What is Caitlyn's most reliable build when she mainly has to suffocate lane and then siege?

Caitlyn's most reliable build is the one that protects her lane pressure and then her ability to hold the right distance in siege. If your item order helps her do neither, it is missing her real job.

When should you truly adapt Caitlyn's build instead of simply pushing standard crit?

You should adapt as soon as the enemy draft stops you from playing your normal setup window. If you need to survive longer, absorb more burst, or answer fast engage, the purchase order has to move earlier.

Which enchant should Caitlyn choose when the real problem is mainly maintaining useful distance through the end of the fight?

Stasis often remains the most reliable choice when Caitlyn mainly needs to keep useful distance until the end of the fight. If this enchant gives her one more repositioning window, it gives a lot of value.

Caitlyn Wild Rift Best Build Guide (Patch 7.2a)

Caitlyn generates value by controlling space before fights even start. Her build must enhance poke, punish positioning mistakes, and maintain constant pressure without exposure.