feat(chat): read receipts (Seen) via the conversation reads map

Observe the partner's last-read timestamp on the conversation doc; show 'Seen · time'
under the last own message once the partner has read past it. No rules change (reuses reads).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/main/java/app/closer/data/remote/FirestoreConversationDataSource.kt

@@ -166,6 +166,20 @@ class FirestoreConversationDataSource @Inject constructor(
         awaitClose { listener.remove() }
     }
 
+    /** Emits the partner's most recent read timestamp for this conversation (0 if never read). */
+    fun observePartnerReadAt(coupleId: String, conversationId: String, currentUserId: String): Flow<Long> = callbackFlow {
+        val listener = conversationsRef(coupleId).document(conversationId)
+            .addSnapshotListener { snap, err ->
+                if (err != null || snap == null) return@addSnapshotListener
+                @Suppress("UNCHECKED_CAST")
+                val reads = (snap.get("reads") as? Map<String, com.google.firebase.Timestamp>).orEmpty()
+                val partnerReadAt = reads.filterKeys { it != currentUserId }
+                    .values.maxOfOrNull { it.toDate().time } ?: 0L
+                trySend(partnerReadAt)
+            }
+        awaitClose { listener.remove() }
+    }
+
     suspend fun loadDecryptedMedia(coupleId: String, mediaUrl: String): ByteArray? {
         val aead = encryptionManager.aeadFor(coupleId) ?: return null
         val cipher = runCatching { storageDataSource.downloadBytes(mediaUrl) }.getOrNull() ?: return null

app/src/main/java/app/closer/data/repository/ConversationRepositoryImpl.kt

@@ -28,6 +28,9 @@ class ConversationRepositoryImpl @Inject constructor(
     override fun observeMessages(coupleId: String, conversationId: String, limit: Int): Flow<List<QuestionMessage>> =
         dataSource.observeMessages(coupleId, conversationId, limit)
 
+    override fun observePartnerReadAt(coupleId: String, conversationId: String, currentUserId: String): Flow<Long> =
+        dataSource.observePartnerReadAt(coupleId, conversationId, currentUserId)
+
     override suspend fun sendMessage(coupleId: String, conversationId: String, userId: String, text: String) =
         dataSource.sendMessage(coupleId, conversationId, userId, text)
 

app/src/main/java/app/closer/domain/repository/ConversationRepository.kt

@@ -10,6 +10,7 @@ interface ConversationRepository {
     suspend fun ensureQuestionConversation(coupleId: String, questionId: String): String
     suspend fun markRead(coupleId: String, conversationId: String, userId: String)
     fun observeMessages(coupleId: String, conversationId: String, limit: Int): Flow<List<QuestionMessage>>
+    fun observePartnerReadAt(coupleId: String, conversationId: String, currentUserId: String): Flow<Long>
     suspend fun sendMessage(coupleId: String, conversationId: String, userId: String, text: String)
     suspend fun sendImageMessage(coupleId: String, conversationId: String, userId: String, imageBytes: ByteArray)
     suspend fun sendVoiceMessage(coupleId: String, conversationId: String, userId: String, audioBytes: ByteArray, durationMs: Long)

app/src/main/java/app/closer/ui/messages/ConversationScreen.kt

@@ -133,6 +133,7 @@ fun ConversationScreen(
                 contentPadding = PaddingValues(horizontal = 14.dp, vertical = 8.dp),
                 verticalArrangement = Arrangement.spacedBy(8.dp)
             ) {
+                val lastOwnIndex = state.messages.indexOfLast { it.userId == viewModel.currentUserId }
                 itemsIndexed(state.messages, key = { _, m -> m.id }) { index, message ->
                     val isMe = message.userId == viewModel.currentUserId
                     val isLastInRun = index == state.messages.lastIndex ||
@@ -141,12 +142,15 @@ fun ConversationScreen(
                     if (prev == null || !isSameChatDay(prev.createdAt, message.createdAt)) {
                         ChatDaySeparator(message.createdAt)
                     }
+                    val seen = isMe && index == lastOwnIndex &&
+                        message.createdAt > 0 && state.partnerReadAt >= message.createdAt
                     ChatMessageRow(
                         message = message,
                         isCurrentUser = isMe,
                         partnerAvatarUrl = state.partnerPhotoUrl,
                         showAvatar = isLastInRun,
                         showTimestamp = isLastInRun,
+                        showSeen = seen,
                         loadDecryptedMedia = viewModel::loadDecryptedMedia
                     )
                 }

app/src/main/java/app/closer/ui/messages/ConversationViewModel.kt

@@ -34,6 +34,7 @@ data class ConversationUiState(
     val messages: List<QuestionMessage> = emptyList(),
     val pendingMedia: List<PendingMedia> = emptyList(),
     val canLoadMore: Boolean = false,
+    val partnerReadAt: Long = 0L,
     val messageInput: String = "",
     val isLoading: Boolean = true
 )
@@ -109,6 +110,11 @@ class ConversationViewModel @Inject constructor(
                         runCatching { repository.markRead(coupleId, conversationId, currentUserId) }
                     }
             }
+
+            launch {
+                repository.observePartnerReadAt(coupleId, conversationId, currentUserId)
+                    .collect { readAt -> _uiState.update { it.copy(partnerReadAt = readAt) } }
+            }
         }
     }
 

app/src/main/java/app/closer/ui/messages/components/ChatComponents.kt

@@ -90,6 +90,7 @@ fun ChatMessageRow(
     partnerAvatarUrl: String?,
     showAvatar: Boolean,
     showTimestamp: Boolean,
+    showSeen: Boolean = false,
     loadDecryptedMedia: suspend (String) -> ByteArray?
 ) {
     val bubbleShape = if (isCurrentUser) {
@@ -130,8 +131,9 @@ fun ChatMessageRow(
         }
 
         if (showTimestamp) {
+            val time = formatClockTime(message.createdAt)
             Text(
-                text = formatClockTime(message.createdAt),
+                text = if (showSeen) "Seen · $time" else time,
                 style = MaterialTheme.typography.labelSmall,
                 color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.55f),
                 modifier = Modifier