So even if you have a set number of days, your manager can still fire you for taking them. Your manager can fire you or not fire you for any reason. So you could take 30 days off and not get fired if your manager doesn't want to.
With "at will" employment there really aren't any concrete rules in play. Everything is just at the discretion of the employer. Regardless of the employee handbook, PTO or really anything. You could be fired for coming in too early. Coming in too late. Not working on the weekends. Working on the weekends. Probably even something as silly as gaining too much weight. Really anything unless it is within a few specific protected classes such as race or sex.
The only variable that exists is whether or not the terminated employee would qualify for unemployment benefits.
Edit: I should mention this is US specific as most US states have "at will" employment laws.
For doing something that is specified in the employment agreement? Pretty sure that would fall under fraud/misrepresentation.
What makes you think I haven't, are you saying that there is no fraud exception? You don't go into any detail to support your "absolute" confidence.
There's ALWAYS a limit. Try taking a year long holiday and see how that goes. With UPTO the limit is up to your manager.