What is Karma's most reliable build when she mainly has to win tempo and territory before real contact?

The most reliable build on Karma 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 Karma's build instead of simply pushing her standard utility profile?

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 Karma choose when the real issue is mainly replaying favorable approaches several times?

redemption is often the most stable choice because it directly supports this game plan: maintain constant spell spam to control space and support allies.