Crew chat: subtle "New" divider for messages since last visit

A returning member couldn't tell new messages from old ones. Add the universal
unread-divider pattern (Slack/Discord-style) directly inside the chat:

- useCrewChatRead: per-crew, per-pubkey last-seen timestamp in localStorage
  (local-only, zero network cost, works for both NIP-17 and Cordn transports).
- CrewChat snapshots last-seen once per open so the divider stays put while
  reading, draws a minimal "New" line above the first message since last visit,
  and quietly advances last-seen to the newest rendered message.

No new fetches, no config, nothing for the user to manage — it just works.

Co-authored-by: shakespeare.diy <assistant@shakespeare.diy>

src/components/CrewChat.tsx

@@ -22,6 +22,7 @@ import {
   type DirectMessage,
 } from '@/hooks/useDirectMessages';
 import { useCordnChat } from '@/hooks/useCordnChat';
+import { useCrewChatRead } from '@/hooks/useCrewChatRead';
 import { resolveCordnEndpoint } from '@/lib/cordn/endpoint';
 import type { CordnMessage } from '@/lib/cordn/types';
 import { genUserName } from '@/lib/genUserName';
@@ -205,6 +206,37 @@ export function CrewChat({
   const isLoading = usingCordn ? cordn.isLoading : nip17Loading;
   const isPending = usingCordn ? cordn.isSending : nip17Sending;
 
+  // ── "New messages" divider ──
+  // Snapshot the last-seen time ONCE per open so the divider stays put while the
+  // member reads, instead of jumping as fresh messages stream in. Anything after
+  // that timestamp (and not authored by me) is "new since your last visit".
+  const { lastSeen, markSeen } = useCrewChatRead(crewCoord);
+  const seenAtOpenRef = useRef<number | null>(null);
+  if (seenAtOpenRef.current === null && lastSeen !== undefined) {
+    seenAtOpenRef.current = lastSeen;
+  }
+  const seenAtOpen = seenAtOpenRef.current ?? 0;
+
+  // The first message id that falls after the snapshot — the divider sits above
+  // it. Skip when there's nothing older (a brand-new reader sees no divider).
+  const firstUnreadId = useMemo(() => {
+    if (!user || seenAtOpen <= 0) return null;
+    const hasOlder = messages.some((m) => m.createdAt <= seenAtOpen);
+    if (!hasOlder) return null;
+    const firstNew = messages.find(
+      (m) => m.createdAt > seenAtOpen && m.pubkey !== user.pubkey,
+    );
+    return firstNew?.id ?? null;
+  }, [messages, seenAtOpen, user]);
+
+  // Keep the stored "last seen" caught up to the newest message we've rendered,
+  // so the next visit only flags genuinely newer messages.
+  useEffect(() => {
+    if (messages.length === 0) return;
+    const newest = messages.reduce((max, m) => Math.max(max, m.createdAt), 0);
+    if (newest > (lastSeen ?? 0)) markSeen(newest);
+  }, [messages, lastSeen, markSeen]);
+
   // Auto-scroll to newest message when the list grows.
   const lastCount = useRef(0);
   useEffect(() => {
@@ -349,14 +381,24 @@ export function CrewChat({
               {messages
                 ?.filter((m) => canModerate || !hiddenIds?.has(m.id))
                 .map((m) => (
-                  <CrewMessageBubble
-                    key={m.id}
-                    message={m}
-                    isOwn={m.pubkey === user.pubkey}
-                    isHidden={hiddenIds?.has(m.id)}
-                    canModerate={canModerate}
-                    onHide={handleHideMessage}
-                  />
+                  <div key={m.id}>
+                    {m.id === firstUnreadId && (
+                      <div className="flex items-center gap-2 py-1.5" aria-label="New messages">
+                        <span className="h-px flex-1 bg-teal-500/30" />
+                        <span className="text-[10px] font-bold uppercase tracking-wide text-teal-400">
+                          New
+                        </span>
+                        <span className="h-px flex-1 bg-teal-500/30" />
+                      </div>
+                    )}
+                    <CrewMessageBubble
+                      message={m}
+                      isOwn={m.pubkey === user.pubkey}
+                      isHidden={hiddenIds?.has(m.id)}
+                      canModerate={canModerate}
+                      onHide={handleHideMessage}
+                    />
+                  </div>
                 ))}
             </div>
 

src/hooks/useCrewChatRead.ts

@@ -0,0 +1,29 @@
+import { useCallback } from 'react';
+import { useLocalStorage } from '@/hooks/useLocalStorage';
+import { useCurrentUser } from '@/hooks/useCurrentUser';
+
+/**
+ * Per-crew "last seen the chat" timestamp (unix seconds), stored per-pubkey +
+ * per-crew in localStorage. Used only to draw a subtle "new messages" divider
+ * when a member returns to a chat — no network cost, works for every transport.
+ *
+ * We deliberately keep this local-only: crew chat is casual and the divider is a
+ * convenience, not a synced read-receipt. Nothing here leaves the device.
+ */
+export function useCrewChatRead(crewCoord: string | undefined) {
+  const { user } = useCurrentUser();
+  const key =
+    user && crewCoord
+      ? `crew-chat-last-seen:${user.pubkey}:${crewCoord}`
+      : 'crew-chat-last-seen:anon';
+  const [lastSeen, setLastSeen] = useLocalStorage<number>(key, 0);
+
+  const markSeen = useCallback(
+    (ts?: number) => {
+      setLastSeen(ts ?? Math.floor(Date.now() / 1000));
+    },
+    [setLastSeen],
+  );
+
+  return { lastSeen, markSeen };
+}