fix(notifications): stop grouping chat notifications

apps/flipcash/shared/notifications/src/main/kotlin/com/flipcash/app/notifications/NotificationActionReceiver.kt

@@ -32,7 +32,6 @@ class NotificationActionReceiver : BroadcastReceiver() {
         const val ACTION_MARK_READ = "com.flipcash.app.notifications.ACTION_MARK_READ"
         const val KEY_CHAT_ID_HEX = "chat_id_hex"
         const val KEY_NOTIFICATION_ID = "notification_id"
-        const val KEY_GROUP_KEY = "group_key"
         const val KEY_TEXT_REPLY = "key_text_reply"
     }
 
@@ -70,8 +69,6 @@ class NotificationActionReceiver : BroadcastReceiver() {
             ?.toString()
             ?: return
 
-        val groupKey = intent.getStringExtra(KEY_GROUP_KEY)
-
         chatCoordinator.sendMessage(chatId, replyText)
             .onSuccess {
                 val notificationId = intent.getIntExtra(KEY_NOTIFICATION_ID, chatId.hashCode())
@@ -96,12 +93,9 @@ class NotificationActionReceiver : BroadcastReceiver() {
                     .setColor(context.getColor(R.color.notification_color))
                     .setStyle(existingStyle)
                     .setGroupAlertBehavior(NotificationCompat.GROUP_ALERT_CHILDREN)
-                    .addAction(buildReplyAction(context, chatId, notificationId, groupKey))
-                    .addAction(buildMarkAsReadAction(context, chatId, groupKey))
+                    .addAction(buildReplyAction(context, chatId, notificationId))
+                    .addAction(buildMarkAsReadAction(context, chatId))
                     .setAutoCancel(true)
-                    .apply {
-                        if (groupKey != null) setGroup(groupKey)
-                    }
                     .build()
 
                 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU &&
@@ -129,7 +123,7 @@ class NotificationActionReceiver : BroadcastReceiver() {
     }
 
     @OptIn(ExperimentalStdlibApi::class)
-    private fun buildReplyAction(context: Context, chatId: ChatId, notificationId: Int, groupKey: String?): NotificationCompat.Action {
+    private fun buildReplyAction(context: Context, chatId: ChatId, notificationId: Int): NotificationCompat.Action {
         val remoteInput = RemoteInput.Builder(KEY_TEXT_REPLY)
             .setLabel(context.getString(R.string.notification_action_reply))
             .build()
@@ -138,7 +132,6 @@ class NotificationActionReceiver : BroadcastReceiver() {
             action = ACTION_REPLY
             putExtra(KEY_CHAT_ID_HEX, chatId.bytes.toHexString())
             putExtra(KEY_NOTIFICATION_ID, notificationId)
-            if (groupKey != null) putExtra(KEY_GROUP_KEY, groupKey)
         }
 
         val pendingIntent = PendingIntent.getBroadcast(
@@ -156,11 +149,10 @@ class NotificationActionReceiver : BroadcastReceiver() {
     }
 
     @OptIn(ExperimentalStdlibApi::class)
-    private fun buildMarkAsReadAction(context: Context, chatId: ChatId, groupKey: String?): NotificationCompat.Action {
+    private fun buildMarkAsReadAction(context: Context, chatId: ChatId): NotificationCompat.Action {
         val intent = Intent(context, NotificationActionReceiver::class.java).apply {
             action = ACTION_MARK_READ
             putExtra(KEY_CHAT_ID_HEX, chatId.bytes.toHexString())
-            if (groupKey != null) putExtra(KEY_GROUP_KEY, groupKey)
         }
 
         val pendingIntent = PendingIntent.getBroadcast(

apps/flipcash/shared/notifications/src/main/kotlin/com/flipcash/app/notifications/NotificationGroupPlanner.kt

@@ -0,0 +1,21 @@
+package com.flipcash.app.notifications
+
+/**
+ * The group a notification is posted under, or null to post it ungrouped with no summary.
+ *
+ * A chat is never grouped. It posts one notification, under its chat id, and folds every new
+ * message into it, so a group of its own would only ever hold that one child. Android 16 force
+ * groups exactly that shape: it cancels the app's summary and moves the child into a system
+ * group, and every new message moves the child back out for a few seconds before it is moved in
+ * again. The summary has no content, so for those seconds it shows as an empty notification.
+ *
+ * Other pushes keep the payload's key, because they post a new notification each time and several
+ * can share one group.
+ *
+ * @param payloadGroupKey `NotificationPayload.groupKey`, where blank means none
+ * @param isChat whether the notification is rendered as a chat conversation
+ */
+fun planNotificationGroup(payloadGroupKey: String?, isChat: Boolean): String? {
+    if (isChat) return null
+    return payloadGroupKey?.takeIf { it.isNotEmpty() }
+}

apps/flipcash/shared/notifications/src/main/kotlin/com/flipcash/app/notifications/NotificationService.kt

@@ -270,7 +270,9 @@ class NotificationService : FirebaseMessagingService(),
             )
         }
 
+        val isChat = chatId != null && styling != null
         val groupKey = payload?.groupKey?.takeIf { it.isNotEmpty() }
+        val group = planNotificationGroup(payloadGroupKey = groupKey, isChat = isChat)
 
         val builder = NotificationCompat.Builder(this, channel.id)
             .setPriority(NotificationCompat.PRIORITY_HIGH)
@@ -280,7 +282,7 @@ class NotificationService : FirebaseMessagingService(),
             .setAutoCancel(true)
             .setContentIntent(buildContentIntent(styling?.chatType, payload?.navigation))
             .apply {
-                if (groupKey != null) setGroup(groupKey)
+                if (group != null) setGroup(group)
             }
 
         val notificationId = if (chatId != null && styling != null) {
@@ -292,16 +294,16 @@ class NotificationService : FirebaseMessagingService(),
 
         notificationManager.notify(notificationId, builder.build())
 
-        if (groupKey != null) {
+        if (group != null) {
             val summary = NotificationCompat.Builder(this, channel.id)
                 .setSmallIcon(R.drawable.flipcash_logo)
                 .setColor(getColor(R.color.notification_color))
-                .setGroup(groupKey)
+                .setGroup(group)
                 .setGroupSummary(true)
                 .setGroupAlertBehavior(NotificationCompat.GROUP_ALERT_CHILDREN)
                 .setAutoCancel(true)
                 .build()
-            notificationManager.notify(groupKey.hashCode(), summary)
+            notificationManager.notify(group.hashCode(), summary)
         }
     }
 
@@ -413,8 +415,8 @@ class NotificationService : FirebaseMessagingService(),
 
         setStyle(style)
             .setGroupAlertBehavior(NotificationCompat.GROUP_ALERT_CHILDREN)
-            .addAction(buildReplyAction(chatId, notificationId, groupKey))
-            .addAction(buildMarkAsReadAction(chatId, groupKey))
+            .addAction(buildReplyAction(chatId, notificationId))
+            .addAction(buildMarkAsReadAction(chatId))
 
         return notificationId
     }
@@ -529,7 +531,7 @@ class NotificationService : FirebaseMessagingService(),
     }
 
     @OptIn(ExperimentalStdlibApi::class)
-    private fun buildReplyAction(chatId: ChatId, notificationId: Int, groupKey: String?): NotificationCompat.Action {
+    private fun buildReplyAction(chatId: ChatId, notificationId: Int): NotificationCompat.Action {
         val remoteInput = RemoteInput.Builder(NotificationActionReceiver.KEY_TEXT_REPLY)
             .setLabel(getString(R.string.notification_action_reply))
             .build()
@@ -538,7 +540,6 @@ class NotificationService : FirebaseMessagingService(),
             action = NotificationActionReceiver.ACTION_REPLY
             putExtra(NotificationActionReceiver.KEY_CHAT_ID_HEX, chatId.bytes.toHexString())
             putExtra(NotificationActionReceiver.KEY_NOTIFICATION_ID, notificationId)
-            if (groupKey != null) putExtra(NotificationActionReceiver.KEY_GROUP_KEY, groupKey)
         }
 
         val pendingIntent = PendingIntent.getBroadcast(
@@ -556,11 +557,10 @@ class NotificationService : FirebaseMessagingService(),
     }
 
     @OptIn(ExperimentalStdlibApi::class)
-    private fun buildMarkAsReadAction(chatId: ChatId, groupKey: String?): NotificationCompat.Action {
+    private fun buildMarkAsReadAction(chatId: ChatId): NotificationCompat.Action {
         val intent = Intent(this, NotificationActionReceiver::class.java).apply {
             action = NotificationActionReceiver.ACTION_MARK_READ
             putExtra(NotificationActionReceiver.KEY_CHAT_ID_HEX, chatId.bytes.toHexString())
-            if (groupKey != null) putExtra(NotificationActionReceiver.KEY_GROUP_KEY, groupKey)
         }
 
         val pendingIntent = PendingIntent.getBroadcast(

apps/flipcash/shared/notifications/src/test/kotlin/com/flipcash/app/notifications/NotificationGroupPlannerTest.kt

@@ -0,0 +1,28 @@
+package com.flipcash.app.notifications
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+
+class NotificationGroupPlannerTest {
+
+    @Test
+    fun `chat notification is not grouped`() {
+        // One notification per chat, so its group would only ever hold that one. Android 16 cancels
+        // the summary of a group like that and regroups the child, and the summary shows empty
+        // in between.
+        assertNull(planNotificationGroup(payloadGroupKey = "chat-a", isChat = true))
+    }
+
+    @Test
+    fun `non-chat notification keeps the payload's group`() {
+        // Pushes such as CONTACT_JOIN post a fresh notification each time under one key.
+        assertEquals("CONTACT_JOIN", planNotificationGroup(payloadGroupKey = "CONTACT_JOIN", isChat = false))
+    }
+
+    @Test
+    fun `blank group key is no group`() {
+        assertNull(planNotificationGroup(payloadGroupKey = "", isChat = false))
+        assertNull(planNotificationGroup(payloadGroupKey = null, isChat = false))
+    }
+}