feat: read MIP-01 group metadata from MLS GroupContext extensions

Implement end-to-end reading of MarmotGroupData (extension 0xF2EE)
from the MLS GroupContext.extensions and sync to the UI layer.

Quartz (protocol):
- MarmotGroupData.decodeTls(): deserialize from TLS wire format
  (version, nostrGroupId, name, description, admin pubkeys, relays,
  image fields)
- MarmotGroupData.fromExtensions(): find and decode from extension list
- MlsGroup.extensions: expose groupContext.extensions publicly

Commons (shared logic):
- MarmotGroupChatroom: add description, adminPubkeys, relays fields
  as MutableStateFlow for reactive UI
- MarmotManager.groupMetadata(): extract MIP-01 data from group
- MarmotManager.syncMetadataTo(): sync metadata + member count to
  a MarmotGroupChatroom

Sync points (amethyst):
- Account init: sync metadata after restoreAll() for all restored groups
- GiftWrapEventHandler: sync after Welcome processing (group join)
- GroupEventHandler: sync after CommitProcessed (epoch advances may
  update extensions via GroupContextExtensions proposals)

UI (GroupInfoScreen):
- Display group description from MIP-01 metadata
- Display relay URLs from MIP-01 metadata
- Mark admin members with "- admin" suffix (from adminPubkeys)

https://claude.ai/code/session_0194SxKfAU61PY92eqP4cCXM

amethyst/src/main/java/com/vitorpamplona/amethyst/model/Account.kt

@@ -2335,6 +2335,11 @@ class Account(
         if (marmotManager != null) {
             scope.launch(Dispatchers.IO) {
                 marmotManager.restoreAll()
+                // Sync MIP-01 metadata from restored groups to chatrooms
+                marmotManager.activeGroupIds().forEach { groupId ->
+                    val chatroom = marmotGroupList.getOrCreateGroup(groupId)
+                    marmotManager.syncMetadataTo(groupId, chatroom)
+                }
             }
         }
 

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

@@ -326,6 +326,10 @@ class GiftWrapEventHandler(
             is WelcomeResult.Joined -> {
                 Log.d("GiftWrapEventHandler", "Joined Marmot group ${result.nostrGroupId}")
 
+                // Sync MIP-01 metadata from group extensions to chatroom
+                val chatroom = account.marmotGroupList.getOrCreateGroup(result.nostrGroupId)
+                manager.syncMetadataTo(result.nostrGroupId, chatroom)
+
                 // Rotate KeyPackages if needed
                 if (result.needsKeyPackageRotation) {
                     account.publishMarmotKeyPackages()
@@ -483,6 +487,9 @@ class GroupEventHandler(
 
                 is GroupEventResult.CommitProcessed -> {
                     Log.d("GroupEventHandler", "Commit processed for group ${result.groupId}, epoch=${result.newEpoch}")
+                    // Sync MIP-01 metadata after epoch advance (extensions may have changed)
+                    val chatroom = account.marmotGroupList.getOrCreateGroup(result.groupId)
+                    manager.syncMetadataTo(result.groupId, chatroom)
                 }
 
                 is GroupEventResult.CommitPending -> {

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

@@ -78,6 +78,9 @@ fun MarmotGroupInfoScreen(
             accountViewModel.account.marmotGroupList.getOrCreateGroup(nostrGroupId)
         }
     val displayName by chatroom.displayName.collectAsStateWithLifecycle()
+    val groupDescription by chatroom.description.collectAsStateWithLifecycle()
+    val adminPubkeys by chatroom.adminPubkeys.collectAsStateWithLifecycle()
+    val groupRelays by chatroom.relays.collectAsStateWithLifecycle()
     var members by remember { mutableStateOf(emptyList<GroupMemberInfo>()) }
     var showLeaveDialog by remember { mutableStateOf(false) }
     val scope = rememberCoroutineScope()
@@ -130,18 +133,28 @@ fun MarmotGroupInfoScreen(
                         style = MaterialTheme.typography.headlineSmall,
                         fontWeight = FontWeight.Bold,
                     )
+                    if (!groupDescription.isNullOrEmpty()) {
+                        Text(
+                            text = groupDescription!!,
+                            style = MaterialTheme.typography.bodyMedium,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant,
+                            modifier = Modifier.padding(top = 4.dp),
+                        )
+                    }
                     Text(
                         text = "${members.size} members",
                         style = MaterialTheme.typography.bodyMedium,
                         color = MaterialTheme.colorScheme.onSurfaceVariant,
                         modifier = Modifier.padding(top = 4.dp),
                     )
-                    Text(
+                    if (groupRelays.isNotEmpty()) {
-                        text = "Group ID: ${nostrGroupId.take(16)}...",
+                        Text(
-                        style = MaterialTheme.typography.bodySmall,
+                            text = "Relays: ${groupRelays.joinToString(", ")}",
-                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                            style = MaterialTheme.typography.bodySmall,
-                        modifier = Modifier.padding(top = 2.dp),
+                            color = MaterialTheme.colorScheme.onSurfaceVariant,
-                    )
+                            modifier = Modifier.padding(top = 2.dp),
+                        )
+                    }
                     val epoch = accountViewModel.account.marmotManager?.groupEpoch(nostrGroupId)
                     if (epoch != null) {
                         Text(
@@ -170,6 +183,7 @@ fun MarmotGroupInfoScreen(
                 MemberRow(
                     member = member,
                     isMe = member.pubkey == myPubkey,
+                    isAdmin = member.pubkey in adminPubkeys,
                     accountViewModel = accountViewModel,
                     nav = nav,
                 )
@@ -222,6 +236,7 @@ fun MarmotGroupInfoScreen(
 fun MemberRow(
     member: GroupMemberInfo,
     isMe: Boolean,
+    isAdmin: Boolean,
     accountViewModel: AccountViewModel,
     nav: INav,
 ) {
@@ -243,24 +258,19 @@ fun MemberRow(
         Column(modifier = Modifier.weight(1f)) {
             LoadUser(baseUserHex = member.pubkey, accountViewModel = accountViewModel) { user ->
                 val displayName = user?.toBestDisplayName() ?: "${member.pubkey.take(16)}..."
+                val suffix =
+                    buildString {
+                        if (isMe) append(" (you)")
+                        if (isAdmin) append(" - admin")
+                    }
                 Text(
-                    text =
+                    text = "$displayName$suffix",
-                        if (isMe) {
-                            "$displayName (you)"
-                        } else {
-                            displayName
-                        },
                     style = MaterialTheme.typography.bodyMedium,
                     maxLines = 1,
                     overflow = TextOverflow.Ellipsis,
-                    fontWeight = if (isMe) FontWeight.Bold else FontWeight.Normal,
+                    fontWeight = if (isMe || isAdmin) FontWeight.Bold else FontWeight.Normal,
                 )
             }
-            Text(
-                text = "Leaf #${member.leafIndex}",
-                style = MaterialTheme.typography.bodySmall,
-                color = MaterialTheme.colorScheme.onSurfaceVariant,
-            )
         }
     }
 }

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

@@ -20,6 +20,7 @@
  */
 package com.vitorpamplona.amethyst.commons.marmot
 
+import com.vitorpamplona.amethyst.commons.model.marmotGroups.MarmotGroupChatroom
 import com.vitorpamplona.quartz.marmot.GroupEventResult
 import com.vitorpamplona.quartz.marmot.MarmotInboundProcessor
 import com.vitorpamplona.quartz.marmot.MarmotOutboundProcessor
@@ -31,6 +32,7 @@ import com.vitorpamplona.quartz.marmot.WelcomeResult
 import com.vitorpamplona.quartz.marmot.mip00KeyPackages.KeyPackageEvent
 import com.vitorpamplona.quartz.marmot.mip00KeyPackages.KeyPackageRotationManager
 import com.vitorpamplona.quartz.marmot.mip00KeyPackages.KeyPackageUtils
+import com.vitorpamplona.quartz.marmot.mip01Groups.MarmotGroupData
 import com.vitorpamplona.quartz.marmot.mip02Welcome.WelcomeEvent
 import com.vitorpamplona.quartz.marmot.mip03GroupMessages.GroupEvent
 import com.vitorpamplona.quartz.marmot.mls.group.MlsGroupManager
@@ -287,6 +289,37 @@ class MarmotManager(
      * Get the current epoch for a group.
      */
     fun groupEpoch(nostrGroupId: HexKey): Long? = groupManager.getGroup(nostrGroupId)?.epoch
+
+    /**
+     * Get the MIP-01 group metadata from the MLS GroupContext extensions.
+     * Returns null if the group doesn't exist or has no MarmotGroupData extension.
+     */
+    fun groupMetadata(nostrGroupId: HexKey): MarmotGroupData? {
+        val group = groupManager.getGroup(nostrGroupId) ?: return null
+        return MarmotGroupData.fromExtensions(group.extensions)
+    }
+
+    /**
+     * Sync MIP-01 metadata and member info from the MLS group into a [MarmotGroupChatroom].
+     * Call after joining a group, processing a commit, or restoring from storage.
+     */
+    fun syncMetadataTo(
+        nostrGroupId: HexKey,
+        chatroom: MarmotGroupChatroom,
+    ) {
+        val metadata = groupMetadata(nostrGroupId)
+        if (metadata != null) {
+            if (metadata.name.isNotEmpty()) {
+                chatroom.displayName.value = metadata.name
+            }
+            if (metadata.description.isNotEmpty()) {
+                chatroom.description.value = metadata.description
+            }
+            chatroom.adminPubkeys.value = metadata.adminPubkeys
+            chatroom.relays.value = metadata.relays
+        }
+        chatroom.memberCount.value = memberCount(nostrGroupId)
+    }
 }
 
 /**

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/marmotGroups/MarmotGroupChatroom.kt

@@ -42,6 +42,9 @@ class MarmotGroupChatroom(
 ) : NotesGatherer {
     var messages: Set<Note> = setOf()
     var displayName = MutableStateFlow<String?>(null)
+    var description = MutableStateFlow<String?>(null)
+    var adminPubkeys = MutableStateFlow<List<HexKey>>(emptyList())
+    var relays = MutableStateFlow<List<String>>(emptyList())
     var memberCount = MutableStateFlow(0)
     var newestMessage: Note? = null
 

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/marmot/mip01Groups/MarmotGroupData.kt

@@ -21,7 +21,10 @@
 package com.vitorpamplona.quartz.marmot.mip01Groups
 
 import androidx.compose.runtime.Immutable
+import com.vitorpamplona.quartz.marmot.mls.codec.TlsReader
+import com.vitorpamplona.quartz.marmot.mls.tree.Extension
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.toHexKey
 
 /**
  * Marmot Group Data Extension (MIP-01) — extension ID 0xF2EE.
@@ -91,5 +94,86 @@ data class MarmotGroupData(
 
         /** MLS extension type identifier for marmot_group_data */
         const val EXTENSION_ID: UShort = 0xF2EEu
+        const val EXTENSION_ID_INT: Int = 0xF2EE
+
+        /**
+         * Find and decode the MarmotGroupData extension from a list of MLS extensions.
+         * Returns null if no extension with type 0xF2EE is present.
+         */
+        fun fromExtensions(extensions: List<Extension>): MarmotGroupData? {
+            val ext = extensions.find { it.extensionType == EXTENSION_ID_INT } ?: return null
+            return decodeTls(ext.extensionData)
+        }
+
+        /**
+         * Decode MarmotGroupData from TLS wire format bytes.
+         *
+         * Wire format:
+         * ```
+         * uint16 version
+         * opaque nostr_group_id[32]
+         * opaque name<0..2^16-1>
+         * opaque description<0..2^16-1>
+         * opaque admin_pubkeys<0..2^16-1>   // concatenated 32-byte keys
+         * RelayUrl relays<0..2^16-1>        // length-prefixed UTF-8 strings
+         * opaque image_hash<0..32>
+         * opaque image_key<0..32>
+         * opaque image_nonce<0..12>
+         * opaque image_upload_key<0..32>
+         * ```
+         */
+        fun decodeTls(data: ByteArray): MarmotGroupData? =
+            try {
+                val reader = TlsReader(data)
+                val version = reader.readUint16()
+
+                val nostrGroupIdBytes = reader.readBytes(32)
+                val nostrGroupId = nostrGroupIdBytes.toHexKey()
+
+                val nameBytes = reader.readOpaque2()
+                val name = nameBytes.decodeToString()
+
+                val descriptionBytes = reader.readOpaque2()
+                val description = descriptionBytes.decodeToString()
+
+                // Admin pubkeys: concatenated 32-byte keys within a length-prefixed block
+                val adminBlock = reader.readOpaque2()
+                val adminPubkeys = mutableListOf<HexKey>()
+                var i = 0
+                while (i + 32 <= adminBlock.size) {
+                    adminPubkeys.add(adminBlock.copyOfRange(i, i + 32).toHexKey())
+                    i += 32
+                }
+
+                // Relays: length-prefixed block of length-prefixed UTF-8 strings
+                val relaysBlock = reader.readOpaque2()
+                val relays = mutableListOf<String>()
+                val relayReader = TlsReader(relaysBlock)
+                while (relayReader.hasRemaining) {
+                    val relayBytes = relayReader.readOpaque2()
+                    relays.add(relayBytes.decodeToString())
+                }
+
+                // Optional fields — read if remaining
+                val imageHash = if (reader.hasRemaining) reader.readOpaque2().takeIf { it.isNotEmpty() }?.toHexKey() else null
+                val imageKey = if (reader.hasRemaining) reader.readOpaque2().takeIf { it.isNotEmpty() } else null
+                val imageNonce = if (reader.hasRemaining) reader.readOpaque2().takeIf { it.isNotEmpty() } else null
+                val imageUploadKey = if (reader.hasRemaining) reader.readOpaque2().takeIf { it.isNotEmpty() } else null
+
+                MarmotGroupData(
+                    version = version,
+                    nostrGroupId = nostrGroupId,
+                    name = name,
+                    description = description,
+                    adminPubkeys = adminPubkeys,
+                    relays = relays,
+                    imageHash = imageHash,
+                    imageKey = imageKey,
+                    imageNonce = imageNonce,
+                    imageUploadKey = imageUploadKey,
+                )
+            } catch (e: Exception) {
+                null
+            }
     }
 }

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/marmot/mls/group/MlsGroup.kt

@@ -107,6 +107,7 @@ class MlsGroup private constructor(
     val groupId: ByteArray get() = groupContext.groupId
     val epoch: Long get() = groupContext.epoch
     val leafIndex: Int get() = myLeafIndex
+    val extensions: List<com.vitorpamplona.quartz.marmot.mls.tree.Extension> get() = groupContext.extensions
 
     // --- State Persistence ---