feat: rank conversation participants first in @-mention suggestions

Adds an optional priorityPubkeys supplier to UserSuggestionState that
stable-sorts search results so the current conversation's participants
appear before network-wide matches (ranking only, never filters).

Wired per chat context:
- MLS/Marmot groups: live MLS member list
- NIP-17 DMs/groups: the room's users
- Public chats (NIP-28): authors who have posted in the channel
- Nests audio rooms: MeetingSpaceEvent participants + host

https://claude.ai/code/session_013NWdjCSegsf2FYSPPANX3n

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/creators/userSuggestions/UserSuggestionState.kt

@@ -28,6 +28,7 @@ import com.vitorpamplona.amethyst.logTime
 import com.vitorpamplona.amethyst.model.Account
 import com.vitorpamplona.amethyst.model.User
 import com.vitorpamplona.amethyst.service.relayClient.searchCommand.SearchQueryState
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.core.toHexKey
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.normalizeRelayUrlOrNull
 import com.vitorpamplona.quartz.nip05DnsIdentifiers.INip05Client
@@ -58,10 +59,20 @@ val userUriPrefixes =
         DualCase("nostr:nprofile"),
     )
 
+/**
+ * Drives the @-mention autocomplete dropdown: searches the local cache,
+ * relays, and NIP-05 identifiers for the word currently being typed.
+ *
+ * [priorityPubkeys] is a live supplier of pubkeys to rank first in the
+ * results — pass the current conversation's participants (NIP-17 room
+ * users, public-chat authors, MLS group members, …) so they beat
+ * network-wide matches. Ranking only; it never filters anyone out.
+ */
 @Stable
 class UserSuggestionState(
     val account: Account,
     val nip05Client: INip05Client,
+    val priorityPubkeys: () -> Set<HexKey> = { emptySet() },
 ) {
     val invalidations = MutableStateFlow(0)
     val currentWord = MutableStateFlow("")
@@ -158,7 +169,13 @@ class UserSuggestionState(
             }
             if (prefix != null) {
                 logTime("UserSuggestionState Search $prefix version $version") {
-                    account.cache.findUsersStartingWith(prefix, account)
+                    val found = account.cache.findUsersStartingWith(prefix, account)
+                    val priority = priorityPubkeys()
+                    if (priority.isEmpty()) {
+                        found
+                    } else {
+                        found.sortedByDescending { it.pubkeyHex in priority }
+                    }
                 }
             } else {
                 emptyList()

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/marmotGroup/MarmotGroupChatView.kt

@@ -190,7 +190,12 @@ fun MarmotGroupMessageComposer(
 
     val userSuggestions =
         remember(nostrGroupId) {
-            UserSuggestionState(accountViewModel.account, accountViewModel.nip05ClientBuilder())
+            val group = accountViewModel.account.marmotGroupList.getOrCreateGroup(nostrGroupId)
+            UserSuggestionState(
+                accountViewModel.account,
+                accountViewModel.nip05ClientBuilder(),
+                priorityPubkeys = { group.members.value.mapTo(mutableSetOf()) { it.pubkey } },
+            )
         }
 
     DisposableEffect(nostrGroupId) {

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/privateDM/send/ChatNewMessageViewModel.kt

@@ -261,7 +261,12 @@ class ChatNewMessageViewModel :
         this.canAddZapRaiser = hasLnAddress()
 
         this.userSuggestions?.reset()
-        this.userSuggestions = UserSuggestionState(accountVM.account, accountVM.nip05ClientBuilder())
+        this.userSuggestions =
+            UserSuggestionState(
+                accountVM.account,
+                accountVM.nip05ClientBuilder(),
+                priorityPubkeys = { room.value?.users ?: emptySet() },
+            )
 
         this.emojiSuggestions?.reset()
         this.emojiSuggestions = EmojiSuggestionState(accountVM.account)

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/send/ChannelNewMessageViewModel.kt

@@ -188,7 +188,14 @@ open class ChannelNewMessageViewModel :
         this.canAddZapRaiser = hasLnAddress()
 
         this.userSuggestions?.reset()
-        this.userSuggestions = UserSuggestionState(accountVM.account, accountVM.nip05ClientBuilder())
+        this.userSuggestions =
+            UserSuggestionState(
+                accountVM.account,
+                accountVM.nip05ClientBuilder(),
+                priorityPubkeys = {
+                    channel?.participatingAuthors(0)?.mapTo(mutableSetOf()) { it.pubkeyHex } ?: emptySet()
+                },
+            )
 
         this.emojiSuggestions?.reset()
         this.emojiSuggestions = EmojiSuggestionState(accountVM.account)

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/nests/room/chat/NestNewMessageViewModel.kt

@@ -194,7 +194,16 @@ open class NestNewMessageViewModel :
         this.canAddZapRaiser = hasLnAddress()
 
         this.userSuggestions?.reset()
-        this.userSuggestions = UserSuggestionState(accountVM.account, accountVM.nip05ClientBuilder())
+        this.userSuggestions =
+            UserSuggestionState(
+                accountVM.account,
+                accountVM.nip05ClientBuilder(),
+                priorityPubkeys = {
+                    (room?.event as? MeetingSpaceEvent)?.let { space ->
+                        space.participantKeys().toMutableSet().apply { add(space.pubKey) }
+                    } ?: emptySet()
+                },
+            )
 
         this.emojiSuggestions?.reset()
         this.emojiSuggestions = EmojiSuggestionState(accountVM.account)