feat(buzz): Concord-style threading for Buzz chat replies

Concord threads chat messages with kind-1111 minichat comments, but Buzz relays
reject kind-1111 — so Buzz replies fell back to inline 40002 and rendered as flat
quotes, never opening a thread.

Buzz already threads over 40002 NIP-10 markers (matching block/buzz): a reply-marked,
non-`broadcast` 40002 is a thread reply; a `broadcast=1` one is an inline timeline
sibling. Teach Amethyst's minichat to speak that dialect:

- Add `isMinichatReply(event)`: kind-1111 CommentEvent, OR a Buzz 40002 thread reply
  (reply-marked, non-broadcast). Used by all three read sites so they agree.
- `LocalCache.computeReplyTo`: link a 40002 thread reply into its parent's replies.
- Timeline filter, minichat reply-count, and minichat feed now key on that predicate,
  so 40002 thread replies leave the timeline, get counted on the "N replies" chip, and
  render inside the minichat.
- Send: an INLINE reply on Buzz sets `broadcast=1` (stays inline); MINICHAT omits it
  (threads). `sendMinichatReply` posts a 40002 thread reply on Buzz instead of kind-1111.

Verified on device: a message shows an "N replies" chip, opens the Thread view with the
root + replies + composer, replies post and increment the count, and thread replies no
longer appear inline in the main chat.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -34,6 +34,7 @@ import com.vitorpamplona.amethyst.commons.connectedApps.signers.NostrSignerPermi
 import com.vitorpamplona.amethyst.commons.connectedApps.signers.NostrSignerPermissionStore
 import com.vitorpamplona.amethyst.commons.marmot.MarmotManager
 import com.vitorpamplona.amethyst.commons.model.IAccount
+import com.vitorpamplona.amethyst.commons.model.buzz.BuzzRelayDialect
 import com.vitorpamplona.amethyst.commons.model.concord.ConcordChannel
 import com.vitorpamplona.amethyst.commons.model.concord.ConcordChannelListState
 import com.vitorpamplona.amethyst.commons.model.concord.ConcordSessionManager
@@ -157,6 +158,10 @@ import com.vitorpamplona.quartz.buzz.dm.DmAddMemberEvent
 import com.vitorpamplona.quartz.buzz.dm.DmHideEvent
 import com.vitorpamplona.quartz.buzz.dm.DmOpenEvent
 import com.vitorpamplona.quartz.buzz.presence.TypingIndicatorEvent
+import com.vitorpamplona.quartz.buzz.stream.StreamMessageV2Event
+import com.vitorpamplona.quartz.buzz.threading.buzzThread
+import com.vitorpamplona.quartz.buzz.threading.buzzThreadReply
+import com.vitorpamplona.quartz.buzz.threading.buzzThreadRoot
 import com.vitorpamplona.quartz.concord.cord02Community.ConcordCommunityListEntry
 import com.vitorpamplona.quartz.concord.cord02Community.ConcordCommunityListEvent
 import com.vitorpamplona.quartz.concord.cord02Community.HeldRoot
@@ -229,6 +234,7 @@ import com.vitorpamplona.quartz.nip01Core.tags.events.ETag
 import com.vitorpamplona.quartz.nip01Core.tags.hashtags.hasMoreHashtagsThan
 import com.vitorpamplona.quartz.nip01Core.tags.hashtags.hashtags
 import com.vitorpamplona.quartz.nip01Core.tags.people.PTag
+import com.vitorpamplona.quartz.nip01Core.tags.people.pTag
 import com.vitorpamplona.quartz.nip01Core.tags.people.taggedUserIds
 import com.vitorpamplona.quartz.nip01Core.tags.references.references
 import com.vitorpamplona.quartz.nip03Timestamp.OtsResolver
@@ -2286,12 +2292,25 @@ class Account(
         gatherers?.firstNotNullOfOrNull { it as? RelayGroupChannel }?.let { group ->
             val hostRelay = group.groupId.relayUrl
             val signed =
-                signer.sign(
-                    CommentEvent.replyBuilder(text, EventHintBundle(rootEvent, hostRelay)) {
-                        hTag(group.groupId.id)
-                        previous(group.previousEventRefs(pubKey))
-                    },
-                )
+                if (BuzzRelayDialect.isBuzz(hostRelay)) {
+                    // Buzz rejects kind-1111, so its minichat threads with a 40002 marked at the message's
+                    // root (never `broadcast` — a minichat reply always lives in the thread).
+                    val root = rootEvent.tags.buzzThreadRoot() ?: rootEvent.tags.buzzThreadReply() ?: rootEvent.id
+                    signer.sign(
+                        StreamMessageV2Event.build(group.groupId.id, text) {
+                            buzzThread(root, rootEvent.id)
+                            rootNote.author?.pubkeyHex?.let { pTag(PTag(it)) }
+                            previous(group.previousEventRefs(pubKey))
+                        },
+                    )
+                } else {
+                    signer.sign(
+                        CommentEvent.replyBuilder(text, EventHintBundle(rootEvent, hostRelay)) {
+                            hTag(group.groupId.id)
+                            previous(group.previousEventRefs(pubKey))
+                        },
+                    )
+                }
             cache.justConsumeMyOwnEvent(signed)
             client.publish(signed, setOf(hostRelay))
             return true

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

@@ -1237,6 +1237,12 @@ object LocalCache : ILocalCache, ICacheProvider {
                 event.tagsWithoutCitations().mapNotNull { checkGetOrCreateNote(it) }
             }
 
+            is StreamMessageV2Event -> {
+                // A Buzz thread reply links to the message it answers (its `reply`-marked e-tag) so it
+                // lands in that message's replies (the minichat). A plain message / non-reply has no marker.
+                listOfNotNull(event.tags.buzzThreadReply()?.let { checkGetOrCreateNote(it) })
+            }
+
             is VoiceReplyEvent -> {
                 event.markedReplyTos().mapNotNull { checkGetOrCreateNote(it) }
             }

amethyst/src/main/java/com/vitorpamplona/amethyst/service/relayClient/reqCommand/event/EventObservers.kt

@@ -30,10 +30,10 @@ import com.vitorpamplona.amethyst.model.Note
 import com.vitorpamplona.amethyst.model.NoteState
 import com.vitorpamplona.amethyst.model.User
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.isMinichatReply
 import com.vitorpamplona.quartz.nip01Core.core.Event
 import com.vitorpamplona.quartz.nip18Reposts.GenericRepostEvent
 import com.vitorpamplona.quartz.nip18Reposts.RepostEvent
-import com.vitorpamplona.quartz.nip22Comments.CommentEvent
 import com.vitorpamplona.quartz.nip72ModCommunities.approval.CommunityPostApprovalEvent
 import com.vitorpamplona.quartz.nip72ModCommunities.definition.CommunityDefinitionEvent
 import com.vitorpamplona.quartz.nip72ModCommunities.isForCommunity
@@ -240,11 +240,11 @@ fun observeNoteMinichatReplyCount(
                 .flow()
                 .replies.stateFlow
                 .sample(200)
-                .mapLatest { it.note.replies.count { reply -> reply.event is CommentEvent } }
+                .mapLatest { it.note.replies.count { reply -> isMinichatReply(reply.event) } }
                 .distinctUntilChanged()
         }
 
-    return flow.collectAsStateWithLifecycle(note.replies.count { it.event is CommentEvent })
+    return flow.collectAsStateWithLifecycle(note.replies.count { isMinichatReply(it.event) })
 }
 
 @Composable

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

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.screen.loggedIn.chats
+
+import com.vitorpamplona.quartz.buzz.stream.StreamMessageV2Event
+import com.vitorpamplona.quartz.buzz.threading.buzzThreadReply
+import com.vitorpamplona.quartz.nip01Core.core.Event
+import com.vitorpamplona.quartz.nip22Comments.CommentEvent
+
+/**
+ * Whether [event] is a **minichat thread reply** — a reply that lives inside the thread opened from
+ * its parent message, NOT as a flat sibling in the main timeline. Two dialects express the same idea:
+ *
+ * - **NIP-28/NIP-29 (public chats, Concord)**: a kind-1111 [CommentEvent].
+ * - **Buzz workspaces**: a kind-40002 [StreamMessageV2Event] carrying a NIP-10 `reply`-marked `e` tag
+ *   and NOT flagged `broadcast` (Buzz rejects kind-1111, so it threads chat with 40002 markers; a
+ *   `broadcast=1` reply is an inline timeline sibling, matching block/buzz's `isThreadReply`).
+ *
+ * The timeline filter drops these (they belong in the minichat), the minichat count counts them, and
+ * the minichat feed shows them — so all three agree on one definition.
+ */
+fun isMinichatReply(event: Event?): Boolean =
+    when (event) {
+        is CommentEvent -> true
+        is StreamMessageV2Event -> !event.isBroadcast() && event.tags.buzzThreadReply() != null
+        else -> false
+    }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/minichat/MinichatFeedViewModel.kt

@@ -25,7 +25,7 @@ import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.viewModelScope
 import com.vitorpamplona.amethyst.model.Account
 import com.vitorpamplona.amethyst.model.Note
-import com.vitorpamplona.quartz.nip22Comments.CommentEvent
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.isMinichatReply
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.SharingStarted
@@ -57,7 +57,7 @@ class MinichatFeedViewModel(
 
     private fun collectReplies(): List<Note> =
         rootNote.replies
-            .filter { it.event is CommentEvent && account.isAcceptable(it) }
+            .filter { isMinichatReply(it.event) && account.isAcceptable(it) }
             .sortedWith(compareBy({ it.createdAt() ?: 0L }, { it.idHex }))
 
     class Factory(

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/dal/ChannelFeedFilter.kt

@@ -26,7 +26,7 @@ import com.vitorpamplona.amethyst.model.Note
 import com.vitorpamplona.amethyst.ui.dal.AdditiveFeedFilter
 import com.vitorpamplona.amethyst.ui.dal.ChangesFlowFilter
 import com.vitorpamplona.amethyst.ui.dal.sortedByDefaultFeedOrder
-import com.vitorpamplona.quartz.nip22Comments.CommentEvent
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.isMinichatReply
 
 class ChannelFeedFilter(
     val channel: Channel,
@@ -37,10 +37,10 @@ class ChannelFeedFilter(
 
     override fun changesFlow() = channel.changesFlow()
 
-    // A kind-1111 comment is a *minichat* reply — it lives in the thread opened from its
-    // root message, not as a flat sibling in the main timeline (an inline reply is a normal
-    // kind-9/42 message and stays). Everything else the channel gathered is a timeline message.
-    private fun isTimelineMessage(note: Note): Boolean = note.event !is CommentEvent && account.isAcceptable(note)
+    // A minichat reply — a kind-1111 comment, or a Buzz 40002 thread reply (reply-marked, non-broadcast)
+    // — lives in the thread opened from its root message, not as a flat sibling in the main timeline.
+    // An inline reply (kind-9/42, or a Buzz broadcast=1 reply) is a normal message and stays.
+    private fun isTimelineMessage(note: Note): Boolean = !isMinichatReply(note.event) && account.isAcceptable(note)
 
     override fun feed(): List<Note> = sort(channel.notes.filterIntoSet { _, it -> isTimelineMessage(it) })
 

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

@@ -773,7 +773,11 @@ open class ChannelNewMessageViewModel :
                 // verified Buzz events), not a channel subtype: channel instances are
                 // captured by screens for their whole life, so the dialect must be
                 // able to flip mid-session without swapping objects.
-                StreamMessageV2Event.build(channel.groupId.id, tagger.message) {
+                // Reply routing (Buzz has no kind-1111): an INLINE reply is flagged `broadcast` so it stays
+                // a flat timeline sibling; a MINICHAT reply omits it so the thread markers pull it into the
+                // message's minichat (mirrors block/buzz's broadcast-vs-thread split). A non-reply is neither.
+                val broadcastReply = replyTo.value != null && replyMode.value == ReplyMode.INLINE
+                StreamMessageV2Event.build(channel.groupId.id, tagger.message, broadcast = broadcastReply) {
                     replyTo.value?.let { parent ->
                         // The parent's root marker (when it is itself a nested reply),
                         // else the parent's OWN reply target (a direct reply's collapsed