fix(messages): stabilize conversation ordering by real message time

web/src/utils/private-messages.ts

@@ -32,16 +32,31 @@ function timestamp(value: string): number {
   return Number.isFinite(time) ? time : 0;
 }
 
+function conversationTime(conversation: Conversation): number {
+  const time = Date.parse(conversation.last_message_at || '');
+  return Number.isFinite(time) ? time : Number.NEGATIVE_INFINITY;
+}
+
 export function mergeConversations(previous: Conversation[], incoming: Conversation[]): Conversation[] {
   const merged = new Map(previous.map((conversation) => [conversationKey(conversation), conversation]));
   const seen = new Set<string>();
   for (const conversation of incoming) {
     const key = conversationKey(conversation);
-    if (!seen.has(key)) merged.set(key, conversation);
+    const existing = merged.get(key);
+    const incomingTime = conversationTime(conversation);
+    const existingTime = existing ? conversationTime(existing) : Number.NEGATIVE_INFINITY;
+    // Late snapshots cannot roll back newer messages. For equal times, keep the
+    // first incoming page so overlapping later pages cannot replace its copy.
+    if (existing && (incomingTime < existingTime || (seen.has(key) && incomingTime === existingTime))) continue;
+    merged.set(key, conversation);
     seen.add(key);
   }
-  return [...merged.values()].sort((a, b) => timestamp(b.last_message_at) - timestamp(a.last_message_at)
-    || conversationKey(a).localeCompare(conversationKey(b)));
+  return [...merged.values()].sort((a, b) => {
+    const aTime = conversationTime(a), bTime = conversationTime(b);
+    if (aTime !== bTime) return aTime > bTime ? -1 : 1;
+    if (a.account_id !== b.account_id) return a.account_id < b.account_id ? -1 : 1;
+    return a.peer_uid === b.peer_uid ? 0 : a.peer_uid < b.peer_uid ? -1 : 1;
+  });
 }
 
 export function mergeMessages(previous: PrivateMessage[], incoming: PrivateMessage[]): PrivateMessage[] {