@@ -13,8 +13,8 @@ pub struct ControllerConfig {
     pub windowing: Option<WindowingConfig>,
     pub sketch_parameters: Option<SketchParameterOverrides>,
     pub aggregate_cleanup: Option<AggregateCleanupConfig>,
-    /// Optional hint: per-metric label sets used as a fallback when Prometheus
-    /// returns no series for a metric. Prometheus-inferred labels take priority.
+    /// Optional authoritative per-metric label sets. Prometheus discovery fills
+    /// only metrics that have no hint.
     #[serde(default)]
     pub metrics: Option<Vec<MetricDefinition>>,
     /// Current streaming config, passed as context for repeated reconfiguration.
 
@@ -165,10 +165,18 @@ pub fn build_schema_from_prometheus(
     queries: &[String],
 ) -> Result<PromQLSchema, ControllerError> {
     let metric_names = extract_metric_names(queries);
+    build_schema_from_metric_names(prometheus_url, &metric_names)
+}
+
+/// Build a `PromQLSchema` by querying Prometheus for the supplied metric names.
+pub(crate) fn build_schema_from_metric_names(
+    prometheus_url: &str,
+    metric_names: &HashSet<String>,
+) -> Result<PromQLSchema, ControllerError> {
     debug!("Inferred metric names from queries: {:?}", metric_names);
     let mut schema = PromQLSchema::new();
 
-    for metric_name in &metric_names {
+    for metric_name in metric_names {
         match fetch_labels_for_metric(prometheus_url, metric_name)? {
             Some(labels) => {
                 debug!("Inferred labels for metric '{}': {:?}", metric_name, labels);
 
@@ -1,8 +1,5 @@
-use std::path::Path;
-use tracing::debug;
-
 use asap_types::PromQLSchema;
-use promql_utilities::data_model::KeyByLabelNames;
+use std::path::Path;
 
 use super::generator;
 use crate::config::input::ControllerConfig;
@@ -26,10 +23,10 @@ impl Controller {
         }
     }
 
-    /// Build a `Controller` from a config file, fetching metric labels from Prometheus.
+    /// Build a `Controller` from a config file, using metric hints before Prometheus discovery.
     ///
     /// `prometheus_url` is queried via `GET /api/v1/series?match[]=<metric>` for each metric
-    /// name found in the config's PromQL queries.
+    /// name found in the config's PromQL queries that has no `metrics` hint.
     pub fn from_file(
         path: &Path,
         opts: RuntimeOptions,
@@ -48,23 +45,18 @@ impl Controller {
             .iter()
             .flat_map(|qg| qg.queries.clone())
             .collect();
-        let mut schema =
-            prometheus_client::build_schema_from_prometheus(prometheus_url, &all_queries)?;
-        // For any metric that Prometheus had no series for, fall back to the
-        // `metrics` hint in the config file (if present).
-        if let Some(metric_hints) = &config.metrics {
-            for hint in metric_hints {
-                if !schema.config.contains_key(&hint.metric) {
-                    debug!(
-                        "Prometheus had no series for '{}'; falling back to config-file hint with labels {:?}",
-                        hint.metric, hint.labels
-                    );
-                    schema = schema.add_metric(
-                        hint.metric.clone(),
-                        KeyByLabelNames::new(hint.labels.clone()),
-                    );
-                }
-            }
+        let mut schema = config.schema_from_hints();
+        let metric_names = prometheus_client::extract_metric_names(&all_queries);
+        let missing_metric_names = metric_names
+            .into_iter()
+            .filter(|metric_name| !schema.config.contains_key(metric_name))
+            .collect();
+        let discovered_schema = prometheus_client::build_schema_from_metric_names(
+            prometheus_url,
+            &missing_metric_names,
+        )?;
+        for (metric_name, labels) in discovered_schema.config {
+            schema = schema.add_metric(metric_name, labels);
         }
         Ok(Self {
             config,
 
@@ -1,6 +1,8 @@
 use asap_planner::{Controller, ControllerError, PromQLSchema, RuntimeOptions, StreamingEngine};
 use promql_utilities::data_model::KeyByLabelNames;
 use promql_utilities::query_logics::enums::AggregationType;
+use std::io::{Read, Write};
+use std::net::TcpListener;
 use std::path::Path;
 
 // ─── helpers ─────────────────────────────────────────────────────────────────
@@ -28,6 +30,29 @@ fn http_requests_schema() -> PromQLSchema {
     )
 }
 
+fn single_request_prometheus_server(
+    status: &str,
+    body: &str,
+) -> (String, std::thread::JoinHandle<String>) {
+    let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+    let url = format!("http://{}", listener.local_addr().unwrap());
+    let status = status.to_string();
+    let body = body.to_string();
+    let server = std::thread::spawn(move || {
+        let (mut stream, _) = listener.accept().unwrap();
+        let mut request = [0u8; 4096];
+        let bytes_read = stream.read(&mut request).unwrap();
+        let response = format!(
+            "HTTP/1.1 {status}\r\nContent-Length: {}\r\nContent-Type: application/json\r\nConnection: close\r\n\r\n{}",
+            body.len(),
+            body
+        );
+        stream.write_all(response.as_bytes()).unwrap();
+        String::from_utf8_lossy(&request[..bytes_read]).into_owned()
+    });
+    (url, server)
+}
+
 #[test]
 fn config_file_sliding_window_override_generates_per_query_candidates() {
     let controller = Controller::from_file_with_schema(
@@ -806,6 +831,129 @@ metrics:
     assert!(result.is_ok());
 }
 
+#[test]
+fn hinted_metric_skips_prometheus_schema_discovery() {
+    let config = tempfile::NamedTempFile::new().unwrap();
+    std::fs::write(
+        config.path(),
+        r#"
+query_groups:
+  - id: 1
+    queries:
+      - "rate(http_requests_total[5m])"
+    repetition_delay_ms: 300000
+metrics:
+  - metric: "http_requests_total"
+    labels: ["instance"]
+"#,
+    )
+    .unwrap();
+
+    let unused_listener = TcpListener::bind("127.0.0.1:0").unwrap();
+    let unused_port = unused_listener.local_addr().unwrap().port();
+    drop(unused_listener);
+
+    // The port has no listener. A successful construction proves the hinted
+    // metric did not attempt URL-based discovery.
+    let controller = Controller::from_file(
+        config.path(),
+        default_opts(),
+        &format!("http://127.0.0.1:{unused_port}"),
+    )
+    .unwrap();
+
+    assert_eq!(controller.generate().unwrap().inference_query_count(), 1);
+}
+
+#[test]
+fn unhinted_metric_discovers_schema_from_prometheus() {
+    let config = tempfile::NamedTempFile::new().unwrap();
+    std::fs::write(
+        config.path(),
+        r#"
+query_groups:
+  - id: 1
+    queries:
+      - "rate(http_requests_total[5m])"
+    repetition_delay_ms: 300000
+"#,
+    )
+    .unwrap();
+
+    let (url, server) = single_request_prometheus_server(
+        "200 OK",
+        r#"{"status":"success","data":[{"__name__":"http_requests_total","instance":"one"}]}"#,
+    );
+
+    let controller = Controller::from_file(config.path(), default_opts(), &url).unwrap();
+
+    assert_eq!(controller.generate().unwrap().inference_query_count(), 1);
+    assert!(server
+        .join()
+        .unwrap()
+        .starts_with("GET /api/v1/series?match%5B%5D=http_requests_total"));
+}
+
+#[test]
+fn hints_remain_authoritative_while_unhinted_metrics_are_discovered() {
+    let config = tempfile::NamedTempFile::new().unwrap();
+    std::fs::write(
+        config.path(),
+        r#"
+query_groups:
+  - id: 1
+    queries:
+      - "sum by (hint_label) (hinted_metric)"
+      - "rate(unhinted_metric[5m])"
+    repetition_delay_ms: 300000
+metrics:
+  - metric: "hinted_metric"
+    labels: ["hint_label"]
+"#,
+    )
+    .unwrap();
+    let (url, server) = single_request_prometheus_server(
+        "200 OK",
+        r#"{"status":"success","data":[{"__name__":"unhinted_metric","instance":"one"}]}"#,
+    );
+
+    let controller = Controller::from_file(config.path(), default_opts(), &url).unwrap();
+
+    assert_eq!(controller.generate().unwrap().inference_query_count(), 2);
+    assert!(server
+        .join()
+        .unwrap()
+        .starts_with("GET /api/v1/series?match%5B%5D=unhinted_metric"));
+}
+
+#[test]
+fn unhinted_metric_propagates_prometheus_discovery_error() {
+    let config = tempfile::NamedTempFile::new().unwrap();
+    std::fs::write(
+        config.path(),
+        r#"
+query_groups:
+  - id: 1
+    queries:
+      - "rate(http_requests_total[5m])"
+    repetition_delay_ms: 300000
+"#,
+    )
+    .unwrap();
+    let (url, server) = single_request_prometheus_server(
+        "422 Unprocessable Entity",
+        r#"{"status":"error","error":"too many series"}"#,
+    );
+
+    let result = Controller::from_file(config.path(), default_opts(), &url);
+
+    assert!(matches!(result, Err(ControllerError::PrometheusClient(_))));
+    assert!(server
+        .join()
+        .unwrap()
+        .starts_with("GET /api/v1/series?match%5B%5D=http_requests_total"));
+}
+
 // --- Overlapping window tests ---
 // Queries where range vector > t_repeat: e.g. [5m] repeated every 60s.
 // Windows are always tumbling (sliding disabled); the planner emits windowSize=t_repeat