Securely start a State-Machine with pulses or edges

Now it seems that we're slowly on the same level. Right, the Start_IN signal is already from a synchronized core with a synchronous reset, is read in synchronous by the second core (which also has an synchronous reset) and the result is on synchronous outputs. No asynchronous logic in between.

Well, now the really generalized question is (see initial post) what are the best (securest) ways to detect edges or one-clock-pulses (everything synchronized) to trigger the start of a state-machine.

This is a general question and not for debugging a special code.

I will ask, if I can publish my code to you. (Company problem)

PS: I think there are so much "synchronous" in this post, we can call Guinness. :)

PPS: To be sure: synchronous :D