What is Hecarim's most reliable build when he has to convert speed into real fight presence?

The most reliable build on Hecarim 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 Hecarim's build instead of pushing standard engage?

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 Hecarim choose when the real issue is mainly surviving after the charge?

glorious is often the most stable choice because it directly supports this game plan: maximize engage impact while surviving post-dive.

Hecarim Wild Rift Best Build Guide (Patch 7.2a)

Hecarim creates value through fast engages and forcing positioning mistakes. His build must maximize initial impact while allowing him to stay in fights.