The question is about action economy. I want to know whether you need to finish a continuous action to start an instant action. I am only interested in RAW answers and combat applications, where you measure time in turns, not as a freeform narration.
Alyssa the thief wants to steal keys from one of the two guards. Borok, the barbarian picks a fight with the other one as a diversion. While they are having a go at each other, Alyssa would like to sneak past the guard, stealing the keys while on the way. She uses a move action to sneak and a standard one to steal the keys. The "safe spot" she wants to reach is within her normal sneaking distance for a single move action. Does she have to sneak behind the guard, steal the keys and then wait until her next move action to sneak away, or can she do it in one swift motion?
Example 2: Arg the orc jumped on a warg mount. The mount is rowdy, so he needs to use his move action to control him in combat. He commands him to charge and overrun an opponent, but he also wants to slash him with his bardiche, a reach weapon. Can Arg swing his bardiche in time while the mount is charging or does he have to wait until he finishes movement? Or, does he need to wait until the warg finishes the whole charge-and-overrun combo?
Example 3: Zif the mage casts a spell for a full turn. He also needs to take a 5-foot step. He wants to start casting in one square, but finish in the other one because of reasons. Does he have to either take a step before or after casting or can he take that step mid-sentence?