feat(chat): chat-styled minichat screen + route, chip opens it

Adds the "chat within a chat" screen the N-replies chip now opens: the root
message pinned at top, its kind-1111 thread replies below as chat bubbles (reusing
ChatroomMessageCompose so they look identical to the main chat), and a composer
that posts a kind-1111 rooted at that message — flat, so replying inside a minichat
doesn't spawn sub-threads.

- Route.ChatMinichat(rootId) + AppNavigation registration + MinichatScreen.
- The shared "N replies" chip now navigates to the minichat instead of the generic
  thread view.
- Account.sendMinichatReply resolves the chat context from the note's gatherer and
  drives the Concord channel path (kind-1111 on the plane). Observing the root's
  replies also loads kind-1111s from relays, so public-chat minichats already
  display; their send path (NIP-28/NIP-29) is the remaining follow-up.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CzJ2Cwo8tg4oZq43oRa3ig

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

@@ -1986,6 +1986,26 @@ class Account(
         return true
     }
 
+    /**
+     * Post [text] into [rootNote]'s minichat — a kind-1111 thread reply rooted at that
+     * message. Resolves the chat context from the note's gatherer; today it drives the
+     * Concord channel path (NIP-28/NIP-29 public-chat minichats are a follow-up). Returns
+     * false if the message isn't in a chat we can post a thread reply to.
+     */
+    suspend fun sendMinichatReply(
+        rootNote: Note,
+        text: String,
+    ): Boolean {
+        val concord = rootNote.inGatherers?.firstNotNullOfOrNull { it as? ConcordChannel } ?: return false
+        return sendConcordChannelMessage(
+            concord.channelId.communityId,
+            concord.channelId.channelId,
+            text,
+            rootNote,
+            ReplyMode.MINICHAT,
+        )
+    }
+
     /**
      * React to a Concord message with [reaction] (e.g. `"+"`, an emoji). Mirrors
      * [sendConcordChannelMessage]: builds a kind-7 rumor bound to the message's

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/AppNavigation.kt

@@ -97,6 +97,7 @@ import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.marmotGroup.EditGroup
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.marmotGroup.MarmotGroupChatScreen
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.marmotGroup.MarmotGroupInfoScreen
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.marmotGroup.MarmotGroupListScreen
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.minichat.MinichatScreen
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.privateDM.ChatroomByAuthorScreen
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.privateDM.ChatroomScreen
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.privateDM.send.NewGroupDMScreen
@@ -602,6 +603,14 @@ fun BuildNavigation(
             )
         }
 
+        composableFromEndArgs<Route.ChatMinichat> {
+            MinichatScreen(
+                rootId = it.rootId,
+                accountViewModel = accountViewModel,
+                nav = nav,
+            )
+        }
+
         composableFromEndArgs<Route.ConcordServer> {
             ConcordChannelListScreen(
                 communityId = it.communityId,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/navigation/routes/Routes.kt

@@ -707,6 +707,13 @@ sealed class Route {
 
     @Serializable object Concords : Route()
 
+    // The "minichat" of a chat message: its kind-1111 thread replies, opened from the message and
+    // rendered as a chat-within-a-chat. Keyed by the root message id; the screen resolves the chat
+    // context (Concord channel, public chat, relay group) from the note's gatherer.
+    @Serializable data class ChatMinichat(
+        val rootId: HexKey,
+    ) : Route()
+
     @Serializable data class ChannelMetadataEdit(
         val id: String? = null,
     ) : Route()

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

@@ -415,7 +415,7 @@ private fun MinichatReplyChip(
         Surface(
             shape = RoundedCornerShape(6.dp),
             color = MaterialTheme.colorScheme.secondaryContainer,
-            modifier = Modifier.clickable { nav.nav(Route.Note(note.idHex)) },
+            modifier = Modifier.clickable { nav.nav(Route.ChatMinichat(note.idHex)) },
         ) {
             Row(
                 verticalAlignment = Alignment.CenterVertically,

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

@@ -0,0 +1,178 @@
+/*
+ * 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.minichat
+
+import android.widget.Toast
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.text.input.TextFieldState
+import androidx.compose.foundation.text.input.clearText
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.HorizontalDivider
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextFieldDefaults
+import androidx.compose.material3.TopAppBar
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.derivedStateOf
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.text.font.FontWeight
+import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
+import com.vitorpamplona.amethyst.model.LocalCache
+import com.vitorpamplona.amethyst.service.relayClient.reqCommand.event.observeNoteReplies
+import com.vitorpamplona.amethyst.ui.components.ThinPaddingTextField
+import com.vitorpamplona.amethyst.ui.navigation.navs.INav
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.feed.ChatroomMessageCompose
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.utils.ThinSendButton
+import com.vitorpamplona.amethyst.ui.stringRes
+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.placeholderText
+import com.vitorpamplona.quartz.nip22Comments.CommentEvent
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import com.vitorpamplona.amethyst.commons.icons.symbols.Icon as SymbolIcon
+
+/**
+ * The minichat ("chat within a chat") of a single chat message: the message pinned at
+ * top, then its kind-1111 thread replies as chat bubbles, with a composer that always
+ * posts a kind-1111 rooted at that message (flat — replying inside a minichat doesn't
+ * spawn sub-threads). Opened from the "N replies" chip on any chat message.
+ *
+ * It reuses [ChatroomMessageCompose] so the bubbles look exactly like the main chat.
+ * Observing the root's replies also loads them from relays for public chats; Concord's
+ * thread replies keep arriving over the account-wide plane ingestion.
+ */
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun MinichatScreen(
+    rootId: String,
+    accountViewModel: AccountViewModel,
+    nav: INav,
+) {
+    val rootNote = remember(rootId) { LocalCache.getOrCreateNote(rootId) }
+
+    // Loads + reacts to the root's replies (kind-1111 among them).
+    val replyState by observeNoteReplies(rootNote, accountViewModel)
+    val replies =
+        remember(replyState) {
+            rootNote.replies
+                .filter { it.event is CommentEvent }
+                .sortedWith(compareBy({ it.createdAt() ?: 0L }, { it.idHex }))
+        }
+
+    val composer = remember { TextFieldState() }
+    val scope = rememberCoroutineScope()
+    val context = LocalContext.current
+    val canPost by remember { derivedStateOf { composer.text.isNotBlank() } }
+
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = { Text(stringRes(R.string.chat_minichat_title), fontWeight = FontWeight.Bold, maxLines = 1) },
+                navigationIcon = {
+                    IconButton(onClick = { nav.popBack() }) {
+                        SymbolIcon(symbol = MaterialSymbols.AutoMirrored.ArrowBack, contentDescription = stringRes(R.string.back))
+                    }
+                },
+            )
+        },
+    ) { padding ->
+        Column(Modifier.fillMaxHeight().padding(padding)) {
+            LazyColumn(Modifier.fillMaxWidth().weight(1f, true)) {
+                item("root") {
+                    ChatroomMessageCompose(
+                        baseNote = rootNote,
+                        routeForLastRead = null,
+                        accountViewModel = accountViewModel,
+                        nav = nav,
+                        onWantsToReply = {},
+                        onWantsToEditDraft = {},
+                    )
+                    HorizontalDivider()
+                }
+                items(replies, key = { it.idHex }) { reply ->
+                    ChatroomMessageCompose(
+                        baseNote = reply,
+                        routeForLastRead = null,
+                        accountViewModel = accountViewModel,
+                        nav = nav,
+                        onWantsToReply = {},
+                        onWantsToEditDraft = {},
+                    )
+                }
+            }
+
+            Column(modifier = EditFieldModifier) {
+                ThinPaddingTextField(
+                    state = composer,
+                    modifier = Modifier.fillMaxWidth(),
+                    shape = EditFieldBorder,
+                    placeholder = {
+                        Text(
+                            text = stringRes(R.string.reply_here),
+                            color = MaterialTheme.colorScheme.placeholderText,
+                        )
+                    },
+                    trailingIcon = {
+                        ThinSendButton(
+                            isActive = canPost,
+                            modifier = EditFieldTrailingIconModifier,
+                        ) {
+                            val text = composer.text.toString().trim()
+                            if (text.isNotEmpty()) {
+                                composer.clearText()
+                                scope.launch(Dispatchers.IO) {
+                                    try {
+                                        accountViewModel.account.sendMinichatReply(rootNote, text)
+                                    } catch (e: Exception) {
+                                        launch(Dispatchers.Main) {
+                                            Toast.makeText(context, "Failed to send message: ${e.message}", Toast.LENGTH_SHORT).show()
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    },
+                    colors =
+                        TextFieldDefaults.colors(
+                            focusedIndicatorColor = Color.Transparent,
+                            unfocusedIndicatorColor = Color.Transparent,
+                        ),
+                )
+            }
+        }
+    }
+}

amethyst/src/main/res/values/strings.xml

@@ -352,6 +352,8 @@
     <!-- Reply-mode toggle in the chat composer: reply inline in the timeline vs pull it aside into a thread. -->
     <string name="chat_reply_in_chat">In chat</string>
     <string name="chat_reply_in_thread">In thread</string>
+    <!-- Title of the minichat (thread) screen opened from a chat message. -->
+    <string name="chat_minichat_title">Thread</string>
     <!-- Chip on a chat message that opens its thread ("minichat") of kind-1111 replies. -->
     <plurals name="chat_minichat_reply_count">
         <item quantity="one">%1$d reply</item>