feat(nip17): render subject-only renames as a system line instead of an empty bubble

A NIP-17 message that only sets a subject (no text) drew an empty bubble
under the subject divider, whose only content was the time and delivery
ticks. Render it as a centered system pill instead: the renamer's avatar,
"Alice renamed the conversation" / "You renamed the conversation", and
the tappable time with delivery ticks. Inside a reply quote, where no
divider names the subject, the sentence includes the new name.

ChatSystemMessage gains a trailing slot for the time.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TMJHLxbswamX91WDaPT2uR

commonsUI/src/commonMain/composeResources/values/strings.xml

@@ -2323,6 +2323,10 @@
     <string name="chat_system_created_channel">%1$s created the channel %2$s</string>
     <string name="chat_system_created_channel_unnamed">%1$s created the channel</string>
     <string name="chat_system_updated_channel">%1$s updated the channel profile</string>
+    <string name="chat_system_renamed_conversation">%1$s renamed the conversation</string>
+    <string name="chat_system_renamed_conversation_you">You renamed the conversation</string>
+    <string name="chat_system_renamed_conversation_to">%1$s renamed the conversation to %2$s</string>
+    <string name="chat_system_renamed_conversation_to_you">You renamed the conversation to %1$s</string>
     <string name="buzz_message_edited">(edited)</string>
     <string name="buzz_diff_truncated">(diff truncated)</string>
     <string name="buzz_system_member_joined">%1$s joined</string>

commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/chats/ui/ChatSystemMessage.kt

@@ -54,12 +54,17 @@ import com.vitorpamplona.amethyst.commons.ui.theme.grayText
  * [leading] is an optional slot rendered inside the pill, before the text — used to
  * put the avatar of whoever the line is about ("Alice joined") next to the sentence,
  * so a membership change is recognizable without reading the name.
+ *
+ * [trailing] is an optional slot rendered inside the pill, after the text — used by
+ * system lines that are real messages (a NIP-17 rename) to keep their time and
+ * delivery ticks without wrapping them in an otherwise empty bubble.
  */
 @Composable
 fun ChatSystemMessage(
     text: String,
     onClick: (() -> Unit)? = null,
     leading: (@Composable () -> Unit)? = null,
+    trailing: (@Composable () -> Unit)? = null,
 ) {
     Row(
         modifier =
@@ -78,16 +83,27 @@ fun ChatSystemMessage(
                     Modifier
                 },
         ) {
-            if (leading == null) {
+            if (leading == null && trailing == null) {
                 SystemMessageText(text)
             } else {
                 Row(
                     verticalAlignment = Alignment.CenterVertically,
                     horizontalArrangement = Arrangement.spacedBy(6.dp),
-                    modifier = Modifier.padding(start = 8.dp),
+                    modifier =
+                        Modifier.padding(
+                            start = if (leading != null) 8.dp else 0.dp,
+                            end = if (trailing != null) 10.dp else 0.dp,
+                        ),
                 ) {
-                    leading()
-                    SystemMessageText(text, startPadding = 0.dp)
+                    leading?.invoke()
+                    SystemMessageText(
+                        text = text,
+                        startPadding = if (leading != null) 0.dp else 12.dp,
+                        endPadding = if (trailing != null) 0.dp else 12.dp,
+                        // Lets a long sentence wrap instead of pushing the trailing slot out of the pill.
+                        modifier = Modifier.weight(1f, fill = false),
+                    )
+                    trailing?.invoke()
                 }
             }
         }
@@ -98,13 +114,15 @@ fun ChatSystemMessage(
 private fun SystemMessageText(
     text: String,
     startPadding: Dp = 12.dp,
+    endPadding: Dp = 12.dp,
+    modifier: Modifier = Modifier,
 ) {
     Text(
         text = text,
         fontSize = Font12SP,
         color = MaterialTheme.colorScheme.grayText,
         textAlign = TextAlign.Center,
-        modifier = Modifier.padding(start = startPadding, end = 12.dp, top = 5.dp, bottom = 5.dp),
+        modifier = modifier.padding(start = startPadding, end = endPadding, top = 5.dp, bottom = 5.dp),
     )
 }
 
@@ -118,5 +136,10 @@ private fun ChatSystemMessagePreview() {
             "Bob was added by Alice",
             leading = { Box(Modifier.size(Size18dp).clip(CircleShape).background(MaterialTheme.colorScheme.primary)) },
         )
+        ChatSystemMessage(
+            "You renamed the conversation",
+            leading = { Box(Modifier.size(Size18dp).clip(CircleShape).background(MaterialTheme.colorScheme.primary)) },
+            trailing = { Text("10:42", fontSize = Font12SP, color = MaterialTheme.colorScheme.grayText) },
+        )
     }
 }

commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/feed/ChatMessageCompose.kt

@@ -67,6 +67,7 @@ import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.Re
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.RenderChannelAdminSystemMessage
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.RenderChatClip
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.RenderChatRaid
+import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.RenderChatSubjectChange
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.RenderChatZap
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.RenderConcordTimerNotice
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.RenderDraftEvent
@@ -78,6 +79,7 @@ import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.Re
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.hasEncryptedMediaV2
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.hasMip04Media
 import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.isBuzzActivityRow
+import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.types.isSubjectOnlyChatMessage
 import com.vitorpamplona.amethyst.commons.ui.theme.ReactionRowZapraiser
 import com.vitorpamplona.amethyst.commons.ui.theme.StdVertSpacer
 import com.vitorpamplona.amethyst.commons.viewmodels.AccountViewModel
@@ -178,6 +180,9 @@ fun ChatroomMessageCompose(
             } else if (event is ConcordTimerNoticeEvent) {
                 // Concord kind-1740: "Alice set disappearing messages to 30 days" (CORD-08 §4).
                 RenderConcordTimerNotice(baseNote, accountViewModel, nav)
+            } else if (isSubjectOnlyChatMessage(event)) {
+                // NIP-17 rename with no text: a system line under the subject divider, not an empty bubble.
+                RenderChatSubjectChange(baseNote, innerQuote, accountViewModel, nav)
             } else if (isBuzzActivityRow(event)) {
                 // Buzz agent-job (43xxx) and huddle (48xxx) lifecycle narration. Huddles
                 // especially must be caught here — their content is JSON, not chat text.

commonsUI/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/screen/loggedIn/chats/feed/types/RenderChatSubjectChange.kt

@@ -0,0 +1,104 @@
+/*
+ * 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.commons.ui.screen.loggedIn.chats.feed.types
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import com.vitorpamplona.amethyst.commons.chats.ui.ChatSystemMessage
+import com.vitorpamplona.amethyst.commons.model.Note
+import com.vitorpamplona.amethyst.commons.model.navigation.Route
+import com.vitorpamplona.amethyst.commons.resources.Res
+import com.vitorpamplona.amethyst.commons.resources.chat_system_renamed_conversation
+import com.vitorpamplona.amethyst.commons.resources.chat_system_renamed_conversation_to
+import com.vitorpamplona.amethyst.commons.resources.chat_system_renamed_conversation_to_you
+import com.vitorpamplona.amethyst.commons.resources.chat_system_renamed_conversation_you
+import com.vitorpamplona.amethyst.commons.ui.navigation.navs.INav
+import com.vitorpamplona.amethyst.commons.ui.note.UserPicture
+import com.vitorpamplona.amethyst.commons.ui.screen.loggedIn.chats.feed.ChatTimeWithDelivery
+import com.vitorpamplona.amethyst.commons.ui.stringRes
+import com.vitorpamplona.amethyst.commons.ui.theme.Size18dp
+import com.vitorpamplona.amethyst.commons.viewmodels.AccountViewModel
+import com.vitorpamplona.quartz.nip01Core.core.Event
+import com.vitorpamplona.quartz.nip14Subject.subject
+import com.vitorpamplona.quartz.nip17Dm.messages.ChatMessageEvent
+
+/**
+ * A NIP-17 message that only renames the conversation: it carries a `subject` tag and no text.
+ * The room's subject divider already announces the new name above it, so drawing it as a bubble
+ * left an empty balloon under the divider whose only content was the time.
+ */
+fun isSubjectOnlyChatMessage(event: Event?): Boolean = event is ChatMessageEvent && event.content.isBlank() && event.subject() != null
+
+/**
+ * A rename ([isSubjectOnlyChatMessage]) as a centered system line — "Alice renamed the
+ * conversation" with Alice's avatar — under the subject divider that carries the new name.
+ *
+ * Unlike the other system lines this one is a real message with a sender and a delivery, so the
+ * pill keeps the bubble's tappable time and, on our own renames, its relay-acceptance ticks.
+ *
+ * Inside a reply quote there is no divider to name the subject, so the sentence includes it and
+ * the time is dropped, as on any quoted message.
+ */
+@Composable
+fun RenderChatSubjectChange(
+    note: Note,
+    innerQuote: Boolean,
+    accountViewModel: AccountViewModel,
+    nav: INav,
+) {
+    val event = note.event as? ChatMessageEvent ?: return
+    val isLoggedInUser = remember(event.pubKey) { accountViewModel.isLoggedUser(event.pubKey) }
+
+    val text =
+        if (innerQuote) {
+            val subject = remember(event) { event.subject() ?: "" }
+            if (isLoggedInUser) {
+                stringRes(Res.string.chat_system_renamed_conversation_to_you, subject)
+            } else {
+                stringRes(Res.string.chat_system_renamed_conversation_to, observeUserNameByHex(event.pubKey, accountViewModel), subject)
+            }
+        } else {
+            if (isLoggedInUser) {
+                stringRes(Res.string.chat_system_renamed_conversation_you)
+            } else {
+                stringRes(Res.string.chat_system_renamed_conversation, observeUserNameByHex(event.pubKey, accountViewModel))
+            }
+        }
+
+    ChatSystemMessage(
+        text = text,
+        onClick = { nav.nav(Route.Profile(event.pubKey)) },
+        leading = {
+            UserPicture(
+                userHex = event.pubKey,
+                size = Size18dp,
+                accountViewModel = accountViewModel,
+                nav = nav,
+            )
+        },
+        trailing =
+            if (innerQuote) {
+                null
+            } else {
+                { ChatTimeWithDelivery(note, isLoggedInUser, accountViewModel, nav) }
+            },
+    )
+}