fix(billing-cost-management-mcp-server): format cost-optimization get_recommendation timestamp like list_recommendations (#4859)

get_recommendation built last_refresh_timestamp with str(), so a live call
returned '2026-10-23 21:40:14+00:00' where list_recommendations returns
'2026-10-23T21:40:14' for the same recommendation, and a response without
lastRefreshTimestamp (GetRecommendation has no required output members)
returned the string 'None'. It now uses format_timestamp, as
list_recommendations does, and returns None when the field is absent.

Also remove the `if not recommendation` warning branch. botocore always
adds ResponseMetadata, so the response is never empty; a missing
recommendation raises ResourceNotFoundException (confirmed live), which
is already reported as a warning naming the ID. The branch only ran for a
mocked {} response, and its two tests are removed.

Author: finklen-amazon

src/billing-cost-management-mcp-server/awslabs/billing_cost_management_mcp_server/tools/cost_optimization_hub_helpers.py

@@ -221,23 +221,9 @@ async def get_recommendation(
 
         # Make the API call
         await ctx_logger.info(f'Fetching recommendation {recommendation_id}')
-        response = coh_client.get_recommendation(**request_params)
-
-        # The response IS the recommendation data
-        recommendation = response
-
-        if not recommendation:
-            await ctx_logger.warning(
-                f'No recommendation found for recommendation {recommendation_id}'
-            )
-            return format_response(
-                'warning',
-                {
-                    'recommendation_id': recommendation_id,
-                    'message': 'No recommendation found for the specified recommendation.',
-                },
-                'No recommendation found. The recommendation may not have optimization opportunities, or the recommendation ID may be incorrect.',
-            )
+        # The response IS the recommendation data. A missing recommendation raises
+        # ResourceNotFoundException (handled below); boto3 never returns an empty response.
+        recommendation = coh_client.get_recommendation(**request_params)
 
         # Build response using actual API fields
         formatted_response = {
@@ -255,7 +241,7 @@ async def get_recommendation(
             'currency_code': recommendation.get('currencyCode'),
             'implementation_effort': recommendation.get('implementationEffort'),
             'source': recommendation.get('source'),
-            'last_refresh_timestamp': str(recommendation.get('lastRefreshTimestamp')),
+            'last_refresh_timestamp': format_timestamp(recommendation.get('lastRefreshTimestamp')),
             'lookback_period_in_days': recommendation.get('recommendationLookbackPeriodInDays'),
             'cost_calculation_lookback_period_in_days': recommendation.get(
                 'costCalculationLookbackPeriodInDays'

src/billing-cost-management-mcp-server/tests/tools/test_cost_optimization_hub_helpers.py

@@ -30,7 +30,7 @@
     EFFICIENCY_PARETO_MAX_PAGES,
     EFFICIENCY_PARETO_PAGE_SIZE,
 )
-from datetime import datetime
+from datetime import datetime, timezone
 from fastmcp import Context
 from unittest.mock import AsyncMock, MagicMock
 
@@ -646,23 +646,6 @@ async def test_non_client_error_returns_structured_error(self, mock_context, moc
 class TestGetRecommendationErrorHandling:
     """Test error handling scenarios for get_recommendation."""
 
-    async def test_empty_recommendation_response(self, mock_context, mock_coh_client):
-        """Test get_recommendation with empty recommendation in response."""
-        mock_coh_client.get_recommendation.return_value = {}
-
-        result = await get_recommendation(mock_context, mock_coh_client, 'i-1234567890abcdef0')
-
-        assert result['status'] == 'warning'
-
-    async def test_no_recommendation_key(self, mock_context, mock_coh_client):
-        """Test get_recommendation with no recommendation key in response."""
-        mock_coh_client.get_recommendation.return_value = {}
-
-        result = await get_recommendation(mock_context, mock_coh_client, 'i-1234567890abcdef0')
-
-        assert result['status'] == 'warning'
-        assert 'No recommendation found' in result['message']
-
     async def test_validation_exception(self, mock_context, mock_coh_client):
         """Test get_recommendation ValidationException handling."""
         from botocore.exceptions import ClientError
@@ -1002,6 +985,29 @@ async def test_recommendation_without_optional_fields(self, mock_context, mock_c
         assert rec['source'] is None
         assert rec['lookback_period_in_days'] is None
         assert rec['estimated_monthly_savings'] is None
+        assert rec['last_refresh_timestamp'] is None
+
+    async def test_last_refresh_timestamp_matches_list_recommendations(
+        self, mock_context, mock_coh_client
+    ):
+        """get_recommendation formats lastRefreshTimestamp the same way list_recommendations does."""
+        refreshed = datetime(2026, 6, 1, tzinfo=timezone.utc)
+        mock_coh_client.get_recommendation.return_value = {
+            'recommendationId': 'rec-1',
+            'lastRefreshTimestamp': refreshed,
+        }
+        mock_coh_client.list_recommendations.return_value = {
+            'items': [{'recommendationId': 'rec-1', 'lastRefreshTimestamp': refreshed}]
+        }
+
+        got = await get_recommendation(mock_context, mock_coh_client, 'rec-1')
+        listed = await list_recommendations(mock_context, mock_coh_client)
+
+        assert got['data']['last_refresh_timestamp'] == '2026-06-01T00:00:00'
+        assert (
+            listed['data']['recommendations'][0]['last_refresh_timestamp']
+            == got['data']['last_refresh_timestamp']
+        )
 
     async def test_recommendation_with_cost_breakdown_no_implementation(
         self, mock_context, mock_coh_client