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-data/adapters/postgres/src/candidate_selection.rs

@@ -1255,11 +1255,11 @@ fn map_candidate_selection_row(
         key_name: row.try_get("key_name").map_postgres_err()?,
         key_auth_type: row.try_get("key_auth_type").map_postgres_err()?,
         key_is_active: row.try_get("key_is_active").map_postgres_err()?,
-        key_api_formats: parse_string_list(
+        key_api_formats: parse_key_policy_string_list(
             row.try_get("key_api_formats").map_postgres_err()?,
             "provider_api_keys.api_formats",
         )?,
-        key_allowed_models: parse_string_list(
+        key_allowed_models: parse_key_policy_string_list(
             row.try_get("key_allowed_models").map_postgres_err()?,
             "provider_api_keys.allowed_models",
         )?,
@@ -1301,6 +1301,79 @@ fn parse_string_list(
     parse_string_list_value(&value, field_name)
 }
 
+fn parse_key_policy_string_list(
+    value: Option<serde_json::Value>,
+    field_name: &str,
+) -> Result<Option<Vec<String>>, DataLayerError> {
+    let Some(value) = value else {
+        return Ok(None);
+    };
+    parse_key_policy_string_list_value(&value, field_name)
+}
+
+fn parse_key_policy_string_list_value(
+    value: &serde_json::Value,
+    field_name: &str,
+) -> Result<Option<Vec<String>>, DataLayerError> {
+    match value {
+        serde_json::Value::Null => Err(DataLayerError::UnexpectedValue(format!(
+            "{field_name} contains JSON null; use SQL NULL for an unset policy"
+        ))),
+        serde_json::Value::Array(array) => {
+            parse_key_policy_string_list_array(array, field_name).map(Some)
+        }
+        serde_json::Value::String(raw) => parse_embedded_key_policy_string_list(raw, field_name),
+        _ => Err(DataLayerError::UnexpectedValue(format!(
+            "{field_name} is not a JSON array"
+        ))),
+    }
+}
+
+fn parse_embedded_key_policy_string_list(
+    raw: &str,
+    field_name: &str,
+) -> Result<Option<Vec<String>>, DataLayerError> {
+    let raw = raw.trim();
+    if raw.is_empty() {
+        return Err(DataLayerError::UnexpectedValue(format!(
+            "{field_name} contains an empty string"
+        )));
+    }
+    if raw.eq_ignore_ascii_case("null") {
+        return Err(DataLayerError::UnexpectedValue(format!(
+            "{field_name} contains stringified JSON null; use SQL NULL for an unset policy"
+        )));
+    }
+
+    if let Ok(decoded) = serde_json::from_str::<serde_json::Value>(raw) {
+        return parse_key_policy_string_list_value(&decoded, field_name);
+    }
+
+    Ok(Some(vec![raw.to_string()]))
+}
+
+fn parse_key_policy_string_list_array(
+    array: &[serde_json::Value],
+    field_name: &str,
+) -> Result<Vec<String>, DataLayerError> {
+    let mut items = Vec::with_capacity(array.len());
+    for item in array {
+        let Some(item) = item.as_str() else {
+            return Err(DataLayerError::UnexpectedValue(format!(
+                "{field_name} contains a non-string item"
+            )));
+        };
+        let item = item.trim();
+        if item.is_empty() {
+            return Err(DataLayerError::UnexpectedValue(format!(
+                "{field_name} contains an empty item"
+            )));
+        }
+        items.push(item.to_string());
+    }
+    Ok(items)
+}
+
 fn parse_string_list_value(
     value: &serde_json::Value,
     field_name: &str,
@@ -1505,9 +1578,9 @@ mod tests {
     use serde_json::json;
 
     use super::{
-        parse_provider_model_mappings, parse_string_list, pool_key_candidate_selection_sql,
-        requested_model_selection_page_sql, requested_model_selection_sql,
-        SqlxMinimalCandidateSelectionReadRepository,
+        parse_key_policy_string_list, parse_provider_model_mappings, parse_string_list,
+        pool_key_candidate_selection_sql, requested_model_selection_page_sql,
+        requested_model_selection_sql, SqlxMinimalCandidateSelectionReadRepository,
         LIST_FOR_EXACT_API_FORMAT_AND_GLOBAL_MODEL_SQL, LIST_FOR_EXACT_API_FORMAT_SQL,
         LIST_POOL_KEYS_FOR_GROUP_SQL, PROVIDER_MODEL_MAPPING_API_FORMAT_MATCH_MARKER,
         PROVIDER_MODEL_MAPPING_API_FORMAT_MATCH_SQL,
@@ -1747,6 +1820,29 @@ mod tests {
         assert_eq!(parsed, Some(vec!["gpt-5.2".to_string()]));
     }
 
+    #[test]
+    fn malformed_key_policy_never_degrades_to_unrestricted() {
+        for value in [
+            json!(null),
+            json!("null"),
+            json!(""),
+            json!(["openai:chat", null]),
+        ] {
+            assert!(
+                parse_key_policy_string_list(Some(value), "provider_api_keys.api_formats",)
+                    .is_err()
+            );
+        }
+        assert_eq!(
+            parse_key_policy_string_list(
+                Some(json!(["openai:chat"])),
+                "provider_api_keys.api_formats",
+            )
+            .expect("valid key policy should parse"),
+            Some(vec!["openai:chat".to_string()])
+        );
+    }
+
     #[test]
     fn parse_provider_model_mappings_accepts_stringified_array() {
         let parsed = parse_provider_model_mappings(Some(json!(