perf(cache): O(1) author lookup for metadata invalidation

consumeMetadata() was looping ALL notes in cache (O(N)) to find notes
by the author whose metadata changed. With hundreds of cached notes,
this caused lag on every metadata event.

Added notesByAuthor index (ConcurrentHashMap<HexKey, MutableSet<Note>>)
populated at loadEvent time. consumeMetadata now looks up notes by
author in O(1) instead of scanning the entire cache.

Before: ~500 notes × per metadata event = lag
After: ~3 notes per author × per metadata event = instant

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/cache/DesktopLocalCache.kt

@@ -85,8 +85,18 @@ class DesktopLocalCache : ICacheProvider {
     companion object {
     }
 
+    /** Index of notes by author pubkey — for fast metadata invalidation */
+    private val notesByAuthor = ConcurrentHashMap<HexKey, MutableSet<Note>>()
+
     val paymentTracker = NwcPaymentTracker()
 
+    private fun trackNoteAuthor(
+        note: Note,
+        authorPubkey: HexKey,
+    ) {
+        notesByAuthor.getOrPut(authorPubkey) { ConcurrentHashMap.newKeySet() }.add(note)
+    }
+
     // ----- User operations -----
 
     override fun getUserIfExists(pubkey: HexKey): User? = users.get(pubkey)
@@ -156,10 +166,9 @@ class DesktopLocalCache : ICacheProvider {
             if (newUserMetadata != null) {
                 user.updateUserInfo(newUserMetadata, event)
                 _metadataVersion.value++
-                // Invalidate metadata flows on notes by this author that have observers
+                // Invalidate metadata flows on notes by this author (O(K) via index)
-                // so QuotedNoteEmbed/FeedNoteCard recompose with updated avatar/name
+                notesByAuthor[event.pubKey]?.forEach { note ->
-                notes.forEach { _, note ->
+                    if (note.flowSet?.metadata?.hasObservers() == true) {
-                    if (note.author?.pubkeyHex == event.pubKey && note.flowSet?.metadata?.hasObservers() == true) {
                         note.flowSet?.metadata?.invalidateData()
                     }
                 }
@@ -245,6 +254,7 @@ class DesktopLocalCache : ICacheProvider {
         val author = getOrCreateUser(event.pubKey)
         val repliesTo = event.tagsWithoutCitations().map { getOrCreateNote(it) }
         note.loadEvent(event, author, repliesTo)
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
         repliesTo.forEach { it.addReply(note) }
         return true
@@ -263,6 +273,7 @@ class DesktopLocalCache : ICacheProvider {
         val author = getOrCreateUser(event.pubKey)
         val repliesTo = event.tagsWithoutCitations().map { getOrCreateNote(it) }
         note.loadEvent(event, author, repliesTo)
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
         repliesTo.forEach { it.addReply(note) }
         return true
@@ -283,6 +294,7 @@ class DesktopLocalCache : ICacheProvider {
             event.originalPost().mapNotNull { getNoteIfExists(it) } +
                 event.taggedAddresses().mapNotNull { addressableNotes.get(it.toValue()) }
         note.loadEvent(event, author, reactedTo)
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
         reactedTo.forEach { it.addReaction(note) }
         return true
@@ -300,6 +312,7 @@ class DesktopLocalCache : ICacheProvider {
         if (note.event != null) return false
         val author = getOrCreateUser(event.pubKey)
         note.loadEvent(event, author, emptyList())
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
         return true
     }
@@ -331,6 +344,7 @@ class DesktopLocalCache : ICacheProvider {
                 event.taggedAddresses().mapNotNull { addressableNotes.get(it.toValue()) }
 
         note.loadEvent(event, author, zappedNotes)
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
 
         // Link zap to target notes
@@ -358,6 +372,7 @@ class DesktopLocalCache : ICacheProvider {
         val boostedNote = boostedId?.let { getOrCreateNote(it) }
         val repliesTo = listOfNotNull(boostedNote)
         note.loadEvent(event, author, repliesTo)
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
         boostedNote?.addBoost(note)
         return true
@@ -377,6 +392,7 @@ class DesktopLocalCache : ICacheProvider {
         val boostedNote = event.boostedEventId()?.let { getOrCreateNote(it) }
         val repliesTo = listOfNotNull(boostedNote)
         note.loadEvent(event, author, repliesTo)
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
         boostedNote?.addBoost(note)
         return true
@@ -408,6 +424,7 @@ class DesktopLocalCache : ICacheProvider {
         if (note.event != null) return false
         val author = getOrCreateUser(event.pubKey)
         note.loadEvent(event, author, emptyList())
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
         return true
     }
@@ -467,6 +484,7 @@ class DesktopLocalCache : ICacheProvider {
         if (note.event != null) return false
 
         note.loadEvent(event, author, emptyList())
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
 
         zappedNote?.addZapPayment(note, null)
@@ -498,6 +516,7 @@ class DesktopLocalCache : ICacheProvider {
         if (note.event != null) return false
 
         note.loadEvent(event, author, emptyList())
+        trackNoteAuthor(note, event.pubKey)
         relay?.let { note.addRelay(it) }
 
         // Link response to zapped note via request
@@ -617,6 +636,7 @@ class DesktopLocalCache : ICacheProvider {
         _followedUsers.value = emptySet()
         followerCounts.clear()
         followingCounts.clear()
+        notesByAuthor.clear()
         lastContactListCreatedAt = 0L
     }
 }