Fix dedupe for frontend raw packet delivery

frontend/src/utils/rawPacketIdentity.ts

@@ -0,0 +1,31 @@
+import type { RawPacket } from '../types';
+
+/**
+ * Distinguish real-time RF observations from storage identity.
+ * observation_id is emitted per WS event; id is the DB row identity fallback.
+ */
+export function getRawPacketObservationKey(
+  packet: Pick<RawPacket, 'id' | 'observation_id'>
+): string {
+  if (packet.observation_id !== undefined && packet.observation_id !== null) {
+    return `obs-${packet.observation_id}`;
+  }
+  return `db-${packet.id}`;
+}
+
+export function appendRawPacketUnique(
+  prev: RawPacket[],
+  packet: RawPacket,
+  maxPackets: number
+): RawPacket[] {
+  const packetKey = getRawPacketObservationKey(packet);
+  if (prev.some((p) => getRawPacketObservationKey(p) === packetKey)) {
+    return prev;
+  }
+
+  const updated = [...prev, packet];
+  if (updated.length > maxPackets) {
+    return updated.slice(-maxPackets);
+  }
+  return updated;
+}