fix(combine_psbt): Propagate Psbt::combine errors

src/handlers/offline.rs

@@ -765,7 +765,7 @@ impl AppCommand<AppContext<OfflineOperations<'_>>> for CombinePsbtCommand {
             psbts
                 .into_iter()
                 .try_fold::<_, _, Result<Psbt, Error>>(init_psbt, |mut acc, x| {
-                    let _ = acc.combine(x);
+                    acc.combine(x)?;
                     Ok(acc)
                 })?;
 

tests/integration/online.rs

@@ -358,6 +358,35 @@ mod test_online {
         );
     }
 
+    #[test]
+    fn test_combine_psbt_rejects_mismatched_psbts() {
+        let (cli, mut cmd_init, env) = setup_online_wallet();
+        cmd_init.assert().success();
+        fund_and_sync_wallet(&cli, &env);
+
+        // Two PSBTs spending the same UTXO but paying different amounts: their
+        // unsigned transactions differ, so BIP174 forbids combining them.
+        let psbt_a = cli_create_tx(&cli, &format!("{RECIPIENT}:15000"));
+        let psbt_b = cli_create_tx(&cli, &format!("{RECIPIENT}:25000"));
+
+        let output = cli
+            .wallet_cmd(&["--wallet", WALLET_NAME, "combine_psbt", &psbt_a, &psbt_b])
+            .output()
+            .expect("failed to spawn `combine_psbt`");
+
+        assert!(
+            !output.status.success(),
+            "combine_psbt should fail on PSBTs with different unsigned transactions, got: {}",
+            String::from_utf8_lossy(&output.stdout)
+        );
+
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        assert!(
+            stderr.contains("different unsigned transaction"),
+            "unexpected error message: {stderr}"
+        );
+    }
+
     #[test]
     fn test_bump_fee_replaces_unconfirmed_tx() {
         let (cli, mut cmd_init, env) = setup_online_wallet();