Are the program's extents available to the g-code?

pgf wrote:

Thanks. But it's your very first sentence I have trouble with. Given that the length of the bit is variable, there is no single actual lower hardware limit. It depends on how far the bit protrudes from the collet. Given that, what's the use of the limit? When would it do me any good?

First, stop mixing stuff, you're making it harder on yourself.
Machine is a CNC machine, tools are a separate topic that is used on CNC machines.
The limits are there to protect the machine, not the tools, but those same limits consequently also protect the tools to a certain extent.
Breaking a tool is not the end of the world ... or the machine in this case, breaking the spindle ramming it into material/table at full speed is a costly end of that machine.
Tools are dispensable, machine is not.
You have to figure out what works for you, while using the machine, trying to figure out tolling without using them is OK, but do not preoccupy to much with it.
Not sure my explanation is helping, but i went through the same process back when i built my first small vertical mill, turns out it's as easy, propping something up when tool is short, removing vise when tool is long, moving the spindle mount, etc, so there are options, always.