Simplifies if a chatroom sender intersects with the follow list.

app/src/main/java/com/vitorpamplona/amethyst/model/Chatroom.kt

@@ -27,6 +27,7 @@ import com.vitorpamplona.quartz.utils.TimeUtils
 
 @Stable
 class Chatroom() {
+    var authors: Set<User> = setOf()
     var roomMessages: Set<Note> = setOf()
     var subject: String? = null
     var subjectCreatedAt: Long? = null
@@ -38,6 +39,12 @@ class Chatroom() {
         if (msg !in roomMessages) {
             roomMessages = roomMessages + msg
 
+            msg.author?.let { author ->
+                if (author !in authors) {
+                    authors += author
+                }
+            }
+
             val newSubject = msg.event?.subject()
 
             if (newSubject != null && (msg.createdAt() ?: 0) > (subjectCreatedAt ?: 0)) {
@@ -51,8 +58,8 @@ class Chatroom() {
     fun removeMessageSync(msg: Note) {
         checkNotInMainThread()
 
-        if (msg !in roomMessages) {
+        if (msg in roomMessages) {
-            roomMessages = roomMessages + msg
+            roomMessages = roomMessages - msg
 
             roomMessages
                 .filter { it.event?.subject() != null }
@@ -66,7 +73,7 @@ class Chatroom() {
     }
 
     fun senderIntersects(keySet: Set<HexKey>): Boolean {
-        return roomMessages.any { it.author?.pubkeyHex in keySet }
+        return authors.any { it.pubkeyHex in keySet }
     }
 
     fun pruneMessagesToTheLatestOnly(): Set<Note> {

app/src/main/java/com/vitorpamplona/amethyst/model/User.kt

@@ -394,7 +394,7 @@ class User(val pubkeyHex: String) {
     fun hasSentMessagesTo(key: ChatroomKey?): Boolean {
         val messagesToUser = privateChatrooms[key] ?: return false
 
-        return messagesToUser.roomMessages.any { this.pubkeyHex == it.author?.pubkeyHex }
+        return messagesToUser.authors.any { this == it }
     }
 
     fun hasReport(