fix(plugins): handle duplicate-address keystores and add import warning

- KeystoreUpdate: findKeystoreByAddress now detects multiple keystores
  with the same address and returns an error with file list, instead of
  silently picking one nondeterministically.
- KeystoreImport: scan directory before writing and print WARNING if a
  keystore for the same address already exists. Import still proceeds
  (legitimate use case) but user is made aware.
- KeystoreUpdate: strip UTF-8 BOM from password file before parsing.
- KeystoreUpdate: add comment clarifying old password skips validation.
- KeystoreList: add version != 3 check to filter non-keystore JSON.

Author: Barbatos

plugins/src/main/java/common/org/tron/plugins/KeystoreImport.java

@@ -76,10 +76,10 @@ public Integer call() {
             + " for the selected algorithm.");
         return 1;
       }
+      String address = Credentials.create(keyPair).getAddress();
+      warnIfAddressExists(keystoreDir, address);
       String fileName = WalletUtils.generateWalletFile(password, keyPair, keystoreDir, true);
       KeystoreCliUtils.setOwnerOnly(new File(keystoreDir, fileName));
-
-      String address = Credentials.create(keyPair).getAddress();
       if (json) {
         KeystoreCliUtils.printJson(KeystoreCliUtils.jsonMap(
             "address", address, "file", fileName));
@@ -136,4 +136,29 @@ private String readPrivateKey() throws IOException {
   private boolean isValidPrivateKey(String key) {
     return !StringUtils.isEmpty(key) && HEX_PATTERN.matcher(key).matches();
   }
+
+  private void warnIfAddressExists(File dir, String address) {
+    if (!dir.exists() || !dir.isDirectory()) {
+      return;
+    }
+    File[] files = dir.listFiles((d, name) -> name.endsWith(".json"));
+    if (files == null) {
+      return;
+    }
+    com.fasterxml.jackson.databind.ObjectMapper mapper =
+        KeystoreCliUtils.mapper();
+    for (File file : files) {
+      try {
+        org.tron.keystore.WalletFile wf =
+            mapper.readValue(file, org.tron.keystore.WalletFile.class);
+        if (address.equals(wf.getAddress())) {
+          System.err.println("WARNING: keystore for address "
+              + address + " already exists: " + file.getName());
+          return;
+        }
+      } catch (Exception e) {
+        // Skip invalid files
+      }
+    }
+  }
 }

plugins/src/main/java/common/org/tron/plugins/KeystoreUpdate.java

@@ -183,16 +183,26 @@ private File findKeystoreByAddress(String targetAddress) {
     if (files == null) {
       return null;
     }
+    java.util.List<File> matches = new java.util.ArrayList<>();
     for (File file : files) {
       try {
         WalletFile wf = MAPPER.readValue(file, WalletFile.class);
         if (targetAddress.equals(wf.getAddress())) {
-          return file;
+          matches.add(file);
         }
       } catch (Exception e) {
         // Skip invalid files
       }
     }
-    return null;
+    if (matches.size() > 1) {
+      System.err.println("Multiple keystores found for address "
+          + targetAddress + ":");
+      for (File m : matches) {
+        System.err.println("  " + m.getName());
+      }
+      System.err.println("Please remove duplicates and retry.");
+      return null;
+    }
+    return matches.isEmpty() ? null : matches.get(0);
   }
 }