feat: persist highlight metadata and offline events to localStorage

- Add localStorage persistence for highlightMetadataCache Map
- Add localStorage persistence for offlineCreatedEvents Set
- Load both caches from localStorage on module initialization
- Save to localStorage whenever caches are updated
- Update metadata cache during sync operations (isSyncing changes)
- Ensures airplane icon displays correctly after page reloads
- Gracefully handles localStorage errors and corrupted data

src/services/highlightEventProcessor.ts

@@ -21,38 +21,63 @@ const {
   getHighlightAttributions
 } = Helpers
 
+const METADATA_CACHE_KEY = 'highlightMetadataCache'
+
+type HighlightMetadata = {
+  publishedRelays?: string[]
+  isLocalOnly?: boolean
+  isSyncing?: boolean
+}
+
+/**
+ * Load highlight metadata from localStorage
+ */
+function loadHighlightMetadataFromStorage(): Map<string, HighlightMetadata> {
+  try {
+    const raw = localStorage.getItem(METADATA_CACHE_KEY)
+    if (!raw) return new Map()
+    
+    const parsed = JSON.parse(raw) as Record<string, HighlightMetadata>
+    return new Map(Object.entries(parsed))
+  } catch {
+    // Silently fail on parse errors or if storage is unavailable
+    return new Map()
+  }
+}
+
+/**
+ * Save highlight metadata to localStorage
+ */
+function saveHighlightMetadataToStorage(cache: Map<string, HighlightMetadata>): void {
+  try {
+    const record = Object.fromEntries(cache.entries())
+    localStorage.setItem(METADATA_CACHE_KEY, JSON.stringify(record))
+  } catch {
+    // Silently fail if storage is full or unavailable
+  }
+}
+
 /**
  * Cache for highlight metadata that persists across EventStore serialization
  * Key: event ID, Value: { publishedRelays, isLocalOnly, isSyncing }
  */
-const highlightMetadataCache = new Map<string, {
-  publishedRelays?: string[]
-  isLocalOnly?: boolean
-  isSyncing?: boolean
-}>()
+const highlightMetadataCache = loadHighlightMetadataFromStorage()
 
 /**
  * Store highlight metadata for an event ID
  */
 export function setHighlightMetadata(
   eventId: string,
-  metadata: {
-    publishedRelays?: string[]
-    isLocalOnly?: boolean
-    isSyncing?: boolean
-  }
+  metadata: HighlightMetadata
 ): void {
   highlightMetadataCache.set(eventId, metadata)
+  saveHighlightMetadataToStorage(highlightMetadataCache)
 }
 
 /**
  * Get highlight metadata for an event ID
  */
-export function getHighlightMetadata(eventId: string): {
-  publishedRelays?: string[]
-  isLocalOnly?: boolean
-  isSyncing?: boolean
-} | undefined {
+export function getHighlightMetadata(eventId: string): HighlightMetadata | undefined {
   return highlightMetadataCache.get(eventId)
 }
 

src/services/offlineSyncService.ts

@@ -3,11 +3,42 @@ import { NostrEvent } from 'nostr-tools'
 import { IEventStore } from 'applesauce-core'
 import { RELAYS } from '../config/relays'
 import { isLocalRelay } from '../utils/helpers'
+import { setHighlightMetadata, getHighlightMetadata } from './highlightEventProcessor'
+
+const OFFLINE_EVENTS_KEY = 'offlineCreatedEvents'
 
 let isSyncing = false
 
+/**
+ * Load offline events from localStorage
+ */
+function loadOfflineEventsFromStorage(): Set<string> {
+  try {
+    const raw = localStorage.getItem(OFFLINE_EVENTS_KEY)
+    if (!raw) return new Set()
+    
+    const parsed = JSON.parse(raw) as string[]
+    return new Set(parsed)
+  } catch {
+    // Silently fail on parse errors or if storage is unavailable
+    return new Set()
+  }
+}
+
+/**
+ * Save offline events to localStorage
+ */
+function saveOfflineEventsToStorage(events: Set<string>): void {
+  try {
+    const array = Array.from(events)
+    localStorage.setItem(OFFLINE_EVENTS_KEY, JSON.stringify(array))
+  } catch {
+    // Silently fail if storage is full or unavailable
+  }
+}
+
 // Track events created during offline period
-const offlineCreatedEvents = new Set<string>()
+const offlineCreatedEvents = loadOfflineEventsFromStorage()
 
 // Track events currently being synced
 const syncingEvents = new Set<string>()
@@ -20,6 +51,7 @@ const syncStateListeners: Array<(eventId: string, isSyncing: boolean) => void> =
  */
 export function markEventAsOfflineCreated(eventId: string): void {
   offlineCreatedEvents.add(eventId)
+  saveOfflineEventsToStorage(offlineCreatedEvents)
 }
 
 /**
@@ -94,6 +126,7 @@ export async function syncLocalEventsToRemote(
     if (eventsToSync.length === 0) {
       isSyncing = false
       offlineCreatedEvents.clear()
+      saveOfflineEventsToStorage(offlineCreatedEvents)
       return
     }
 
@@ -102,10 +135,17 @@ export async function syncLocalEventsToRemote(
       new Map(eventsToSync.map(e => [e.id, e])).values()
     )
 
-    // Mark all events as syncing
+    // Mark all events as syncing and update metadata
     uniqueEvents.forEach(event => {
       syncingEvents.add(event.id)
       notifySyncStateChange(event.id, true)
+      
+      // Update metadata cache to reflect syncing state
+      const existingMetadata = getHighlightMetadata(event.id)
+      setHighlightMetadata(event.id, {
+        ...existingMetadata,
+        isSyncing: true
+      })
     })
 
     // Publish to remote relays
@@ -125,13 +165,32 @@ export async function syncLocalEventsToRemote(
       syncingEvents.delete(eventId)
       offlineCreatedEvents.delete(eventId)
       notifySyncStateChange(eventId, false)
+      
+      // Update metadata cache: sync complete, no longer local-only
+      const existingMetadata = getHighlightMetadata(eventId)
+      setHighlightMetadata(eventId, {
+        ...existingMetadata,
+        isSyncing: false,
+        isLocalOnly: false
+      })
     })
     
+    // Save updated offline events set to localStorage
+    saveOfflineEventsToStorage(offlineCreatedEvents)
+    
     // Clear syncing state for failed events
     uniqueEvents.forEach(event => {
       if (!successfulIds.includes(event.id)) {
         syncingEvents.delete(event.id)
         notifySyncStateChange(event.id, false)
+        
+        // Update metadata cache: sync failed, still local-only
+        const existingMetadata = getHighlightMetadata(event.id)
+        setHighlightMetadata(event.id, {
+          ...existingMetadata,
+          isSyncing: false
+          // Keep isLocalOnly as true (sync failed)
+        })
       }
     })
   } catch (error) {