[Fix] - SensitiveDataMasker converts lists to string (#15420)

* fix: preserve lists in SensitiveDataMasker to prevent string conversion

Added 'list' to allowed primitive types in mask_dict() to prevent lists like
tags from being converted to string representations in API responses.

Before: {"tags": "['East US 2', 'production', 'test']"}
After:  {"tags": ["East US 2", "production", "test"]}

* add: unit test

litellm/litellm_core_utils/sensitive_data_masker.py

@@ -75,7 +75,7 @@ class SensitiveDataMasker:
                     masked_data[k] = self._mask_value(str_value)
                 else:
                     masked_data[k] = (
-                        v if isinstance(v, (int, float, bool, str)) else str(v)
+                        v if isinstance(v, (int, float, bool, str, list)) else str(v)
                     )
             except Exception:
                 masked_data[k] = "<unable to serialize>"
@@ -89,12 +89,14 @@ masker = SensitiveDataMasker()
 data = {
     "api_key": "sk-1234567890abcdef",
     "redis_password": "very_secret_pass",
-    "port": 6379
+    "port": 6379,
+    "tags": ["East US 2", "production", "test"]
 }
 masked = masker.mask_dict(data)
 # Result: {
 #    "api_key": "sk-1****cdef",
 #    "redis_password": "very****pass",
-#    "port": 6379
+#    "port": 6379,
+#    "tags": ["East US 2", "production", "test"]
 # }
 """

tests/test_litellm/litellm_core_utils/test_sensitive_data_masker.py

@@ -0,0 +1,31 @@
+"""
+Unit tests for SensitiveDataMasker - List Preservation
+"""
+
+import os
+import sys
+
+import pytest
+
+# Add the parent directory to the system path
+sys.path.insert(0, os.path.abspath("../../.."))
+
+from litellm.litellm_core_utils.sensitive_data_masker import SensitiveDataMasker
+
+
+def test_lists_are_preserved_not_converted_to_strings():
+    """
+    Regression test: Ensure lists are preserved as JSON arrays, not converted to strings.
+    Previously, tags field in /model/info was returned as "['tag1', 'tag2']" instead of ["tag1", "tag2"]
+    """
+    masker = SensitiveDataMasker()
+    
+    data = {
+        "tags": ["East US 2", "production", "test"],
+    }
+    
+    masked = masker.mask_dict(data)
+    
+    # Must be a list, not a string
+    assert isinstance(masked["tags"], list)
+    assert masked["tags"] == ["East US 2", "production", "test"]