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-contracts/src/result.rs

@@ -1,4 +1,5 @@
 use std::collections::BTreeMap;
+use std::fmt;
 
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
@@ -22,7 +23,7 @@ pub struct ExecutionTelemetry {
     pub upstream_bytes: Option<u64>,
 }
 
-#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[derive(Clone, Serialize, Deserialize, PartialEq)]
 pub struct ResponseBody {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub json_body: Option<Value>,
@@ -30,7 +31,27 @@ pub struct ResponseBody {
     pub body_bytes_b64: Option<String>,
 }
 
-#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+impl fmt::Debug for ResponseBody {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        formatter
+            .debug_struct("ResponseBody")
+            .field("has_json_body", &self.json_body.is_some())
+            .field(
+                "json_body_bytes",
+                &self
+                    .json_body
+                    .as_ref()
+                    .and_then(|body| serde_json::to_vec(body).ok().map(|bytes| bytes.len())),
+            )
+            .field(
+                "body_bytes_b64_len",
+                &self.body_bytes_b64.as_ref().map(String::len),
+            )
+            .finish()
+    }
+}
+
+#[derive(Clone, Serialize, Deserialize, PartialEq)]
 pub struct ExecutionResult {
     pub request_id: String,
     #[serde(default, skip_serializing_if = "Option::is_none")]
@@ -47,3 +68,73 @@ pub struct ExecutionResult {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub error: Option<ExecutionError>,
 }
+
+impl fmt::Debug for ExecutionResult {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut debug = formatter.debug_struct("ExecutionResult");
+        debug
+            .field("request_id", &self.request_id)
+            .field("candidate_id", &self.candidate_id)
+            .field("status_code", &self.status_code)
+            .field("header_names", &self.headers.keys().collect::<Vec<_>>())
+            .field("response_observation", &self.response_observation)
+            .field("body", &self.body)
+            .field("telemetry", &self.telemetry)
+            .field("has_error", &self.error.is_some());
+        if let Some(error) = self.error.as_ref() {
+            // ExecutionError::message can contain an upstream response or URL.
+            debug
+                .field("error_kind", &error.kind)
+                .field("error_phase", &error.phase)
+                .field("error_upstream_status", &error.upstream_status)
+                .field("error_retryable", &error.retryable)
+                .field("error_failover_recommended", &error.failover_recommended);
+        }
+        debug.finish()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{ExecutionResult, ResponseBody};
+    use crate::{ExecutionError, ExecutionErrorKind, ExecutionPhase};
+    use std::collections::BTreeMap;
+
+    #[test]
+    fn debug_does_not_render_response_headers_body_or_error_message() {
+        let result = ExecutionResult {
+            request_id: "request-1".into(),
+            candidate_id: None,
+            status_code: 401,
+            headers: BTreeMap::from([(
+                "set-cookie".into(),
+                "session=response-header-secret".into(),
+            )]),
+            response_observation: None,
+            body: Some(ResponseBody {
+                json_body: Some(serde_json::json!({"access_token": "response-body-secret"})),
+                body_bytes_b64: None,
+            }),
+            telemetry: None,
+            error: Some(ExecutionError {
+                kind: ExecutionErrorKind::Upstream4xx,
+                phase: ExecutionPhase::Finalize,
+                message: "upstream detail error-secret".into(),
+                upstream_status: Some(401),
+                retryable: false,
+                failover_recommended: false,
+            }),
+        };
+
+        let debug = format!("{result:?}");
+        for secret in [
+            "response-header-secret",
+            "response-body-secret",
+            "error-secret",
+        ] {
+            assert!(!debug.contains(secret), "debug leaked {secret}: {debug}");
+        }
+        assert!(debug.contains("header_names"));
+        assert!(debug.contains("has_error"));
+    }
+}