fix: reject self-transfer in transfer() to match transfer_from (#84)

CHANGELOG.md

@@ -34,6 +34,14 @@ package version is bumped.
 - **[#67] Prevent self-transfer allowance drain in `transfer_from` and fix storage re-fetch TOCTOU in `spend_allowance`.**
   `transfer_from` now panics with `"token: cannot transfer to self"` when `from == to`, preventing spenders from burning an owner's allowance without transferring tokens. `spend_allowance` in `storage.rs` now accepts the `&Allowance` struct directly instead of re-fetching from persistent storage with `.unwrap()`, eliminating a potential TOCTOU window.
 
+- **[#84] Reject self-transfer in `transfer` to match `transfer_from`.**
+  `transfer_from` already rejected `from == to` (see #67 above), but `transfer`
+  had no equivalent guard: a self-transfer silently succeeded as a no-op while
+  still consuming the caller's `require_auth()` signature — the same security-
+  model inconsistency #67 was fixed to prevent, just on the other entry point.
+  `transfer` now panics with `"token: cannot transfer to self"` when
+  `from == to`, matching `transfer_from`'s existing message exactly.
+
 #### `reward-engine`
 
 - **[#71] Make `approve_proof` and the approve path of `resolve_dispute`

contracts/eco-token/src/token.rs

@@ -187,6 +187,7 @@ impl TokenContract {
     /// # Panics
     ///
     /// * Panics if `amount <= 0`
+    /// * Panics if `from == to`
     /// * Panics if `from` has insufficient balance
     ///
     /// # Auth
@@ -200,6 +201,10 @@ impl TokenContract {
             panic!("token: amount must be positive");
         }
 
+        if from == to {
+            panic!("token: cannot transfer to self");
+        }
+
         let from_balance = storage::read_balance(&e, &from);
         if from_balance < amount {
             panic!("token: insufficient balance");
@@ -1525,6 +1530,7 @@ mod test {
     }
 
     #[test]
+    #[should_panic(expected = "token: cannot transfer to self")]
     fn test_transfer_to_self() {
         let e = Env::default();
         let admin = Address::generate(&e);
@@ -1542,8 +1548,30 @@ mod test {
         e.mock_all_auths();
         client.mint(&user, &1000);
         client.transfer(&user, &user, &500);
+    }
 
-        assert_eq!(client.balance(&user), 1000);
+    #[test]
+    fn test_transfer_valid_addresses_still_works() {
+        let e = Env::default();
+        let admin = Address::generate(&e);
+        let from = Address::generate(&e);
+        let to = Address::generate(&e);
+        let contract_id = e.register(TokenContract, ());
+        let client = TokenContractClient::new(&e, &contract_id);
+
+        client.initialize(
+            &admin,
+            &String::from_str(&e, "ECO"),
+            &String::from_str(&e, "ECO"),
+            &7,
+        );
+
+        e.mock_all_auths();
+        client.mint(&from, &1000);
+        client.transfer(&from, &to, &400);
+
+        assert_eq!(client.balance(&from), 600);
+        assert_eq!(client.balance(&to), 400);
     }
 
     #[test]