Hide format_conversion_disabled skips when exact-format candidate shares the same key

Also switch failover test to surface an auth failure instead of a 502 upstream error.

apps/aether-gateway/src/ai_pipeline/planner/candidate_affinity.rs

@@ -1196,6 +1196,62 @@ mod tests {
         assert_eq!(skipped[0].skip_reason, "format_conversion_disabled");
     }
 
+    #[tokio::test]
+    async fn realtime_gate_hides_cross_format_disablement_when_same_key_has_exact_endpoint() {
+        let provider_catalog = InMemoryProviderCatalogReadRepository::seed(
+            vec![sample_provider_with_options("provider-shared", false, 0)],
+            vec![
+                sample_endpoint_for_provider("provider-shared", "endpoint-exact", "openai:chat"),
+                sample_endpoint_for_provider("provider-shared", "endpoint-cross", "claude:chat"),
+            ],
+            vec![sample_key_for_provider_with_options(
+                "provider-shared",
+                "key-shared",
+                "",
+                true,
+                Some(json!(["openai:chat", "claude:chat"])),
+                None,
+            )],
+        );
+        let data_state = GatewayDataState::with_provider_transport_reader_for_tests(
+            std::sync::Arc::new(provider_catalog),
+            "development-key",
+        );
+        let state = AppState::new()
+            .expect("state should build")
+            .with_data_state_for_tests(data_state);
+
+        let (ranked, skipped) = filter_and_rank_local_execution_candidates(
+            PlannerAppState::new(&state),
+            vec![
+                sample_priority_candidate(
+                    "provider-shared",
+                    "endpoint-exact",
+                    "key-shared",
+                    "openai:chat",
+                    Some(0),
+                    0,
+                ),
+                sample_priority_candidate(
+                    "provider-shared",
+                    "endpoint-cross",
+                    "key-shared",
+                    "claude:chat",
+                    Some(0),
+                    0,
+                ),
+            ],
+            "openai:chat",
+            "gpt-4.1",
+            None,
+        )
+        .await;
+
+        assert_eq!(ranked.len(), 1);
+        assert_eq!(ranked[0].candidate.endpoint_id, "endpoint-exact");
+        assert!(skipped.is_empty());
+    }
+
     #[tokio::test]
     async fn realtime_gate_allows_cross_format_candidates_when_endpoint_acceptance_is_enabled() {
         let mut endpoint_cross =

apps/aether-gateway/src/ai_pipeline/planner/candidate_eligibility.rs

@@ -1,6 +1,7 @@
 use tracing::warn;
 
 use aether_scheduler_core::SchedulerMinimalCandidateSelectionCandidate;
+use std::collections::BTreeSet;
 
 use crate::ai_pipeline::{GatewayProviderTransportSnapshot, PlannerAppState};
 
@@ -92,6 +93,7 @@ where
 {
     let mut selectable = Vec::with_capacity(candidates.len());
     let mut skipped = Vec::new();
+    let normalized_client_api_format = client_api_format.trim().to_ascii_lowercase();
 
     for candidate in candidates {
         let Some(transport) = read_candidate_transport_snapshot(state, &candidate).await else {
@@ -118,6 +120,28 @@ where
         }
     }
 
+    let exact_selectable_keys = selectable
+        .iter()
+        .filter(|candidate| {
+            candidate
+                .provider_api_format
+                .eq_ignore_ascii_case(normalized_client_api_format.as_str())
+        })
+        .map(|candidate| {
+            (
+                candidate.candidate.provider_id.clone(),
+                candidate.candidate.key_id.clone(),
+            )
+        })
+        .collect::<BTreeSet<_>>();
+    skipped.retain(|candidate| {
+        candidate.skip_reason != "format_conversion_disabled"
+            || !exact_selectable_keys.contains(&(
+                candidate.candidate.provider_id.clone(),
+                candidate.candidate.key_id.clone(),
+            ))
+    });
+
     let ranked = rank_eligible_local_execution_candidates(
         state,
         selectable,