feat(app): unread message indicator (channel view, header, hamburger)

Tracks per-lane unread counts for finalized assistant messages. A message
counts as unread unless the user is actively reading that lane (current
lane, app focused, newest content at the bottom of the viewport).

- ChatStore: ephemeral per-lane unread map (markUnread/markLaneRead/unreadFor).
- IrisController: 'being read' decision on incoming messages; clears the
  current lane when the app returns to the foreground at the bottom.
- Bridges: push foreground changes to the controller.
- ChatScreen: per-channel badges in the drawer/rail, an 'N new' pill in the
  header (tap glides to the latest message), and a red dot on the hamburger
  (single-pane/mobile only) when another channel has unread.

Closes #3.

app/shared/src/commonMain/kotlin/iris/data/ChatStore.kt

@@ -149,6 +149,13 @@ class ChatStore {
     private val _todos = MutableStateFlow<Map<String, List<TodoItem>>>(emptyMap())
     val todos: StateFlow<Map<String, List<TodoItem>>> = _todos.asStateFlow()
 
+    /** Unread message count per lane (M8: unread indicator). Ephemeral
+     *  (in-memory): a process death resets it, and the `sync` delta re-counts
+     *  genuinely new messages on reconnect. A lane absent from the map has
+     *  no unread messages. */
+    private val _unread = MutableStateFlow<Map<String, Int>>(emptyMap())
+    val unread: StateFlow<Map<String, Int>> = _unread.asStateFlow()
+
     private var localSeq = 0
 
     /** When false, `message.start`/`message.update` frames are ignored and each
@@ -694,6 +701,24 @@ class ChatStore {
         if (changed) _lanes.value = map
     }
 
+    /** M8: a new message arrived in [lane] that the user hasn't seen —
+     *  increment its unread count. */
+    fun markUnread(lane: String) {
+        val map = _unread.value.toMutableMap()
+        map[lane] = (map[lane] ?: 0) + 1
+        _unread.value = map
+    }
+
+    /** M8: the user is now viewing [lane]'s newest content — clear its unread
+     *  count. Idempotent (a lane with no unread is a no-op). */
+    fun markLaneRead(lane: String) {
+        val map = _unread.value.toMutableMap()
+        if (map.remove(lane) != null) _unread.value = map
+    }
+
+    /** M8: unread count for a single lane (0 when none). */
+    fun unreadFor(lane: String): Int = _unread.value[lane] ?: 0
+
     /** M5: mark the user message [messageId] as read (read.receipt). */
     fun markRead(messageId: String) {
         val map = _lanes.value.toMutableMap()
@@ -904,5 +929,6 @@ class ChatStore {
 
     fun clear() {
         _lanes.value = emptyMap()
+        _unread.value = emptyMap()
     }
 }

app/shared/src/commonMain/kotlin/iris/state/IrisController.kt

@@ -152,6 +152,42 @@ class IrisController(
     private val _gatewayStatus = MutableStateFlow<String?>(null)
     val gatewayStatus: StateFlow<String?> = _gatewayStatus.asStateFlow()
 
+    // ── M8: unread indicator ──────────────────────────────────────────────
+
+    /** True while the current lane's newest content sits at the bottom of the
+     *  viewport (set by the UI from its scroll state). Used to decide whether
+     *  an incoming message in the current lane is "being read" (not unread).
+     *  @Volatile: written on the UI thread, read on the frame-handler
+     *  coroutine (Dispatchers.Default). */
+    @Volatile
+    var currentLaneAtBottom: Boolean = true
+
+    /** App foreground state (M8: clear the current lane's unread when the app
+     *  is focused and the user is at the bottom). Mirrors the platform bridge
+     *  ([isAppForeground]); the bridges push changes via [setForeground]. */
+    private val _foreground = MutableStateFlow(isAppForeground())
+    val foreground: StateFlow<Boolean> = _foreground.asStateFlow()
+
+    /** Bridge entry point: the platform shell reports a focus change. */
+    fun setForeground(fg: Boolean) {
+        _foreground.value = fg
+    }
+
+    /** M8: a finalized assistant message arrived in [lane]. Count it as unread
+     *  unless the user is actively reading that lane right now (it is the
+     *  current lane, the app is focused, and the newest content is at the
+     *  bottom of the viewport). */
+    private fun noteIncomingAssistantMessage(lane: String) {
+        val beingRead = lane == chat.currentLane.value && isAppForeground() && currentLaneAtBottom
+        if (!beingRead) chat.markUnread(lane)
+    }
+
+    /** M8: the user is now viewing the current lane's newest content — clear
+     *  its unread count. */
+    fun markCurrentLaneRead() {
+        chat.markLaneRead(chat.currentLane.value)
+    }
+
     // Latches the restart pair: set when the "restarting" notice is posted
     // (on the gateway's status{restarting} frame), consumed by the matching
     // "online" notice on the next reconnect. A plain network drop never sets
@@ -465,6 +501,15 @@ class IrisController(
         scope.launch {
             chat.currentLane.debounce(CACHE_SAVE_DEBOUNCE_MS).collect { chatDb.metaPut(META_LAST_LANE, it) }
         }
+        // M8: when the app returns to the foreground and the user is at the
+        // bottom of the current lane, its newest content is on screen — clear
+        // any unread that accumulated while backgrounded. (The UI separately
+        // clears on scroll-to-bottom while already focused.)
+        scope.launch {
+            foreground.collect { fg ->
+                if (fg && currentLaneAtBottom) markCurrentLaneRead()
+            }
+        }
         scope.launch {
             client.events.collect { frame ->
                 try {
@@ -511,6 +556,12 @@ class IrisController(
                             when (frame.type) {
                                 TYPE_MESSAGE_STOP -> {
                                     frame.payloadAs<MessageStopPayload>()?.let {
+                                        // M8: a finalized streaming reply is new
+                                        // content — count it as unread unless the
+                                        // user is reading this lane right now.
+                                        frame.chatId?.let { cid ->
+                                            noteIncomingAssistantMessage(chat.laneKey(cid, frame.threadId))
+                                        }
                                         if (!isPushedReplay(frame)) {
                                             notifyMessageIfBackgrounded(frame.chatId, frame.threadId, it.finalText)
                                         }
@@ -519,8 +570,14 @@ class IrisController(
 
                                 TYPE_MESSAGE -> {
                                     frame.payloadAs<MessagePayload>()?.let {
-                                        if (it.role == ROLE_ASSISTANT && !isPushedReplay(frame)) {
-                                            notifyMessageIfBackgrounded(frame.chatId, frame.threadId, it.text)
+                                        if (it.role == ROLE_ASSISTANT) {
+                                            // M8: a finalized (non-streaming) reply.
+                                            frame.chatId?.let { cid ->
+                                                noteIncomingAssistantMessage(chat.laneKey(cid, frame.threadId))
+                                            }
+                                            if (!isPushedReplay(frame)) {
+                                                notifyMessageIfBackgrounded(frame.chatId, frame.threadId, it.text)
+                                            }
                                         }
                                     }
                                 }

app/shared/src/commonMain/kotlin/iris/ui/screens/ChatScreen.kt

@@ -177,6 +177,22 @@ fun ChatScreen(controller: IrisController) {
     val currentChannel = channels.firstOrNull { it.chatId == currentChatId }
     val threads = channels.filter { it.kind == "thread" && it.parentChatId == currentChatId }
 
+    // M8: unread counts. Per-lane from the store; per-channel aggregated
+    // (flat lane + all threads) for the drawer/rail badges.
+    val unreadMap by controller.chat.unread.collectAsState()
+    val channelUnread: Map<String, Int> =
+        remember(unreadMap, channels) {
+            val threadsByParent = channels.filter { it.kind == "thread" }.groupBy { it.parentChatId }
+            channels.filter { it.kind != "thread" }.associate { ch ->
+                val flat = unreadMap[ch.chatId] ?: 0
+                val threadTotal =
+                    (threadsByParent[ch.chatId].orEmpty()).sumOf { t ->
+                        unreadMap[controller.chat.laneKey(ch.chatId, t.chatId)] ?: 0
+                    }
+                ch.chatId to (flat + threadTotal)
+            }
+        }
+
     val listState = rememberLazyListState()
     // "At the bottom" when the list can't scroll further forward, or the last
     // row's bottom edge is within a small tolerance of the viewport bottom
@@ -203,6 +219,16 @@ fun ChatScreen(controller: IrisController) {
         }.collect { isAtBottom = it }
     }
 
+    // M8: publish the scroll position to the controller (it drives the
+    // "being read" decision for incoming messages) and clear the current
+    // lane's unread once its newest content is at the bottom of the viewport
+    // (the "bottom anchor in viewport" condition). Re-fires on lane change so
+    // opening a lane marks it read (the view lands on the latest message).
+    LaunchedEffect(isAtBottom, currentLane) {
+        controller.currentLaneAtBottom = isAtBottom
+        if (isAtBottom) controller.markCurrentLaneRead()
+    }
+
     // Scroll so the newest row's BOTTOM edge is visible: first bring the last
     // row into view (top-aligned), then, if it is taller than the viewport,
     // align its bottom with the viewport bottom. A plain scrollToItem(last)
@@ -500,8 +526,28 @@ fun ChatScreen(controller: IrisController) {
                 verticalAlignment = Alignment.CenterVertically,
             ) {
                 if (showHamburger) {
-                    HeaderIconButton(onClick = onOpenDrawer) {
-                        Text("☰", fontSize = 18.sp)
+                    // M8: red dot when another channel has unread messages. In
+                    // single-pane (mobile) the channel rail isn't visible, so
+                    // the drawer's per-channel badges aren't enough — this
+                    // flags "something happened elsewhere." Desktop always
+                    // shows the rail (showHamburger = false), so no dot there.
+                    val otherChannelsUnread =
+                        channelUnread.entries.sumOf { (chId, c) -> if (chId != currentChatId) c else 0 }
+                    Box {
+                        HeaderIconButton(onClick = onOpenDrawer) {
+                            Text("☰", fontSize = 18.sp)
+                        }
+                        if (otherChannelsUnread > 0) {
+                            Box(
+                                modifier =
+                                    Modifier
+                                        .align(Alignment.TopEnd)
+                                        .padding(top = 5.dp, end = 5.dp)
+                                        .size(9.dp)
+                                        .clip(CircleShape)
+                                        .background(IrisColors.statusRed),
+                            )
+                        }
                     }
                 }
                 val headerClipboard = LocalClipboardManager.current
@@ -509,6 +555,28 @@ fun ChatScreen(controller: IrisController) {
                     headerClipboard.setText(AnnotatedString(id))
                     toastMessage = "Copied $id"
                 }
+                // M8: unread indicator for the current lane. Appears when new
+                // messages arrived while the user was scrolled up (or in
+                // another lane); a tap glides back to the latest message.
+                val currentLaneUnread = unreadMap[currentLane] ?: 0
+                if (currentLaneUnread > 0) {
+                    Spacer(modifier = Modifier.width(6.dp))
+                    Box(
+                        modifier =
+                            Modifier
+                                .clip(RoundedCornerShape(10.dp))
+                                .background(IrisColors.primary)
+                                .clickable { drawerScope.launch { scrollToBottom(animate = true) } }
+                                .padding(horizontal = 8.dp, vertical = 4.dp),
+                    ) {
+                        Text(
+                            "$currentLaneUnread new",
+                            color = Color.White,
+                            fontSize = 12.sp,
+                            fontWeight = FontWeight.SemiBold,
+                        )
+                    }
+                }
                 Spacer(modifier = Modifier.width(6.dp))
                 StatusBubble(state) { toastMessage = statusToastText(state) }
                 Spacer(modifier = Modifier.width(4.dp))
@@ -1029,6 +1097,7 @@ fun ChatScreen(controller: IrisController) {
                 ChannelRail(
                     channels = nonThreadChannels,
                     currentChatId = currentChatId,
+                    channelUnread = channelUnread,
                     selectedIndex = railIndex,
                     onSelectedIndex = { railIndex = it },
                     focusRequester = railFocusRequester,
@@ -1065,6 +1134,7 @@ fun ChatScreen(controller: IrisController) {
                         ChannelDrawer(
                             channels = nonThreadChannels,
                             currentChatId = currentChatId,
+                            channelUnread = channelUnread,
                             onOpen = { ch ->
                                 controller.openChannel(ch.chatId)
                                 drawerScope.launch { drawerState.close() }
@@ -1531,6 +1601,31 @@ private fun ChannelBadges(ch: ChannelInfo) {
     }
 }
 
+/**
+ * M8: unread-count badge for a channel row (drawer / rail). Hidden when the
+ *  channel has no unread messages. Caps at "99+" so a long backlog doesn't
+ *  blow out the row.
+ */
+@Composable
+private fun UnreadBadge(count: Int) {
+    if (count <= 0) return
+    Box(
+        modifier =
+            Modifier
+                .padding(start = 6.dp)
+                .clip(RoundedCornerShape(8.dp))
+                .background(IrisColors.primary)
+                .padding(horizontal = 6.dp, vertical = 2.dp),
+    ) {
+        Text(
+            if (count > 99) "99+" else count.toString(),
+            color = Color.White,
+            fontSize = 11.sp,
+            fontWeight = FontWeight.SemiBold,
+        )
+    }
+}
+
 /**
  * Long-press / right-click context menu for a channel row: rename, favorite
  * (state-aware), icon (state-aware), automation (state-aware), delete. The
@@ -1686,6 +1781,7 @@ private fun ChannelIconDialog(
 private fun ChannelDrawer(
     channels: List<ChannelInfo>,
     currentChatId: String,
+    channelUnread: Map<String, Int>,
     onOpen: (ChannelInfo) -> Unit,
     onNewChannel: () -> Unit,
     onRename: (ChannelInfo) -> Unit,
@@ -1729,6 +1825,7 @@ private fun ChannelDrawer(
                             modifier = Modifier.weight(1f),
                         )
                         ChannelBadges(ch)
+                        UnreadBadge(channelUnread[ch.chatId] ?: 0)
                     }
                     ChannelContextMenu(
                         expanded = menuOpen,
@@ -1763,6 +1860,7 @@ private fun ChannelDrawer(
 private fun ChannelRail(
     channels: List<ChannelInfo>,
     currentChatId: String,
+    channelUnread: Map<String, Int>,
     selectedIndex: Int,
     onSelectedIndex: (Int) -> Unit,
     focusRequester: FocusRequester,
@@ -1858,6 +1956,7 @@ private fun ChannelRail(
                             modifier = Modifier.weight(1f),
                         )
                         ChannelBadges(ch)
+                        UnreadBadge(channelUnread[ch.chatId] ?: 0)
                     }
                     ChannelContextMenu(
                         expanded = menuOpen,