Add provider key cycle stats reset handling

apps/aether-gateway/src/orchestration/effects.rs

@@ -731,6 +731,10 @@ fn local_candidate_failure_should_record_pool_error(
     classification: LocalFailoverClassification,
     status_code: u16,
 ) -> bool {
+    if status_code == 400 {
+        return false;
+    }
+
     local_candidate_failure_should_invalidate_affinity(classification, status_code)
 }
 
@@ -1441,6 +1445,10 @@ mod tests {
             LocalFailoverClassification::StopErrorPattern,
             400,
         ));
+        assert!(!local_candidate_failure_should_record_pool_error(
+            LocalFailoverClassification::RetryUpstreamFailure,
+            400,
+        ));
         assert!(local_candidate_failure_should_record_pool_error(
             LocalFailoverClassification::RetryUpstreamFailure,
             429,

apps/aether-gateway/src/orchestration/health.rs

@@ -144,6 +144,9 @@ fn local_candidate_failure_should_project_health(
     if status_code < 400 {
         return false;
     }
+    if status_code == 400 {
+        return false;
+    }
 
     match classification {
         LocalFailoverClassification::RetrySuccessPattern
@@ -216,6 +219,18 @@ mod tests {
         .is_none());
     }
 
+    #[test]
+    fn failure_projection_ignores_client_bad_request() {
+        assert!(project_local_failure_health(
+            None,
+            "openai:chat",
+            LocalFailoverClassification::RetryUpstreamFailure,
+            400,
+            1_760_000_000,
+        )
+        .is_none());
+    }
+
     #[test]
     fn success_projection_resets_only_target_format() {
         let projected = project_local_success_health(