diff --git a/data_plane/src/drivers/query/servers/http.rs b/data_plane/src/drivers/query/servers/http.rs
index 3640572ca..a9d292ca8 100644
--- a/data_plane/src/drivers/query/servers/http.rs
+++ b/data_plane/src/drivers/query/servers/http.rs
@@ -945,6 +945,64 @@ async fn process_via_simple_engine(
                 Err(status) => status.into_response()}
         }
         None => {
+            // Legacy `handle_query` returned None — likely the
+            // sketch-vs-precompute query gap pinned in #252:
+            // `query_precomputes_by_agg` only picks up
+            // `AggKind::ExactAgg` sids, never `AggKind::Sketch`. Try
+            // the modern `ASAPQueryEngine::execute(&str)` trait path
+            // before falling through to the unsupported-query branch
+            // — `execute` uses
+            // `idx.sids_for_policy(fp)` + `SketchReducer::evaluate`
+            // and handles sketches natively.
+            //
+            // Trait dispatch loses `KeyByLabelNames` (the trait
+            // returns just `QueryResult`); we surface an empty
+            // `KeyByLabelNames`, identical to how `process_via_router`
+            // handles the same trait surface — the Prometheus
+            // adapter renders an empty `metric: {}` object, a valid
+            // shape that PromQL clients accept.
+            use crate::query_engines::routing::query_engine_routing::QueryEngine;
+            let modern_result = state
+                .query_engine
+                .execute(&parsed_request.query)
+                .await;
+            if let Ok(query_result) = modern_result {
+                debug!(
+                    "Modern execute() handled what legacy handle_query missed \
+                     (query='{}')",
+                    parsed_request.query
+                );
+                use crate::drivers::query::adapters::QueryExecutionResult;
+                let execution_result = QueryExecutionResult {
+                    query_output_labels: promql_utilities::data_model::KeyByLabelNames::default(),
+                    query_result,
+                };
+                let total_duration = start_time.elapsed();
+                debug!(
+                    "Total request processing took (modern fallback): {:.2}ms",
+                    total_duration.as_secs_f64() * 1000.0
+                );
+                return match state
+                    .adapter
+                    .format_success_response(&execution_result)
+                    .await
+                {
+                    Ok(response) => {
+                        annotate_data_source(
+                            response,
+                            StorageBackend::SketchStore.data_source_id(),
+                        )
+                        .await
+                    }
+                    Err(status) => status.into_response(),
+                };
+            }
+            debug!(
+                "Both legacy handle_query AND modern execute() returned None/Err for \
+                 query='{}', falling through to fallback / unsupported",
+                parsed_request.query
+            );
+
             let total_duration = start_time.elapsed();
             debug!("=== QUERY ENGINE RETURNED NONE ===");
             debug!(
diff --git a/data_plane/tests/e2e_controller_plans_and_backend_serves.rs b/data_plane/tests/e2e_controller_plans_and_backend_serves.rs
index 8626b7856..ff321b4a8 100644
--- a/data_plane/tests/e2e_controller_plans_and_backend_serves.rs
+++ b/data_plane/tests/e2e_controller_plans_and_backend_serves.rs
@@ -130,10 +130,11 @@ async fn start_backend_http_server() -> (u16, HotReloadStreamingConfig) {
     use data_plane::storage_engines::types::StreamingConfig;
 
     let hot_reload = HotReloadStreamingConfig::new(StreamingConfig::default());
-    let query_engine = Arc::new(ASAPQueryEngine::new_with_hot_reload(
-        hot_reload.clone(),
-        15_000,
-    ));
+    let sketch_index = Arc::new(SketchStore::new());
+    let query_engine = Arc::new(
+        ASAPQueryEngine::new_with_hot_reload(hot_reload.clone(), 15_000)
+            .with_sketch_index(sketch_index.clone()),
+    );
 
     let adapter_config = AdapterConfig::prometheus_promql(
         "http://127.0.0.1:9999".to_string(), // unused — no forwarding in this test
@@ -145,7 +146,6 @@ async fn start_backend_http_server() -> (u16, HotReloadStreamingConfig) {
         adapter_config,
     };
 
-    let sketch_index = Arc::new(SketchStore::new());
     let server = HttpServer::new(http_config, query_engine, sketch_index)
         .with_hot_reload_config(hot_reload.clone());
 
@@ -283,10 +283,16 @@ async fn start_full_stack(otlp_http_port: u16, otlp_grpc_port: u16) -> FullStack
         handle_http_requests: true,
         adapter_config,
     };
-    let query_engine = Arc::new(ASAPQueryEngine::new_with_hot_reload(
-        hot_reload.clone(),
-        15_000,
-    ));
+    let query_engine = Arc::new(
+        ASAPQueryEngine::new_with_hot_reload(hot_reload.clone(), 15_000)
+            // CRITICAL: without this the engine's `sketch_index` is
+            // None and every fast path that reads sid → SketchInstance
+            // metadata is silently skipped. Sketches DO land in
+            // `sketch_index` via OTLP ingest (the engine's
+            // `precompute_engine` shares the Arc), but the query
+            // path can't see them without this binding.
+            .with_sketch_index(sketch_index.clone()),
+    );
     let server = HttpServer::new(http_config, query_engine, sketch_index)
         .with_hot_reload_config(hot_reload.clone());
     let backend_port = server
@@ -704,4 +710,13 @@ async fn controller_plan_to_query_full_roundtrip_ddsketch() {
         "PromQL response missing `status` field — HTTP layer is unhealthy\n{}",
         serde_json::to_string_pretty(&response).unwrap_or_default()
     );
+    let status = response["status"].as_str().unwrap_or("(missing)");
+    assert_eq!(
+        status, "success",
+        "PromQL query did not succeed after the modern-execute() fallback in \
+         process_via_simple_engine. The legacy handle_query path can't read \
+         sketch-backed sids (#252), but the fallback should now reach them via \
+         the trait-dispatch path. Response:\n{}",
+        serde_json::to_string_pretty(&response).unwrap_or_default()
+    );
 }