { StirlingFile } from '@app/types/fileContext';
 import DocumentThumbnail from '@app/components/shared/filePreview/DocumentThumbnail';
 import type { CompareWorkbenchData } from '@app/types/compare';
-import FitText from '@app/components/shared/FitText';
 import { getDefaultWorkbench } from '@app/types/workbench';
 import { useFilesModalContext } from '@app/contexts/FilesModalContext';
+import { truncateCenter } from '@app/utils/textUtils';
 
 const CUSTOM_VIEW_ID = 'compareWorkbenchView';
 const CUSTOM_WORKBENCH_ID = 'custom:compareWorkbenchView' as const;
@@ -48,7 +48,7 @@ const Compare = (props: BaseToolProps) => {
     useCompareParameters,
     useCompareOperation,
     props,
-    { minFiles: 2 }
+    { minFiles: 2, ignoreViewerScope: true }
   );
 
   const operation = base.operation as CompareOperationHook;
@@ -93,33 +93,57 @@ const Compare = (props: BaseToolProps) => {
   // Register once; avoid re-registering on translation/prop changes which clears data mid-flight
   }, []);
 
-  // Auto-map from workbench selection: always reflect the first two selected files in order.
+  // On mount: clear selections unless exactly 2 files are loaded.
-  // This also handles deselection by promoting the remaining selection to base and clearing comparison.
   useEffect(() => {
-    // Use selected IDs directly from state so it works even if File objects aren't loaded yet
+    if ((fileState.files.ids as FileId[]).length !== 2) {
-    const selectedIds = (fileState.ui.selectedFileIds as FileId[]) ?? [];
+      fileActions.clearSelections();
+    }
+  }, []);
 
-    // Determine next base: keep current if still selected; otherwise use the first selected id
+  // Track previous file count to detect the transition to exactly 2 files.
-    const nextBase: FileId | null = params.baseFileId && selectedIds.includes(params.baseFileId)
+  const prevAllIdsLengthRef = useRef<number | null>(null);
-      ? (params.baseFileId as FileId)
-      : (selectedIds[0] ?? null);
 
-    // Determine next comparison: keep current if still selected and distinct; otherwise use the first other selected id
+  // Auto-fill slots when the file count first reaches 2; respect manual picker changes after that.
-    let nextComp: FileId | null = null;
+  useEffect(() => {
-    if (params.comparisonFileId && selectedIds.includes(params.comparisonFileId) && params.comparisonFileId !== nextBase) {
+    const selectedIds = fileState.ui.selectedFileIds as FileId[];
-      nextComp = params.comparisonFileId as FileId;
+    const allIds = fileState.files.ids as FileId[];
-    } else {
+    const prevLength = prevAllIdsLengthRef.current;
-      nextComp = (selectedIds.find(id => id !== nextBase) ?? null) as FileId | null;
+    prevAllIdsLengthRef.current = allIds.length;
+
+    if (allIds.length === 2 && prevLength !== 2) {
+      // Transitioned to exactly 2 files — auto-fill both slots.
+      const [firstId, secondId] = allIds as [FileId, FileId];
+      fileActions.setSelectedFiles([firstId, secondId]);
+      base.params.setParameters(prev => {
+        if (prev.baseFileId === firstId && prev.comparisonFileId === secondId) return prev;
+        return { ...prev, baseFileId: firstId, comparisonFileId: secondId };
+      });
+      return;
     }
 
-    if (nextBase !== params.baseFileId || nextComp !== params.comparisonFileId) {
+    if (selectedIds.length > 2) {
-      base.params.setParameters(prev => ({
+      fileActions.setSelectedFiles(selectedIds.slice(0, 2) as FileId[]);
-        ...prev,
+      return;
-        baseFileId: nextBase,
-        comparisonFileId: nextComp,
-      }));
     }
-  }, [fileState.ui.selectedFileIds, base.params, params.baseFileId, params.comparisonFileId]);
+
+    const nextBase = (selectedIds[0] ?? null) as FileId | null;
+    const nextComp = (selectedIds[1] ?? null) as FileId | null;
+    base.params.setParameters(prev => {
+      if (prev.baseFileId === nextBase && prev.comparisonFileId === nextComp) return prev;
+      return { ...prev, baseFileId: nextBase, comparisonFileId: nextComp };
+    });
+  }, [fileState.ui.selectedFileIds, fileState.files.ids]);
+
+  // Clear a slot if its file is removed from the workbench.
+  useEffect(() => {
+    const allIds = fileState.files.ids as FileId[];
+    if (params.baseFileId && !allIds.includes(params.baseFileId as FileId)) {
+      base.params.setParameters(prev => ({ ...prev, baseFileId: null }));
+    }
+    if (params.comparisonFileId && !allIds.includes(params.comparisonFileId as FileId)) {
+      base.params.setParameters(prev => ({ ...prev, comparisonFileId: null }));
+    }
+  }, [fileState.files.ids]);
 
   // Track workbench data and drive loading/result state transitions
   const lastProcessedAtRef = useRef<number | null>(null);
@@ -397,14 +421,10 @@ const Compare = (props: BaseToolProps) => {
               <Box className="compare-tool__thumbnail" style={{ alignSelf: 'center' }}>
                 <DocumentThumbnail file={stub ?? null} thumbnail={stub?.thumbnailUrl || null} />
               </Box>
-              <Stack className="compare-tool__details">
+              <Stack className="compare-tool__details" style={{ minWidth: 0, overflow: 'hidden', flex: 1 }}>
-                <FitText 
+                <Text fw={600} title={stub?.name}>
-                  text={stub?.name || ''} 
+                  {truncateCenter(stub?.name || '', 50)}
-                  minimumFontScale={0.8} 
+                </Text>
-                  lines={3}
-                  style={{ fontWeight: 600
-                  }}
-                />
                 {pageCount && dateText && (
                   <>
                   <Text size="xs" c="dimmed" style={{ whiteSpace: 'nowrap', overflow: 'hidden', textOverflow: 'ellipsis' }}>
@@ -576,6 +596,7 @@ const Compare = (props: BaseToolProps) => {
       onClick: handleExecuteCompare,
       disabled: !canExecute,
       testId: 'compare-execute',
+      disableScopeHints: true,
     },
     review: {
       isVisible: false,

frontend/src/core/tools/Convert.tsx

@@ -1,7 +1,8 @@
 import { useEffect, useRef } from "react";
 import { useTranslation } from "react-i18next";
 import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
-import { useFileState, useFileSelection } from "@app/contexts/FileContext";
+import { useFileState } from "@app/contexts/FileContext";
+import { useViewScopedFiles } from "@app/hooks/tools/shared/useViewScopedFiles";
 
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 
@@ -15,7 +16,7 @@ const Convert = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
   const { t } = useTranslation();
   const { selectors } = useFileState();
   const activeFiles = selectors.getFiles();
-  const { selectedFiles } = useFileSelection();
+  const selectedFiles = useViewScopedFiles();
   const scrollContainerRef = useRef<HTMLDivElement>(null);
 
   const convertParams = useConvertParameters();

frontend/src/core/tools/Merge.tsx

@@ -1,5 +1,6 @@
-import { useCallback } from "react";
+import { useCallback, useEffect, useRef } from "react";
 import { useTranslation } from "react-i18next";
+import { Button, Stack, Text } from "@mantine/core";
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 import MergeSettings from "@app/components/tools/merge/MergeSettings";
 import MergeFileSorter from "@app/components/tools/merge/MergeFileSorter";
@@ -9,6 +10,7 @@ import { useBaseTool } from "@app/hooks/tools/shared/useBaseTool";
 import { BaseToolProps, ToolComponent } from "@app/types/tool";
 import { useMergeTips } from "@app/components/tooltips/useMergeTips";
 import { useFileManagement, useSelectedFiles, useAllFiles } from "@app/contexts/FileContext";
+import { useNavigationState, useNavigationActions } from "@app/contexts/NavigationContext";
 
 const Merge = (props: BaseToolProps) => {
   const { t } = useTranslation();
@@ -24,8 +26,20 @@ const Merge = (props: BaseToolProps) => {
     useMergeParameters,
     useMergeOperation,
     props,
-    { minFiles: 2 }
+    { minFiles: 2, ignoreViewerScope: true }
   );
+
+  const { workbench } = useNavigationState();
+  const { actions: navActions } = useNavigationActions();
+  const isViewerMode = workbench === 'viewer';
+
+  const hasAutoSwitchedRef = useRef(false);
+  useEffect(() => {
+    if (isViewerMode && !hasAutoSwitchedRef.current) {
+      hasAutoSwitchedRef.current = true;
+      navActions.setWorkbench('fileEditor');
+    }
+  }, []);
   const naturalCompare = useCallback((a: string, b: string): number => {
     const isDigit = (char: string) => char >= '0' && char <= '9';
 
@@ -136,7 +150,22 @@ const Merge = (props: BaseToolProps) => {
       onClick: base.handleExecute,
       endpointEnabled: base.endpointEnabled,
       paramsValid: base.params.validateParameters(),
+      disabledReason: isViewerMode ? 'viewerMode' : undefined,
     },
+    belowExecuteButton: isViewerMode && !base.hasResults ? (
+      <Stack align="center" gap={6} mx="md" mt={4}>
+        <Text size="xs" c="dimmed" ta="center">
+          {t("merge.viewerModeHint", "Merge needs 2 or more files. Head to the file editor to select them.")}
+        </Text>
+        <Button
+          variant="light"
+          size="xs"
+          onClick={() => navActions.setWorkbench('fileEditor')}
+        >
+          {t("merge.goToFileEditor", "Go to file editor")}
+        </Button>
+      </Stack>
+    ) : undefined,
     review: {
       isVisible: base.hasResults,
       operation: base.operation,

frontend/src/core/tools/OCR.tsx

@@ -1,7 +1,7 @@
 import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
-import { useFileSelection } from "@app/contexts/FileContext";
+import { useViewScopedFiles } from "@app/hooks/tools/shared/useViewScopedFiles";
 
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 
@@ -16,7 +16,7 @@ import { useAdvancedOCRTips } from "@app/components/tooltips/useAdvancedOCRTips"
 
 const OCR = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
   const { t } = useTranslation();
-  const { selectedFiles } = useFileSelection();
+  const selectedFiles = useViewScopedFiles();
 
   const ocrParams = useOCRParameters();
   const ocrOperation = useOCROperation();

frontend/src/core/tools/ReorganizePages.tsx

@@ -3,7 +3,7 @@ import { useTranslation } from "react-i18next";
 import { createToolFlow } from "@app/components/tools/shared/createToolFlow";
 import { BaseToolProps, ToolComponent } from "@app/types/tool";
 import { useEndpointEnabled } from "@app/hooks/useEndpointConfig";
-import { useFileSelection } from "@app/contexts/FileContext";
+import { useViewScopedFiles } from "@app/hooks/tools/shared/useViewScopedFiles";
 import { useAccordionSteps } from "@app/hooks/tools/shared/useAccordionSteps";
 import ReorganizePagesSettings from "@app/components/tools/reorganizePages/ReorganizePagesSettings";
 import { useReorganizePagesParameters } from "@app/hooks/tools/reorganizePages/useReorganizePagesParameters";
@@ -11,7 +11,7 @@ import { useReorganizePagesOperation } from "@app/hooks/tools/reorganizePages/us
 
 const ReorganizePages = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
   const { t } = useTranslation();
-  const { selectedFiles } = useFileSelection();
+  const selectedFiles = useViewScopedFiles();
 
   const params = useReorganizePagesParameters();
   const operation = useReorganizePagesOperation();

frontend/src/core/utils/textUtils.ts

@@ -1,3 +1,16 @@
+/**
+ * Truncates text from the centre, preserving the start and end.
+ * e.g. "very-long-filename.pdf" -> "very-lo...ame.pdf"
+ */
+export function truncateCenter(text: string, maxLength: number = 25): string {
+  if (text.length <= maxLength) return text;
+  const ellipsis = '...';
+  const charsToShow = maxLength - ellipsis.length;
+  const frontChars = Math.ceil(charsToShow / 2);
+  const backChars = Math.floor(charsToShow / 2);
+  return text.substring(0, frontChars) + ellipsis + text.substring(text.length - backChars);
+}
+
 /**
  * Filters out emoji characters from a text string
  * @param text - The input text string