Function handle_export_reflection 

pub fn handle_export_reflection(
    conn: &Connection,
    params: &Value,
) -> Result<Value, String>

Wire shape:

{
  "content": "---\nmemory_id: ...\n...",
  "suggested_filename": "<namespace-with-slashes>/<id>.md"
}

Errors:

• memory_id is required — caller omitted the parameter.
• memory_id cannot be empty.
• memory not found: <id> — substrate doesn’t know this id.
• memory is not a reflection: <id> — caller passed an observation.
• unsupported export format '<x>' — format was neither md nor json.