Fix same-second same-message collision in room servers with per-sender disambiguation at DB level

frontend/src/utils/messageIdentity.ts

@@ -1,10 +1,14 @@
 import type { Message } from '../types';
 
-// Content identity matches the frontend's message-level dedup contract.
+// Content identity matches the backend's message-level dedup indexes.
 export function getMessageContentKey(msg: Message): string {
   // When sender_timestamp exists, dedup by content (catches radio-path duplicates with different IDs).
   // When null, include msg.id so each message gets a unique key — avoids silently dropping
   // different messages that share the same text and received_at second.
   const ts = msg.sender_timestamp ?? `r${msg.received_at}-${msg.id}`;
-  return `${msg.type}-${msg.conversation_key}-${msg.text}-${ts}`;
+  // For incoming PRIV messages (room-server posts), include sender_key so that
+  // two different room participants sending identical text in the same second
+  // are not collapsed.  Mirrors idx_messages_incoming_priv_dedup.
+  const senderSuffix = msg.type === 'PRIV' && msg.sender_key ? `-${msg.sender_key}` : '';
+  return `${msg.type}-${msg.conversation_key}-${msg.text}-${ts}${senderSuffix}`;
 }