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/gemini_cli/auth.rs

@@ -1,15 +1,26 @@
 use serde_json::Value;
+use std::fmt;
 
 use super::super::snapshot::GatewayProviderTransportSnapshot;
 
 pub const GEMINI_CLI_PROVIDER_TYPE: &str = "gemini_cli";
 
-#[derive(Debug, Clone, Default, PartialEq, Eq)]
+#[derive(Clone, Default, PartialEq, Eq)]
 pub struct GeminiCliRequestAuth {
     pub project_id: Option<String>,
     pub session_id: Option<String>,
 }
 
+impl fmt::Debug for GeminiCliRequestAuth {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter
+            .debug_struct("GeminiCliRequestAuth")
+            .field("project_id", &self.project_id)
+            .field("has_session_id", &self.session_id.is_some())
+            .finish()
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum GeminiCliRequestAuthSupport {
     Supported(GeminiCliRequestAuth),

crates/aether-provider/transport/src/gemini_cli/request.rs

@@ -1,13 +1,31 @@
 use serde_json::{Map, Value};
+use std::fmt;
 
 use super::auth::GeminiCliRequestAuth;
 
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Clone, PartialEq)]
 pub enum GeminiCliRequestEnvelopeSupport {
     Supported(Value),
     Unsupported(GeminiCliRequestEnvelopeUnsupportedReason),
 }
 
+impl fmt::Debug for GeminiCliRequestEnvelopeSupport {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Supported(body) => formatter
+                .debug_struct("Supported")
+                .field(
+                    "body_bytes",
+                    &serde_json::to_vec(body).ok().map(|bytes| bytes.len()),
+                )
+                .finish(),
+            Self::Unsupported(reason) => {
+                formatter.debug_tuple("Unsupported").field(reason).finish()
+            }
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum GeminiCliRequestEnvelopeUnsupportedReason {
     NonObjectBody,