fix(node): use timezone-aware datetime in deploy_contract fallback

backend/node/base.py

@@ -805,7 +805,7 @@ async def deploy_contract(
 
         transaction_datetime = self._date_from_str(transaction_created_at)
         if transaction_datetime is None:
-            transaction_datetime = datetime.datetime.now()
+            transaction_datetime = datetime.datetime.now(tz=datetime.timezone.utc)
 
         return await self._run_genvm(
             from_address,

backend/services/usage_metrics_service.py

@@ -4,7 +4,7 @@
 import math
 import os
 from typing import Any, Optional
-from datetime import datetime
+from datetime import datetime, timezone
 import aiohttp
 from loguru import logger
 
@@ -464,7 +464,7 @@ def _safe_int(self, value: Any) -> int:
     def _format_created_at(self, created_at) -> str:
         """Format created_at to ISO8601 string."""
         if created_at is None:
-            return datetime.utcnow().isoformat()
+            return datetime.now(timezone.utc).isoformat()
 
         if isinstance(created_at, datetime):
             return created_at.isoformat()

tests/unit/test_leader_llm_recovery.py

@@ -1,5 +1,6 @@
 """Unit tests for leader/validator fatal error handling in Node._run_genvm()."""
 
+import asyncio
 import pytest
 from unittest.mock import MagicMock, AsyncMock, patch
 
@@ -198,3 +199,38 @@ async def test_validator_fatal_error_returns_receipt():
     assert receipt.vote == Vote.DETERMINISTIC_VIOLATION
     assert receipt.genvm_result["raw_error"]["fatal"] is True
     assert receipt.genvm_result["error_code"] == GenVMErrorCode.LLM_NO_PROVIDER
+
+
+def test_deploy_contract_fallback_is_timezone_aware():
+    """When transaction_created_at is None, deploy_contract must fall back to
+    a timezone-aware datetime so _run_genvm's assert on tzinfo does not fire."""
+    import datetime as _dt
+    from unittest.mock import AsyncMock, patch
+    from backend.node.base import Node
+    from backend.node.types import Receipt
+
+    node = Node(
+        contract_snapshot=_make_snapshot(),
+        validator_mode=ExecutionMode.LEADER,
+        validator=_make_validator(),
+        leader_receipt=None,
+        msg_handler=MagicMock(),
+        contract_snapshot_factory=None,
+        manager=MagicMock(),
+    )
+    mock_genvm = AsyncMock(return_value=MagicMock(spec=Receipt))
+    with patch.object(node, "_run_genvm", mock_genvm):
+        with patch("backend.node.base.datetime") as mock_dt:
+            mock_dt.datetime.now.return_value = _dt.datetime(2024, 1, 1, 12, 0, 0, tzinfo=_dt.timezone.utc)
+            loop = asyncio.new_event_loop()
+            try:
+                loop.run_until_complete(node.deploy_contract(
+                    from_address="0x00000000000000000000000000000001234",
+                    code_to_deploy=b"",
+                    calldata=b"",
+                    transaction_created_at=None,
+                ))
+            finally:
+                loop.close()
+    td = mock_genvm.call_args.kwargs["transaction_datetime"]
+    assert td.tzinfo is not None

tests/unit/test_usage_metrics_service.py

@@ -378,3 +378,18 @@ def test_extract_llm_calls_falls_back_to_primary_without_token_metrics():
             "costUsd": 0,
         }
     ]
+
+
+def test_format_created_at_returns_utc_isoformat():
+    service = UsageMetricsService()
+    result = service._format_created_at(None)
+    assert "+" in result  # timezone-aware ISO string includes offset like "+00:00"
+    assert "Z" not in result  # should use +00:00, not Z suffix
+
+
+def test_format_created_at_returns_original_datetime_isoformat():
+    from datetime import datetime, timezone
+    service = UsageMetricsService()
+    dt = datetime(2024, 1, 1, 12, 0, 0, tzinfo=timezone.utc)
+    result = service._format_created_at(dt)
+    assert result == "2024-01-01T12:00:00+00:00"