feat: add @-mention user search and tagging to Marmot group chat composer

Brings the MLS/Marmot message composer to parity with NIP-17 DMs:
typing @ shows the shared user-suggestion dropdown (local cache +
NIP-05 resolution), selecting a user inserts @npub…, and on send
NewMessageTagger rewrites mentions into nostr: URIs and collects
the referenced users as p-tags on the inner kind:9 rumor. Mentions
stay inside the MLS ciphertext; the outer kind:445 is unchanged.

Also applies MentionPreservingInputTransformation and
UrlUserTagOutputTransformation to the field so mentions render
highlighted while composing, matching the DM editor.

https://claude.ai/code/session_013NWdjCSegsf2FYSPPANX3n

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/AccountViewModel.kt

@@ -106,6 +106,7 @@ import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerInternal
 import com.vitorpamplona.quartz.nip01Core.signers.SignerExceptions
 import com.vitorpamplona.quartz.nip01Core.signers.eventTemplate
+import com.vitorpamplona.quartz.nip01Core.tags.people.PTag
 import com.vitorpamplona.quartz.nip01Core.tags.people.PubKeyReferenceTag
 import com.vitorpamplona.quartz.nip01Core.tags.people.isTaggedUser
 import com.vitorpamplona.quartz.nip02FollowList.ContactListEvent
@@ -1626,6 +1627,7 @@ class AccountViewModel(
         text: String,
         replyToInnerEventId: HexKey? = null,
         replyToInnerAuthorPubKey: HexKey? = null,
+        mentions: List<PTag> = emptyList(),
     ) {
         // Inner event construction lives on MarmotManager so CLI and UI don't drift.
         // persistOwn=false because Account.sendMarmotGroupMessage routes the outer
@@ -1638,6 +1640,7 @@ class AccountViewModel(
                     replyToEventId = replyToInnerEventId,
                     replyToAuthorPubKey = replyToInnerAuthorPubKey,
                     persistOwn = false,
+                    mentions = mentions,
                 )
                 ?: return
         val relays = account.marmotGroupRelays(nostrGroupId)

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

@@ -50,12 +50,18 @@ import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.commons.ui.text.currentWord
 import com.vitorpamplona.amethyst.model.Note
+import com.vitorpamplona.amethyst.ui.actions.MentionPreservingInputTransformation
+import com.vitorpamplona.amethyst.ui.actions.NewMessageTagger
+import com.vitorpamplona.amethyst.ui.actions.UrlUserTagOutputTransformation
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectFromGallery
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectedMedia
 import com.vitorpamplona.amethyst.ui.components.ThinPaddingTextField
 import com.vitorpamplona.amethyst.ui.feeds.WatchLifecycleAndUpdateModel
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
+import com.vitorpamplona.amethyst.ui.note.creators.userSuggestions.ShowUserSuggestionList
+import com.vitorpamplona.amethyst.ui.note.creators.userSuggestions.UserSuggestionState
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.feed.RefreshingChatroomFeedView
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.marmotGroup.send.MarmotFileSender
@@ -69,6 +75,7 @@ import com.vitorpamplona.amethyst.ui.theme.DoubleVertSpacer
 import com.vitorpamplona.amethyst.ui.theme.EditFieldBorder
 import com.vitorpamplona.amethyst.ui.theme.EditFieldModifier
 import com.vitorpamplona.amethyst.ui.theme.EditFieldTrailingIconModifier
+import com.vitorpamplona.amethyst.ui.theme.SuggestionListDefaultHeightChat
 import com.vitorpamplona.amethyst.ui.theme.placeholderText
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import kotlinx.collections.immutable.ImmutableList
@@ -181,6 +188,15 @@ fun MarmotGroupMessageComposer(
             )
         }
 
+    val userSuggestions =
+        remember(nostrGroupId) {
+            UserSuggestionState(accountViewModel.account, accountViewModel.nip05ClientBuilder())
+        }
+
+    DisposableEffect(nostrGroupId) {
+        onDispose { userSuggestions.reset() }
+    }
+
     // Upload dialog
     uploadState.multiOrchestrator?.let {
         MarmotGroupFileUploadDialog(
@@ -200,11 +216,33 @@ fun MarmotGroupMessageComposer(
     }
 
     Column(modifier = EditFieldModifier) {
+        ShowUserSuggestionList(
+            userSuggestions,
+            onSelect = { user ->
+                userSuggestions.replaceCurrentWord(messageState, messageState.currentWord(), user)
+                userSuggestions.reset()
+            },
+            accountViewModel = accountViewModel,
+            modifier = SuggestionListDefaultHeightChat,
+        )
+
         ThinPaddingTextField(
             state = messageState,
+            onTextChanged = {
+                if (messageState.selection.collapsed) {
+                    val lastWord = messageState.currentWord()
+                    if (lastWord.startsWith("@")) {
+                        userSuggestions.processCurrentWord(lastWord)
+                    } else {
+                        userSuggestions.reset()
+                    }
+                }
+            },
             onContentReceived = { uri, mimeType ->
                 uploadState.load(persistentListOf(SelectedMedia(uri, mimeType)))
             },
+            inputTransformation = MentionPreservingInputTransformation,
+            outputTransformation = UrlUserTagOutputTransformation(MaterialTheme.colorScheme.primary),
             modifier = Modifier.fillMaxWidth(),
             shape = EditFieldBorder,
             placeholder = {
@@ -235,11 +273,16 @@ fun MarmotGroupMessageComposer(
                         val replyAuthor = parentEvent?.pubKey
                         scope.launch(Dispatchers.IO) {
                             try {
+                                // Rewrites @npub…/@nprofile… mentions into nostr: URIs and
+                                // collects the referenced users as p-tags for the inner event.
+                                val tagger = NewMessageTagger(text, null, null, accountViewModel)
+                                tagger.run()
                                 accountViewModel.sendMarmotGroupMessage(
                                     nostrGroupId = nostrGroupId,
-                                    text = text,
+                                    text = tagger.message,
                                     replyToInnerEventId = replyId,
                                     replyToInnerAuthorPubKey = replyAuthor,
+                                    mentions = tagger.pTags?.map { it.toPTag() } ?: emptyList(),
                                 )
                                 messageState.clearText()
                                 replyTo.value = null

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/marmot/MarmotManager.kt

@@ -46,6 +46,8 @@ import com.vitorpamplona.quartz.nip01Core.core.hexToByteArray
 import com.vitorpamplona.quartz.nip01Core.core.toHexKey
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
+import com.vitorpamplona.quartz.nip01Core.tags.people.PTag
+import com.vitorpamplona.quartz.nip01Core.tags.people.pTags
 import com.vitorpamplona.quartz.nip18Reposts.quotes.QEventTag
 import com.vitorpamplona.quartz.nip18Reposts.quotes.quote
 import com.vitorpamplona.quartz.utils.Log
@@ -178,6 +180,11 @@ class MarmotManager(
      * `persistOwn = false`. Headless callers (CLI) should leave it at
      * the default.
      *
+     * [mentions] become p-tags on the inner kind:9 (users referenced via
+     * `nostr:npub…`/`nostr:nprofile…` in [text]), mirroring how NIP-17
+     * chat messages tag mentioned users. They stay inside the MLS
+     * ciphertext — the outer kind:445 never carries member pubkeys.
+     *
      * @return the signed kind:445 outer event together with the inner kind:9
      *   rumor id, so the caller can reference it for replies/reactions.
      */
@@ -187,10 +194,12 @@ class MarmotManager(
         replyToEventId: HexKey? = null,
         replyToAuthorPubKey: HexKey? = null,
         persistOwn: Boolean = true,
+        mentions: List<PTag> = emptyList(),
     ): TextMessageBundle {
         val template =
             com.vitorpamplona.quartz.nip01Core.signers
                 .eventTemplate<Event>(kind = 9, description = text) {
+                    pTags(mentions)
                     if (replyToEventId != null) {
                         // Mirror ChatEvent.reply(): NIP-18 q-tag references the
                         // parent inner kind:9 by id (+ optional author, no