[FSSDK-12368] Restore holdout evaluation in decide flow, remove only flag-level include/exclude fields

The previous cleanup removed the entire holdout evaluation from the decide
flow. This restores holdout checking while keeping the removal of legacy
includedFlags/excludedFlags fields — all running holdouts now apply to all
flags uniformly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: FarhanAnjum-opti

optimizely/decision_service.py

@@ -733,7 +733,30 @@ def get_decision_for_flag(
         reasons = decide_reasons.copy() if decide_reasons else []
         user_id = user_context.user_id
 
-        # Check experiments then rollouts
+        # Check holdouts
+        holdouts = project_config.get_holdouts_for_flag(feature_flag.key)
+        for holdout in holdouts:
+            holdout_decision = self.get_variation_for_holdout(holdout, user_context, project_config)
+            reasons.extend(holdout_decision['reasons'])
+
+            decision = holdout_decision['decision']
+            # Check if user was bucketed into holdout (has a variation)
+            if decision.variation is None:
+                continue
+
+            message = (
+                f"The user '{user_id}' is bucketed into holdout '{holdout.key}' "
+                f"for feature flag '{feature_flag.key}'."
+            )
+            self.logger.info(message)
+            reasons.append(message)
+            return {
+                'decision': holdout_decision['decision'],
+                'error': False,
+                'reasons': reasons
+            }
+
+        # If no holdout decision, check experiments then rollouts
         if feature_flag.experimentIds:
             for experiment_id in feature_flag.experimentIds:
                 experiment = project_config.get_experiment_from_id(experiment_id)

optimizely/project_config.py

@@ -93,6 +93,7 @@ def __init__(self, datafile: str | bytes, logger: Logger, error_handler: Any):
         holdouts_data: list[types.HoldoutDict] = config.get('holdouts', [])
         self.holdouts: list[entities.Holdout] = []
         self.holdout_id_map: dict[str, entities.Holdout] = {}
+        self.flag_holdouts_map: dict[str, list[entities.Holdout]] = {}
 
         # Convert holdout dicts to Holdout entities
         for holdout_data in holdouts_data:
@@ -239,6 +240,11 @@ def __init__(self, datafile: str | bytes, logger: Logger, error_handler: Any):
                             everyone_else_variation.variables, 'id', entities.Variation.VariableUsage
                         )
 
+            # Map all running holdouts to this flag
+            applicable_holdouts = list(self.holdout_id_map.values())
+            if applicable_holdouts:
+                self.flag_holdouts_map[feature.key] = applicable_holdouts
+
             rollout = None if len(feature.rolloutId) == 0 else self.rollout_id_map[feature.rolloutId]
             if rollout:
                 for exp in rollout.experiments:
@@ -872,6 +878,20 @@ def get_flag_variation(
 
         return None
 
+    def get_holdouts_for_flag(self, flag_key: str) -> list[entities.Holdout]:
+        """ Helper method to get holdouts from an applied feature flag.
+
+        Args:
+            flag_key: Key of the feature flag.
+
+        Returns:
+            The holdouts that apply for a specific flag as Holdout entity objects.
+        """
+        if not self.holdouts:
+            return []
+
+        return self.flag_holdouts_map.get(flag_key, [])
+
     def get_holdout(self, holdout_id: str) -> Optional[entities.Holdout]:
         """ Helper method to get holdout from holdout ID.
 

tests/test_decision_service_holdout.py

@@ -863,9 +863,6 @@ def test_decide_all_with_global_holdout(self):
 
     def test_decide_all_with_included_flags(self):
         """Should apply holdout only to included flags in decide_all."""
-        # Get feature flag IDs
-        feature1_id = '91111'  # test_feature_in_experiment
-
         config_dict_with_holdouts = self.config_dict_with_features.copy()
         config_dict_with_holdouts['holdouts'] = [
             {
@@ -907,8 +904,6 @@ def test_decide_all_with_included_flags(self):
 
     def test_decide_all_with_excluded_flags(self):
         """Should exclude holdout from excluded flags in decide_all."""
-        feature1_id = '91111'  # test_feature_in_experiment
-
         config_dict_with_holdouts = self.config_dict_with_features.copy()
         config_dict_with_holdouts['holdouts'] = [
             {
@@ -949,9 +944,6 @@ def test_decide_all_with_excluded_flags(self):
 
     def test_decide_all_with_multiple_holdouts(self):
         """Should handle multiple holdouts with correct priority."""
-        feature1_id = '91111'
-        feature2_id = '91112'
-
         config_dict_with_holdouts = self.config_dict_with_features.copy()
         config_dict_with_holdouts['holdouts'] = [
             # Global holdout (applies to all)