pub fn tick(
tasks_path: &Path,
task_id: &str,
expected_line_hash: &str,
) -> Result<(), String>Expand description
Ticks task_id: writes x into its [ ], one byte, nothing else.
Refused when the task’s line no longer hashes to expected_line_hash,
when its box is anything but a single space ([~], []), and when it
is a parent with an open nested task.