feat(security): harden gateway boundaries and usage policies

Consolidate subscription usage policy enforcement, privacy-safe persistence, and gateway security hardening into one reviewable change.

Includes bounded HTTP and execution envelopes, header and protocol guards, DNS and relay validation, authentication and secret projection hardening, secure backup/install paths, and regression coverage.

crates/aether-usage/runtime/src/worker.rs

@@ -15,8 +15,9 @@ use crate::runtime::{
     UsageBillingEventEnricher, UsageRuntimeAccess, UsageWorkerRecordConcurrencyGate,
 };
 use crate::{
-    build_upsert_usage_record_from_event, settle_usage_if_needed, UsageEvent, UsageEventType,
-    UsageQueue, UsageRuntimeConfig, UsageSettlementWriter,
+    build_upsert_usage_record_from_event, reconcile_usage_policy_cost_for_event,
+    settle_usage_if_needed, UsageEvent, UsageEventType, UsageQueue, UsageRuntimeConfig,
+    UsageSettlementWriter,
 };
 
 const USAGE_WORKER_DB_PRESSURE_DEFER_MS: u64 = 10;
@@ -676,6 +677,7 @@ pub async fn write_event_record<T>(data: &T, event: &UsageEvent) -> Result<(), D
 where
     T: UsageRecordWriter + UsageSettlementWriter + Send + Sync,
 {
+    reconcile_usage_policy_cost_for_event(data, event).await?;
     let record = build_upsert_usage_record_from_event(event)?;
     if let Some(stored) = data.upsert_usage_record(record).await? {
         settle_usage_if_needed(data, &stored).await?;
@@ -728,7 +730,8 @@ mod tests {
     use std::time::Duration;
 
     use aether_data_contracts::repository::settlement::{
-        StoredUsageSettlement, UsageSettlementInput,
+        ReconcileUsagePolicyCostInput, StoredUsagePolicyCostReservation, StoredUsageSettlement,
+        UsageSettlementInput,
     };
     use aether_data_contracts::repository::usage::{StoredRequestUsageAudit, UpsertUsageRecord};
     use aether_data_contracts::DataLayerError;
@@ -755,6 +758,7 @@ mod tests {
     struct TestUsageStore {
         records: Mutex<Vec<UpsertUsageRecord>>,
         settlements: Mutex<Vec<UsageSettlementInput>>,
+        reconciliations: Mutex<Vec<ReconcileUsagePolicyCostInput>>,
         enrich_calls: Mutex<Vec<String>>,
         manual_proxy_counter_calls: AtomicUsize,
     }
@@ -958,6 +962,17 @@ mod tests {
             true
         }
 
+        async fn reconcile_usage_policy_cost(
+            &self,
+            input: ReconcileUsagePolicyCostInput,
+        ) -> Result<Option<StoredUsagePolicyCostReservation>, DataLayerError> {
+            self.reconciliations
+                .lock()
+                .expect("reconciliations lock")
+                .push(input);
+            Ok(None)
+        }
+
         async fn settle_usage(
             &self,
             input: UsageSettlementInput,
@@ -1147,6 +1162,39 @@ mod tests {
         assert_eq!(settlements[0].request_id, "req-worker-123");
     }
 
+    #[tokio::test]
+    async fn same_request_id_terminal_events_reconcile_each_reservation_token_before_upsert() {
+        let store = TestUsageStore::default();
+        let mut first = sample_event();
+        first.request_id = "shared-client-trace".to_string();
+        first.data.actual_total_cost_usd = Some(0.25);
+        first.data.request_metadata = Some(serde_json::json!({
+            "plan_usage_reservation_token": "server-token-a"
+        }));
+        let mut second = first.clone();
+        second.data.actual_total_cost_usd = Some(0.75);
+        second.data.request_metadata = Some(serde_json::json!({
+            "plan_usage_reservation_token": "server-token-b"
+        }));
+
+        write_event_record(&store, &first)
+            .await
+            .expect("first terminal event");
+        write_event_record(&store, &second)
+            .await
+            .expect("second terminal event");
+
+        let reconciliations = store.reconciliations.lock().expect("reconciliations lock");
+        assert_eq!(reconciliations.len(), 2);
+        assert_eq!(reconciliations[0].request_id, "shared-client-trace");
+        assert_eq!(reconciliations[0].reservation_token, "server-token-a");
+        assert_eq!(reconciliations[0].actual_cost_units, 25_000_000);
+        assert_eq!(reconciliations[1].request_id, "shared-client-trace");
+        assert_eq!(reconciliations[1].reservation_token, "server-token-b");
+        assert_eq!(reconciliations[1].actual_cost_units, 75_000_000);
+        assert_eq!(store.records.lock().expect("records lock").len(), 2);
+    }
+
     #[tokio::test]
     async fn replayable_usage_write_does_not_duplicate_transport_owned_proxy_counter() {
         let store = TestUsageStore::default();