✨(backend) implement feature flags in Posthog analytics backend

Implement feature flags related functions in
Posthog analytics backend.
We cache the results in django cache to avoid
too frequent calls to Posthog.
Especially for when we are checking multiple features in
the same user request.

src/backend/core/tests/analytics/test_posthog.py

@@ -12,6 +12,7 @@ import pytest
 
 from core.analytics.events import AnalyticsEvent
 from core.analytics.posthog import PostHogAnalytics
+from core.analytics.user_feature_flags import UserFeatureFlag
 from core.factories import UserFactory
 
 pytestmark = pytest.mark.django_db
@@ -248,6 +249,60 @@ def test_capture_logs_the_failing_event_name_on_exception(mock_posthog_cls, capl
     assert any("PostHog capture failed" in record.message for record in caplog.records)
 
 
+# ==============================
+# feature flags
+# ==============================
+
+
+@patch("core.analytics.posthog.Posthog")
+def test_compute_feature_flags_returns_all_catalog_entries(mock_posthog_cls):
+    """Should map every declared feature flag key to the SDK evaluated value."""
+    backend = PostHogAnalytics(api_key="test-api-key")
+    user = UserFactory()
+
+    mock_posthog_cls.return_value.evaluate_flags.return_value.get_flag.return_value = (
+        True
+    )
+
+    flags = backend._fetch_user_feature_flags(user)
+
+    assert flags == {UserFeatureFlag.TRANSCRIPT_SUMMARY_ENABLED: True}
+    mock_posthog_cls.return_value.evaluate_flags.assert_called_once_with(str(user.pk))
+    mock_posthog_cls.return_value.evaluate_flags.return_value.get_flag.assert_called_once_with(
+        UserFeatureFlag.TRANSCRIPT_SUMMARY_ENABLED.value
+    )
+
+
+@patch("core.analytics.posthog.cache.get_or_set")
+@patch("core.analytics.posthog.Posthog")
+def test_get_feature_flags_uses_cache_get_or_set(
+    mock_posthog_cls, mock_cache_get_or_set
+):
+    """Should cache feature flags by user distinct id with configured TTL."""
+    cached_flags = {UserFeatureFlag.TRANSCRIPT_SUMMARY_ENABLED: False}
+    mock_cache_get_or_set.return_value = cached_flags
+    backend = PostHogAnalytics(api_key="test-api-key", feature_flags_cache_ttl=120)
+    user = UserFactory()
+
+    flags = backend.get_user_feature_flags(user)
+
+    assert flags == cached_flags
+    mock_cache_get_or_set.assert_called_once()
+    args, kwargs = mock_cache_get_or_set.call_args
+    assert kwargs["timeout"] == 120
+    assert args[0] == f"user_feature_flags:{user.pk}"
+    assert callable(kwargs["default"])
+
+
+@patch("core.analytics.posthog.Posthog")
+def test_get_feature_flags_returns_empty_dict_on_exception(mock_posthog_cls):
+    """Should swallow failures and return an empty mapping."""
+    backend = PostHogAnalytics(api_key="test-api-key")
+    user = UserFactory()
+    with patch("core.analytics.posthog.cache.get_or_set", side_effect=RuntimeError):
+        assert backend.get_user_feature_flags(user) == {}
+
+
 # ==============================
 # shutdown
 # ==============================