pub fn parse_command(line: &[u8]) -> ParsedExpand description
Parse + validate one request line. Pure: no hardware, no I/O, fully
unit-testable. Bad JSON, an unknown op, or a missing required field resolve
to Parsed::Error with a stable E_* code; a beep pattern is clamped
into the safe bounds here so an out-of-range request is corrected, never
rejected outright (the operator still gets a bounded beep). An empty line is
a clean E_BAD_REQUEST, never a panic.