diff --git a/Rosetta/Core/Crypto/MessageCrypto.swift b/Rosetta/Core/Crypto/MessageCrypto.swift
index 9f5b6c3..3d7dd0f 100644
--- a/Rosetta/Core/Crypto/MessageCrypto.swift
+++ b/Rosetta/Core/Crypto/MessageCrypto.swift
@@ -176,10 +176,21 @@ enum MessageCrypto {
             var seen = Set<String>()
             return candidates.filter { seen.insert($0).inserted }
         }
-        // Group key or plain password — try hex(utf8Bytes) first (Desktop parity:
-        // Desktop encrypts group attachments with Buffer.from(groupKey).toString('hex')).
+        // Group key or plain password — Desktop encrypts group attachments with
+        // Buffer.from(groupKey).toString('hex') (hex of UTF-8 bytes).
+        // If stored is already hex-encoded (128+ chars, all hex digits), use as-is
+        // to avoid generating a 256-char double-hex garbage candidate.
+        let isAlreadyHex = stored.count >= 128 && stored.allSatisfy { $0.isHexDigit }
+        if isAlreadyHex {
+            // Try hex as-is (Desktop) + un-hexed original (iOS/Android plain group key)
+            let decoded = Data(hexString: stored)
+            if let original = String(data: decoded, encoding: .utf8), !original.isEmpty {
+                return [stored, original]
+            }
+            return [stored]
+        }
         let hexVariant = Data(stored.utf8).map { String(format: "%02x", $0) }.joined()
-        return hexVariant == stored ? [stored] : [hexVariant, stored]
+        return [hexVariant, stored]
     }
 
     // MARK: - Android-Compatible UTF-8 Decoder
diff --git a/Rosetta/Core/Services/SessionManager.swift b/Rosetta/Core/Services/SessionManager.swift
index 32c21cc..1effb9b 100644
--- a/Rosetta/Core/Services/SessionManager.swift
+++ b/Rosetta/Core/Services/SessionManager.swift
@@ -1360,6 +1360,7 @@ final class SessionManager {
                 self.syncRequestInFlight = false
                 self.syncBatchInProgress = false
                 self.pendingIncomingMessages.removeAll()
+                self.enqueuedMessageIds.removeAll()
                 self.isProcessingIncomingMessages = false
 
                 // Cancel stale retry timers from previous connection —
@@ -1566,7 +1567,18 @@ final class SessionManager {
         DialogRepository.shared.updateDialogFromMessages(opponentKey: safeKey)
     }
 
+    /// Dedup set for the current processing queue — prevents the same messageId
+    /// from being enqueued twice (real-time + sync overlap). Cleared after queue drains.
+    private var enqueuedMessageIds: Set<String> = []
+
     private func enqueueIncomingMessage(_ packet: PacketMessage) {
+        // Queue-level dedup: if the same messageId is already pending, skip.
+        // This catches the common real-time + sync overlap case without
+        // burning CPU on duplicate crypto + DB upsert.
+        let msgId = packet.messageId
+        if !msgId.isEmpty && enqueuedMessageIds.contains(msgId) { return }
+        if !msgId.isEmpty { enqueuedMessageIds.insert(msgId) }
+
         pendingIncomingMessages.append(packet)
         guard !isProcessingIncomingMessages else { return }
         isProcessingIncomingMessages = true
@@ -1595,6 +1607,7 @@ final class SessionManager {
 
         if batching { MessageRepository.shared.endBatchUpdates() }
         isProcessingIncomingMessages = false
+        enqueuedMessageIds.removeAll()
         signalQueueDrained()
     }
 
@@ -1612,6 +1625,16 @@ final class SessionManager {
         let opponentKey = context.dialogKey
         let isGroupDialog = context.kind == .group
         let wasKnownBefore = MessageRepository.shared.hasMessage(packet.messageId)
+
+        // Optimization: skip expensive crypto + upsert for incoming messages
+        // already stored in DB. Only outgoing messages need re-processing
+        // (sync may update delivery status from .waiting → .delivered).
+        // This also eliminates any race-condition window between real-time
+        // and sync delivery of the same messageId.
+        if wasKnownBefore && !fromMe {
+            return
+        }
+
         let groupKey: String? = {
             guard isGroupDialog, let currentPrivateKeyHex else { return nil }
             return GroupRepository.shared.groupKey(