fn parse_rtdl_assistant_response(raw: &str) -> Result<(String, Value)>Expand description
Parses one VLM reply in RTDL envelope form.
The model must emit a JSON object (single root) whose only keys are
content and rtdl: content is user-facing narration (string); rtdl
is the declarative ops tree (another JSON object) consumed by
expand_rtdl_to_plan.
Returns (content, rtdl) on success — the string is cloned for callers;
rtdl is a serde_json::Value object subtree (not validated beyond
“rtdl is an object”).
Fails if raw is not valid JSON, the root is not an object, the key set
is not exactly {content, rtdl}, content is not a JSON string, or
rtdl is not a JSON object.