fix(core) default RejectConfig.request_permissions (#14165)

## Summary
Adds a default here so existing config deserializes

## Testing
- [x] Added a unit test

codex-rs/protocol/src/protocol.rs

@@ -527,6 +527,7 @@ pub struct RejectConfig {
     /// Reject prompts triggered by execpolicy `prompt` rules.
     pub rules: bool,
     /// Reject approval prompts related to built-in permission requests.
+    #[serde(default)]
     pub request_permissions: bool,
     /// Reject MCP elicitation prompts.
     pub mcp_elicitations: bool,
@@ -3487,6 +3488,26 @@ mod tests {
         );
     }
 
+    #[test]
+    fn reject_config_defaults_missing_request_permissions_to_false() {
+        let decoded = serde_json::from_value::<RejectConfig>(serde_json::json!({
+            "sandbox_approval": true,
+            "rules": false,
+            "mcp_elicitations": true,
+        }))
+        .expect("legacy reject config should deserialize");
+
+        assert_eq!(
+            decoded,
+            RejectConfig {
+                sandbox_approval: true,
+                rules: false,
+                request_permissions: false,
+                mcp_elicitations: true,
+            }
+        );
+    }
+
     #[test]
     fn workspace_write_restricted_read_access_includes_effective_writable_roots() {
         let cwd = if cfg!(windows) {