fix(router): apply per-route thresholds before max_k truncation

redisvl/extensions/router/semantic.py

@@ -437,22 +437,20 @@ def _build_aggregate_request(
             aggregation_func = reducers.avg
 
         aggregate_query = str(vector_range_query).split(" RETURN")[0]
-        aggregate_request = (
+        # FT.AGGREGATE runs its steps in the order given, and redis-py emits them
+        # in call order. FILTER must precede SORTBY ... MAX, or the max_k closest
+        # routes are kept before their thresholds are checked.
+        return (
             AggregateRequest(aggregate_query)
             .group_by(
                 "@route_name",  # type: ignore
                 aggregation_func("vector_distance").alias("distance"),
             )
+            .filter(self._distance_threshold_filter())
             .sort_by("@distance", max=max_k)  # type: ignore
             .dialect(2)
         )
 
-        filter = self._distance_threshold_filter()
-
-        aggregate_request.filter(filter)
-
-        return aggregate_request
-
     def _get_route_matches(
         self,
         vector: list[float],

tests/integration/test_semantic_router.py

@@ -616,6 +616,39 @@ def test_routes_different_distance_thresholds_get_one(
                 router.delete()
 
 
+def test_threshold_filter_applies_before_max_k_truncation(
+    client, routes, hf_vectorizer, redis_test_name
+):
+    """A closer route that misses its own threshold must not crowd out a
+    farther one that meets its threshold."""
+    skip_if_no_redis_search(client)
+    # With all-mpnet-base-v2 and avg aggregation, "hello" sits ~0.07 from
+    # greeting and ~0.60 from farewell. (Under min, greeting would be ~0.)
+    routes[0].distance_threshold = 0.01
+    routes[1].distance_threshold = 0.8
+
+    router = SemanticRouter(
+        name=redis_test_name("test_threshold_filter_before_max_k"),
+        routes=routes,
+        routing_config=RoutingConfig(
+            max_k=1, aggregation_method=DistanceAggregationMethod.avg
+        ),
+        redis_client=client,
+        overwrite=True,
+        vectorizer=hf_vectorizer,
+    )
+    try:
+        assert router("hello").name == "farewell"
+
+        # max_k comes from the routing config; route() always uses max_k=1.
+        assert [match.name for match in router.route_many("hello")] == ["farewell"]
+    finally:
+        with suppress(Exception):
+            router.clear()
+        with suppress(Exception):
+            router.delete()
+
+
 def test_add_delete_route_references(semantic_router):
     skip_if_redis_version_below(semantic_router._index.client, "7.0.0")