fix: carry session affinity through Gemini files

apps/aether-gateway/src/ai_serving/planner/decision_input.rs

@@ -28,6 +28,7 @@ pub(crate) struct LocalAuthenticatedDecisionInput {
     pub(crate) auth_context: ExecutionRuntimeAuthContext,
     pub(crate) auth_snapshot: GatewayAuthApiKeySnapshot,
     pub(crate) required_capabilities: Option<serde_json::Value>,
+    pub(crate) client_session_affinity: Option<ClientSessionAffinity>,
 }
 
 struct GatewayAuthenticatedDecisionInputPort<'a> {
@@ -108,6 +109,7 @@ pub(crate) fn build_local_authenticated_decision_input(
         auth_context: resolved_input.auth_context,
         auth_snapshot: resolved_input.auth_snapshot,
         required_capabilities: resolved_input.required_capabilities,
+        client_session_affinity: None,
     }
 }