What is Katarina's most reliable build when she mainly has to open and then chain resets?

The most reliable build on Katarina is the one that preserves the first spike while still keeping an escape valve. If your item order prevents you from playing the champion's first real window, the build may look strong on paper but it is not reliable.

When should you truly adapt Katarina's build instead of simply pushing the standard reset-assassin route?

You should adapt as soon as the enemy draft stops you from playing the timing the build was meant to serve. If you need to survive longer, absorb more poke, or answer a specific engage pattern, the purchase order must move before you even think about the final six-slot build.

Which enchant should Katarina choose when the real issue is mainly surviving long enough for the second rotation?

stasis is often the most stable choice because it directly supports this game plan: maximize initial burst to trigger resets and dominate teamfights.

Katarina Wild Rift Best Build Guide (Patch 7.2a)

Katarina Wild Rift Best Build Guide

Reset assassin build for chaos punishment: Katarina wins when the first kill or first forced cooldown makes the rest of the fight unreadable. The build must therefore support access, the minimum safety of first commit, and reset continuity.