diff --git a/frontend/src/core/components/viewer/ZoomAPIBridge.tsx b/frontend/src/core/components/viewer/ZoomAPIBridge.tsx
index 9cec9e9da..ddc362e2b 100644
--- a/frontend/src/core/components/viewer/ZoomAPIBridge.tsx
+++ b/frontend/src/core/components/viewer/ZoomAPIBridge.tsx
@@ -209,7 +209,7 @@ export function ZoomAPIBridge() {
   ]);
 
   useEffect(() => {
-    if (!zoom || typeof zoom.onZoomChange !== 'function') {
+    if (!zoom) {
       return;
     }
 
@@ -222,9 +222,7 @@ export function ZoomAPIBridge() {
     });
 
     return () => {
-      if (typeof unsubscribe === 'function') {
-        unsubscribe();
-      }
+      unsubscribe();
     };
   }, [zoom, triggerImmediateZoomUpdate]);
 
diff --git a/frontend/src/core/contexts/ViewerContext.tsx b/frontend/src/core/contexts/ViewerContext.tsx
index 076cf86f7..44c3b741e 100644
--- a/frontend/src/core/contexts/ViewerContext.tsx
+++ b/frontend/src/core/contexts/ViewerContext.tsx
@@ -6,115 +6,35 @@ import React, {
   useRef,
   useCallback,
 } from 'react';
-import { SpreadMode } from '@embedpdf/plugin-spread/react';
 import { useNavigation } from '@app/contexts/NavigationContext';
-
-// Bridge API interfaces - these match what the bridges provide
-interface ScrollAPIWrapper {
-  scrollToPage: (params: { pageNumber: number }) => void;
-  scrollToPreviousPage: () => void;
-  scrollToNextPage: () => void;
-}
-
-interface ZoomAPIWrapper {
-  zoomIn: () => void;
-  zoomOut: () => void;
-  toggleMarqueeZoom: () => void;
-  requestZoom: (level: number) => void;
-}
-
-interface PanAPIWrapper {
-  enable: () => void;
-  disable: () => void;
-  toggle: () => void;
-}
-
-interface SelectionAPIWrapper {
-  copyToClipboard: () => void;
-  getSelectedText: () => string | any;
-  getFormattedSelection: () => any;
-}
-
-interface SpreadAPIWrapper {
-  setSpreadMode: (mode: SpreadMode) => void;
-  getSpreadMode: () => SpreadMode | null;
-  toggleSpreadMode: () => void;
-}
-
-interface RotationAPIWrapper {
-  rotateForward: () => void;
-  rotateBackward: () => void;
-  setRotation: (rotation: number) => void;
-  getRotation: () => number;
-}
-
-interface SearchAPIWrapper {
-  search: (query: string) => Promise<any>;
-  clear: () => void;
-  next: () => void;
-  previous: () => void;
-}
-
-interface ThumbnailAPIWrapper {
-  renderThumb: (pageIndex: number, scale: number) => { toPromise: () => Promise<Blob> };
-}
-
-interface ExportAPIWrapper {
-  download: () => void;
-  saveAsCopy: () => { toPromise: () => Promise<ArrayBuffer> };
-}
-
-
-// State interfaces - represent the shape of data from each bridge
-interface ScrollState {
-  currentPage: number;
-  totalPages: number;
-}
-
-interface ZoomState {
-  currentZoom: number;
-  zoomPercent: number;
-}
-
-interface PanState {
-  isPanning: boolean;
-}
-
-interface SelectionState {
-  hasSelection: boolean;
-}
-
-interface SpreadState {
-  spreadMode: SpreadMode;
-  isDualPage: boolean;
-}
-
-interface RotationState {
-  rotation: number;
-}
-
-interface SearchResult {
-  pageIndex: number;
-  rects: Array<{
-    origin: { x: number; y: number };
-    size: { width: number; height: number };
-  }>;
-}
-
-interface SearchState {
-  results: SearchResult[] | null;
-  activeIndex: number;
-}
-
-interface ExportState {
-  canExport: boolean;
-}
-
-// Bridge registration interface - bridges register with state and API
-interface BridgeRef<TState = unknown, TApi = unknown> {
-  state: TState;
-  api: TApi;
-}
+import {
+  BridgeRef,
+  BridgeApiMap,
+  BridgeStateMap,
+  BridgeKey,
+  ViewerBridgeRegistry,
+  createBridgeRegistry,
+  registerBridge as setBridgeRef,
+  ScrollAPIWrapper,
+  ScrollState,
+  ZoomAPIWrapper,
+  ZoomState,
+  PanAPIWrapper,
+  PanState,
+  SelectionAPIWrapper,
+  SelectionState,
+  SpreadAPIWrapper,
+  SpreadState,
+  RotationAPIWrapper,
+  RotationState,
+  SearchAPIWrapper,
+  SearchState,
+  SearchResult,
+  ThumbnailAPIWrapper,
+  ExportAPIWrapper,
+  ExportState,
+} from '@core/contexts/viewer/viewerBridges';
+import { SpreadMode } from '@embedpdf/plugin-spread/react';
 
 function useImmediateNotifier<Args extends unknown[]>() {
   const callbackRef = useRef<((...args: Args) => void) | null>(null);
@@ -232,7 +152,7 @@ interface ViewerContextType {
   };
 
   // Bridge registration - internal use by bridges  
-  registerBridge: (type: string, ref: BridgeRef) => void;
+  registerBridge: (type: BridgeKey, ref: BridgeRef) => void;
 }
 
 export const ViewerContext = createContext<ViewerContextType | null>(null);
@@ -252,17 +172,7 @@ export const ViewerProvider: React.FC<ViewerProviderProps> = ({ children }) => {
   useNavigation();
 
   // Bridge registry - bridges register their state and APIs here
-  const bridgeRefs = useRef({
-    scroll: null as BridgeRef<ScrollState, ScrollAPIWrapper> | null,
-    zoom: null as BridgeRef<ZoomState, ZoomAPIWrapper> | null,
-    pan: null as BridgeRef<PanState, PanAPIWrapper> | null,
-    selection: null as BridgeRef<SelectionState, SelectionAPIWrapper> | null,
-    search: null as BridgeRef<SearchState, SearchAPIWrapper> | null,
-    spread: null as BridgeRef<SpreadState, SpreadAPIWrapper> | null,
-    rotation: null as BridgeRef<RotationState, RotationAPIWrapper> | null,
-    thumbnail: null as BridgeRef<unknown, ThumbnailAPIWrapper> | null,
-    export: null as BridgeRef<ExportState, ExportAPIWrapper> | null,
-  });
+  const bridgeRefs = useRef<ViewerBridgeRegistry>(createBridgeRegistry());
 
   const {
     register: registerImmediateZoomUpdate,
@@ -298,38 +208,15 @@ export const ViewerProvider: React.FC<ViewerProviderProps> = ({ children }) => {
     [triggerImmediateSpreadInternal]
   );
 
-  const registerBridge = (type: string, ref: BridgeRef) => {
-    // Type-safe assignment - we know the bridges will provide correct types
-    switch (type) {
-      case 'scroll':
-        bridgeRefs.current.scroll = ref as BridgeRef<ScrollState, ScrollAPIWrapper>;
-        break;
-      case 'zoom':
-        bridgeRefs.current.zoom = ref as BridgeRef<ZoomState, ZoomAPIWrapper>;
-        break;
-      case 'pan':
-        bridgeRefs.current.pan = ref as BridgeRef<PanState, PanAPIWrapper>;
-        break;
-      case 'selection':
-        bridgeRefs.current.selection = ref as BridgeRef<SelectionState, SelectionAPIWrapper>;
-        break;
-      case 'search':
-        bridgeRefs.current.search = ref as BridgeRef<SearchState, SearchAPIWrapper>;
-        break;
-      case 'spread':
-        bridgeRefs.current.spread = ref as BridgeRef<SpreadState, SpreadAPIWrapper>;
-        break;
-      case 'rotation':
-        bridgeRefs.current.rotation = ref as BridgeRef<RotationState, RotationAPIWrapper>;
-        break;
-      case 'thumbnail':
-        bridgeRefs.current.thumbnail = ref as BridgeRef<unknown, ThumbnailAPIWrapper>;
-        break;
-      case 'export':
-        bridgeRefs.current.export = ref as BridgeRef<ExportState, ExportAPIWrapper>;
-        break;
-    }
-  };
+  const registerBridge = useCallback(
+    <K extends BridgeKey>(
+      type: K,
+      ref: BridgeRef<BridgeStateMap[K], BridgeApiMap[K]>
+    ) => {
+      setBridgeRef(bridgeRefs.current, type, ref);
+    },
+    []
+  );
 
   const toggleThumbnailSidebar = () => {
     setIsThumbnailSidebarVisible(prev => !prev);
diff --git a/frontend/src/core/contexts/viewer/viewerBridges.ts b/frontend/src/core/contexts/viewer/viewerBridges.ts
new file mode 100644
index 000000000..25b7fa1e4
--- /dev/null
+++ b/frontend/src/core/contexts/viewer/viewerBridges.ts
@@ -0,0 +1,171 @@
+import { SpreadMode } from '@embedpdf/plugin-spread/react';
+
+export interface ScrollAPIWrapper {
+  scrollToPage: (params: { pageNumber: number }) => void;
+  scrollToPreviousPage: () => void;
+  scrollToNextPage: () => void;
+}
+
+export interface ZoomAPIWrapper {
+  zoomIn: () => void;
+  zoomOut: () => void;
+  toggleMarqueeZoom: () => void;
+  requestZoom: (level: number) => void;
+}
+
+export interface PanAPIWrapper {
+  enable: () => void;
+  disable: () => void;
+  toggle: () => void;
+}
+
+export interface SelectionAPIWrapper {
+  copyToClipboard: () => void;
+  getSelectedText: () => string | any;
+  getFormattedSelection: () => any;
+}
+
+export interface SpreadAPIWrapper {
+  setSpreadMode: (mode: SpreadMode) => void;
+  getSpreadMode: () => SpreadMode | null;
+  toggleSpreadMode: () => void;
+}
+
+export interface RotationAPIWrapper {
+  rotateForward: () => void;
+  rotateBackward: () => void;
+  setRotation: (rotation: number) => void;
+  getRotation: () => number;
+}
+
+export interface SearchAPIWrapper {
+  search: (query: string) => Promise<any>;
+  clear: () => void;
+  next: () => void;
+  previous: () => void;
+}
+
+export interface ThumbnailAPIWrapper {
+  renderThumb: (pageIndex: number, scale: number) => {
+    toPromise: () => Promise<Blob>;
+  };
+}
+
+export interface ExportAPIWrapper {
+  download: () => void;
+  saveAsCopy: () => { toPromise: () => Promise<ArrayBuffer> };
+}
+
+export interface ScrollState {
+  currentPage: number;
+  totalPages: number;
+}
+
+export interface ZoomState {
+  currentZoom: number;
+  zoomPercent: number;
+}
+
+export interface PanState {
+  isPanning: boolean;
+}
+
+export interface SelectionState {
+  hasSelection: boolean;
+}
+
+export interface SpreadState {
+  spreadMode: SpreadMode;
+  isDualPage: boolean;
+}
+
+export interface RotationState {
+  rotation: number;
+}
+
+export interface SearchResult {
+  pageIndex: number;
+  rects: Array<{
+    origin: { x: number; y: number };
+    size: { width: number; height: number };
+  }>;
+}
+
+export interface SearchState {
+  results: SearchResult[] | null;
+  activeIndex: number;
+}
+
+export interface ExportState {
+  canExport: boolean;
+}
+
+export interface BridgeRef<TState = unknown, TApi = unknown> {
+  state: TState;
+  api: TApi;
+}
+
+export interface BridgeStateMap {
+  scroll: ScrollState;
+  zoom: ZoomState;
+  pan: PanState;
+  selection: SelectionState;
+  spread: SpreadState;
+  rotation: RotationState;
+  search: SearchState;
+  thumbnail: unknown;
+  export: ExportState;
+}
+
+export interface BridgeApiMap {
+  scroll: ScrollAPIWrapper;
+  zoom: ZoomAPIWrapper;
+  pan: PanAPIWrapper;
+  selection: SelectionAPIWrapper;
+  spread: SpreadAPIWrapper;
+  rotation: RotationAPIWrapper;
+  search: SearchAPIWrapper;
+  thumbnail: ThumbnailAPIWrapper;
+  export: ExportAPIWrapper;
+}
+
+export type BridgeKey = keyof BridgeStateMap;
+
+export type ViewerBridgeRegistry = {
+  [K in BridgeKey]: BridgeRef<BridgeStateMap[K], BridgeApiMap[K]> | null;
+};
+
+export const createBridgeRegistry = (): ViewerBridgeRegistry => ({
+  scroll: null,
+  zoom: null,
+  pan: null,
+  selection: null,
+  spread: null,
+  rotation: null,
+  search: null,
+  thumbnail: null,
+  export: null,
+});
+
+export function registerBridge<K extends BridgeKey>(
+  registry: ViewerBridgeRegistry,
+  type: K,
+  ref: BridgeRef<BridgeStateMap[K], BridgeApiMap[K]>
+): void {
+  registry[type] = ref;
+}
+
+export function getBridgeState<K extends BridgeKey>(
+  registry: ViewerBridgeRegistry,
+  type: K,
+  fallback: BridgeStateMap[K]
+): BridgeStateMap[K] {
+  return registry[type]?.state ?? fallback;
+}
+
+export function getBridgeApi<K extends BridgeKey>(
+  registry: ViewerBridgeRegistry,
+  type: K
+): BridgeApiMap[K] | null {
+  return registry[type]?.api ?? null;
+}
diff --git a/frontend/src/core/utils/viewerZoom.ts b/frontend/src/core/utils/viewerZoom.ts
index d185398c0..1fa1fb492 100644
--- a/frontend/src/core/utils/viewerZoom.ts
+++ b/frontend/src/core/utils/viewerZoom.ts
@@ -167,7 +167,7 @@ export function useFitWidthResize({
         return;
       }
 
-      if (typeof timeoutId === 'number') {
+      if (timeoutId !== undefined) {
         window.clearTimeout(timeoutId);
       }
 
@@ -179,7 +179,7 @@ export function useFitWidthResize({
 
     window.addEventListener('resize', handleResize);
     return () => {
-      if (typeof timeoutId === 'number') {
+      if (timeoutId !== undefined) {
         window.clearTimeout(timeoutId);
       }
       window.removeEventListener('resize', handleResize);