fix(chats): stable per-chatroom LazyColumn key for messages list

The chatroom list keyed each row by `if (index == 0) index else item.idHex`.
Two problems:

1. Position 0 was hardcoded to key `0`, so when a new chatroom moved to
   the top, the existing composition slot was reused with state from the
   previous chatroom — observed as "the row updated and reordered but
   still shows the old result" right at the top.
2. For other positions, the key was the latest message's `idHex`. When a
   new message arrived in any chatroom the chatroom's representative
   Note got replaced (different idHex), so Compose threw away the row
   and rebuilt it from scratch — wasted work.

Fix: derive a stable key from chatroom identity instead of message id —
nostr group id for marmot rooms, channel id for public/ephemeral
channels, sorted user set for DMs. Falls back to `item.idHex` for
unrecognized event types (drafts etc.). Reorders now move the row;
new-message updates re-use the slot.

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/rooms/feed/ChatroomListFeedView.kt

@@ -25,14 +25,16 @@ import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.LazyListState
-import androidx.compose.foundation.lazy.itemsIndexed
+import androidx.compose.foundation.lazy.items
 import androidx.compose.material3.HorizontalDivider
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.ui.Modifier
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
+import com.vitorpamplona.amethyst.commons.model.marmotGroups.MarmotGroupChatroom
 import com.vitorpamplona.amethyst.commons.ui.feeds.FeedContentState
 import com.vitorpamplona.amethyst.commons.ui.feeds.FeedState
+import com.vitorpamplona.amethyst.model.Note
 import com.vitorpamplona.amethyst.ui.actions.CrossfadeIfEnabled
 import com.vitorpamplona.amethyst.ui.feeds.FeedEmpty
 import com.vitorpamplona.amethyst.ui.feeds.FeedError
@@ -45,6 +47,12 @@ import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.rooms.ChatroomHeaderCompose
 import com.vitorpamplona.amethyst.ui.theme.DividerThickness
 import com.vitorpamplona.amethyst.ui.theme.FeedPadding
+import com.vitorpamplona.quartz.experimental.ephemChat.chat.EphemeralChatEvent
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip17Dm.base.ChatroomKeyable
+import com.vitorpamplona.quartz.nip28PublicChat.admin.ChannelCreateEvent
+import com.vitorpamplona.quartz.nip28PublicChat.admin.ChannelMetadataEvent
+import com.vitorpamplona.quartz.nip28PublicChat.message.ChannelMessageEvent
 
 @Composable
 fun ChatroomListFeedView(
@@ -103,14 +111,16 @@ private fun FeedLoaded(
 ) {
     val items by loaded.feed.collectAsStateWithLifecycle()
 
+    val myPubKey = accountViewModel.userProfile().pubkeyHex
+
     LazyColumn(
         contentPadding = rememberFeedContentPadding(FeedPadding),
         state = listState,
     ) {
-        itemsIndexed(
+        items(
             items.list,
-            key = { index, item -> if (index == 0) index else item.idHex },
-        ) { _, item ->
+            key = { item -> chatroomLazyKey(item, myPubKey) },
+        ) { item ->
             Row(Modifier.fillMaxWidth()) {
                 ChatroomHeaderCompose(
                     item,
@@ -125,3 +135,40 @@ private fun FeedLoaded(
         }
     }
 }
+
+// Stable per-chatroom key — derived from chatroom identity, not the latest
+// message id, so reorders move the row instead of recreating it.
+private fun chatroomLazyKey(
+    item: Note,
+    myPubKey: HexKey,
+): String {
+    item.inGatherers
+        ?.firstNotNullOfOrNull { it as? MarmotGroupChatroom }
+        ?.let { return "marmot:${it.nostrGroupId}" }
+
+    return when (val event = item.event) {
+        is ChannelMessageEvent -> {
+            "ch:${event.channelId() ?: item.idHex}"
+        }
+
+        is ChannelMetadataEvent -> {
+            "ch:${event.channelId() ?: item.idHex}"
+        }
+
+        is ChannelCreateEvent -> {
+            "ch:${event.id}"
+        }
+
+        is EphemeralChatEvent -> {
+            "eph:${event.roomId()?.toKey() ?: item.idHex}"
+        }
+
+        is ChatroomKeyable -> {
+            "dm:${event.chatroomKey(myPubKey).users.sorted().joinToString(",")}"
+        }
+
+        else -> {
+            item.idHex
+        }
+    }
+}