fix: keep scheduler affinity out of runtime checks

apps/aether-gateway/src/scheduler/candidate/resolution.rs

@@ -1,6 +1,6 @@
 use std::collections::BTreeSet;
 
-use aether_scheduler_core::{candidate_key, SchedulerAffinityTarget};
+use aether_scheduler_core::candidate_key;
 
 use super::runtime::{current_candidate_runtime_skip_reason, CandidateRuntimeSelectionSnapshot};
 use super::{SchedulerMinimalCandidateSelectionCandidate, SchedulerSkippedCandidate};
@@ -9,7 +9,6 @@ pub(super) fn resolve_scheduler_candidate_selectability(
     candidates: Vec<SchedulerMinimalCandidateSelectionCandidate>,
     runtime_snapshot: &CandidateRuntimeSelectionSnapshot,
     now_unix_secs: u64,
-    cached_affinity_target: Option<&SchedulerAffinityTarget>,
 ) -> (
     Vec<SchedulerMinimalCandidateSelectionCandidate>,
     Vec<SchedulerSkippedCandidate>,
@@ -21,12 +20,9 @@ pub(super) fn resolve_scheduler_candidate_selectability(
 
     for candidate in candidates {
         let key = candidate_key(&candidate);
-        if let Some(skip_reason) = current_candidate_runtime_skip_reason(
-            &candidate,
-            runtime_snapshot,
-            now_unix_secs,
-            cached_affinity_target,
-        ) {
+        if let Some(skip_reason) =
+            current_candidate_runtime_skip_reason(&candidate, runtime_snapshot, now_unix_secs)
+        {
             if emitted_skipped_keys.insert(key) {
                 skipped.push(SchedulerSkippedCandidate {
                     candidate,

apps/aether-gateway/src/scheduler/candidate/runtime.rs

@@ -8,7 +8,7 @@ use aether_data_contracts::repository::provider_catalog::StoredProviderCatalogKe
 use aether_scheduler_core::{
     auth_api_key_concurrency_limit_reached, build_provider_concurrent_limit_map,
     candidate_is_selectable_with_runtime_state, candidate_runtime_skip_reason_with_state,
-    CandidateRuntimeSelectabilityInput, SchedulerAffinityTarget,
+    CandidateRuntimeSelectabilityInput,
 };
 
 use crate::data::auth::GatewayAuthApiKeySnapshot;
@@ -100,7 +100,6 @@ pub(super) fn is_candidate_selectable(
     candidate: &SchedulerMinimalCandidateSelectionCandidate,
     snapshot: &CandidateRuntimeSelectionSnapshot,
     now_unix_secs: u64,
-    cached_affinity_target: Option<&SchedulerAffinityTarget>,
 ) -> bool {
     let pool_group = snapshot
         .pool_provider_ids
@@ -111,7 +110,6 @@ pub(super) fn is_candidate_selectable(
         provider_concurrent_limits: &snapshot.provider_concurrent_limits,
         provider_key_rpm_states: &snapshot.provider_key_rpm_states,
         now_unix_secs,
-        cached_affinity_target,
         provider_quota_blocks_requests: snapshot
             .provider_quota_blocks_requests
             .get(candidate.provider_id.as_str())
@@ -145,7 +143,6 @@ pub(super) fn current_candidate_runtime_skip_reason(
     candidate: &SchedulerMinimalCandidateSelectionCandidate,
     snapshot: &CandidateRuntimeSelectionSnapshot,
     now_unix_secs: u64,
-    cached_affinity_target: Option<&SchedulerAffinityTarget>,
 ) -> Option<&'static str> {
     let pool_group = snapshot
         .pool_provider_ids
@@ -171,7 +168,6 @@ pub(super) fn current_candidate_runtime_skip_reason(
         provider_concurrent_limits: &snapshot.provider_concurrent_limits,
         provider_key_rpm_states: &snapshot.provider_key_rpm_states,
         now_unix_secs,
-        cached_affinity_target,
         provider_quota_blocks_requests,
         account_quota_exhausted: !pool_group
             && snapshot

apps/aether-gateway/src/scheduler/candidate/tests/affinity.rs

@@ -11,9 +11,10 @@ use aether_data_contracts::repository::candidates::{
 };
 use aether_scheduler_core::{
     apply_scheduler_candidate_ranking, candidate_affinity_hash,
-    enumerate_minimal_candidate_selection, EnumerateMinimalCandidateSelectionInput,
-    SchedulerMinimalCandidateSelectionCandidate, SchedulerPriorityMode, SchedulerRankableCandidate,
-    SchedulerRankingContext, SchedulerRankingMode,
+    enumerate_minimal_candidate_selection, ClientSessionAffinity,
+    EnumerateMinimalCandidateSelectionInput, SchedulerMinimalCandidateSelectionCandidate,
+    SchedulerPriorityMode, SchedulerRankableCandidate, SchedulerRankingContext,
+    SchedulerRankingMode,
 };
 
 use crate::cache::SchedulerAffinityTarget;
@@ -45,12 +46,49 @@ async fn select_candidate(
         require_streaming,
         None,
         auth_snapshot,
+        None,
         now_unix_secs,
         false,
     )
     .await
 }
 
+#[test]
+fn scheduler_affinity_cache_key_uses_session_scope_when_available() {
+    let auth_snapshot = sample_auth_snapshot("api-key-1");
+    let first_session = ClientSessionAffinity::new(
+        Some("generic".to_string()),
+        Some("session=conversation-a".to_string()),
+    );
+    let second_session = ClientSessionAffinity::new(
+        Some("generic".to_string()),
+        Some("session=conversation-b".to_string()),
+    );
+
+    let first_key = build_scheduler_affinity_cache_key(
+        Some(&auth_snapshot),
+        "openai:chat",
+        "gpt-4.1",
+        Some(&first_session),
+    )
+    .expect("first key should build");
+    let second_key = build_scheduler_affinity_cache_key(
+        Some(&auth_snapshot),
+        "openai:chat",
+        "gpt-4.1",
+        Some(&second_session),
+    )
+    .expect("second key should build");
+    let legacy_key =
+        build_scheduler_affinity_cache_key(Some(&auth_snapshot), "openai:chat", "gpt-4.1", None)
+            .expect("legacy key should build");
+
+    assert_ne!(first_key, second_key);
+    assert_ne!(first_key, legacy_key);
+    assert!(first_key.starts_with("scheduler_affinity:v2:"));
+    assert!(!first_key.contains("conversation-a"));
+}
+
 #[tokio::test]
 async fn same_priority_candidates_are_distributed_by_affinity_key() {
     let mut first = sample_row();
@@ -168,7 +206,7 @@ async fn reuses_cached_scheduler_affinity_candidate_before_sorted_fallback() {
 
     let auth_snapshot = sample_auth_snapshot("affinity-key-1");
     let cache_key =
-        build_scheduler_affinity_cache_key(Some(&auth_snapshot), "openai:chat", "gpt-4.1")
+        build_scheduler_affinity_cache_key(Some(&auth_snapshot), "openai:chat", "gpt-4.1", None)
             .expect("cache key should build");
     state.scheduler_affinity_cache.insert(
         cache_key,
@@ -199,7 +237,7 @@ async fn reuses_cached_scheduler_affinity_candidate_before_sorted_fallback() {
 }
 
 #[tokio::test]
-async fn cached_affinity_candidate_can_use_reserved_provider_key_rpm_capacity() {
+async fn cached_affinity_candidate_cannot_use_reserved_provider_key_rpm_capacity() {
     let mut first = sample_row();
     first.provider_id = "provider-a".to_string();
     first.provider_name = "openai-a".to_string();
@@ -273,7 +311,7 @@ async fn cached_affinity_candidate_can_use_reserved_provider_key_rpm_capacity()
 
     let auth_snapshot = sample_auth_snapshot("api-key-cached-user");
     let cache_key =
-        build_scheduler_affinity_cache_key(Some(&auth_snapshot), "openai:chat", "gpt-4.1")
+        build_scheduler_affinity_cache_key(Some(&auth_snapshot), "openai:chat", "gpt-4.1", None)
             .expect("cache key should build");
     state.scheduler_affinity_cache.insert(
         cache_key,
@@ -299,6 +337,6 @@ async fn cached_affinity_candidate_can_use_reserved_provider_key_rpm_capacity()
     .expect("selection should succeed")
     .expect("candidate should exist");
 
-    assert_eq!(selected.provider_id, "provider-a");
-    assert_eq!(selected.key_id, "key-a");
+    assert_eq!(selected.provider_id, "provider-b");
+    assert_eq!(selected.key_id, "key-b");
 }

apps/aether-gateway/src/tests/architecture/runtime_and_security.rs

@@ -311,8 +311,8 @@ fn scheduler_candidate_runtime_paths_depend_on_scheduler_core_and_state_trait()
         "candidate/runtime.rs should depend on core selectable predicate helper"
     );
     assert!(
-        runtime.contains("SchedulerAffinityTarget"),
-        "candidate/runtime.rs should depend on core SchedulerAffinityTarget"
+        !runtime.contains("SchedulerAffinityTarget"),
+        "candidate/runtime.rs should keep affinity out of runtime eligibility checks"
     );
     assert!(
         runtime.contains("auth_api_key_concurrency_limit_reached"),