Reject duplicate venue signers in create_venue and update_venue_signers

pallets/runtime/tests/src/settlement_test.rs

@@ -2317,6 +2317,59 @@ fn assert_number_of_venue_signers() {
     })
 }
 
+#[test]
+fn duplicate_venue_signers_rejected() {
+    ExtBuilder::default().build().execute_with(|| {
+        let alice = User::new(Sr25519Keyring::Alice);
+        let venue_id = VenueCounter::<TestStorage>::get();
+        let bob = Sr25519Keyring::Bob.to_account_id();
+        let charlie = Sr25519Keyring::Charlie.to_account_id();
+
+        // Duplicates in create_venue rejected.
+        assert_noop!(
+            Settlement::create_venue(
+                alice.origin(),
+                VenueDetails::default(),
+                vec![bob.clone(), bob.clone()],
+                VenueType::Exchange
+            ),
+            Error::DuplicateSigners
+        );
+
+        // Create venue with unique signers.
+        assert_ok!(Settlement::create_venue(
+            alice.origin(),
+            VenueDetails::default(),
+            vec![bob.clone(), charlie.clone()],
+            VenueType::Exchange
+        ));
+        assert_eq!(NumberOfVenueSigners::<TestStorage>::get(venue_id), 2);
+
+        // Duplicates in remove rejected — counter stays in sync.
+        assert_noop!(
+            Settlement::update_venue_signers(
+                alice.origin(),
+                venue_id,
+                vec![bob.clone(), bob.clone()],
+                false
+            ),
+            Error::DuplicateSigners
+        );
+        assert_eq!(NumberOfVenueSigners::<TestStorage>::get(venue_id), 2);
+
+        // Duplicates in add rejected.
+        assert_noop!(
+            Settlement::update_venue_signers(
+                alice.origin(),
+                venue_id,
+                vec![Sr25519Keyring::Dave.to_account_id(); 2],
+                true
+            ),
+            Error::DuplicateSigners
+        );
+    });
+}
+
 #[test]
 fn reject_instruction_with_zero_amount() {
     test_with_did_registrar(|_eve| {

pallets/settlement/src/lib.rs

@@ -585,6 +585,8 @@ pub mod pallet {
         InvalidTaskName,
         /// The receipt has expired and can no longer be claimed.
         ReceiptExpired,
+        /// The signers list contains duplicate entries.
+        DuplicateSigners,
     }
 
     const STORAGE_VERSION: StorageVersion = StorageVersion::new(4);
@@ -809,6 +811,10 @@ pub mod pallet {
             let did = pallet_identity::Pallet::<T>::ensure_perms(origin)?;
             ensure_string_limited::<T>(&details)?;
 
+            let mut seen = BTreeSet::new();
+            for signer in &signers {
+                ensure!(seen.insert(signer), Error::<T>::DuplicateSigners);
+            }
             ensure!(
                 signers.len() <= T::MaxNumberOfVenueSigners::get() as usize,
                 Error::<T>::NumberOfVenueSignersExceeded
@@ -2562,6 +2568,11 @@ impl<T: Config> Pallet<T> {
         // Ensure venue exists & sender is its creator.
         Self::ensure_venue_creator(&venue_id, &did)?;
 
+        let mut seen = BTreeSet::new();
+        for signer in &signers {
+            ensure!(seen.insert(signer), Error::<T>::DuplicateSigners);
+        }
+
         if add_signers {
             let current_number_of_signers = NumberOfVenueSigners::<T>::get(venue_id);
             ensure!(