Function parse_command 

pub fn parse_command(status: u16, body: Value) -> Result<CommandResponse>

Interpret a raw (status, body) pair as the command envelope, applying the box’s error conventions:

• 200 + success: true is the only success shape.
• 501 means the box image predates the endpoint (Error::UnsupportedByBox).
• Everything else (including success: false with HTTP 200, which the box uses for cross-role instrument conflicts) is Error::Box.