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.

apps/aether-gateway/src/execution_runtime/fallback.rs

@@ -355,6 +355,7 @@ pub(crate) fn resolve_core_stream_direct_finalize_report_kind(plan_kind: &str) -
 
 #[cfg(test)]
 mod tests {
+    use aether_crypto::DEVELOPMENT_ENCRYPTION_KEY;
     use std::collections::BTreeSet;
 
     use aether_contracts::{ExecutionError, ExecutionErrorKind, ExecutionPhase, ExecutionResult};
@@ -435,6 +436,15 @@ mod tests {
     }
 
     fn sample_key() -> StoredProviderCatalogKey {
+        let credential_state = AppState::new()
+            .expect("credential state should build")
+            .with_data_state_for_tests(
+                GatewayDataState::disabled()
+                    .with_encryption_key_for_tests(DEVELOPMENT_ENCRYPTION_KEY),
+            );
+        let encrypted_api_key = credential_state
+            .seal_provider_catalog_key_api_key("provider-1", "key-1", "plain-upstream-key")
+            .expect("api key should encrypt");
         StoredProviderCatalogKey::new(
             "key-1".to_string(),
             "provider-1".to_string(),
@@ -446,7 +456,7 @@ mod tests {
         .expect("key should build")
         .with_transport_fields(
             Some(serde_json::json!(["openai:chat"])),
-            "plain-upstream-key".to_string(),
+            encrypted_api_key,
             None,
             None,
             Some(serde_json::json!({"openai:chat": 1})),
@@ -466,7 +476,7 @@ mod tests {
         );
         let data_state = GatewayDataState::with_provider_transport_reader_for_tests(
             std::sync::Arc::new(provider_catalog),
-            "development-key",
+            DEVELOPMENT_ENCRYPTION_KEY,
         );
         AppState::new()
             .expect("state should build")