Introduce failure for test

Author: ishymko

src/a2a/utils/constants.py

@@ -1,8 +1,14 @@
 """Constants for well-known URIs used throughout the A2A Python SDK."""
 
+import os  # CI test: unused import to trigger ruff F401
 from enum import Enum
 
 
+def _ci_test_bad_return() -> int:
+    """CI test: returns str but annotated as int to trigger mypy."""
+    return 'not an int'
+
+
 AGENT_CARD_WELL_KNOWN_PATH = '/.well-known/agent-card.json'
 DEFAULT_RPC_URL = '/'
 DEFAULT_LIST_TASKS_PAGE_SIZE = 50