fix(): project refactoring and minor fixes

src/backend/apps/decision/services.py

@@ -12,7 +12,12 @@ from apps.conflicts.models import ExperimentConflictDomain
 from apps.conflicts.services import resolve_domain_conflict
 from apps.events.models import Decision
 from apps.events.services import decision_create
-from apps.experiments.models import Experiment, ExperimentStatus, Variant
+from apps.experiments.models import (
+    ACTIVE_STATUSES,
+    Experiment,
+    ExperimentStatus,
+    Variant,
+)
 from apps.experiments.selectors import active_experiment_for_flag
 from apps.flags.models import FeatureFlag
 from apps.flags.selectors import feature_flag_get_by_key
@@ -33,7 +38,7 @@ MAX_CONCURRENT_EXPERIMENTS = 3
 COOLDOWN_DAYS = 7
 
 
-def _hash_subject(subject_id: str, experiment_id: str, salt: str) -> float:
+def _hash_subject(subject_id: str, experiment_id: str, salt: str) -> Decimal:
     hash_input = f"{subject_id}:{experiment_id}:{salt}".encode()
     hash_bytes = hashlib.sha256(hash_input).digest()
     hash_int = int.from_bytes(hash_bytes[:8], byteorder="big")
@@ -112,6 +117,9 @@ def _check_participation_limits(
             subject_id=subject_id,
             reason="experiment_assigned",
             experiment_id__isnull=False,
+            experiment_id__in=Experiment.objects.filter(
+                status__in=ACTIVE_STATUSES,
+            ).values("pk"),
         )
         .exclude(experiment_id=experiment_pk)
         .values("experiment_id")

src/backend/apps/events/services.py

@@ -22,6 +22,7 @@ from apps.events.selectors import (
     pending_event_exists,
     pending_events_for_decision,
 )
+from config.errors import ConflictError
 
 PENDING_TTL_DAYS = 7
 
@@ -124,20 +125,19 @@ def _process_exposure_event(
 ) -> None:
     decision_id = event_data["decision_id"]
     subject_id = event_data["subject_id"]
-    timestamp = parse_datetime(event_data["timestamp"]) or timezone.now()
+    timestamp = parse_datetime(event_data["timestamp"])
+    if timestamp is None:
+        raise ValidationError(
+            "Field 'timestamp' must be a valid ISO 8601 datetime."
+        )
 
     decision = decision_get(decision_id)
-    experiment_id = None
-    variant_id = None
     if decision:
-        experiment_id = decision.experiment_id
+        with suppress(ConflictError):
-        variant_id = decision.variant_id
-
-    with suppress(IntegrityError):
             Exposure.objects.create(
                 decision_id=decision_id,
-            experiment_id=experiment_id,
+                experiment_id=decision.experiment_id,
-            variant_id=variant_id,
+                variant_id=decision.variant_id,
                 subject_id=subject_id,
                 timestamp=timestamp,
             )
@@ -158,7 +158,7 @@ def _process_exposure_event(
 def _promote_pending_events(decision_id: str) -> None:
     pending = pending_events_for_decision(decision_id)
     for pe in pending:
-        with suppress(IntegrityError):
+        with suppress(ConflictError):
             Event.objects.create(
                 event_id=pe.event_id,
                 event_type=pe.event_type,
@@ -178,7 +178,11 @@ def _process_conversion_event(
 ) -> None:
     decision_id = event_data["decision_id"]
     subject_id = event_data["subject_id"]
-    timestamp = parse_datetime(event_data["timestamp"]) or timezone.now()
+    timestamp = parse_datetime(event_data["timestamp"])
+    if timestamp is None:
+        raise ValidationError(
+            "Field 'timestamp' must be a valid ISO 8601 datetime."
+        )
     properties = event_data.get("properties", {})
 
     if not event_type_obj.requires_exposure or exposure_exists(decision_id):

src/backend/apps/experiments/services.py

@@ -23,8 +23,10 @@ from apps.notifications.services import (
     notification_enqueue,
 )
 from apps.reviews.selectors import (
+    approver_group_get_by_experimenter,
     can_user_approve_experimenter,
     get_min_approvals_for_experimenter,
+    review_settings_load,
 )
 from apps.users.models import User
 from config.errors import ForbiddenError
@@ -130,6 +132,15 @@ def variant_create(
     is_control: bool = False,
 ) -> Variant:
     ensure_owner_or_admin(experiment, user)
+    if experiment.status != ExperimentStatus.DRAFT:
+        raise ValidationError(
+            {
+                "experiment": (
+                    "Variants can only be added while the experiment "
+                    f"is in '{ExperimentStatus.DRAFT}' status."
+                )
+            }
+        )
     validate_value_for_type(value, experiment.flag.value_type)
     variant = Variant(
         experiment=experiment,
@@ -154,6 +165,15 @@ def variant_update(
     is_control: bool | None = None,
 ) -> Variant:
     ensure_owner_or_admin(variant.experiment, user)
+    if variant.experiment.status != ExperimentStatus.DRAFT:
+        raise ValidationError(
+            {
+                "experiment": (
+                    "Variants can only be updated while the experiment "
+                    f"is in '{ExperimentStatus.DRAFT}' status."
+                )
+            }
+        )
     if name is not None:
         variant.name = name
     if value is not None:
@@ -228,6 +248,20 @@ def _validate_experiment_ready_for_review(experiment: Experiment) -> None:
                 )
             }
         )
+    approver_group = approver_group_get_by_experimenter(experiment.owner)
+    if (
+        approver_group is None
+        and not review_settings_load().allow_any_approver
+    ):
+        raise ValidationError(
+            {
+                "approvers": (
+                    "No approvers available for this experiment's owner. "
+                    "Configure an approver group or enable "
+                    "'allow_any_approver'."
+                )
+            }
+        )
 
 
 def _validate_no_active_flag_conflict(experiment: Experiment) -> None:

src/backend/apps/experiments/tests/test_services.py

@@ -157,6 +157,9 @@ class VariantCrudTest(TestCase):
 
 class SubmitForReviewTest(TestCase):
     def test_submit_with_valid_variants(self) -> None:
+        review_settings_update(
+            default_min_approvals=1, allow_any_approver=True
+        )
         exp = make_experiment(suffix="_sr")
         add_two_variants(exp)
         exp = experiment_submit_for_review(experiment=exp, user=exp.owner)
@@ -478,6 +481,9 @@ class LifecycleFlowTest(TestCase):
 class OwnershipPermissionTest(TestCase):
     @override
     def setUp(self) -> None:
+        review_settings_update(
+            default_min_approvals=1, allow_any_approver=True
+        )
         self.owner = make_experimenter("_own")
         self.other = make_experimenter("_oth")
         self.admin = make_admin("_adm")

src/backend/apps/flags/migrations/0003_alter_featureflag_key.py

@@ -0,0 +1,19 @@
+# Generated by Django 5.2.11 on 2026-02-24 04:52
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('flags', '0002_alter_featureflag_key'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='featureflag',
+            name='key',
+            field=models.CharField(help_text='Unique identifier for the feature flag', max_length=100, unique=True, validators=[django.core.validators.RegexValidator(message='Flag key must follow snake_case, camelCase, or PascalCase.', regex='^[A-Za-z][A-Za-z0-9_]*$')], verbose_name='key'),
+        ),
+    ]

src/backend/apps/flags/models.py

@@ -62,7 +62,7 @@ class FeatureFlag(BaseModel):
             RegexValidator(
                 regex=FLAG_KEY_PATTERN,
                 message=(
-                    "Event type name must follow snake_case, "
+                    "Flag key must follow snake_case, "
                     "camelCase, or PascalCase."
                 ),
             )

src/backend/apps/reports/services.py

@@ -46,24 +46,6 @@ def _count_events(
     return qs.count()
 
 
-def _count_unique_subjects(
-    decision_ids: list[str],
-    event_type_name: str,
-    start_date: datetime | None = None,
-    end_date: datetime | None = None,
-) -> int:
-    qs = Event.objects.filter(
-        decision_id__in=decision_ids,
-        event_type__name=event_type_name,
-        is_attributed=True,
-    )
-    if start_date:
-        qs = qs.filter(timestamp__gte=start_date)
-    if end_date:
-        qs = qs.filter(timestamp__lt=end_date)
-    return qs.values("subject_id").distinct().count()
-
-
 def _average_property(
     decision_ids: list[str],
     event_type_name: str,