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/schema/src/lib.rs

@@ -893,6 +893,30 @@ mod tests {
         ));
     }
 
+    #[test]
+    fn mysql_column_type_override_can_select_binary_collation() {
+        let mut schema = announcements_schema();
+        schema
+            .tables
+            .get_mut("announcements")
+            .expect("fixture table exists")
+            .columns
+            .first_mut()
+            .expect("fixture id column exists")
+            .driver
+            .mysql = Some(DriverColumnOverride {
+            sql_type: Some(
+                "VARCHAR(64) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_bin".to_string(),
+            ),
+            default: None,
+            nullable: None,
+        });
+
+        let mysql_sql = mysql::emit_schema(&schema);
+        assert!(mysql_sql
+            .contains("`id` VARCHAR(64) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_bin NOT NULL"));
+    }
+
     #[test]
     fn extracts_create_table_names_across_driver_quoting() {
         let tables = extract_create_table_names(