feat(chat): message timestamps + day separators

Show a muted clock time under the last bubble of each sender-run (side-aligned),
and a centered Today/Yesterday/date pill between messages from different days.
Falls back to now for a just-sent message whose server timestamp is unresolved.

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

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

@@ -39,7 +39,9 @@ import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
 import androidx.hilt.navigation.compose.hiltViewModel
 import app.closer.ui.messages.components.ChatComposer
+import app.closer.ui.messages.components.ChatDaySeparator
 import app.closer.ui.messages.components.ChatMessageRow
+import app.closer.ui.messages.components.isSameChatDay
 import app.closer.ui.theme.closerBackgroundBrush
 import coil.compose.AsyncImage
 
@@ -98,13 +100,18 @@ fun ConversationScreen(
             ) {
                 itemsIndexed(state.messages, key = { _, m -> m.id }) { index, message ->
                     val isMe = message.userId == viewModel.currentUserId
-                    val showAvatar = index == state.messages.lastIndex ||
+                    val isLastInRun = index == state.messages.lastIndex ||
                         state.messages[index + 1].userId != message.userId
+                    val prev = state.messages.getOrNull(index - 1)
+                    if (prev == null || !isSameChatDay(prev.createdAt, message.createdAt)) {
+                        ChatDaySeparator(message.createdAt)
+                    }
                     ChatMessageRow(
                         message = message,
                         isCurrentUser = isMe,
                         partnerAvatarUrl = state.partnerPhotoUrl,
-                        showAvatar = showAvatar,
+                        showAvatar = isLastInRun,
+                        showTimestamp = isLastInRun,
                         loadDecryptedMedia = viewModel::loadDecryptedMedia
                     )
                 }

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

@@ -14,6 +14,7 @@ import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.aspectRatio
@@ -87,6 +88,7 @@ fun ChatMessageRow(
     isCurrentUser: Boolean,
     partnerAvatarUrl: String?,
     showAvatar: Boolean,
+    showTimestamp: Boolean,
     loadDecryptedMedia: suspend (String) -> ByteArray?
 ) {
     val bubbleShape = if (isCurrentUser) {
@@ -95,6 +97,7 @@ fun ChatMessageRow(
         RoundedCornerShape(topStart = 4.dp, topEnd = 16.dp, bottomStart = 16.dp, bottomEnd = 16.dp)
     }
 
+    Column(modifier = Modifier.fillMaxWidth()) {
         Row(
             modifier = Modifier.fillMaxWidth(),
             horizontalArrangement = if (isCurrentUser) Arrangement.End else Arrangement.Start,
@@ -124,6 +127,36 @@ fun ChatMessageRow(
                 }
             }
         }
+
+        if (showTimestamp) {
+            Text(
+                text = formatClockTime(message.createdAt),
+                style = MaterialTheme.typography.labelSmall,
+                color = MaterialTheme.colorScheme.onSurfaceVariant.copy(alpha = 0.55f),
+                modifier = Modifier
+                    .align(if (isCurrentUser) Alignment.End else Alignment.Start)
+                    .padding(start = if (isCurrentUser) 0.dp else 40.dp, end = if (isCurrentUser) 6.dp else 0.dp, top = 2.dp)
+            )
+        }
+    }
+}
+
+/** A centered date pill shown between messages from different days. */
+@Composable
+fun ChatDaySeparator(epochMillis: Long) {
+    Box(modifier = Modifier.fillMaxWidth().padding(vertical = 6.dp), contentAlignment = Alignment.Center) {
+        Surface(
+            shape = RoundedCornerShape(12.dp),
+            color = MaterialTheme.colorScheme.surfaceVariant.copy(alpha = 0.7f)
+        ) {
+            Text(
+                text = chatDayLabel(epochMillis),
+                style = MaterialTheme.typography.labelSmall,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+                modifier = Modifier.padding(horizontal = 12.dp, vertical = 3.dp)
+            )
+        }
+    }
 }
 
 @Composable
@@ -522,3 +555,33 @@ private fun formatDuration(ms: Long): String {
     val s = totalSec % 60
     return "%d:%02d".format(m, s)
 }
+
+/** "3:45 PM" — falls back to now for a just-sent message whose server timestamp hasn't resolved. */
+private fun formatClockTime(ms: Long): String {
+    val t = if (ms > 0) ms else System.currentTimeMillis()
+    return java.text.SimpleDateFormat("h:mm a", java.util.Locale.getDefault()).format(java.util.Date(t))
+}
+
+/** "Today" / "Yesterday" / "March 4" for day separators. */
+fun chatDayLabel(ms: Long): String {
+    val t = if (ms > 0) ms else System.currentTimeMillis()
+    val cal = java.util.Calendar.getInstance().apply { timeInMillis = t }
+    val today = java.util.Calendar.getInstance()
+    val yesterday = (today.clone() as java.util.Calendar).apply { add(java.util.Calendar.DAY_OF_YEAR, -1) }
+    return when {
+        isSameCalendarDay(cal, today) -> "Today"
+        isSameCalendarDay(cal, yesterday) -> "Yesterday"
+        else -> java.text.SimpleDateFormat("MMMM d", java.util.Locale.getDefault()).format(java.util.Date(t))
+    }
+}
+
+/** True when two epoch millis fall on the same calendar day (0 is treated as now). */
+fun isSameChatDay(a: Long, b: Long): Boolean {
+    val ca = java.util.Calendar.getInstance().apply { timeInMillis = if (a > 0) a else System.currentTimeMillis() }
+    val cb = java.util.Calendar.getInstance().apply { timeInMillis = if (b > 0) b else System.currentTimeMillis() }
+    return isSameCalendarDay(ca, cb)
+}
+
+private fun isSameCalendarDay(a: java.util.Calendar, b: java.util.Calendar): Boolean =
+    a.get(java.util.Calendar.YEAR) == b.get(java.util.Calendar.YEAR) &&
+        a.get(java.util.Calendar.DAY_OF_YEAR) == b.get(java.util.Calendar.DAY_OF_YEAR)