fix: show date in timestamps; fix history divider appearing immediately

- MessagePane: show date in timestamps (Yesterday/MMM D) for messages
  not from today; divider now appears at the top of history on load
  rather than waiting for a live message to create the boundary
- TUI: same date-aware timestamp formatting (Yesterday / Jan 2)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/tui/main.go

@@ -383,7 +383,7 @@ func (m model) refreshViewport() model {
 	w := m.vpContentWidth()
 	var sb strings.Builder
 	for _, e := range m.messages[room] {
-		ts := styleMsgTime.Render(e.at.Format("15:04"))
+		ts := styleMsgTime.Render(formatMsgTime(e.at))
 		var from string
 		if e.fromMe {
 			from = styleMsgMe.Render(e.from)
@@ -614,6 +614,17 @@ func filterIDs(ids []proto.PeerID, remove proto.PeerID) []proto.PeerID {
 	return out
 }
 
+func formatMsgTime(t time.Time) string {
+	now := time.Now()
+	if t.Year() == now.Year() && t.YearDay() == now.YearDay() {
+		return t.Format("15:04")
+	}
+	if t.Year() == now.Year() && t.YearDay() == now.YearDay()-1 {
+		return "Yesterday " + t.Format("15:04")
+	}
+	return t.Format("Jan 2 15:04")
+}
+
 func min(a, b int) int {
 	if a < b {
 		return a

web/src/components/MessagePane.tsx

@@ -1,6 +1,18 @@
 import { useEffect, useRef, useState } from 'react'
 import { useWaste } from '../store'
 
+const today = new Date()
+today.setHours(0, 0, 0, 0)
+const todayMs = today.getTime()
+const yesterdayMs = todayMs - 86400000
+
+function formatTs(ts: number): string {
+  const time = new Date(ts).toLocaleTimeString([], { hour: '2-digit', minute: '2-digit', hour12: false })
+  if (ts >= todayMs) return time
+  if (ts >= yesterdayMs) return `Yesterday ${time}`
+  return new Date(ts).toLocaleDateString([], { month: 'short', day: 'numeric' }) + ' ' + time
+}
+
 export function MessagePane() {
   const { messages, historyCutoff, activeRoom, activeNetworkId, localPeer, connectedPeers, send } = useWaste()
   const [draft, setDraft] = useState('')
@@ -8,6 +20,16 @@ export function MessagePane() {
   const roomMessages = messages[activeRoom] ?? []
   const cutoff = historyCutoff[activeRoom] ?? 0
 
+  // Find the index of the first live message (ts > cutoff).
+  // The divider appears just before this index, or at the top if all are history.
+  const firstLiveIdx = cutoff > 0
+    ? roomMessages.findIndex(m => m.ts > cutoff)
+    : -1
+  // If all messages are history (no live yet), put divider at the start.
+  const dividerIdx = cutoff > 0
+    ? (firstLiveIdx === -1 ? 0 : firstLiveIdx)
+    : -1
+
   useEffect(() => {
     bottomRef.current?.scrollIntoView({ behavior: 'smooth' })
   }, [roomMessages.length])
@@ -43,20 +65,20 @@ export function MessagePane() {
       <div className="message-pane-header">{roomLabel}</div>
 
       <div className="messages">
+        {dividerIdx === 0 && (
+          <div className="history-divider"><span>earlier messages</span></div>
+        )}
         {roomMessages.map((msg, i) => {
           const mine = msg.from === localPeer?.id
-          const alias = aliasFor(msg.from)
-          const time = new Date(msg.ts).toLocaleTimeString([], { hour: '2-digit', minute: '2-digit', hour12: false })
-          const showDivider = cutoff > 0 && i > 0 && roomMessages[i - 1].ts <= cutoff && msg.ts > cutoff
+          const alias = aliasFor(String(msg.from))
+          const ts = formatTs(msg.ts)
           return (
             <div key={msg.mid ?? i}>
-              {showDivider && (
-                <div className="history-divider">
-                  <span>earlier messages</span>
-                </div>
+              {i === dividerIdx && dividerIdx > 0 && (
+                <div className="history-divider"><span>earlier messages</span></div>
               )}
               <div className={`message ${mine ? 'mine' : ''}`}>
-                <span className="message-ts">{time}</span>
+                <span className="message-ts">{ts}</span>
                 <span className="message-alias">{alias}</span>
                 <span className="message-text">{msg.text}</span>
               </div>