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-provider/transport/src/openai_image/mod.rs

@@ -1,4 +1,5 @@
 use std::collections::BTreeMap;
+use std::fmt;
 
 use serde_json::Value;
 
@@ -9,7 +10,7 @@ use crate::rules::apply_local_header_rules_with_request_headers;
 use crate::snapshot::GatewayProviderTransportSnapshot;
 use crate::url::build_openai_image_url;
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Clone, Copy)]
 pub struct ProviderOpenAiImageHeadersInput<'a> {
     pub transport: &'a GatewayProviderTransportSnapshot,
     pub headers: &'a http::HeaderMap,
@@ -21,6 +22,39 @@ pub struct ProviderOpenAiImageHeadersInput<'a> {
     pub original_request_body: &'a Value,
 }
 
+impl fmt::Debug for ProviderOpenAiImageHeadersInput<'_> {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter
+            .debug_struct("ProviderOpenAiImageHeadersInput")
+            .field("transport", &self.transport)
+            .field(
+                "request_header_names",
+                &self
+                    .headers
+                    .keys()
+                    .map(|name| name.as_str())
+                    .collect::<Vec<_>>(),
+            )
+            .field("auth_header", &self.auth_header)
+            .field("has_auth_value", &(!self.auth_value.is_empty()))
+            .field("accept", &self.accept)
+            .field("has_header_rules", &self.header_rules.is_some())
+            .field(
+                "provider_request_body_bytes",
+                &serde_json::to_vec(self.provider_request_body)
+                    .ok()
+                    .map(|bytes| bytes.len()),
+            )
+            .field(
+                "original_request_body_bytes",
+                &serde_json::to_vec(self.original_request_body)
+                    .ok()
+                    .map(|bytes| bytes.len()),
+            )
+            .finish()
+    }
+}
+
 pub fn openai_image_transport_unsupported_reason(
     transport: &GatewayProviderTransportSnapshot,
     api_format: &str,
@@ -98,6 +132,12 @@ pub fn build_openai_image_headers(
     ) {
         return None;
     }
+    let declared_connection_headers =
+        crate::headers::declared_connection_header_names(input.headers, &BTreeMap::new());
+    crate::headers::remove_declared_connection_headers(
+        &mut provider_request_headers,
+        &declared_connection_headers,
+    );
     Some(provider_request_headers)
 }