diff --git a/src/background/fetchJson.ts b/src/background/fetchJson.ts
new file mode 100644
index 0000000..2d47bcc
--- /dev/null
+++ b/src/background/fetchJson.ts
@@ -0,0 +1,21 @@
+/** Fetch JSON with abort timeout; non-OK / network / parse failures return null. */
+
+export async function fetchJsonWithTimeout<T>(
+  url: string,
+  timeoutMs: number,
+): Promise<T | null> {
+  const controller = new AbortController();
+  const timer = setTimeout(() => controller.abort(), timeoutMs);
+  try {
+    const res = await fetch(url, {
+      signal: controller.signal,
+      headers: { Accept: 'application/json' },
+    });
+    if (!res.ok) return null;
+    return (await res.json()) as T;
+  } catch {
+    return null;
+  } finally {
+    clearTimeout(timer);
+  }
+}
diff --git a/src/background/googleBooks.ts b/src/background/googleBooks.ts
index 948793d..f453c82 100644
--- a/src/background/googleBooks.ts
+++ b/src/background/googleBooks.ts
@@ -13,12 +13,15 @@ import type {
 import { isValidIsbn, normalizeIsbn, toIsbn13 } from '@/shared/isbn';
 import type { BookSearchResult } from './openLibrary';
 import { getPreferences } from './storage';
+import { BoundedTtlCache } from './ttlCache';
+import { fetchJsonWithTimeout } from './fetchJson';
 
 const GB_BASE = 'https://www.googleapis.com/books/v1/volumes';
 const REQUEST_TIMEOUT_MS = 12_000;
 const CACHE_TTL_MS = 1000 * 60 * 60 * 6; // 6 hours
 
-const CACHE = new Map<string, { data: unknown; timestamp: number }>();
+export const MAX_CACHE_SIZE = 500;
+const cache = new BoundedTtlCache<unknown>(MAX_CACHE_SIZE, CACHE_TTL_MS);
 
 let googleBooksApiKey: string | null = null;
 
@@ -97,36 +100,20 @@ interface GbVolumesResponse {
 // ─── Cache ───────────────────────────────────────────────────────────
 
 function cacheGet<T>(key: string): T | undefined {
-  const entry = CACHE.get(key);
-  if (!entry) return undefined;
-  if (Date.now() - entry.timestamp > CACHE_TTL_MS) {
-    CACHE.delete(key);
-    return undefined;
-  }
-  return entry.data as T;
+  return cache.get(key) as T | undefined;
 }
 
-export const MAX_CACHE_SIZE = 500;
-
 function cacheSet(key: string, data: unknown): void {
-  if (CACHE.has(key)) {
-    CACHE.delete(key);
-  } else if (CACHE.size >= MAX_CACHE_SIZE) {
-    const oldestKey = CACHE.keys().next().value;
-    if (oldestKey !== undefined) {
-      CACHE.delete(oldestKey);
-    }
-  }
-  CACHE.set(key, { data, timestamp: Date.now() });
+  cache.set(key, data);
 }
 
 /** Test helper — clears in-memory cache. */
 export function clearGoogleBooksCache(): void {
-  CACHE.clear();
+  cache.clear();
 }
 
 export function getGoogleBooksCacheSizeForTesting(): number {
-  return CACHE.size;
+  return cache.size;
 }
 
 export function setGoogleBooksCacheEntryForTesting(key: string, data: unknown): void {
@@ -159,23 +146,7 @@ function volumeSourceUrl(volumeId: string): string {
 // ─── Fetch with timeout ──────────────────────────────────────────────
 
 async function fetchJson<T>(url: string): Promise<T | null> {
-  const controller = new AbortController();
-  const timer = setTimeout(() => controller.abort(), REQUEST_TIMEOUT_MS);
-  try {
-    const res = await fetch(url, {
-      signal: controller.signal,
-      headers: { Accept: 'application/json' },
-    });
-    // Unauthenticated quota / forbidden — fail gracefully
-    if (res.status === 403 || res.status === 401) return null;
-    if (res.status === 404) return null;
-    if (!res.ok) return null;
-    return (await res.json()) as T;
-  } catch {
-    return null;
-  } finally {
-    clearTimeout(timer);
-  }
+  return fetchJsonWithTimeout<T>(url, REQUEST_TIMEOUT_MS);
 }
 
 function buildVolumesUrl(params: Record<string, string | number>): string {
diff --git a/src/background/handlers/library.ts b/src/background/handlers/library.ts
index b01b7a5..d627691 100644
--- a/src/background/handlers/library.ts
+++ b/src/background/handlers/library.ts
@@ -11,6 +11,8 @@ import {
   CheckLibraryStatusRequest,
   CheckLibraryStatusResponse,
   LibraryItem,
+  BroadcastMessage,
+  RatingHistoryEntry,
 } from '@/shared/types';
 import { v4 as uuidv4 } from 'uuid';
 import type { Reflection } from '@/shared/catalogTypes';
@@ -37,7 +39,20 @@ import { isSafeNavMediaId } from '@/shared/mediaIds';
 import { invalidateProfileCache } from '../context';
 import { mergeMediaItems } from '../mediaMerge';
 import { broadcastMessage, parseSetUserNotesRequest, parseUpdateStatusRequest } from './utils';
-import type { RatingHistoryEntry } from '@/shared/types';
+
+async function notifyLibraryUpdated(
+  action: Extract<BroadcastMessage, { type: 'LIBRARY_UPDATED' }>['action'],
+  mediaId: string,
+  libraryItem?: LibraryItem,
+): Promise<void> {
+  invalidateProfileCache();
+  await broadcastMessage({
+    type: 'LIBRARY_UPDATED',
+    action,
+    mediaId,
+    ...(libraryItem ? { libraryItem } : {}),
+  });
+}
 
 /** Max entries kept on `LibraryItem.ratingHistory`. */
 export const RATING_HISTORY_CAP = 50;
@@ -132,13 +147,7 @@ export const libraryHandlers: MessageHandlerMap = {
       await onNewLibraryItemCreated();
     }
 
-    invalidateProfileCache();
-    await broadcastMessage({
-      type: 'LIBRARY_UPDATED',
-      action: 'add',
-      mediaId: libraryItem.mediaId,
-      libraryItem,
-    });
+    await notifyLibraryUpdated('add', libraryItem.mediaId, libraryItem);
     return libraryItem;
   },
 
@@ -156,13 +165,7 @@ export const libraryHandlers: MessageHandlerMap = {
     existing.sanctuaryIntent = intentForStatus(req.status);
     existing.updatedAt = Date.now();
     await putLibraryItem(existing);
-    invalidateProfileCache();
-    await broadcastMessage({
-      type: 'LIBRARY_UPDATED',
-      action: 'update',
-      mediaId: existing.mediaId,
-      libraryItem: existing,
-    });
+    await notifyLibraryUpdated('update', existing.mediaId, existing);
     return { updated: true };
   },
 
@@ -181,13 +184,7 @@ export const libraryHandlers: MessageHandlerMap = {
     existing.userRating = req.rating;
     existing.updatedAt = Date.now();
     await putLibraryItem(existing);
-    invalidateProfileCache();
-    await broadcastMessage({
-      type: 'LIBRARY_UPDATED',
-      action: 'update',
-      mediaId: existing.mediaId,
-      libraryItem: existing,
-    });
+    await notifyLibraryUpdated('update', existing.mediaId, existing);
     return { updated: true };
   },
 
@@ -201,13 +198,7 @@ export const libraryHandlers: MessageHandlerMap = {
     existing.userTags = req.tags;
     existing.updatedAt = Date.now();
     await putLibraryItem(existing);
-    invalidateProfileCache();
-    await broadcastMessage({
-      type: 'LIBRARY_UPDATED',
-      action: 'update',
-      mediaId: existing.mediaId,
-      libraryItem: existing,
-    });
+    await notifyLibraryUpdated('update', existing.mediaId, existing);
     return { updated: true };
   },
 
@@ -246,13 +237,7 @@ export const libraryHandlers: MessageHandlerMap = {
       logger.warn('[Subsume] SET_USER_NOTES reflection append failed:', err);
     }
 
-    invalidateProfileCache();
-    await broadcastMessage({
-      type: 'LIBRARY_UPDATED',
-      action: 'update',
-      mediaId: existing.mediaId,
-      libraryItem: existing,
-    });
+    await notifyLibraryUpdated('update', existing.mediaId, existing);
     return { updated: true };
   },
 
@@ -263,12 +248,7 @@ export const libraryHandlers: MessageHandlerMap = {
       throw new Error('Invalid mediaId');
     }
     await removeLibraryItem(req.mediaId);
-    invalidateProfileCache();
-    await broadcastMessage({
-      type: 'LIBRARY_UPDATED',
-      action: 'remove',
-      mediaId: req.mediaId,
-    });
+    await notifyLibraryUpdated('remove', req.mediaId);
     return { removed: true };
   },
 
diff --git a/src/background/omdb.ts b/src/background/omdb.ts
index 624bbc0..854405a 100644
--- a/src/background/omdb.ts
+++ b/src/background/omdb.ts
@@ -1,34 +1,23 @@
 import { MediaRating } from '@/shared/types';
 import { getPreferences } from './storage';
+import { BoundedTtlCache } from './ttlCache';
 
 const BASE_URL = 'https://www.omdbapi.com/';
 
-const CACHE = new Map<string, { data: MediaRating[]; timestamp: number }>();
 const CACHE_TTL = 1000 * 60 * 60 * 24; // 24 hours
 export const MAX_CACHE_SIZE = 500;
-
-function setCacheEntry(key: string, data: MediaRating[]): void {
-  if (CACHE.has(key)) {
-    CACHE.delete(key);
-  } else if (CACHE.size >= MAX_CACHE_SIZE) {
-    const oldestKey = CACHE.keys().next().value;
-    if (oldestKey !== undefined) {
-      CACHE.delete(oldestKey);
-    }
-  }
-  CACHE.set(key, { data, timestamp: Date.now() });
-}
+const cache = new BoundedTtlCache<MediaRating[]>(MAX_CACHE_SIZE, CACHE_TTL);
 
 export function clearOmdbCache(): void {
-  CACHE.clear();
+  cache.clear();
 }
 
 export function getOmdbCacheSizeForTesting(): number {
-  return CACHE.size;
+  return cache.size;
 }
 
 export function setOmdbCacheEntryForTesting(key: string, data: MediaRating[]): void {
-  setCacheEntry(key, data);
+  cache.set(key, data);
 }
 
 let omdbApiKey: string | null = null;
@@ -92,9 +81,9 @@ export async function fetchOmdbRatings(
   }
 
   const cacheKey = `omdb_${title}_${year}_${type}`;
-  const cached = CACHE.get(cacheKey);
-  if (cached && Date.now() - cached.timestamp < CACHE_TTL) {
-    return cached.data;
+  const cached = cache.get(cacheKey);
+  if (cached !== undefined) {
+    return cached;
   }
 
   const omdbType = type === 'tv' ? 'series' : 'movie';
@@ -112,7 +101,7 @@ export async function fetchOmdbRatings(
       const isTransientError =
         error.includes('Invalid API key') || error.toLowerCase().includes('limit');
       if (!isTransientError) {
-        setCacheEntry(cacheKey, []);
+        cache.set(cacheKey, []);
       }
       return [];
     }
@@ -137,7 +126,7 @@ export async function fetchOmdbRatings(
       }
     }
 
-    setCacheEntry(cacheKey, ratings);
+    cache.set(cacheKey, ratings);
     return ratings;
   } catch (err) {
     console.error('[Subsume OMDb] Fetch failed', err);
diff --git a/src/background/openLibrary.ts b/src/background/openLibrary.ts
index 5130ce6..bd560fe 100644
--- a/src/background/openLibrary.ts
+++ b/src/background/openLibrary.ts
@@ -14,13 +14,16 @@ import type {
   SourceProvenance,
 } from '@/shared/catalogTypes';
 import { isValidIsbn, normalizeIsbn, toIsbn13 } from '@/shared/isbn';
+import { BoundedTtlCache } from './ttlCache';
+import { fetchJsonWithTimeout } from './fetchJson';
 
 const OL_BASE = 'https://openlibrary.org';
 const COVERS_BASE = 'https://covers.openlibrary.org';
 const REQUEST_TIMEOUT_MS = 12_000;
 const CACHE_TTL_MS = 1000 * 60 * 60 * 6; // 6 hours
 
-const CACHE = new Map<string, { data: unknown; timestamp: number }>();
+export const MAX_CACHE_SIZE = 500;
+const cache = new BoundedTtlCache<unknown>(MAX_CACHE_SIZE, CACHE_TTL_MS);
 
 export interface BookSearchQuery {
   query: string;
@@ -147,22 +150,16 @@ interface OlAuthorWorksResponse {
 // ─── Cache ──────────────────────────────────────────────────────────────────
 
 function cacheGet<T>(key: string): T | undefined {
-  const entry = CACHE.get(key);
-  if (!entry) return undefined;
-  if (Date.now() - entry.timestamp > CACHE_TTL_MS) {
-    CACHE.delete(key);
-    return undefined;
-  }
-  return entry.data as T;
+  return cache.get(key) as T | undefined;
 }
 
 function cacheSet(key: string, data: unknown): void {
-  CACHE.set(key, { data, timestamp: Date.now() });
+  cache.set(key, data);
 }
 
 /** Test helper — clears in-memory cache. */
 export function clearOpenLibraryCache(): void {
-  CACHE.clear();
+  cache.clear();
 }
 
 // ─── ID helpers ─────────────────────────────────────────────────────────────
@@ -262,22 +259,7 @@ export function coverUrlFromIsbn(isbn: string, size: 'S' | 'M' | 'L' = 'L'): str
 // ─── Fetch with timeout ─────────────────────────────────────────────────────
 
 async function fetchJson<T>(url: string): Promise<T | null> {
-  const controller = new AbortController();
-  const timer = setTimeout(() => controller.abort(), REQUEST_TIMEOUT_MS);
-  try {
-    const res = await fetch(url, {
-      signal: controller.signal,
-      headers: { Accept: 'application/json' },
-    });
-    if (res.status === 404) return null;
-    if (!res.ok) return null;
-    return (await res.json()) as T;
-  } catch {
-    // AbortError, network failure, parse error — graceful empty
-    return null;
-  } finally {
-    clearTimeout(timer);
-  }
+  return fetchJsonWithTimeout<T>(url, REQUEST_TIMEOUT_MS);
 }
 
 // ─── Mapping helpers ────────────────────────────────────────────────────────
diff --git a/src/background/tmdb.ts b/src/background/tmdb.ts
index 99850e7..de97297 100644
--- a/src/background/tmdb.ts
+++ b/src/background/tmdb.ts
@@ -1,36 +1,25 @@
 import { MediaItem, MediaType, MediaProvider, UserPreferences, CrewRole, StreamingInfo } from '@/shared/types';
 import { getMediaItem, putMediaItem, getAllMediaMap, putMediaItems, getPreferences } from './storage';
 import { fetchOmdbRatings, runWithConcurrency } from './omdb';
+import { BoundedTtlCache } from './ttlCache';
 
 const BASE_URL = 'https://api.themoviedb.org/3';
 export const POSTER_BASE_URL = 'https://image.tmdb.org/t/p/w500';
 
-const CACHE = new Map<string, { data: unknown; timestamp: number }>();
 const CACHE_TTL = 1000 * 60 * 60 * 24; // 24 hours
 export const MAX_CACHE_SIZE = 500;
-
-function setCacheEntry(key: string, data: unknown): void {
-  if (CACHE.has(key)) {
-    CACHE.delete(key);
-  } else if (CACHE.size >= MAX_CACHE_SIZE) {
-    const oldestKey = CACHE.keys().next().value;
-    if (oldestKey !== undefined) {
-      CACHE.delete(oldestKey);
-    }
-  }
-  CACHE.set(key, { data, timestamp: Date.now() });
-}
+const cache = new BoundedTtlCache<unknown>(MAX_CACHE_SIZE, CACHE_TTL);
 
 export function clearTmdbCache(): void {
-  CACHE.clear();
+  cache.clear();
 }
 
 export function getTmdbCacheSizeForTesting(): number {
-  return CACHE.size;
+  return cache.size;
 }
 
 export function setTmdbCacheEntryForTesting(key: string, data: unknown): void {
-  setCacheEntry(key, data);
+  cache.set(key, data);
 }
 
 let tmdbApiKey: string | null = null;
@@ -319,9 +308,9 @@ export async function fetchWatchProviders(
   options?: { releaseDate?: string }
 ): Promise<StreamingInfo[]> {
   const cacheKey = `watch_providers_${type}_${tmdbNumericId}_${region}`;
-  const cached = CACHE.get(cacheKey);
-  if (cached && Date.now() - cached.timestamp < CACHE_TTL) {
-    return cached.data as StreamingInfo[];
+  const cached = cache.get(cacheKey);
+  if (cached !== undefined) {
+    return cached as StreamingInfo[];
   }
 
   try {
@@ -342,7 +331,7 @@ export async function fetchWatchProviders(
       theatricalReleaseDates,
     });
 
-    setCacheEntry(cacheKey, mapped);
+    cache.set(cacheKey, mapped);
     return mapped;
   } catch (err) {
     console.error('[Subsume TMDB] Watch providers fetch failed', err);
@@ -418,9 +407,9 @@ export async function searchTitle(
 ): Promise<MediaItem | null> {
   await loadGenreMap();
   const cacheKey = `search_${title}_${yearGuess}_${typeGuess}`;
-  const cached = CACHE.get(cacheKey);
-  if (cached && Date.now() - cached.timestamp < CACHE_TTL) {
-    return cached.data as MediaItem | null;
+  const cached = cache.get(cacheKey);
+  if (cached !== undefined) {
+    return cached as MediaItem | null;
   }
 
   // If we don't know the type, we search both and take the best match.
@@ -491,7 +480,7 @@ export async function searchTitle(
     const baseItem = mapTmdbToMediaItem(bestResult, finalType);
     const withRatings = await enrichMediaWithOmdbRatings(baseItem);
     const resultItem = await enrichMediaWithStreaming(withRatings, undefined, releaseDate);
-    setCacheEntry(cacheKey, resultItem);
+    cache.set(cacheKey, resultItem);
     return resultItem;
   } catch (err) {
     console.error('[Subsume TMDB] Search failed', err);
@@ -506,9 +495,9 @@ export async function searchTitles(
 ): Promise<MediaItem[]> {
   await loadGenreMap();
   const cacheKey = `search_multi_${query}_${type}_${year}`;
-  const cached = CACHE.get(cacheKey);
-  if (cached && Date.now() - cached.timestamp < CACHE_TTL) {
-    return cached.data as MediaItem[] || [];
+  const cachedMulti = cache.get(cacheKey);
+  if (cachedMulti !== undefined) {
+    return (cachedMulti as MediaItem[]) || [];
   }
 
   const key = await ensureTmdbApiKey();
@@ -555,7 +544,7 @@ export async function searchTitles(
       enrichMediaWithOmdbRatings,
       3
     );
-    setCacheEntry(cacheKey, limited);
+    cache.set(cacheKey, limited);
     return limited;
   } catch (err) {
     console.error('[Subsume TMDB] Multi-search failed', err);
diff --git a/src/background/ttlCache.ts b/src/background/ttlCache.ts
new file mode 100644
index 0000000..8c1a465
--- /dev/null
+++ b/src/background/ttlCache.ts
@@ -0,0 +1,42 @@
+/** FIFO Map with TTL — shared by TMDb, OMDb, Google Books, Open Library in-memory caches. */
+
+export type TtlCacheEntry<T> = { data: T; timestamp: number };
+
+export class BoundedTtlCache<T> {
+  private readonly store = new Map<string, TtlCacheEntry<T>>();
+
+  constructor(
+    private readonly maxSize: number,
+    private readonly ttlMs: number,
+  ) {}
+
+  get size(): number {
+    return this.store.size;
+  }
+
+  get(key: string, now: number = Date.now()): T | undefined {
+    const entry = this.store.get(key);
+    if (!entry) return undefined;
+    if (now - entry.timestamp >= this.ttlMs) {
+      this.store.delete(key);
+      return undefined;
+    }
+    return entry.data;
+  }
+
+  set(key: string, data: T, now: number = Date.now()): void {
+    if (this.store.has(key)) {
+      this.store.delete(key);
+    } else if (this.store.size >= this.maxSize) {
+      const oldestKey = this.store.keys().next().value;
+      if (oldestKey !== undefined) {
+        this.store.delete(oldestKey);
+      }
+    }
+    this.store.set(key, { data, timestamp: now });
+  }
+
+  clear(): void {
+    this.store.clear();
+  }
+}
diff --git a/src/content/bookDetection/index.ts b/src/content/bookDetection/index.ts
index 6be281b..0f067ea 100644
--- a/src/content/bookDetection/index.ts
+++ b/src/content/bookDetection/index.ts
@@ -18,6 +18,7 @@ import {
 } from './isbnContext';
 import { detectViaDomainAdapters } from './domainAdapters';
 import { detectTitleAuthorHeuristics } from './titleAuthorHeuristics';
+import { normalizeTitleKey } from '../titleKey';
 
 export { detectJsonLdBooks } from './jsonLdBooks';
 export { extractIsbnsFromDocument, candidatesFromIsbns } from './isbnContext';
@@ -29,14 +30,6 @@ export { detectTitleAuthorHeuristics } from './titleAuthorHeuristics';
 export const MIN_ANNOTATION_CONFIDENCE = 0.65;
 export const HIGH_CONFIDENCE = 0.85;
 
-function normalizeTitleKey(title: string): string {
-  return title
-    .toLowerCase()
-    .replace(/[^a-z0-9\s]/g, '')
-    .replace(/\s+/g, ' ')
-    .trim();
-}
-
 function authorKey(authors?: string[]): string {
   return (authors || [])
     .map((a) => a.toLowerCase().replace(/[^a-z0-9\s]/g, '').trim())
diff --git a/src/content/bookOverlay.ts b/src/content/bookOverlay.ts
index cc39a5d..ee30e22 100644
--- a/src/content/bookOverlay.ts
+++ b/src/content/bookOverlay.ts
@@ -260,9 +260,7 @@ function isHTMLElement(value: BookPlaqueAnchor): value is HTMLElement {
   return typeof HTMLElement !== 'undefined' && value instanceof HTMLElement;
 }
 
-function truncateTitle(title: string, max = 36): string {
-  return truncateForExcerpt(title, max);
-}
+
 
 /**
  * Manager for book plaques on host pages.
@@ -473,7 +471,7 @@ export class BookPlaqueManager {
 
       const title = document.createElement('span');
       title.className = 'plaque-title';
-      title.textContent = truncateTitle(match.title);
+      title.textContent = truncateForExcerpt(match.title, 36);
       title.title = match.title;
       openBtn.appendChild(title);
 
@@ -512,7 +510,7 @@ export class BookPlaqueManager {
 
       const title = document.createElement('span');
       title.className = 'plaque-title';
-      title.textContent = truncateTitle(match.title);
+      title.textContent = truncateForExcerpt(match.title, 36);
       title.title = match.title;
       root.appendChild(title);
 
diff --git a/src/content/index.ts b/src/content/index.ts
index d625f46..a09405c 100644
--- a/src/content/index.ts
+++ b/src/content/index.ts
@@ -61,8 +61,7 @@ async function resolveAndAttachBookPlaques(
 ): Promise<void> {
   const high = candidates
     .filter((c) => c.confidence >= HIGH_CONFIDENCE)
-    .slice(0, MAX_BOOK_PLAQUE_CANDIDATES)
-    .slice(0, MAX_BOOK_RESOLVE_CALLS);
+    .slice(0, Math.min(MAX_BOOK_PLAQUE_CANDIDATES, MAX_BOOK_RESOLVE_CALLS));
 
   for (const candidate of high) {
     try {
diff --git a/src/content/overlay.ts b/src/content/overlay.ts
index b48a21c..76385a1 100644
--- a/src/content/overlay.ts
+++ b/src/content/overlay.ts
@@ -33,7 +33,6 @@ export function pickDisplayRating(ratings: MediaRating[]): { provider: RatingPro
 
 interface PlaqueProps {
   match: PosterMatch;
-  inLibrary: boolean;
   onReflect: () => void;
 }
 
@@ -185,7 +184,6 @@ const PLAQUE_STYLES = `
 
 interface BadgeState {
   match: PosterMatch;
-  inLibrary: boolean;
   host: HTMLElement;
   shadowRoot: ShadowRoot;
   mount: HTMLElement;
@@ -194,13 +192,7 @@ interface BadgeState {
 
 export class MuseumPlaqueManager {
   private badges = new Map<HTMLImageElement, BadgeState>();
-  private libraryIds = new Set<string>();
   private createdWrappers = new Set<HTMLElement>();
-  private syncListener: ((message: unknown, sender: chrome.runtime.MessageSender) => void) | null = null;
-
-  constructor() {
-    this.setupSyncListener();
-  }
 
   private ensureWrapper(img: HTMLImageElement): HTMLElement {
     const parent = img.parentElement;
@@ -217,39 +209,7 @@ export class MuseumPlaqueManager {
     return wrap;
   }
 
-  private setupSyncListener(): void {
-    if (typeof chrome === 'undefined' || !chrome.runtime?.onMessage) return;
-    this.syncListener = (message: unknown, sender: chrome.runtime.MessageSender) => {
-      if (sender.id !== chrome.runtime.id) return;
-      if (!message || typeof message !== 'object') return;
-      if (!('type' in message) || (message as Record<string, unknown>).type !== 'LIBRARY_UPDATED') return;
-
-      const msg = message as { mediaId?: unknown; libraryItem?: { mediaId?: unknown }; action?: unknown };
-      const mediaId = typeof msg.mediaId === 'string' ? msg.mediaId : (typeof msg.libraryItem?.mediaId === 'string' ? msg.libraryItem.mediaId : undefined);
-      if (!mediaId) return;
-
-      if (msg.action === 'add' || msg.action === 'update') {
-        this.libraryIds.add(mediaId);
-      } else if (msg.action === 'remove') {
-        this.libraryIds.delete(mediaId);
-      }
-
-      for (const state of this.badges.values()) {
-        if (state.mediaId === mediaId) {
-          state.inLibrary = msg.action !== 'remove';
-          this.renderBadge(state);
-        }
-      }
-    };
-    chrome.runtime.onMessage.addListener(this.syncListener);
-  }
-
   public destroy(): void {
-    if (this.syncListener && typeof chrome !== 'undefined' && chrome.runtime?.onMessage) {
-      chrome.runtime.onMessage.removeListener(this.syncListener);
-      this.syncListener = null;
-    }
-
     for (const [img, state] of this.badges.entries()) {
       render(null, state.mount);
       state.host.remove();
@@ -274,7 +234,6 @@ export class MuseumPlaqueManager {
     }
     this.createdWrappers.clear();
     this.badges.clear();
-    this.libraryIds.clear();
   }
 
   attachBadge(img: HTMLImageElement, match: PosterMatch): void {
@@ -296,7 +255,6 @@ export class MuseumPlaqueManager {
 
     const state: BadgeState = {
       match,
-      inLibrary: match.inLibrary || this.libraryIds.has(mediaId),
       host,
       shadowRoot,
       mount,
@@ -312,7 +270,6 @@ export class MuseumPlaqueManager {
     render(
       h(MuseumPlaqueOverlay, {
         match: state.match,
-        inLibrary: state.inLibrary,
         onReflect: () => this.handleReflect(state),
       }),
       state.mount
diff --git a/src/content/screenDetection/index.ts b/src/content/screenDetection/index.ts
index 78c8271..95461a9 100644
--- a/src/content/screenDetection/index.ts
+++ b/src/content/screenDetection/index.ts
@@ -8,6 +8,7 @@ import {
   type ScreenDetectionCandidate,
 } from './jsonLdScreen';
 import { detectViaScreenDomainAdapters } from './domainAdapters';
+import { normalizeTitleKey } from '../titleKey';
 
 export type { ScreenDetectionCandidate, ScreenKind } from './jsonLdScreen';
 export { detectJsonLdScreenWorks } from './jsonLdScreen';
@@ -19,14 +20,6 @@ export {
 /** Minimum confidence to report a screen page candidate (parity with book annotation floor). */
 export const MIN_SCREEN_PAGE_CONFIDENCE = 0.65;
 
-function normalizeTitleKey(title: string): string {
-  return title
-    .toLowerCase()
-    .replace(/[^a-z0-9\s]/g, '')
-    .replace(/\s+/g, ' ')
-    .trim();
-}
-
 function mergeScreen(
   a: ScreenDetectionCandidate,
   b: ScreenDetectionCandidate
diff --git a/src/content/titleKey.ts b/src/content/titleKey.ts
new file mode 100644
index 0000000..a525dd0
--- /dev/null
+++ b/src/content/titleKey.ts
@@ -0,0 +1,8 @@
+/** Shared title key for book/screen candidate dedupe. */
+export function normalizeTitleKey(title: string): string {
+  return title
+    .toLowerCase()
+    .replace(/[^a-z0-9\s]/g, '')
+    .replace(/\s+/g, ' ')
+    .trim();
+}
diff --git a/src/shared/messages.ts b/src/shared/messages.ts
index 4258cf2..c60aaff 100644
--- a/src/shared/messages.ts
+++ b/src/shared/messages.ts
@@ -122,42 +122,25 @@ export function createMessageRouter(
         return false;
       }
 
-      if (options?.onBeforeDispatch) {
-        Promise.resolve(options.onBeforeDispatch())
-          .catch((err) => {
-            console.error('[Subsume] Error in onBeforeDispatch:', err);
-          })
-          .then(() => handler(message.payload, sender))
-          .then((data) => sendResponse({ success: true, data }))
-          .catch((err) => {
-            const msg = err instanceof Error ? err.message : String(err);
-            logDiagnostic('error', 'bg.handler', msg, `type=${message.type}`);
-            sendResponse({
-              success: false,
-              error: msg,
-            });
-          });
-        return true;
-      }
-
-      const result = handler(message.payload, sender);
+      const run = options?.onBeforeDispatch
+        ? Promise.resolve(options.onBeforeDispatch())
+            .catch((err) => {
+              console.error('[Subsume] Error in onBeforeDispatch:', err);
+            })
+            .then(() => handler(message.payload, sender))
+        : handler(message.payload, sender);
 
-      if (result instanceof Promise) {
-        result
-          .then((data) => sendResponse({ success: true, data }))
-          .catch((err) => {
-            const msg = err instanceof Error ? err.message : String(err);
-            logDiagnostic('error', 'bg.handler', msg, `type=${message.type}`);
-            sendResponse({
-              success: false,
-              error: msg,
-            });
+      Promise.resolve(run)
+        .then((data) => sendResponse({ success: true, data }))
+        .catch((err) => {
+          const msg = err instanceof Error ? err.message : String(err);
+          logDiagnostic('error', 'bg.handler', msg, `type=${message.type}`);
+          sendResponse({
+            success: false,
+            error: msg,
           });
-        return true;
-      }
-
-      sendResponse({ success: true, data: result });
-      return false;
+        });
+      return true;
     }
   );
 }
diff --git a/src/ui/App.tsx b/src/ui/App.tsx
index a0c561a..38ff73b 100644
--- a/src/ui/App.tsx
+++ b/src/ui/App.tsx
@@ -16,11 +16,11 @@ import {
   FIRST_INSCRIPTION_GATE_SESSION_KEY,
 } from './components/FirstInscriptionGate';
 import { sendMessage } from '../shared/messages';
-import { MessageType, UserPreferences, LibraryItem, MediaItem, PersonItem } from '../shared/types';
+import { MessageType, UserPreferences } from '../shared/types';
 import { usePrefetch, prefetchPage, prefetchProps, type Page } from './hooks/usePrefetch';
 import { applyThemePreference, applyCinemaAtmosphere, watchSystemTheme } from '../shared/theme';
 import { FilmGrain } from './components/FilmGrain';
-import { ensureDemoLibraryIfEmpty, seedPracticeLibraryIfEmpty } from './lib/ensureDemoLibrary';
+import { seedPracticeLibraryIfEmpty } from './lib/ensureDemoLibrary';
 import { useNotice } from './components/NoticeProvider';
 import { formatUserError } from './utils/formatUserError';
 import { Icon, type IconName } from './components/icons';
@@ -32,11 +32,6 @@ import './styles/app-nav.css';
 const DRAWER_FOCUSABLE_SELECTOR =
   'button:not([disabled]), [href], input:not([disabled]), select:not([disabled]), textarea:not([disabled]), [tabindex]:not([tabindex="-1"])';
 
-interface LibraryStats {
-  movieCount: number;
-  tvCount: number;
-}
-
 interface NavItem {
   key: Page;
   label: string;
@@ -80,18 +75,19 @@ function getInitialPage(): Page {
   return 'home';
 }
 
-function NavIcon({ item }: { item: NavItem }) {
-  if (item.icon === 'I' || item.icon === 'II' || item.icon === 'III') {
-    return <span className="sidebar-nav-roman">{item.icon}</span>;
-  }
-  return <Icon name={item.icon} size={18} className="app-nav-house-icon" />;
-}
-
-function ExploreIcon({ name }: { name: IconName | string }) {
+function NavGlyph({
+  name,
+  size,
+  className,
+}: {
+  name: IconName | 'I' | 'II' | 'III';
+  size: number;
+  className: string;
+}) {
   if (name === 'I' || name === 'II' || name === 'III') {
     return <span className="sidebar-nav-roman">{name}</span>;
   }
-  return <Icon name={name as IconName} size={16} className="app-subnav-icon" />;
+  return <Icon name={name} size={size} className={className} />;
 }
 
 export function App() {
@@ -106,8 +102,6 @@ export function App() {
     return null;
   });
   const [prefs, setPrefs] = useState<UserPreferences | null>(null);
-  const [stats, setStats] = useState<LibraryStats>({ movieCount: 0, tvCount: 0 });
-  const [peopleCount, setPeopleCount] = useState(0);
   const initialPrefetchDone = useRef(false);
   const appOpenCounted = useRef(false);
   const menuToggleRef = useRef<HTMLButtonElement>(null);
@@ -173,18 +167,6 @@ export function App() {
         }
       }
     }).catch(() => {});
-
-    ensureDemoLibraryIfEmpty().then((library) => {
-      const movieCount = library.filter((item) => item.media?.type === 'movie').length;
-      const tvCount = library.filter((item) => item.media?.type === 'tv').length;
-      setStats({ movieCount, tvCount });
-    }).catch(() => {});
-
-    sendMessage<Record<string, unknown>, { people: PersonItem[] }>(MessageType.GET_ALL_PEOPLE, {}).then((res) => {
-      if (res.success && res.data?.people) {
-        setPeopleCount(res.data.people.length);
-      }
-    }).catch(() => {});
   }, []);
 
   // After first archive add, refresh prefs so the first-inscription gate can dismiss
@@ -221,20 +203,6 @@ export function App() {
     }
   }, [currentPage, prefetchPageOnMount]);
 
-  useEffect(() => {
-    const handleMessage = (message: unknown) => {
-      if (message && typeof message === 'object' && 'type' in message && (message as Record<string, unknown>).type === 'FILMMAKERS_UPDATED') {
-        sendMessage<Record<string, unknown>, { people: PersonItem[] }>(MessageType.GET_ALL_PEOPLE, {}).then((res) => {
-          if (res.success && res.data?.people) {
-            setPeopleCount(res.data.people.length);
-          }
-        }).catch(() => {});
-      }
-    };
-    chrome.runtime.onMessage.addListener(handleMessage);
-    return () => chrome.runtime.onMessage.removeListener(handleMessage);
-  }, []);
-
   // Drawer open: move focus in, trap Tab, Esc closes (interruptible spring)
   useEffect(() => {
     if (!drawerOpen) return;
@@ -477,7 +445,7 @@ export function App() {
               aria-current={currentPage === item.key ? 'page' : undefined}
               {...prefetchProps(item.key)}
             >
-              <ExploreIcon name={item.icon} />
+              <NavGlyph name={item.icon} size={16} className="app-subnav-icon" />
               <span className="app-subnav-label-full">{item.label}</span>
             </button>
           ))}
@@ -529,7 +497,7 @@ export function App() {
                 onClick={() => goToPage(item.key)}
                 {...prefetchProps(item.key)}
               >
-                <NavIcon item={item} />
+                <NavGlyph name={item.icon} size={18} className="app-nav-house-icon" />
                 <span className="side-menu-label">{item.label}</span>
               </button>
             ))}
@@ -545,7 +513,7 @@ export function App() {
                 onClick={() => goToPage(item.key)}
                 {...prefetchProps(item.key)}
               >
-                <ExploreIcon name={item.icon} />
+                <NavGlyph name={item.icon} size={16} className="app-subnav-icon" />
                 <span className="side-menu-label">{item.label}</span>
               </button>
             ))}
@@ -561,7 +529,7 @@ export function App() {
                 onClick={() => goToPage(item.key)}
                 {...prefetchProps(item.key)}
               >
-                <ExploreIcon name={item.icon} />
+                <NavGlyph name={item.icon} size={16} className="app-subnav-icon" />
                 <span className="side-menu-label">{item.label}</span>
               </button>
             ))}
diff --git a/src/ui/lib/ensureDemoLibrary.ts b/src/ui/lib/ensureDemoLibrary.ts
index 993ec79..d24db83 100644
--- a/src/ui/lib/ensureDemoLibrary.ts
+++ b/src/ui/lib/ensureDemoLibrary.ts
@@ -1,10 +1,8 @@
 import { sendMessage } from '@/shared/messages';
-import { MessageType, LibraryItem, MediaItem } from '@/shared/types';
+import { MessageType } from '@/shared/types';
+import type { JoinedItem } from '../components/archive/types';
 
-export interface JoinedLibraryItem {
-  library: LibraryItem;
-  media: MediaItem;
-}
+export type JoinedLibraryItem = JoinedItem;
 
 /**
  * Loads the current library. Does **not** auto-seed demo titles.
diff --git a/src/ui/pages/Home.tsx b/src/ui/pages/Home.tsx
index 49baff3..2051f9d 100644
--- a/src/ui/pages/Home.tsx
+++ b/src/ui/pages/Home.tsx
@@ -3,7 +3,6 @@ import { sendMessage } from '@/shared/messages';
 import {
   MessageType,
   MediaItem,
-  LibraryItem,
   Recommendation,
   UserPreferences,
   WeeklyDigest,
@@ -38,11 +37,7 @@ import {
 } from '@/shared/productCopy';
 import { incrementWeeklySelectionOpens } from '@/shared/activationMetrics';
 import { shouldShowDiscoveryFirstInscriptionBanner } from '../components/FirstInscriptionGate';
-
-interface JoinedItem {
-  library: LibraryItem;
-  media: MediaItem;
-}
+import type { JoinedItem } from '../components/archive/types';
 
 interface DigestPick extends WeeklyDigestItem {
   media?: MediaItem;
diff --git a/src/ui/pages/Stats.tsx b/src/ui/pages/Stats.tsx
index 321c63c..64400a3 100644
--- a/src/ui/pages/Stats.tsx
+++ b/src/ui/pages/Stats.tsx
@@ -1,7 +1,8 @@
 import { h } from 'preact';
 import { useState, useEffect, useMemo } from 'preact/hooks';
 import { sendMessage } from '@/shared/messages';
-import { MessageType, LibraryItem, MediaItem } from '@/shared/types';
+import { MessageType } from '@/shared/types';
+import type { JoinedItem } from '../components/archive/types';
 import {
   computeBookReadingStats,
   hasBookReadingActivity,
@@ -17,11 +18,6 @@ import {
 } from '@/shared/productCopy';
 import { EmotionalWeatherChart } from '../components/EmotionalWeatherChart';
 
-interface JoinedItem {
-  library: LibraryItem;
-  media: MediaItem;
-}
-
 interface StatsProps {
   onNavigate?: (page: 'search' | 'library' | 'home') => void;
 }
diff --git a/src/ui/popup.tsx b/src/ui/popup.tsx
index 3f7d786..b1d62d6 100644
--- a/src/ui/popup.tsx
+++ b/src/ui/popup.tsx
@@ -1,7 +1,7 @@
 import { render, h } from 'preact';
 import { useEffect, useState, useRef } from 'preact/hooks';
 import { sendMessage } from '../shared/messages';
-import { MessageType, UserPreferences, LibraryItem, MediaItem, SanctuaryIntent, LibraryStatus } from '../shared/types';
+import { MessageType, UserPreferences, MediaItem, SanctuaryIntent, LibraryStatus } from '../shared/types';
 import { applyThemePreference, applyCinemaAtmosphere, watchSystemTheme } from '../shared/theme';
 import { DEFAULT_EMOTIONS, type EmotionalSpectrum } from '../shared/emotions';
 import { EmotionalSliders } from './components/EmotionalSliders';
@@ -31,11 +31,7 @@ import '../shared/tokens.css';
 import './styles/popup.css';
 import './styles/emotional-components.css';
 import './components/inline-notice.css';
-
-interface JoinedItem {
-  library: LibraryItem;
-  media: MediaItem;
-}
+import type { JoinedItem } from './components/archive/types';
 
 function openSanctuary(page?: string) {
   const url = chrome.runtime.getURL(`ui/index.html${page ? `?page=${page}` : ''}`);
diff --git a/tests/messageRouter.characterization.test.ts b/tests/messageRouter.characterization.test.ts
new file mode 100644
index 0000000..e058c91
--- /dev/null
+++ b/tests/messageRouter.characterization.test.ts
@@ -0,0 +1,107 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { createMessageRouter } from '@/shared/messages';
+import { MessageType } from '@/shared/types';
+
+type MessageListener = (
+  message: { type: MessageType; payload: unknown },
+  sender: chrome.runtime.MessageSender,
+  sendResponse: (response: { success: boolean; data?: unknown; error?: string }) => void
+) => boolean | void;
+
+describe('characterization: message router always returns true after dispatch', () => {
+  const extensionOrigin = 'chrome-extension://test-extension-id/';
+  let listener: MessageListener;
+
+  function install(handlers: Parameters<typeof createMessageRouter>[0], options?: Parameters<typeof createMessageRouter>[1]) {
+    createMessageRouter(handlers, options);
+    listener = vi.mocked(chrome.runtime.onMessage.addListener).mock.calls.at(-1)![0] as MessageListener;
+  }
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    vi.mocked(chrome.runtime.getURL).mockReturnValue(extensionOrigin);
+  });
+
+  function dispatch(
+    type: MessageType,
+    payload: unknown,
+    handlerSetup: () => void
+  ): Promise<{ syncReturn: boolean | void; responses: unknown[] }> {
+    handlerSetup();
+    const responses: unknown[] = [];
+    const sender = { url: `${extensionOrigin}ui/index.html` } as chrome.runtime.MessageSender;
+    const syncReturn = listener({ type, payload }, sender, (r) => {
+      responses.push(r);
+    });
+    return new Promise((resolve) => {
+      queueMicrotask(() => resolve({ syncReturn, responses }));
+    });
+  }
+
+  it('sync handler: one sendResponse, return true', async () => {
+    const { syncReturn, responses } = await dispatch(MessageType.GET_LIBRARY, { x: 1 }, () => {
+      install({ [MessageType.GET_LIBRARY]: () => ({ ok: true }) });
+    });
+    await new Promise((r) => setTimeout(r, 0));
+    expect(syncReturn).toBe(true);
+    expect(responses).toEqual([{ success: true, data: { ok: true } }]);
+  });
+
+  it('async handler: one sendResponse, return true', async () => {
+    install({
+      [MessageType.GET_LIBRARY]: async () => {
+        await Promise.resolve();
+        return { async: true };
+      },
+    });
+    const responses: unknown[] = [];
+    const syncReturn = listener(
+      { type: MessageType.GET_LIBRARY, payload: {} },
+      { url: `${extensionOrigin}ui/index.html` } as chrome.runtime.MessageSender,
+      (r) => responses.push(r)
+    );
+    expect(syncReturn).toBe(true);
+    await vi.waitFor(() => {
+      expect(responses).toEqual([{ success: true, data: { async: true } }]);
+    });
+  });
+
+  it('async throwing handler: one error sendResponse, return true', async () => {
+    install({
+      [MessageType.GET_LIBRARY]: async () => {
+        throw new Error('boom-handler');
+      },
+    });
+    const responses: unknown[] = [];
+    const syncReturn = listener(
+      { type: MessageType.GET_LIBRARY, payload: {} },
+      { url: `${extensionOrigin}ui/index.html` } as chrome.runtime.MessageSender,
+      (r) => responses.push(r)
+    );
+    expect(syncReturn).toBe(true);
+    await vi.waitFor(() => {
+      expect(responses).toEqual([{ success: false, error: 'boom-handler' }]);
+    });
+  });
+
+  it('onBeforeDispatch runs then handler payload is unchanged', async () => {
+    const before = vi.fn(async () => {
+      throw new Error('before-fail');
+    });
+    install(
+      { [MessageType.GET_LIBRARY]: () => ({ after: true }) },
+      { onBeforeDispatch: before }
+    );
+    const responses: unknown[] = [];
+    const syncReturn = listener(
+      { type: MessageType.GET_LIBRARY, payload: { keep: 1 } },
+      { url: `${extensionOrigin}ui/index.html` } as chrome.runtime.MessageSender,
+      (r) => responses.push(r)
+    );
+    expect(syncReturn).toBe(true);
+    await vi.waitFor(() => {
+      expect(before).toHaveBeenCalledOnce();
+      expect(responses).toEqual([{ success: true, data: { after: true } }]);
+    });
+  });
+});
diff --git a/tests/overlay.test.ts b/tests/overlay.test.ts
index 86cb340..6480604 100644
--- a/tests/overlay.test.ts
+++ b/tests/overlay.test.ts
@@ -119,7 +119,7 @@ describe('Act I Discovery Plaque Injection (overlay.ts)', () => {
   });
 
   describe('destroy', () => {
-    it('unmounts Preact roots and removes message listeners', () => {
+    it('unmounts Preact roots and removes plaque hosts', () => {
       const manager = new MuseumPlaqueManager();
       const img = document.createElement('img');
       document.body.appendChild(img);
@@ -135,11 +135,9 @@ describe('Act I Discovery Plaque Injection (overlay.ts)', () => {
       };
 
       manager.attachBadge(img, match);
-      expect(chrome.runtime.onMessage.addListener).toHaveBeenCalled();
 
       manager.destroy();
 
-      expect(chrome.runtime.onMessage.removeListener).toHaveBeenCalled();
       const host = document.body.querySelector('div[data-subsume-badge]');
       expect(host).toBeNull();
     });